It is fair to say that space activities, military and civil, in the early 21st century have not turned out as imagined by futurists at the dawn of the Space Age. Although it is true that many high-profile concepts from the early Space Age seemed stalled, other applications have become the unseen, and out of mind, background of modern society and of modern warfare. A large factor driving space use to the forms seen today has been the economics of launching payloads into low earth orbit (LEO). The high cost of spaceflight has given a strategic flavor to most space applications. The development of ubiquitous space-access technologies, the capability for low cost, and robust and reliable orbital launch, have the potential to disrupt the shape of military space power. However, the technical challenges of space access are great, and have kept many promising technologies stuck always “a few years in the future.” Despite a long list of failed dreams, ubiquitous space access endures as a desired emerging military technology.
Space launch has a proven technology base. The problem is that thus far it is an expensive technology, which while not exactly experimental, is far from casual. These realities of spaceflight have until recently meant that space programs are strategic in nature. The euphemism for spy satellites, “national technical means,” alludes to the strategic nature of these platforms. Individually, many of these platforms are worth billions of dollars. Prominent programs making their way to orbit today, such as the MILSTAR 3/Advanced Extremely High Frequency (AEHF) communication satellite constellation have been in the making for years. In the case of the AEHF program, initial contracts for program definition were awarded in 1999,1 actual development in 2001,2 and the first launch of at least three satellites only occurred in August 2010.3 In addition to the United States waiting for the expanded secure communications provided by the AEHF are its partners in this satellite program: Canada, the Netherlands, and the United Kingdom.
Like other similarly priced national assets, the high cost of military space infrastructure is balanced against the capabilities this infrastructure provides. During the Cold War, space-based strategic reconnaissance and missile early warning were part of the information system that allowed nuclear deterrence to be a viable strategy. Today U.S. military space power, although very costly in itself, is providing savings through force-enhancement services to forces within the atmosphere. The mass use of the NavStar global positioning system (GPS) and satellite communications are the foundations of quick and agile U.S. global power.
Ubiquitous space access, or space access that is robust, reactive, and reasonably low cost, would potentially expand the number of missions that may be undertaken, such that lower levels of the security and defense hierarchy (theatre commanders for instance) could have operational control over space assets. This then leads to the subject of operational responsive space (ORS). What constitutes ORS, like the concept of military transformation, encompasses different things to different groups. Among the more common characteristics for ORS, are efforts to lower the cost of space missions and to shorten the timescales involved. Interest in this capability has resulted in the formation by the U.S. Department of Defense of a Joint Operationally Responsive Space Office at Kirkland air force base in 2007.4 Some degree of ubiquitous space access, for the military at least, would be an enabling capability for meeting ORS-type objectives.
The vertical component of military operations above sea level can be conceptualized as being made up of three layers: the lower layer (where conventional airpower exists), outer space, and an in-between, “near-space,” layer.5 These are not the divisions used by atmospheric science,6 which define layers based on specific physical characteristics. Instead the three layers to consider make up a greatly simplified model for demarcating military operations above the earth's surface, based largely on the state of available aerospace technology today.
The lowest level of this simplified model is where conventional airpower can exist. At these altitudes, the atmosphere is thick enough to: (1) easily generate aerodynamic lift, (2) support the operation of common aviation engines, and (3) limit achievable velocities. In the brief history of heavier-than-air flight, what has been “conventional airpower” has expanded with technological change. The gas turbine jet engine, an emerging military technology of the 1930s and 1940s, expanded the envelope for airpower from the limits of piston engines and propellers to the current state of aviation. The breaking of the sound barrier is another past demarcation for “conventional airpower.” Presently the operational envelope of military aviation is limited to a speed of approximately Mach 2.5, or two and a half times the speed of sound. The now out of service Blackbird family of aircraft represents the extremes of this envelope with 2,000 miles per hour plus maximum speed, and an 85,000-feet-plus service ceiling.7
A principal characteristic of the next layer of the military use of the vertical realm, the near-space region of the atmosphere, is the difficulty in sustaining flight in this region. As altitude increases, atmospheric density decreases, resulting in less lift and less oxygen for gas turbine engine operation. Air resistance and the accompanying heat generated by hypersonic flight, while also decreasing with altitude, remain problems until significantly higher altitudes are reached. Launch vehicles, which thus far have been powered by self-contained rockets, fly trajectories meant to quickly pass through this layer into the emptiness of outer space.
The lack of activity in near space may change with aviation technology. Balloon technology is being proposed as a low-cost method to access these very high altitudes, though without any fine control (due to the limited steering options of ballooning). Moving up the scales of cost and technological challenge are very high-altitude airship and very large wingspan unmanned air vehicle (UAV) concepts. Both lighter-than-air flight and the proposed large UAVs are incapable of high-speed flight, their sedate airspeeds in turn being the selling point of persistence over an area of operation.
Outer space, or the military region above the earth's surface where orbiting is possible, is the final layer in this simplified model. There is no internationally recognized standard for where airspace ends and space begins. International treaties, such as the 1967 Outer Space Treaty (OST), do not define where outer space begins. In the United States the criteria for spaceflight have been dependent on the context and/or the agency involved. At present in the United States, to earn astronaut wings, one must achieve an altitude of at least 50 miles (80 kilometers).8 Another common notational boundary for space is the Kármán line—100 kilometers altitude. Theodore von Kármán calculated that at around 100 kilometers of altitude, the speed needed to generate enough aerodynamic lift to support an object was higher than the velocity of an object in orbit at that altitude. As a result, the object at orbital velocity would be able to avoid hitting the earth without the need for lift generated by aerodynamics. The uneven nature of the atmosphere and the minutia of aerodynamic flight have led to some variations wherein orbital mechanics supersedes aerodynamics. Also, while lift may be negligible at 100 kilometers of altitude, air resistance would prevent long-term unpowered orbiting. Nonetheless, 100 kilometers is close enough to calculated values and is easy enough to remember.
Operationally, the lowest of stable orbits are several dozen kilometers above the Kármán line, meaning LEO is a handy benchmark for ubiquitous space access. Successful orbit is dependent on achieving a high enough velocity perpendicular to a line from the spacecraft to the center of the earth such that while the object is being pulled back toward earth, it falls in such a way that avoids hitting the earth, resulting in a circular path. At extreme altitudes the very thin atmosphere, relative to sea level, permits these velocities to be achieved and sustained without propulsion. Lack of atmosphere density also means a lack of the high temperatures and other destructive forces associated with high speeds within the lower atmosphere. In the domain of conventional airpower, Mach 3 is still remarkable to this day due to the difficulty in achieving this performance. When orbital velocities are expressed in the somewhat problematic unit of Mach numbers,9 Mach 25 is the usual figure for the minimum needed to achieve orbit. From LEO, a host of low-power maneuvering options, such as ion and solar sails, are under investigation for long-duration orbital missions. Dropping back into the upper reaches of the atmosphere to maneuver is something of an emerging military technology in itself—hypersonic gliding has been proposed for decades as a means to both extend range and to allow for large changes in flight path relative to the locked nature of orbital mechanics.
In general, orbital altitude and orbital velocity is achieved via rocket technology. Rockets are an implementation of Newton's third law: for every action, there is an opposite and equal reaction. In the case of a rocket, propulsive thrust in one direction is the reaction to a mass ejected in the opposite direction. The specific propulsive force is a product of the mass and velocity of the expelled reaction mass. A pure rocket is a self-contained system, carrying onboard all the propellant needed for flight. A rocket can be as simple as letting pressure force out a working fluid, or as complex as using electrical and magnetic fields to propel subatomic particles. For ground to LEO access, rockets burning fuel and oxidizer from onboard supplies have been dominant.
A daunting amount of propellant, fuel and oxidizer, is needed to propel a payload from the notional standstill of the launch pad to orbital altitude and velocity. Konstantin Tsiolkovsky's rocket equation relates a vehicle's capacity to change velocity, its delta-V, to its engine performance and its change in mass after a velocity change. A mass change of 90 percent is needed for a single-stage-to-orbit (SSTO) launch vehicle based on today's chemical rockets. This mass change, or mass fraction, represents the mass of propellant that must be expended to achieve orbit, and the remaining 10 percent, or less, represents the engine, propellant tanks, structure, flight control, and finally payload. Although this is certainly not a welcome number from an engineering or at first glance an economic standpoint, the SSTO concept does not cross over into the impossible. Barring alternatives to rocket-powered SSTO technology, orbital access is a matter of safely burning enough fuel and oxidizer. Advances that produce lighter vehicles and engines, material science in particular, may even make this feasible in the near future.10
Not wanting to wait for incredibly lightweight structures and engines, the real world of orbital access has depended on multiple stages, both stacking them on top of one another, as was done on the Saturn V, or through the use of parallel stages that may burn for a portion of flight together, as is done with the space shuttle. The staging concept is attributed again to Tsiolkovsky—the multistage variant of his rocket equation produces significantly higher nonpropellant mass fractions. Staging breaks the problem of reaching orbital velocity into parts. After counteracting gravity and drag, each stage is responsible for only part of the velocity change needed to get up to orbital velocity. Each stage only has to accelerate the payload, the stage itself, its own propellant, and any later stages with their propellant. Additionally, each stage can be tailored for the conditions found in the portion of the trajectory in which it is active. There are differences in the specifics of rockets meant for use in the lower atmosphere and those used in the near vacuum of LEO. The use of multiple stages allows significant increases to the nonpropellant mass fraction, but implies greater cost due to essentially needing multiple vehicles, each of which can unexpectedly end a mission through individual failure. A pure rocket SSTO is feasible today, but would be very large when compared to a multistage launch vehicle of the same payload lifting capability, possibly to the point where to safely fly, it would be more expensive than simply assembling a stack or cluster of smaller less dangerous stages.
