Tutorial on Microgravity Research
page 3: Means of Obtaining Microgravity
Suborbital Rocket Flights (Sounding Rockets)
Microgravity can be achieved with suborbital rocket flights. "Suborbital" means the rockets go up but do not orbit the Earth and these rockets are typically called "sounding rockets." Sounding Rockets offer longer duration and higher quality microgravity conditions than airplanes.
Sounding rockets take their name from the nautical term "to sound" which means to take measurements. Traditionally, sounding rockets are basically divided into two parts -- a solid fueled rocket motor and the payload. Many of the motors used in program are surplus military motors, which keeps down the cost of the rocket. The payload is the section carrying the instruments to conduct the experiment and sends the data back to Earth. Experiments are launched along a parabolic trajectory.
Sounding rockets are used to study the Earth's atmosphere at many different altitudes and the Earth's ionosphere and aurora. Also, since sounding rockets can get above the atmosphere, they are used to study astronomical targets in the ultraviolet and x-ray portions of the electromagnetic spectrum.
At the altitude of 100 km, the air is 10 million times less dense than on Earths surface and the air drag is greatly diminished. Once the rocket engine is cut off, the rocket is in free fall providing from 6 to 15 minutes of microgravity of 10-5 g before re-entering Earths atmosphere.
Below is a profile of a sounding rocket suborbital flight.
The flight profile of a sounding rocket follows a parabolic trajectoryit goes up and comes back down. Flight time is less than 30 minutes. However, invaluable data can be received in this short flight time.
Following the launch, as the rocket motor uses its fuel, it separates from the vehicle and falls back to Earth. The payload continues into space and begins conducting the experiment. As the payload re-enters the atmosphere, a parachute is deployed to bring the payload gently back to Earth. The payload is then retrieved. Retrieving the payload results in tremendous savings because the payload or parts of the payload can be refurbished and flown again.