part0047

The previous chapters covered various approaches that might have some potential for improving our knowledge of the physical sciences and engineering capabilities, since that is what is needed for us to be able to create an affordable transportation system to Mars, right? Wrong! We have technologies available to us today that are perfectly capable of providing regular transportation to Mars and beyond at relatively affordable costs and with limited environmental impacts. We can use rockets to go to Mars if we choose, the problem being that most of the time mankind has a tendency to use them for somewhat less constructive purposes, such as threatening others with nuclear obliteration.

When employing the term rocket, you might be thinking of a device such as the Saturn V rocket that took man to the moon – that is to say a chemically-based, expensive device that was not re-useable (in the case of its successor, the Space Shuttle it was intended to be reusable, but this was still very expensive to launch as well as being somewhat unreliable). But when I talk about a ‘rocket to Mars’ I am not necessarily thinking of this kind of craft. To escape from any massive body, all we need to do is to accelerate to its escape velocity – which is dictated by the mass of the body. Since the mass of the Moon is much less than that of the Earth, launching a rocket to Mars from the Moon would be much easier than from the Earth (one would also not need to worry about complicating factors caused by air resistance).

But whichever body we launch from there is a technology that might well provide significant benefits, specifically the mass driver or accelerator . A mass driver consists of a very long and mainly horizontally aligned launch track or tunnel for space launch, curved upwards at the end. The concept was proposed by Arthur C. Clarke in 1950. Clarke, by the way, was in fact quite a futurist, who many years ago predicted now common technologies such as communication satellites, mobile computerised telecommunication, and the internet. The mass driver could launch vehicles directly to space by accelerating them to very high velocities. This would be facilitated by having the vehicles floating just above the track by using maglev repulsion – rather like some current German trains. The track would probably need incorporation of superconducting magnets to accelerate the vehicle to the necessary very high speeds. The track would be constructed so that it terminated at a relatively high altitude and at an angle that would enable a high-speed vehicle to fly into a low-earth orbit. The power required would probably be provided by superconductive energy storage units distributed along the track. Vehicles could then employ a relatively small on-board rocket motor to change orbit. The main challenge when launching humans into orbit using such technology is that it does require quite high accelerations and most people would not be able to tolerate a sustained acceleration of more than about 2g (i.e. twice that caused by gravity on the surface of the Earth). Therefore, manned vehicles would need relatively long tracks … but, how long? That’s a good question. Well, to get into orbit a craft needs to travel at around 7.9 km/s and Newtonian physics tells us that v2 = u2 + 2as, where v = final velocity = 7900m/s, u = initial velocity = 0, a = acceleration and 1g is around 10 m/s2 and s = distance. Therefore s = v2 /2a. Putting the values in gives us a track length of about 1560 km! This is indeed rather long; but it is worth bearing in mind that if we just wish to accelerate equipment into space a much higher g could be employed – use of 40g would result in a track length of just 78 km which would seem quite attainable.

Although building such a length of mass driver track would still be quite an expensive undertaking, it is important to note that this is only a one-off cost; once built the track could be used to accelerate objects up into orbit frequently and at low cost. As mentioned, it would be much cheaper and easier to launch a rocket to Mars from the Moon, or in fact from Earth orbit, rather than actual terra firma . But the chief difficulty is the high price of launching equipment from Earth to these locations using presently available chemical rockets. Currently, prices are around $10,000 per kg – the amazing fact is that a mass driver could offer potential to reduce this by a factor of 100, to only around $100 per kg! But what about the previously mentioned problem of needing a very long track for launching humans? Well, build a longer track! Railways longer than 2000 km exist and have existed for many years and many were originally built with the limited technologies available in the nineteenth century. A 1560 km long mass driver would be the ultimate solution to low cost transport of humans to Mars; but if in the nearer term a method was required that was not quite as ultimately low cost but perhaps easier or quicker to implement, then a shorter mass driver could be used for launching needed equipment and following this humans could travel up to orbit, or the moon, by riding a good old-fashioned chemical rocket (NASA had few serious problems in reliably achieving repeated manned flights to the Moon even when all they had was 1960’s technology).

"They used to say if man could fly, he'd have wings … but he did fly. He discovered he had to. Do you wish that the first Apollo mission hadn't reached the Moon, or that we hadn't gone on to Mars or the nearest star? That's like saying you wish that you still operated with scalpels and sewed your patients up with catgut like your great-great-great-great-grandfather used to. I'm in command. I could order this. But I'm not … because … Dr McCoy is right in pointing out the enormous danger potential in any contact with life and intelligence as fantastically advanced as this. But I must point out that the possibilities, the potential for knowledge and advancement is equally great. Risk … risk is our business! That's what this starship is all about … that's why we're aboard her!" (You can imagine all the Shatnerisms of being dramatic and speaking/moving in little sharp bursts.)

Sorry, I got a bit carried away there. But what if we, like Kirk, do decide to explore as far as we can. Mars is relatively cold and inhospitable, but modern astronomical observations tell us that there are multitudes of planets – or exo-planets – in our Galaxy that are in the habitable zone of their star. This is very intriguing; can we travel to them and explore? The problem here is that the distances involved are truly vast and so to cross them we will need craft capable of very high velocities. This is where some of the considerations of the last two chapters will become relevant. It is fine and dandy to use a mass driver to launch men and equipment efficiently from the surface of the Earth or Moon, but what happens then? How do we accelerate up to the very high speeds needed to achieve inter-stellar travel in reasonable timescales? Currently, all we essentially have is the good old chemical rocket – which is an invention dating from thousands of years ago and one that has several serious limitations. One of the most serious is the need to carry large amounts of fuel on board in order to accelerate to high speeds, which currently makes launch difficult if not impossible. This is where new understandings of physics could lead to new concepts for propulsion mechanisms, and novel capabilities in engineering design and manufacture will enable fabrication of these new generations of rocket motors. My hope, as described, is that this can be facilitated in the not too distant future, perhaps through judicious application of the new deep learning methodologies outlined earlier. As well as building a rocket capable of high speeds, we also have the little issue of the laws of physics to worry about. For example, in Star Trek it was very easy for Kirk to issue an order to accelerate to warp seven and Scotty would promptly make sure his engines obliged the captain. But warp seven meant a speed well in excess of light and to quickly accelerate the Enterprise up to such a speed, even if it were possible, would result in such g forces that, horrible to contemplate, the Enterprise crew of 430 would be immediately squashed to a pulp!