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Zero G, LasVegas, NV

Not the Vomit Comet

Zero G Corporation operates flights in a converted Boeing 727 with a padded interior that simulate weightlessness and Martian and Lunar gravity. NASA operates similar flights for astronaut training on an aircraft dubbed the “Vomit Comet.” Both NASA’s and Zero G’s flights work on the same principle: they fly in such a way that the passengers and aircraft free-fall together. Unlike NASA’s flights, Zero G’s flights are open to the public, although they come with a hefty price tag.

The Zero G aircraft flies a parabolic flight path, flying upward at 45° and then into a parabolic hump where everyone becomes weightless (Figure 111-1). Once over the hump, the aircraft descends and then pulls up to start another. Weightlessness only occurs when flying the parabola and lasts for about 30 seconds. Each flight consists of 15 parabolic humps, for a total of between 7 and 8 minutes of weightlessness.

Figure 111-1. Zero G flight path

Once weightless, the passengers float inside the Boeing 727 and the pilot maneuvers the plane in an open piece of airspace between 7,000 and 10,000 meters. When the plane pulls out of the parabola, the feeling of gravity returns and increases to about 1.8g (1.8 times normal Earth gravity).

By modifying the shape of the flight path, the plane can be made to simulate weightlessness, or the weight as experienced on the Moon (the Moon’s gravitational force is about 1/6 of the Earth’s) with passengers walking and bouncing like the Apollo astronauts. A different shape of flight creates Martian gravity, about 1/3 of the force experienced on Earth.

Zero G has found that limiting the amount of time spent weightless—by limiting the number of total humps—minimizes motion sickness. NASA, in contrast, pushes the number of parabolic humps to over 40, and the passengers do feel motion sickness. Zero G also prescribes motion sickness medication to take before a flight.

To ease passengers into the feeling of weightlessness, the flight starts out simulating Martian gravity, then Lunar gravity, and finally “no gravity” at all.

Practical Information

Although Zero G is based in Las Vegas, Nevada, it operates flights from other airports around the U.S. Details are at http://www.gozerog.com/.

Weightlessness and Parabolic Flight

The name Zero G is a misnomer—there’s no escaping Earth’s gravity in an aircraft, or even an orbiting spacecraft—but passengers do experience the same thing real astronauts do: weightlessness.

The weight of a person is related to the gravitational force acting on his or her body. When standing on the Earth, a man who has a mass of 75 kilograms feels “weight” because the Earth’s gravity acts upon his body to pull him downward, and at the same time the ground exerts an equal and opposite force upward. The force upward from the ground is felt in his body and he experiences his weight. For more on weight and mass, see Chapter 69.

When a skydiver free-falls from an aircraft, there’s no ground to push upward, and he falls under the force of gravity. The only resistance to the skydiver’s fall is from the air (which is minimal), and the skydiver experiences a feeling of weightlessness.

In an orbiting spacecraft, astronauts are weightless because both they and the spacecraft are free-falling together. The astronaut has no weight relative to the spacecraft, even though the Earth’s gravity is acting upon them both. When a spacecraft is in orbit, it is free-falling at right angles to the Earth with sufficient velocity that it never actually falls to the ground—it keeps falling, but moves horizontally, and ends up rotating around the Earth.

In the Zero G aircraft, gravity still applies, but the parabolic flight means that the passengers and aircraft free-fall together, and relative to the aircraft the passengers have no weight (there’s no force acting on them from the aircraft itself). The Zero G aircraft achieves this by flying a ballistic trajectory with just enough engine power to overcome air resistance.

If a bullet is fired from a gun at an angle, it will fly through the air with only the force of gravity acting on it (assuming that wind resistance is of little consequence). Gravity acts constantly downward on the bullet, and it travels through a parabola. If the bullet started out at ground level—the position (0, 0)—and was fired at an angle θ to the ground with velocity v, then its position at time t is (tv cos θ, tv sin θ - 1/2 gt2), where g is the acceleration due to gravity.

An aircraft flying upward at 45° and then entering the parabola gives the maximum length of ballistic flight, just as firing a gun at 45° results in the longest distance of bullet flight.