Rocket science draws from all other disciplines. Broadly speaking, this includes a fair amount of political science as the history of the Cold War and the bibliographies of leading spaceflight luminaries Wernher von Braun and Sergey Korolyov (Sergei Korolëv) demonstrate. Cold War politics, and the funding it enabled, was key to early Space Age progress. Although there is great potential for a near peer, usually China, to invoke thoughts of another “space race,” the budgets for space activities is presently much more restrictive. These shrinking budgets have brought on calls to develop cheaper space access, and cheaper space missions. The basic rocket-powered multistage launch vehicle dates from the 1950s, and a host of technologies seem to be only a few years away from being ready to not only supplant it but also spark a revolution in space access by lowering cost—however, only after expensive R&D efforts. The other means to lower space-launch costs in the near term would be smaller incremental improvements to familiar multistage rocketry. This then leads to a somewhat political battle between those who favor high payoff, but high-risk technologies such as air-breathing propulsion, and those who favor gradual improvements, largely finding cost savings in operational changes.
Air-breathing propulsion is for many the most intuitive technology needed for advanced spaceflight. High-profile programs such as the long shelved National Aerospace Plane (NASP)/X-30 have certainly touted the potential for exotic new high-speed air-breathing engines, such as the supersonic combustion ramjet (scramjet), to change the nature of space access. If an orbital launch vehicle could eliminate a significant part of the propellant load, such as most of the onboard oxidizer, the launch vehicle would be smaller and potentially cheaper to operate in the long term. A lower propellant mass fraction or, in other words, less propellant to lift an equivalent payload, means less mass that must be accelerated initially; overall, this further contributes to the efficiency in vehicle size.
With respect to ubiquitous military space access, air-breathing propulsion offers several beneficial characteristics. It has been suggested that among other things, a significant reduction of onboard propellant may contribute to flexibility, safety, and ultimately aircraft-like operation. Instead of fixed launch pads, many advance concepts have launch vehicles taking off from little more than long aircraft runways. Among the safety improvements cited is a potential for a controlled (and possibly powered) return to the same runway during a mission abort. It must, however, be noted that air-breathing propulsion is not necessarily a prerequisite for this type of operation; sturdy launch-vehicle construction would seem to be the only mandatory requirement for such carefree operation. Then again, a lighter vehicle at launch would definitely make such a craft easier to contemplate. Somewhat a mixed blessing, certain air-breathing engine technologies require sturdy vehicle design and construction to operate, meaning that carefree operations could be a by-product of the engine.
Several forms of air-breathing propulsion have been proposed. These range from using the atmosphere to simply augment thrust provided by rocket propulsion, to systems that use the atmosphere as a source of oxidizer. Above the atmosphere, pure rocket propulsion would be necessary, leading to criticism that in launch-vehicle applications, air-breathing engines result in significant dead weight in the form of the propulsion system or systems that can only operate for portions of the flight regime. Also, many of the air-breathing propulsion options do not function at low speeds. In response to such criticisms, many idealized air-breathing engine concepts combine multiple modes of operation in one engine. An example would have one engine operating as a self-contained rocket to get the vehicle moving from a standstill, transitioning to air breathing when conditions permit, and transitioning back to pure rocket when air-breathing operation is no longer viable, thus minimizing the dead weight problem. Alternatively, if staging is used, rocket and/or air-breathing engines may be shed when they have done their part of the flight.
Air-breathing technology does not necessarily require any technological breakthroughs, as a conventional gas-turbine-powered aircraft may be used as a “stage.” The carrier or “mother ship” aircraft played a prominent role in several U.S. research aircraft programs, including several X-programs, and the lesser well known U.S. Navy Skyrocket program of the 1950s. Orbital Science's Pegasus launch vehicle is currently air launched from a converted L-1011 airliner. Scaled Composites’ suborbital space tourism vehicles, the X-Prize winning Space Ship One and the larger Space Ship Two, are air launched as well. Instead of being described as a first stage, the launching aircraft may also be described as a booster, or “stage 0,” or simply a launching platform.
Air-launch proponents claim a much higher degree of flexibility to the space-launch system, with the carrier aircraft able to fly to the most suitable launch point. Fixed launch pads have to contend with launch windows, when orbital mechanics allow for a specific initial orbit to be achieved, and the problems of local weather conditions. This implies a degree of robustness in the launch vehicle as it must be able to cope with being carried into the air, and potentially, for long distances before being released.
Orbital launch is part velocity change to get up to orbital velocity and part achieving an altitude where orbital velocity is materially possible; therefore, the higher and faster a vehicle is already moving, the better. Lowered demands on rocket performance can equal lower cost rocket propulsion. However, higher-performance aircraft tend to be more expensive. The low-cost option of modifying existing aircraft for air launch imposes restrictions on configuration (where the launch vehicle is mounted) and maximum size. Orbital Science's Pegasus launch vehicle cannot be enlarged too much11 due to the limits of available carrier aircraft, such as the converted second-hand L-1011 wide-body airliner now in use, or the B-5212 that was used initially.
Many launch-vehicle concepts have wings or wing-like surfaces, which will affect the flight characteristics of the carrier aircraft. Coping with these aerodynamic loads potentially leads to compromises in vehicle performance and/or expensive modifications to the carrier aircraft. Internal carriage of the launch vehicle, while avoiding many aerodynamic issues, is limited by the dimensions of the carrier aircraft's interior.13 Release of the launch vehicle from the inside of a carrier aircraft presents additional engineering and safety challenges.14
The aviation company Scaled Composites on the other hand has undertaken the development of specialized aircraft for air launching spacecraft: their White Knight series of carrier aircraft. This effectively is the development of two complex aerospace machines: a dedicated carrier aircraft and a spacecraft. It does avoid many of the compromises needed to adapt an existing vehicle. Scaled Composites’ carrier aircraft are also being marketed for roles where the payload is not released for independent flight. Pushing the boundaries of conventional aviation, respected aerospace industry magazine Aviation Week made claims in its March 6, 2006, cover story of a covert spacecraft launched from a large high-speed aircraft described as “XB-70 like.”15 For a brief while this article did fuel speculation and debate over this and other similar reports of large high-speed “mother ship” aircraft, but like many supposed secret aircraft being flown above the southwestern United States, it has faded from the mainstream. Without delving into the contentious claims made in the March 2006 Aviation Week article, the very public XB-70 program of the 1950s–1960s was a Mach 3, gas-turbine-powered aircraft,16 and there was some discussion at the time over its potential to assist in boosting small launch vehicles.17
Widening the spectrum further to encompass other forms of “conventional” flight, lighter-than-air balloons have also been proposed as potential launch platforms. High-altitude balloons are a potential low-cost technology for achieving altitudes significantly higher than those possible by conventional aviation. The higher the altitude, the less atmospheric density there is to impede high-speed flight through drag and high temperatures. Balloons, while being relatively inexpensive, are generally regarded as fragile and lack the lifting potential of powered flight.
The use of conventional aviation propulsion in spaceflight for many is at best only a stepping stone, and truly revolutionary space access requires similar revolutionary air-breathing engines. This, however, runs into the many problems of processing the atmosphere for use in the engine, while the whole vehicle is accelerating through the air. A well-designed air intake will, at high speeds, assist the engine it is feeding by compressing the inbound air. In the Blackbird family of aircrafts a portion of the thrust needed to attaining Mach 3 performance is attributed to its complex variable inlet system.18 In this regard, high performance is not simply a matter of having a powerful engine available, but one of integrating the engine with the aircraft.
The most basic jet engine is the ramjet, which dispenses with the turbine-driven compressor and uses the simple fact that the necessary air compression can be produced by having a properly configured duct and being at a high enough speed for the duct to work. It is in the details of the ducting and getting up to the necessary high speeds where this simple concept becomes an expensive and difficult-to-solve engineering problem. Both rockets and gas turbine jet engines are possible options for propelling a craft to the minimum operational speed for a ramjet. During ramjet operation these engines are either throttled down, as in the case of the Blackbird program's J58;19 discarded, as is done in many experiments;20 or carried along as dead weight.
Related to the ramjet is the air-augmented rocket, or ducted rocket, where the high-velocity exhaust of a rocket inside a duct draws in, compresses, and accelerates a large volume of air as additional working mass, resulting in more thrust. Like the similar ejector-lift concept for vertical takeoff aircraft, where jet exhaust is used to draw in a greater working mass, air augmentation is not a new idea, but has found little in the way of real-world application. It would appear that even with rocketry's inherent difficulties, there are more difficult aerospace propulsion technologies to put into practice. For equal performance, a big self-contained rocket is simpler to design and construct than a smaller self-contained rocket plus a duct able to provide worthwhile augmentation.
