The Weightless Wonder we Space Cowboys will be riding is a C9-B aircraft, the military equivalent of the DC-9 passenger plane. Once we get our experiments on board the plane on Tuesday morning, we take off and ascend to an altitude of 24,000 feet. The plane then starts to execute a series of ‘parabolas’ that produce the microgravity environment for our experiments.
During each parabola, the plane climbs 7,000 feet in 20 seconds, with the plane tilted at a 45 degree up-angle. Once it's up to an altitude of 31,000 feet, the engines are throttled back almost to zero power, effectively making the plane a projectile in freefall*. That freefall lasts about 30 to 35 seconds, and during that time we will be experiencing weightlessness. In the diagram, the plane goes ‘over the hill', very much like being on a rollercoaster that is cresting a hill at high speed … except that there’s no track under the airplane. Once the plane is back down to 31,000 feet – traveling now at a 45 degree down-angle - the engines are powered up, and the plane starts its bottoming-out process. It levels off momentarily once back at an altitude of 24,000 feet, and then it starts its next parabola from there. The entire process from climb to peak to descent to the start of the next climb takes a little over a minute.
The flight path gives us twenty of these minute-long parabolas as we fly outbound from Houston over the Gulf of Mexico. The plane then turns around, and it executes 20 more parabolas on the return leg of its trip. The entire flight lasts a little over two hours.
* Even though the plane is initially still rising once the engines are throttled back, it is still said to be in freefall because the only force acting on it at that point is gravity.