In what is defined to be a basic ramjet, the inbound air enters at supersonic speeds, but is slowed to subsonic speeds for combustion, which then leaves the engine at supersonic speeds again. This slowing, due to the airintake configuration, results in the desired compression, but also generates waste heat and drag. A fundamental difficulty of engine/air-intake design and ramjet design in particular, is achieving worthwhile thrust after the drag of the engine itself is overcome. Eventually it no longer becomes worthwhile to decelerate the air flow any further. This of course becomes a limit to the maximum speed the ramjet can operate at. The scramjet is touted as a way to attain higher hypersonic speeds by not slowing the airflow below supersonic speeds. The challenge for the scramjet is maintaining combustion in a supersonic airflow.
Efforts to produce viable scramjet-powered vehicles have led to designs with a high degree of integration between engine and airframe. Many recent concepts involve using the entire lower fuselage in front of the engines as part of the air intake to help compress inbound air. Beyond the engine's exhaust, the airframe slopes upward, acting as an expansion ramp (essentially acting as an engine's nozzle). The simulation work that has resulted in these shapes has been greatly aided by advances in computer technology. Among the many tasks laid before the growing number of supercomputers are simulations on how the atmosphere will interact with these hypersonic aerospace craft and their engines. A computer model is, however, only a simplified version of reality, limited by the complexity of the simulation and the assumptions entered for the atmosphere, the airframe, and the engine. Up until recent physical experiments, the U.S. X-43A21 and the Australian-led international HyShot program,22 there were doubts as to whether a scramjet engine could sustain combustion, and whether the thrust generated could overcome the drag of the system.
Despite the principle behind a scramjet engine being sound, there remain many technological hurdles before this technology becomes practical. Closely related to the actual scramjet engine are technologies related to increasing performance margins. Among the most prominent are systems to recoup energy from the heat generated by hypersonic flight, and by the engine itself. Worthwhile acceleration by scramjet means that the vehicle will have to remain within enough atmosphere to sustain the engine but also exposing it to extreme heating. Although passive heat shielding using advanced materials is possible, many of the higher-performance scramjet concepts use active cooling to not only keep the vehicle from melting, but also to extract otherwise wasted energy. This practice is already in use in some existing rocket engines, where propellant, often a cryogenic liquid, is circulated around the engine and nozzle to keep these components from melting. However, an active cooling system adds mass; once again to be worthwhile, the energy extracted should more than compensate for the burden imposed by the cooling system.
Technical challenges also arise from the fuel being circulated itself. Hydrogen is one candidate fuel for scramjets, and is already in use in many high-performance rocket engines. By weight, liquid hydrogen provides greater energy than hydrocarbon rocket fuels such as RP-1 (a highly refined kerosene) and has no potential to leave carbon deposits or residues to clog up what must be a fast fuel flow. However, hydrogen is potentially damaging to materials due to hydrogen embrittlement—where hydrogen gets absorbed by metal alloys making it more brittle. Ironically the capacity for materials to absorb hydrogen is being investigated as a means for safe fuel storage for ground vehicles. Also, while the extreme cold of liquid hydrogen is useful for cooling, there are material problems with the temperature transition from the superheated surfaces on the outside to the cryogenic temperatures of the fuel flow on the inside. Liquid hydrogen's low density presents a drag problem due to the bulky tanks needed for this propellant. The smaller fuel tanks needed for heavier RP-1 make this less-potent fuel a viable alternative. Compounding the fuel problem for scramjet-powered vehicle concepts are the complex external shapes that airframe-to-engine integration often yields do not result in efficient internal space for fuel tanks. Among the problems plaguing the (less-challenging rocket powered) X-33 program before its cancellation was the production of a lightweight composite fuel tank able to effectively make use of the space inside the irregular lifting body shape.23
Thus far, air-breathing ramjet propulsion has been a prominent technology in extending the range over purely rocket-based systems. Solid-fuelled “ramrockets,” essentially air-augmented rockets where the rocket exhaust contains excess fuel to be burned in the airflow from air augmentation, are being deployed in missiles such as the European Meteor air-to-air missile. These missiles, however, are only operating at conventional aviation speeds, and extended ranges only translate into increasing flight durations at supersonic speeds by minutes. Long duration in the atmosphere is potentially counterproductive to orbital space launch. Conventional rockets quickly clear the atmosphere to reach an altitude where orbital velocity is achievable without having to deal with severe aerodynamic drag and heating. The challenges of in-atmosphere hypersonic flight have contributed to scramjet-powered earth-to-orbit concepts, such as the long-defunct X-30 National Aerospace Plane switching over to rocket propulsion at lower velocities.
Avoiding some, but not all, of the problems of scramjet is the air-breathing rocket. An air-breathing rocket is basically a rocket engine that can have oxidizer supplied either by an onboard oxidizer supply, or from the atmosphere via some processing. Depending on the proposed system, air may simply be cooled and compressed, or it may actually be refined to separate out oxygen for the engines; with the remaining air components such as nitrogen and water vapor dumped overboard. In theory such an engine could operate from ground to deep space. Again to be worthwhile, the air-processing parts of an air-breathing rocket engine must be very lightweight as the mass of oxidizer it replaces must make up for the penalty of having the air-collection system along for all pure-rocket modes of flight it is hauled around with.
As long as air-breathing operations are confined to modest speeds, the air-breathing rocket does not require quite as much integration of the air-collection system with the airframe. One of the more prominent air-breathing rocket concepts being promoted today, Reaction Engine's Skylon, has simply mounted its air-cycle rockets in wingtip pods, leaving the main fuselage to be sturdy cylindrical shaped.24 Skylon is only meant to collect oxidizer from the atmosphere up to moderate hypersonic speeds—a balance of technological risk and trade-offs its backers see as the best way to produce a cost-effective launch system in the near term.
Promises of aircraft-like operations encapsulate the qualities of ubiquitous military orbital access that sets it apart from current space-launch capabilities. It also highlights that these claims have been made before. True aircraft-like operation usually translates into a lack of launch pads or other fixed infrastructure and vehicle preparation that does not involve a complete overhaul. The recently shut down space shuttle program has only been launched from the Kennedy Space Center (KSC) in Florida; with the second facility, Space Launch Complex-6 (SLC-6) at Vandenberg Air Force Base in California, never being used for shuttle missions despite billions being spent (the shuttle launch pad there, SLC-6, being ultimately used for other launch vehicles). Preparation for a shuttle mission takes weeks, and includes carefully assembling the launch stack of orbiter, solid rocket boosters, and external propellant tank.
Every contemporary orbital launch vehicle sitting ready for liftoff is the embodiment of vast quantities of chemical energy. Harnessing this power today requires a large collection of experts and specialist personnel, leading to an expensive payroll. Sacrificing performance for inherent robustness is one potential trade-off: the cost of propellant traded for the cost of staff. Computer diagnostics and embedded sensors have made inroads in aviation, and have resulted in less maintenance hours needed to keep an aircraft fleet flying. All of these technologies and procedures that reduce personnel will of course need to be proven as effective means to safely conduct a space program and not simply corner cutting.25
Related to the personnel and infrastructure costs of present-day LEO access options is the problem of scheduling. Expensive as each space-launch facility is, each at best is only able to perform a few dozen launches a year. Part of the economic debate about the now-retired space shuttle program was over the high fixed and sunk costs that could not be spread out due to the low number of launches per year. This presents the interesting problem of whether low-cost orbital access depends on high flight rates, or whether only high flight rates will truly reduce the cost of orbital access.
Aircraft reusability is one quality that many spaceflight enthusiasts desire, but may not necessarily be worthwhile. Given the same technology base, a reusable launch vehicle will from a mass standpoint be less efficient than an expendable launch vehicle. The equipment needed for recovery: thermal protection, additional flight control, propulsion, parachutes, landing gear, and aerodynamic surfaces, all burden an already constrained nonpropellant mass allowance. As far as fixed costs go, the infrastructure required for vehicle inspection and refurbishment can quickly overtake any savings from reusing hardware, especially if the vehicle does not have the performance margins available to conventional aviation. Reusability becomes a valuable trait only if the price of reusability is lower than its benefits.
Aircraft-like operation implies a high degree of mission flexibility not possible with a limited number of fixed launch pads. Among the reasons for a second shuttle launch facility at Vandenburg Air Force Base during the early days of the shuttle program, was to allow for polar orbit launches not permitted from KSC on safety grounds.26 Horizontal launch and recovery, familiar as an aircraft's runway takeoff, are also implied by the lack of a specialized launch pad.27
The space shuttle program was sold to the U.S. taxpayer as having an aircraft-like operation and in this regard it was a failure. The processing needed to get a shuttle off the ground and back to the launch pad has certainly made “aircraft-like” operation for the shuttle a dubious claim. To be fair, the shuttle produced was not the shuttle originally envisioned due to technology and cost trade-offs that had to be made in the 1970s when the program took shape. Today the shuttle program can be remembered for reaching far, achieving much, yet falling short on the critical goal of revolutionizing spaceflight by making it ubiquitous.
Less exciting than totally new engine concepts, but perhaps of greater potential to transform space access, are operational changes to rocket-based launch. This takes the technology base for propelling a payload to orbit and refines it toward the goals of responsiveness, robustness, and low cost. Outright vehicle performance and sophistication is traded for robustness, reaction time, and cost effectiveness. The use of lower-performance rocketry does not mean a complete avoidance of new technologies. Instead it is more an analysis of existing and potential technologies that prioritizes cost effectiveness over outright performance. Orbital launch rocketry has a proven technology base—an expensive and difficult-to-master technology base, but the basics have been mastered by the United States and others. It only remains to be seen if this existing technology base can be redirected over time to producing ubiquitous space access.
Robust and reactive space access, though not orbital access, is already available today via pure rocket propulsion in the form of the ballistic missile. To achieve intercontinental ranges from a ballistic trajectory, these missiles generally cross all notational boundaries of space; also, due to the nature of nuclear strategy, these missiles must be able to launch within minutes of the command. Nuclear weapon miniaturization and increased missile accuracy have mitigated some of the need for increasing payload capacity; however, these factors produce two opportunities: mobile launch platforms and multiple warheads. Illustrating the robustness of modern ballistic missiles are the Russian off-road truck mobile Topol-M, and submarine-launched ballistic missiles (SLBMs) such as the multiple independent reentry vehicle (MIRV) equipped Trident D-5 used by the U.S. Navy and Royal Navy.
The history of the Cold War, perceptions of threats, and the abilities of each of the superpowers to fund development and production have led to the relatively large number of long-range ballistic missiles that still exist today. Originally, ballistic-missile development was given low priority in the United States. Though the United States possessed quite a bit of rocketry experience, including that found in the form of surrendered Nazi-rocket experts such as Werner Von Braun, it was thought that bomber technology would suffice for the time being. This changed when it eventually became known that the Soviet Union was not pursuing a purely symmetrical nuclear-delivery capability in the form of bombers; instead, it had decided to heavily invest in ballistic-missile development. In today's terms, this would be called an “asymmetrical threat” or “game changer.” Public cognition of the Soviet rocketry threat culminated in the reaction to Sputnik 1 being placed in orbit in 1957. Among other things, fear of the Soviet missile and space threat led to the creation of the Advanced Research Projects Agency (ARPA), later renamed the Defense Advanced Research Projects Agency (DARPA).28 Crash programs quickly led to the first-generation U.S. intercontinental ballistic missile (ICBM), the liquid-fuelled Atlas, and, only a few years later, the first U.S. SLBM, the solid-fuelled Polaris. Another result was, of course, the space race.
The specifics of space launch have led to many critical differences between U.S. orbital space-launch vehicles and ballistic missiles, although they have built from a broadly similar technology base, with several major launch-vehicle families being direct offshoots of ballistic missiles. Weapons development has generally favored rocketry that features robustness and reactive operation over sheer propulsive efficiency. Nuclear warheads are also somewhat more robust than the average satellite in orbit today. Since the retirement of the Titan ICBM, all long-range U.S. ballistic missiles have been solid fuelled.29 In general, solid-fuelled rocket motor technology is less powerful than liquid-fuelled rocket engine technology30 but offers characteristics important to weaponization, such as robustness and short reaction times. Taken further is the concept of the “all-up” or “wooden” round, where complete or near-complete munitions, such as missiles, are manufactured to be sealed in containers for long periods of storage without maintenance, but still can be depended on to operate with little if any preparation. This mode of operation has made few inroads in space launch and satellite construction, where missions are planned years in advance and both satellites and launchers are handled in continuously monitored “clean-room” environments for as long as possible.
Proponents of ORS want to essentially develop a space operations model that is closer to the sortie of a military unit, as opposed to an expedition. A possible endpoint of ORS is to have stocks of launch vehicles in a state of readiness along with payloads, or components for payloads, all of which can be brought together on short notice. The definition of short notice is relative to that of existing space programs, meaning that a mission timeline from approval to orbit being measured in months, as opposed to years, goes a long way toward meeting ORS goals. Niche applications may ultimately see the ORS concept leading to satellites attached to launch vehicles on continuous standby as is done with some nuclear weapon delivery systems.
The problem with niche applications is that their expense has to be justified in a spending environment that is often hard-pressed to sustain more routine expenditures. Arguably the continuous alert maintained for nuclear-armed ballistic missiles is a niche mission in and of itself, if only because of the extreme reluctance to employ nuclear weapons outside all but the most dire of international crises. The threat of such a conflict, and the nature of Cold War international relations, justified the expenditures of the nuclear arms race. Reactive space access, on the other hand, does not have such an easily identified or ever-present existential threat. If there was, then current technology could produce something akin to ORS, but much more expensive than that being proposed. Inventories of contemporary satellites and launch vehicles, given enough funding and personnel, could be produced and maintained in storage on the ground, ready for launch during some national emergency.
The U.S. Space Shuttle, a program both celebrated and criticized for its complexity had, in its final years, adopted something similar to a reactive mode of operation, the launch on need (LON), or rescue mission. Since the Columbia tragedy, space shuttle missions have been publically shadowed by preparations for a LON shuttle mission in case something goes wrong with the orbiting mission. For the most part this rescue mission made use of personnel and the space shuttle already in preparation for the next scheduled flight. However, for the final Hubble Space Telescope (HST) servicing mission, STS-125, the International Space Station (ISS) could not be used as an on-orbit refuge for the weeks it would take for the LON mission to be launched.31 The additional dangers recognized for the crew of the space shuttle Atlantis on STS-125 led to some controversy over actually conducting this last servicing mission. As a precaution, the space shuttle Endeavour was kept on a second launch pad, ready for a quick (within a few days notice) launch during part of the Atlantis STS-125 mission.32 Both the standby rescue shuttle mission and the nuclear strike mission are expensive niche applications for ostensibly undesirable circumstances, but were/are justified by the level of threat.
Necessity has led to something similar, but not the same, as ORS in the form of the Soviet military space program. To this day, versions of the Soviet R-7 ballistic missile from the 1950s continue to be used to launch payloads into orbit. With the end of the Cold War these R-7-derived “carrier rockets,” the Russian nomenclature for launch vehicle, became available for Western payloads looking for low cost, but still reliable, rides to orbit. The R-7 and its derivatives use clusters of relatively small rocket engines burning kerosene, or kerosene substitutes, in liquid oxygen. These rockets are not reusable and are relatively heavy in construction. Although the Soviet Union, and now Russia, has its share of high-performance launch-vehicle development, including many interesting concepts for hypersonic air-breathing SSTOs,33 a combination of influences, including financial constraints and a degree of trust from decades of continuous use, have made R-7-based carrier rockets very hard to replace. The family of launch vehicles spawned from the R-7 can easily be called the “workhorse” of the Soviet and Russian space programs, and an exemplar for advocates of using simpler and cheaper mass-produced rocketry to meet expanded launch needs.
Of particular historical interest to ORS proponents was the Soviet Union's preference and sustainment of short life span satellites. Part of this was choice, and part was due to the lower technology base of the Soviet Union relative to the West. However, satellites designed to do less, and for shorter periods, did have advantages. A single launch or satellite failure has less impact, and planning for frequent replacement presents the opportunity for mass production and for frequent incremental upgrades. As in all comparisons involving the Soviet traditional emphasis on quantity over quality, concerns were raised over the vulnerability of the Western model of having fewer highly capable and long (planned) life span satellites. Now the Soviet model for running long-term space programs is not an example of the full set of ORS goals; it was a method to make up for less-sophisticated technology and not an intentional attempt to create new capabilities by increasing space access. However, the sustained higher launch rates of the past are certainly of interest.
Advances in aerospace technology that may permit the creation of the idealized air-breathing SSTO may also be applicable to robust, reactive, and low-cost multistage launch vehicles. Indeed, work on an idealized SSTO may stall its own deployment by being applied to a nearer-term multistage vehicle. Air launch from high-performance aircraft and other forms of hybrid launch vehicles, where a reusable booster is used with an orbital stage (which may or may not be reusable), can benefit from SSTO research, while at the same time being technically less risky/ambitious and less costly in the near term. The 2010 USAF Technology Horizons report identifies the possibility and utility of developing in the near term (2030s) a vertically launched two-state-to-orbit (TSTO) launch vehicle with a horizontally landing reusable rocket-booster stage, and an orbiter featuring air-breathing propulsion.34 Interestingly, the same report is also advocating a very high-speed strike aircraft based on similar technology to that proposed for the air-breathing engine propelled orbiter.35
Pure rocketry itself has not completed all avenues for development. In general, rocket engines have high thrust-to-weight ratios and, being self-contained, avoid many of the factors that have made air-breathing propulsion technology so difficult. Already there is interest in policies to foster RP-1/LOX (liquid oxygen) rocket engine technology development and production in the United States (over continued use of Russian supplied engine technology).36 Despite being ultimately cancelled, the X-33 program did further research on aero-spike rocket engines, a technology that promises to produce an engine nozzle that maintains high efficiency independent of altitude, instead of only being efficient at one specific altitude.
Solid rocket motors are another example of the trade-off of performance for low cost. A solid rocket motor is the combination of solid fuel and oxidizer in a binding material cast into the motor casing. It is argued that the large quantities of solid fuel needed to launch a small satellite into orbit present safety and handling problems: the rocket is always fully fuelled and therefore always capable of exploding if an accident were to occur.37 Also, once ignited, a solid rocket motor cannot be shut down. Being fully fuelled at all times is, for missile applications, a beneficial quality once safe handling procedures are established. Recycled U.S. ballistic missiles for space launch are now exclusively solid fuelled, though often topped off with a liquid-fuelled stage or stages. Solid rocket motors were prominent in both the manned and unmanned Ares rockets of NASA's Constellation program that was cancelled in 2010. Despite a solid rocket burn through causing the Challenger space shuttle disaster, solid rockets have proven safe when handled correctly, as can be seen in the 100 or so shuttle missions after Challenger, and in the ballistic-missile fleets of the U.S. nuclear deterrent force.
The lack of controllability, and arguably safety, inherent to solid rocket motors can be overcome by replacing the solid oxidizer component of the propellant casting with a fluid oxidizer, which can be shut off or throttled if one desired this additional capability. A solid fuel combusted with a gas or liquid oxidizer forms a hybrid rocket (not to be confused with the earlier hybrid launch vehicle). Although a hybrid rocket would have a load of fuel onboard once constructed, this fuel would not easily burn without exposure to large quantities of oxidizer, which would only be loaded for launch. Hybrid rockets are in use with several manned commercial space projects, Scaled Composites’ Space Ship One and Space Ship Two being two of the more prominent examples from the emerging space tourism industry.
Beyond improvements to existing types of rocketry, there is near-term potential for pulse-detonation technology, which seeks to harness the fact that detonation of fuel in many respects is more efficient than constant rate burning. Pulse detonation and other constant-volume engines also dispense with the heavy pumps or fuel pressurization needed for a high constant flow (and pressure) liquid rocket engines, potentially reducing weight further. In 2008, as part of a U.S. Air Force Research Laboratory (AFRL) program, a pulse-detonation rocket engine was operated in flight for the first time.38 Pulse-detonation technology is also being investigated in air-breathing forms.
A potential trade-off to provide ubiquitous orbital access is flexibility. Some concepts promising to reduce launch costs, and increase launch rates, involve moving part of the mass needed for acceleration to orbital velocity off the launch vehicle. Fixed ground facilities, unlike the launch vehicle, have fewer restrictions on mass and size. The most basic would be the gun launch concept, where a very long, large bore-size gun gives a boost to a very small launch vehicle with onboard rockets. Similar in concept, but capable of boosting significantly larger launch vehicles are rail-boosted concepts, where the launch vehicle is given an initial boost while travelling on a fixed rail. Options for powering rail-based boosting range from rockets, to magnetically levitated (maglev) train technology.
Related to both pulse-detonation engines and the directed energy weapons of the next chapter are concepts of using high-power lasers or microwave beams to superheat a reaction mass. This expanding vaporized material can produce thrust in the same manner as a jet or rocket engine. The origin of this concept is credited to Dr. Arthur Kantrowitz, and the 1972 paper, “propulsion to Orbit by Ground Based Lasers.'39 The expansion caused by sufficiently rapid heating is a detonation—the gas expands faster than its speed of sound. Rapidly cycling on and off, the external energy beam produces a series of detonations able to provide thrust. Dr. Leik Myrabo of the Rensselaer Polytechnic Institute has been prominent since the late 1990s40 in advocating and demonstrating beamed-power pulse-detonation propulsion using the air the craft passes through as reaction mass.41 At higher altitudes, and insufficient atmosphere, Dr. Myrabo's Lightcraft concept switches over to onboard reaction mass. Beamed propulsion is also under investigation globally,42 with small models being powered upward by external laboratory lasers and microwave beams. Projecting power from a ground station to a launch vehicle in flight shares many of the same challenges faced by directed energy weapons; both involve precise transmission of large amounts of energy across hundreds of kilometers/miles of atmosphere.
Technological leadership is important to national power; however, it does not necessarily have to be dependent on direct national funding. In U.S. space circles, at the time of writing, there is a great debate over the future manned spaceflight in United States, specifically over the roles of the government (NASA) and private industry. Contracts have already been signed for private companies, under Commercial Orbital Transportation Services (COTS) funding, to provide supplies to the ISS for unmanned space lifts. Many of the advanced low-cost space launchers already named in this chapter are associated with companies other than the big aerospace companies. Internet entrepreneur Elon Musk has, in only a few short years, started up a private launch company (SpaceX), put into service two new orbital launch vehicles (Falcon 1 and Falcon 9), and constructed a recoverable space capsule for making deliveries of cargo, and potentially crews, to the ISS (Dragon). Investors are also seeing commercial viability in propulsion systems beyond the multistage rocketry used by SpaceX and its contemporaries. This includes the already mentioned Reaction Engines of the United Kingdom with the Skylon air-breathing propulsion SSTO concept.
The thresholds for military adoption and employment of a technology are not necessarily the same as that for commercial purposes. This can already be seen with information technology. In many respects, common-day civilian computer and information applications display a level of sophistication that is not seen in general military use. Making the trade publications recently was a U.S. military program investigating the value of smart phones.43 Smart phones in the civilian world are ubiquitous items and are cited by some as a major factor in contemporary Western culture. However, the relative fragility, both in physical and software terms, of consumer electronics has limited military applications. The commercial failure of the Concord is an example of the opposite; although the military has found the capability for supersonic flight to be a routine requirement for many categories of combat aircraft, this technology base faces greater challenges to being applied to commercial flight. It remains to be seen if the technologies behind the slowly emerging industry of civilian suborbital and orbital access may be suitable for national defense needs.
It should, however, be remembered that for commercial manned spaceflight to become a viable industry beyond serving a small clientele of wealthy adventurers, the cost and timelines of a space launch would have to come down significantly, and reliability would certainly have to increase. Ubiquitous civilian/commercial orbital access may involve technological hurdles beyond that needed for initial fielding of a military form of ubiquitous orbital access. The fact that there are companies out there working to solve the greater problems of commercial manned spaceflight leave open the possibility of ubiquitous military spaceflight being spun-on from the civilian marketplace, instead of civilian spaceflight being a spinoff of military technology. It also raises the specter that lack of attention in the area of civil launch-vehicle development will allow a potential opposition force (OPFOR) to reap the benefits of commercially viable private spaceflight.
Ubiquitous LEO access will affect the options that are available with respect to the exploitation of space. It is consistently reinforced that the conventional-warfare preeminence enjoyed by U.S. military today is linked to its use of space-borne assets; therefore, ubiquitous LEO access will affect today's conventional-warfare paradigms. The ongoing proliferation of space-access technology has the potential to accelerate if ubiquitous LEO access becomes a reality. This proliferation will affect the nature and number of threats to the Western world in general as well as specifically to the United States.
There are longstanding warnings, such as those found in the 2001 Rumsfeld Commission report, concerning the long-term viability of the existing model for U.S. military space supremacy. Recognition of the force enhancement conferred by the long investment in space by the United States has spawned two areas of threat: attempts to emulate U.S. military space power, and attempts to neutralize U.S. military space power. The high cost of LEO access has so far limited the ability of all but near-peer competitors to field such strategies. Near peers such as the People's Republic of China and Russia, possess high-technology economies and military industries, meaning they have the option of developing equivalents to technology that regulations prevent them from importing (legal or otherwise). Even without espionage providing shortcuts, once a basic concept is proven, the research and development of equivalent and counter-technologies is only a matter of time. Potentially, the tech bases of a near peer, or even of traditionally allied nations, could introduce disruptive technology in the form of ubiquitous space access.
Added to the expected threat provided by competing foreign military space programs are concerns about commercial space services as both a threat and as vulnerability. Commercial entities are now providing space services, such as earth imagery, that only a few years ago would have been the exclusive domain of national agencies. Foreign companies that provide these services are beyond the reach of U.S. “shutter control” regulations that U.S. companies are subject to. Among recent operations, the United States bought exclusive rights to all commercial imagery of the Afghanistan theater of war to ensure operational security—a step it had also taken during the Gulf War. These financial methods may not always be available, or effective. Increased use of commercial communication satellites to handle the seemingly endless growth of U.S. military data bandwidth needs has become a necessary stand-in for delayed military programs. In general, the military use of commercial satellites has the potential to mark these satellites as targets in any future conflict.
The academic world often seeks to sort the real world into theoretical boxes or to arrange them into a theoretical spectrum.44 Among the more commonly cited works is USAF Lieutenant Colonel David E. Lupton's On Space Warfare, which divides military space policy and doctrinal positions into: sanctuary, survivability, high ground, and space control.45 The term high ground in particular is often used, with reverence, to describe how far a nation could go with military space power, and defines space as being the critical domain with respect to not just one specific battlefield or conflict on earth, but to a nation's global destiny (see also Evertt Dolman's Astropolitik). The value of specific capabilities and policy doctrines associated with overt space weaponization fluctuate with the price of LEO access. Therefore, the emergence of ubiquitous space launch, and the form it takes, will shape what aspects of these doctrines become viable.
Space as a sanctuary is not a purely pacifist stance, instead it is also a strategy to use diplomacy to safeguard the existing security situation for Western military power. During the Cold War, and to the present day, satellites were part of the nuclear deterrence strategy. Early warning satellites gave adequate notice to ensure a retaliatory strike, and spy satellites (national technical means) promoted stability by first confirming the existence of retaliatory capability, dispelling the temptations of a first strike, and as a confidence-building measure for treaty verification, dispelling the temptation to cheat. Space served as an environment to promote strategic stability in the Cold War. In the age of space-force enhancement, some Western nations, such as Canada, are wary of active space weaponization due to the threat it may bring back on the West. The West and the United States, in particular, have heavy investment in space infrastructure; today space is arguably not just an out-of-mind pillar for Western military power, but also for Western society in general. Preventing the development of space weapons through diplomacy safeguards this pillar. This, however, is a stance that has been under contention for a while, even with space access having a high-cost barrier.
With the introduction of ubiquitous space access, whether through direct military investment or not, space sanctuary, as a policy, may no longer be sustainable. For one thing, the space sanctuary position does not freeze the situation to the West's advantage, allowing others to catch up, something near peers such as China and Russia are openly doing. That is not to say that U.S. force-enhancement capabilities cannot improve, but with precision munitions already having accuracy within single digit measurements in meters, and charges that communications bandwidth is being flaunted for unnecessary multimedia presentations and excessive micromanagement (as opposed to more effective forms of support for front line troops), one can see diminishing returns from purely advancing space-force-enhancement capabilities. Increased access to LEO, unless it is somehow exclusive to the United States, would actually in this regard, threaten U.S. power by facilitating others in replicating U.S. space power capabilities.
In recognition of U.S. satellite vulnerabilities and emerging foreign anti-satellite (ASAT) capabilities there have been recent calls to reduce dependency on space assets as much as possible. However, again it should be remembered that space assets provide the ability to project information superiority into denied parts of the world. Compact satellite telephony services such as Iridium may have been a mismatch for the civilian market; however, its global reach and compact handset (relative to other satellite communications gear) made it ideal for many power projection applications. As long as the United States wishes to retain the capacity to project power globally, and continue to fight with the level of precision to which the West has become accustomed, then some amount of space infrastructure will be needed.
Short of abandoning assured use of space, but without proceeding with a policy of clear and definitive space weaponization, ubiquitous LEO access provides options to quickly reconstitute military space assets in times of war—a strategy of survivability. As noted earlier, this strategy could be put into place today were it not for the extreme cost associated with present-day orbital launchers. A ubiquitous space-launch capability combined with low cost but capable small satellites (see Appendix) would assure U.S. space power through sheer numbers of easily replaced and disposable satellites. It is unlikely that another nation would attack U.S. space assets as a goal in itself. Instead, any attack on U.S. military space infrastructure would be performed as a means of hindering or neutralizing U.S. forces on earth. A recognized capability for U.S. space power to be quickly rebuilt as part of a swift and devastating retaliation would, then, perhaps be deterrence against an ASAT attack in the first place, and possibly even deterrence against whatever activities the opposition force is planning on earth. This would, however, also require maintaining war stocks of critical satellites.
The ability to rapidly reconstitute existing capabilities is only the beginning. With greater access to orbit, there is also the potential to surge space capabilities on demand. Many space assets that could be useful in times of war may not be economical to maintain in orbit in times of peace. The shortened timelines promised by ORS advocates raise the possibility that ingenious new uses of space could be thought of and implemented in the timeframe of a single conventional war. Moreover satellites in orbit, even without open warfare, are continuously exposed to the hostile environment of space, where radiation is plentiful, collisions often involve high energies, and when closer to earth, what little atmosphere is present includes highly reactive single oxygen atoms.
Aside from the high cost of space launch, the exploitation of space (let alone the exploration of space) is expensive due to the challenges of surviving in a hostile environment. The high cost of a space mission today is compounded by the need for engineering perfection due to the very limited capacity for on-orbit tweaking of equipment and repair, which is, for most missions, out of the question. In an odd way, budgeting for loss and failure is a luxury that contemporary use of space cannot enjoy. Keeping space assets on the ground, a space force in potential, while training with earth-bound substitutes and simulations to maintain credibility, could be a low-cost means of maintaining U.S. space power.
Not only do orbital space weapons become more affordable due to effective reductions to launch costs, but the potential targets, both United States and potential opposition force satellites, also increase due to access. Today's satellites are considered strategic assets, and certainly have price tags in the same range as warships. The loss of one of today's militarily critical satellites would be akin to the loss of a major national asset and would demand an appropriate response. Indeed at some stages of the Cold War, an attack on specific satellites, early warning and strategic communications in particular, could have been the beginning of a strategic nuclear war. As ORS and related concepts bring satellite assets to the “tactical” level, through lower cost and greater numbers, their abundance raises the possibility that at least some of these new military space assets would be regarded as being more expendable. Lowered importance creates the problem of an adequate response to a satellite attack, especially now in an age where Western militaries seem to be increasingly constrained by requirements for proportional responses. In other words, if satellites come to be regarded as tactical assets, how much escalation can be justified over the loss of a few of these “tactical satellites?” With escalation, satellite services that are considered critical today come under threat. Once again there is the problem of defense or deterrence. Despite being the low cost and existing solution, there are political barriers to threatening nuclear retaliation for the loss of major space infrastructure— even if it is a pillar of the Western way of war and perhaps even Western society. Like the moral dilemma to nuclear deterrence, solutions range from diplomacy to armaments.
There are many potential futures for the military use of space. To a large degree, these futures are differentiated by the level that space becomes weaponized. At present the existence or nonexistence of space weapons is based largely on what one defines a space weapon to be. Despite actually destroying orbiting satellites, direct ascent (earth-to-space) systems such as the Chinese satellite interceptor that conducted a destructive test in 2007, the U.S. Air-Launched Miniature Homing Vehicle (ALMHV) tested in the 1980s, and the U.S. SM-3 missile system adapted for a satellite interception in 2008, would not be considered space weapons under the space weapons ban recently proposed by China and Russia in the forum of the United Nations (UN) sponsored Prevention of an Arms Race in Outer Space (PAROS), where space weapons are defined as orbiting weapons and not satellite-destroying weapons.46 It should be noted that the Chinese government's own direct ascent testing did not stop them from protesting the 2008 U.S. satellite shoot down, which was less a weapons test and more of an action to mitigate the threat of a chemical accident if the failed U.S. satellite had been allowed to crash intact.47 The present state of space weaponization is arguably unclear and somewhat “fuzzy.”
Historically, a space weapon defined as an orbiting weapon has been deployed, though only temporarily. The Soviet Union mounted cannon armament on at least one of the Almaz series of military space stations, which were covertly orbited as members of the civilian Salyut program.48 The 1967OST does not ban conventional weapons in orbit, and disguising the Almaz program had more to do with it being a reconnaissance (spy) platform. The ease at which a satellite's true purpose may be disguised presents serious problems to treaty verification. Indeed the whole subject of satellite “inspection” becomes problematic due to the weapons-related nature of this capability. An orbiting space weapons ban could ironically ban the means to verify compliance of its own terms.
Among ground-based systems that are often overlooked as space weapons are electronic warfare (EW) systems meant to disrupt receiving services broadcast by satellites. GPS jammers were deployed by Iraq in a failed bid to interfere with U.S. precision munitions during the 2003 war.49 The U.S. Counter Communication System (CounterCom) is listed in publically available budget documents under the category of “Counterspace Systems.”50 Now EW is often overlooked in general: it is kept secret intentionally as it is related to signals intelligence and other forms of espionage, and the lack of destructive (or “kinetic” despite kinetic meaning something else in physics) effect leads to a degree of natural obscurity to the public, and possibly even policy makers. Now CounterCom is effectively a portable satellite communications station, and by all descriptions has a generally benign appearance. An on-orbit EW system on the other hand may well garner much more attention.51
Less clear examples of potential notational space weapons begin with long-range ballistic missiles, where range is achieved by having ballistic courses that cross not only all notational boundaries of space, but also go beyond some definitions of LEO up to some medium orbits. If orbiting is important, then one cannot leave out the Soviet Union's fractional orbit bombardment system (FOBS), a nuclear weapon delivery system deployed for a short time toward the end of the Cold War. To this day, the “legality” of FOBS, under the 1967 OST, which specifically bans orbiting nuclear weapons,52 is the subject of academic debate.53
Another potential candidate for inclusion as a destructive space system would be ground- and air-launched weapons that utilize satellite support for their accuracy in hitting fixed ground targets. Weapons such as bombs equipped with the Joint Direct Attack Munition (JDAM) system are satellite assisted; these exhibit very different levels of accuracy when based purely on inertial guidance vis-a-vis inertial guidance with GPS assistance. For the JDAM weapon system, this is a dramatic reduction of circular error probability (CEP), a measure of accuracy, from 30 meters on inertial guidance down to only 5 meters when GPS is available.54
Combining all of the earlier mentioned aspects is the Chinese antiship ballistic missile (ASBM). This is a long-range land-based naval weapon thought to be based on the DongFeng-21 (DF-21), or CSS-5 under NATO nomenclature, ballistic missile.55 The ballistic missile is used to deliver a warhead capable of terminal guidance and maneuvering to hit a mobile seaborne target. Interestingly there is speculation that other offshoots of the DF-21 program include the booster thought to have been used to deploy the ASAT used in the destructive 2007 test, the booster for the Chinese anti–ballistic missile (ABM) program, and a commercial solid-fuelled launch vehicle.56 The solid-fuelled DF-21 medium-range ballistic missile is known to be road mobile, appearing occasionally in military parades. The lack of transparency by the People's Republic of China on military matters in general also shrouds the specifics of these four programs, though both the ASAT test57 and the later ABM test in 201058 were eventually acknowledged by Chinese government sources. In comparison, the United States has been publically debating the value of ASAT weapons, missile defense, and prompt global strike via converted ballistic missiles—all systems that utilize large solid rocket motors, as do U.S. commercial launchers based on surplus ICBMs.
There is also the matter of ad hoc weaponization, where a spacecraft capable of maneuver is used to cause damage, but is otherwise not specifically designed to be a weapon. This group includes the Canadian-designed shuttle remote manipulator system (RMS) or Canadarm, which did figure as part of Soviet fears about the U.S. Space Shuttle program. Earlier U.S. and Soviet space weapons research had plans for military crews aboard existing space capsules rendezvousing with target satellites for inspection and neutralization. To this day the phrase “satellite inspection,” continues to raise alarm in segments of the disarmament community.59 Essentially any on-orbit rendezvous capability, no matter how benign its intentions are, can be construed into a weapon. Among the more worrisome of “benign” concepts are space tugs for moving large satellites into mission orbits, extending mission life when onboard propellant is exhausted, and removing satellites from mission orbits once a satellite is at the end of its life. Moving a satellite unwillingly from its mission orbit is an on-orbit attack without any of the problems of debris.
The unclear nature of what constitutes a space weapon also presents a case to be made that the mechanism of coercive force (in space) is less important to widespread weaponization of space than access to space itself. Space as a sanctuary from warfare is largely by “default,” a product not purely of pacifist intentions, but instead of budget and strategic realities for all actors on the international stage. Dropping a digit or two of the cost per pound or kilogram to orbit will therefore enable not just the major powers to actively threaten each other's orbital assets, but potentially open the door for other forms of conflict in space. Commercial dispute over one of the limited number of lucrative geostationary orbital slots has resulted in what can be described as belligerent acts between satellite operators, as was the case with Palapa B1. The stakes are higher for nationally owned military satellites. These assets are in the same price range as major warships, as is arguably their importance as a military asset; this perhaps lends an additional level of restraint. Low-cost access to orbit may effectively lower the value of individual space assets, and therefore perhaps lower the restraint-inhibiting military action. The specifics of the “military action” are limited only by the laws of physics and imagination, once the price is right of course.
Though much has been said about the specific wording of the space policies of individual U.S. presidencies, there have also been significant continuations of policy across several decades concerning the prospect of space weapons. Although U.S. counter-satellite (counter space) activities have so far been modest (the CounterCom system for instance only has a budget measured in millions of dollars60) the policies for several presidencies have consistently included statements related to maintaining freedom of action in space for United States and allies, and the capability to deny or disrupt the space capabilities of threats. As with past presidents, the space policy of the Obama administration continues the U.S. stance against arms control measures that “impair the rights of the United States to conduct research, development, testing, and operations or other activities in space for U.S. national interest.”61
Space access is only proliferating, and almost by definition, ubiquitous space access implies a degree of international access. Easy international access to space means potential for greatly increased international competition. There is already growing competition today in military space applications even without easy access to orbit. Despite the high cost of establishing the large constellation of satellites necessary for a global positioning service, and despite the United States offering reasonably accurate and reliable access to its own NavStar GPS as a “global public good,” there are several competing systems emerging: the European Union Galileo system slowly being orbited, Russia's reconstituted Soviet era GLONASS, and China's current ambitions to expand its regional positioning system into a global system. These independent satellite navigation systems are already a point of concern, if not outright alarm, for the U.S. defense community. However, for their backers, the lack of a navigation system independent of U.S. control is a source of concern and alarm. In the case of competing navigation systems, there have been efforts among some of the technical groups involved to avoid potential signal interference, and recognition of the potential unwanted consequences of this competition. However, not all potential space competitions may involve such agreement over the need for consultation and coordination.
Low-cost space access is a disruptive military technology, with the potential to change the perceptions that have limited the weaponization of space. As with many introductions of disruptive technologies there is potential for an arms race to develop. One nation's attempt to seize the initiative, or at least build up a defense, triggers another nation to embark on a competing weapons program. This second nation's competing program is interpreted as a threat by the first nation, necessitating a response in the form of increases to its own weapons program. The second nation, on seeing another increase in the weapons program of the first nation, is pressured to do the same, leading to an escalating cycle. Ubiquitous space access may make the initial stages of a space weapons arms race affordable. Once a space arms race develops, then for a while at least there is increased tolerance for the expense such weapons may bring.
Among nonpacifist arguments against space weapons development, is the point that initiation of overt space weaponization will not only start an arms race, but also an arms race on a nearly level playing field. The counterargument is that the success of U.S. space-force enhancement over the last two decades itself is cause for space weaponization. Not only are others emulating U.S. space-enhancement capabilities, potentially creating targets for future U.S. counter-space systems, but others are also already looking into countermeasures to existing U.S. space enhancement. The Chinese GPS plans provide a possible case of the former, and the Chinese ASAT program is an example potentially of the latter.62 Without active hostilities, however, all this remains in the theory and potential capability stage.
If outer space is the highest of the high ground, as it is often regarded, there will always be a military or security component to space activities. As long as space is not an overtly weaponized environment there will be pressure to do so. Although comparisons are drawn between space and other seemingly weapons-free environments, such as Antarctica and the depths of the seabed, it must be remembered that at present there is little human activity, let alone military interest, in Antarctica and the harsh depths of the sea. Orbit, on the other hand, has been a military and strategic concern from the very beginning of the Space Age. Relaxed access to the earth's orbit can only bring more pressure on a nation, any nation with a comparable high technology base as the United States, to be the first to overtly weaponize space.
Over the history of launch-vehicle development, techniques to deliver performance gains have faced real-world engineering problems that often erase any theoretical bonuses. Often this has been a result of technology simply not being mature enough for real-world use, or unforeseen problems with integrating many new and promising technologies into a solution. This has led to debate between those who back investment in revolutionary but risky technologies versus incremental changes to multistage launch vehicles that, to a large extent, still depend on pure rocket propulsion to reach orbit. On one end of the mainstream there is the reusable air-breathing engine powered SSTO launch vehicle. On the other end is the refinement of multistage rocket-powered launch-vehicle technology into something that is robust, can be launched on demand, and procured cheaply enough to greatly expand the possible uses of space.
1. Global Security, “Advanced Extremely High Frequency (AEHF),” http://www.globalsecurity.org/space/systems/aehf.htm
2. Lockheed Martin, “Advanced Extremely High Frequency (AEHF),” http://www.lockheedmartin.com/us/products/advanced-extremely-high-frequency—aehf-.html.
3. United States Air Force, “Factsheets: Advanced Extremely High Frequency (AEHF) System,” http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=5319.
4. Sheila Rupp, “Operationally Responsive Space,” Air Force Print News, May 22, 2007, http://www.kirtland.af.mil/news/story.asp?id=123054292.
5. The term suborbital is also used sometimes, but suborbital trajectories can and do reach altitudes well above LEO altitudes.
6. The principal atmosphere science layers are usually given as: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Other layers in the vertical realm important to specific earth sciences include the ozone layer and ionosphere.
7. National Museum of the U.S. Air Force, “Fact Sheet: Lockheed B-71 (SR-71),” http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2699.
8. James Oberg, “Astronaut.” World Book Online Reference Center. 2005. Chicago, IL: World Book, Inc., http://www.worldbookonline.com/wb/Article?id=ar034800.
9. A Mach number is the speed of an object divided by the speed of sound in that medium. With no medium for the transmission of sound in outer space, this usage of Mach generally relates to a comparable speed within the atmosphere under specific pressure and temperatures.
10. Indeed some engineering studies and literature, such as Andrew J. Butrica's Single Stage to Orbit: Politics, Space Technology, and the Quest for Reusable Rocketry, claim the high performance of the Saturn V third stage, the one responsible for the lunar trajectory, could have allowed adaption of the Saturn V third stage into an expendable SSTO launch vehicle.
11. For larger payloads, Pegasus stages are stacked on top of another rocket stage, for launch pad launch, forming the Taurus I launch vehicle.
12. Early Pegasus launches were from a NASA B-52. According to NASA public relations material, the same B-52, under NASA tail number 008, was used as mother ship for many experimental high-speed aircraft, including the X-15 program, which earned a handful of test pilots astronaut status.
13. Internal carriage was recently explored by Air Launch LLC's Quick Reach launch vehicle under funding from DARPA's Force Application and Launch from CONUS (FALCON)—Small Launch-Vehicle program.
14. Marti Sarigul-Klinjn, et al., “Trade Studies for Air Launching a Small Launch Vehicle from a Cargo Aircraft” (Reston, VA: [0] American Institute of Aeronautics and Astronautics, 2005), http://www.airlaunchllc.com/AIAA-2005–0621.pdf.
15. William B. Scott, “Two-Stage-to-Orbit ‘Blackstar’ System Shelved at Groom Lake?” Aviation Week, March 6, 2006, www.aviationweek.com.
16. The XB-70 is the largest Mach 3 capable aircraft of making it into the sky, if only for a fleeting few experimental flights in the 1960s.
17. William G. Holder and William D. Siuru, Jr., Captain USAF. “Some Thoughts on Reusable Launch Vehicles,” Air University Review, November-December 1970, http://www.airpower.au.af.mil/airchronicles/aureview/1970/nov-dec/holder.html.
18. See also former Lockheed Skunk Work's head Ben Rich's account of Blackbird development in his 1994 book Skunk Works, coauthored with Leo Janos, which includes his involvement with the propulsion system as an engineer under the first Skunk Works leader, Kelly Johnson.
19. The high proportion of air that bypasses the turbine sections of the J58 engines to be fed directly into the afterburners has the old Blackbird family of aircraft's propulsion system sometimes described as a turbo-ramjet.
20. Experimental ramjets have been launched on top of multistage expendable boosters, including Orbital Science's Pegasus.
21. NASA, “NASA's X-43A Scramjet Breaks Speed Record,” November 16, 2004, http://www.nasa.gov/missions/research/x43_schedule.html.
22. University of Queensland, “Hyshot,” http://www.uq.edu.au/hypersonics/?page=19501.
23. NASA, March 1, 2001, Press Release, http://www.nasa.gov/home/hqnews/2001/01–031.txt.
24. Reaction Engines LTD., “Current Projects: SKYLON,” http://www.reactionengines.co.uk/skylon.html.
25. There are proposals for some bulk low-cost payloads such as propellant supplies for on orbit refueling, where a high failure rate is acceptable as long as the cost of the lost payload does not surpass the savings from mass-produced cheap “dumb” boosters. These proposals would also minimize the cost of launch insurance as well by simply accepting the cost of lost payload as a part of the business model.
26. A polar launch from KSC would involve a trajectory passing over, and potentially dropping boosters and other debris on populated areas.
27. There is nothing in the nomenclature of aircraft-like operation to rule out a vertical launch and recovery; however, to avoid excessive ground damage, launch pads are equipped with various means to redirect and diffuse the sound, pressure, and heat that result from a rocket launch.
28. Except for a brief period in the 1990s, when DARPA went back to the Advanced Research Projects Agency (ARPA) name.
29. The Soviet Union persisted with storable liquid-fuelled rocket engines in their land- and submarine-based ballistic missiles up to the end of the Cold War.
30. Solid rockets use the term “motors,” whereas liquid-fuelled rockets use the term “engines.”
31. The ISS and HST have very different orbits, making it impossible for a single space shuttle mission to visit both.
32. NASA, “STS-400: Ready and Waiting,” May 5, 2009, http://www.nasa.gov/audience/foreducators/sts400-ready-and-waiting.html.
33. Among published Russian concepts is the Russian Hypersonic System Research Institute's AJAX, an aerospace craft/propulsion system that uses electromagnetic techniques to overcome energy losses inherent in scramjet operation.
34. United States Air Force, Report on Technology Horizons: A Vision for Air Force Science & Technology During 2010–2030 Volume l, May 15, 2010, http://www.af.mil/shared/media/document/AFD-100727–053.pdf.
35. Ibid.
36. Brian Berger and Amy Klamper, “NASA Propulsion Plans Resonate with Some in Rocket Industry,” Space News, February 26, 2010, http://www.spacenews.com/launch/100226-nasa-propulsion-plans-resonate-rocket-industry.html.
37. Brazil's indigenous launch-vehicle program suffered such a loss in 2003 when a prototype Veículo Lançador de Satélites (VLS), an all-solid-fuel orbital launch vehicle, exploded days before launch, killing several ground crew and destroying the launch pad.
38. Larine Barr, 88th Air Base Wing Public Affairs, United States Air Force, “Pulsed Detonation Engine Flies into History,” Air Force Print News Today, May 16, 2008, http://www.afmc.af.mil/news/story_print.asp?id=123098900.
39. American Institute of Beamed Energy Propulsion, Inc., http://www.aibep.org/Kantrowitz.htm.
40. Leik N. Myrabo and Donald G. Messittf, “Ground and Flight Tests of a Laser Propelled Vehicle,” 1997, http://pdf.aiaa.org/downloads/1998/1998_1001.pdf?CFID=1326408&CFTOKEN=88988801&.
41. Brittany Sauser, “Riding an Energy Beam to Space,” Technology Review, August 5, 2009, http://www.technologyreview.com/blog/deltav/23928/.
42. Christopher Mims, “Microwave-Powered Rocket Ascends without Fuel,” Technology Review, September 7, 2010, http://www.technologyreview.com/blog/mimssbits/25701/.
43. U.S. Army, “Connecting Soldiers to Digital Applications.” Stand-To!, July 15, 2010, http://www.army.mil/standto/archive/2010/07/15/.
44. Mueller, Karl P., “Totem and Taboo: Depolarizing the Space Weaponization Debate.” Paper based on presentation given to Weaponization of Space Project of the Eliot School of International Affairs Space Policy Institute and Security Policy Studies Program, George Washington University, December 3, 2001, http://www.gwu.edu/~spi/spaceforum/TotemandTabooGWUpaperRevised%5B1%5D.pdf.
45. David E. Lupton, Lieutenant Colonel, USAF. On Space Warfare, 1998, http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA421942.
46. “Draft Treaty for the Prevention of Placement of Weapons in Outer Space,” February 12, 2008, http://www.ln.mid.ru/brp_4.nsf/e78a48070f128a7b43256999005bcbb3/0d6e0c64d34f8cfac32573ee002d082a?OpenDocument.
47. Tom Bowman, “China Protests after U.S. Shoots Down Satellite,” National Public Radio, February 21, 2008, http://www.npr.org/templates/story/story.php?storyId=19246330.
48. David S. F. Portree, “NASA, Mir Hardware Heritage,” March 1995, http://ston.jsc.nasa.gov/collections/TRS/_techrep/RP1357.pdf.
49. Jim Garamone, American Forces Press Service, “CENTCOM Charts Operation Iraqi Freedom Progress,” March 25, 2003, http://www.defenselink.mil/news/newsarticle.aspx?id=29230.
50. United States Air Force, “Program Elements FY2009—Counterspace Systems,” February 2008, http://www.js.pentagon.mil/descriptivesum/Y2009/AirForce/0604421F.pdf.
51. The commercial satellite industry is already well aware of the effects of on-orbit signals interference. In the 1990s there were the exploits of Palapa B1, an Indonesian-owned commercial communication satellite, at the center of several disputes over the use of a geostationary orbital slot claimed by the island nation of Tonga and leased to third-party satellite operators. Notable belligerent acts include this satellite and another satellite hazardously attempting to occupy the same orbital slot in 1992, and accusations of radio-frequency interference (jamming) with another satellite it was in dispute with in 1996. More recently in 2010 another large GEO communications satellite, Galaxy-15, began drifting, due to suspected damaging from natural solar activity, but inexplicably was transmitting on its own for several months, despite efforts of ground control to shut it down, earning to the chagrin of its owners the nickname of “Zombie-sat.” Several other satellites serving North America had to be repositioned to avoid Galaxy-15 and the signals interference it was causing as it strayed into the orbital slots of working satellites in the GEO belt.
52. 1967 OST.
53. Instead of lobbing multiple nuclear weapons on a high ballistic arc, FOBS used a variation on a Soviet “heavy” ICBM to loft a nuclear warhead into a very low orbit. Before completing one orbit, the warhead would reenter the atmosphere to hit a surface target. An orbital flight path allowed the warhead to approach from any direction, allowing it to attack through gaps then present in U.S. ballistic missile early warning system.
54. United States Air Force, “Factsheet: JOINT DIRECT ATTACK MUNITION GBU-31/32/38,” November 2007, http://www.af.mil/factsheets/factsheet.asp?id=108.
55. Department of Defense, Military and Security Developments Involving the People's Republic of China 2010, http://www.defense.gov/pubs/pdfs/2010_CMPR_Final.pdf.
56. Global Security, “DF-21/CSS-5,” http://www.globalsecurity.org/wmd/world/china/df-21.htm.
57. Shirley Kan, China's Anti-Satellite Weapon Test, Congressional Research Service Report for Congress, April 23, 2007, http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA468025&Location=U2&doc=GetTRDoc.pdf.
58. Russell Hsiao, “Aims and Motives of China's Recent Missile Defense Test,” China Brief 10(2), January 21, 2010, http://www.jamestown.org/single/?no_cache=1&tx_ttnews[tt_news]=35943.
59. Wilson W. S. Wong and James Fergusson, Military Space Power (Santa Barbara: Praeger, 2010), 91.
60. United States Air Force, “Program Elements FY2009—Counterspace Systems,” February 2008, http://www.js.pentagon.mil/descriptivesum/Y2009/AirForce/0604421F.pdf.
61. National Space Policy of the United States of America, June 28, 2010, http://www.whitehouse.gov/sites/default/files/national_space_policy_6–28–10.pdf.
62. Department of Defense, Military and Security Developments Involving the People's Republic of China 2010, http://www.defense.gov/pubs/pdfs/2010_CMPR_Final.pdf.