A reduced gravity aircraft is a type of fixed-wing aircraft that briefly provides a nearly weightless environment in which to train astronauts, conduct research and film motion pictures. Versions of such airplanes have in the past been operated by NASA Reduced Gravity Research Program,[1] where the unofficial nickname originated. NASA has adopted the official nickname Weightless Wonder for publication.[2]
Contents |
The aircraft gives its occupants the sensation of weightlessness by following an (approximately parabolic) elliptic flight path relative to the center of the Earth.[3] While following this path, the aircraft and its payload are in free fall at certain points of its flight path. The aircraft is used in this way to demonstrate to astronauts what it is like to orbit the Earth. During this time the aircraft does not exert any ground reaction force on its contents, causing the sensation of weightlessness.
Initially the aircraft climbs with a pitch angle of 45 degrees. The sensation of weightlessness is achieved by reducing thrust and lowering the nose to maintain a zero-lift angle of attack. Weightlessness begins while ascending and lasts all the way "up-and-over the hump", until the craft reaches a declined angle of 30 degrees. At this point, the craft is pointed downward at high speed, and must begin to pull back into the nose-up attitude to repeat the maneuver. The forces are then roughly twice that of gravity on the way down, at the bottom, and up again. This lasts all the way until the aircraft is again halfway up its upward trajectory, and the pilot again initiates the zero-g flight path.[4]
This aircraft is used to train astronauts in zero-g maneuvers, giving them about 25 seconds of weightlessness out of 65 seconds of flight in each parabola. In about two thirds of cases,[5] this motion produces nausea due to airsickness, especially in novices, giving the plane its nickname.
NASA has flown zero-g flights on various aircraft for many years. In 1959, Project Mercury astronauts trained in a C-131 Samaritan aircraft, which was dubbed the "Vomit Comet".[6]
Twin KC-135 Stratotankers were used until December 2004 but have since been retired. One, a KC-135A known as NASA 930, was also used by Universal Pictures and Imagine Entertainment for filming scenes involving weightlessness in the movie Apollo 13; that aircraft was retired in 2000 and is now on display at Ellington Field, near the Johnson Space Center. The KC-135A is estimated to have flown over 58,000 parabolas. The other (N931NA or NASA 931) made its final flight on October 29, 2004, and is permanently stored in the Pima Air & Space Museum in Tucson, Arizona.
In 2005, NASA replaced the aircraft with a McDonnell Douglas C-9B Skytrain II that was formerly owned by KLM Royal Dutch Airlines and the United States Navy.[7]
The Italian Space Agency contracts SpaceLand, an Italian parabolic flight and sub-orbital flight engineering and operational agency to support research, development and educational flight campaigns.
The Canadian Space Agency and the National Research Council have a Falcon 20 used for microgravity research.[8] The small plane is normally not used for people to float freely and experience weightlessness, however comedian Rick Mercer did so for a segment on his show.[9]
The first zero G plane to enter service in Latin America is a T-39 Sabreliner nicknamed CONDOR. CONDOR has been in operation for the Ecuadorian Civilian Space Agency and the Ecuadorian Air Force since May, 2008.[10] On June 19, 2008, this plane carried 7 year old Jules Nader as he set the Guinness world record for the youngest human being to fly in microgravity. Nader worked on a hydrodynamics experiment designed by his brother.[11]
Since 1984, the ESA and the CNES flew similar reduced-gravity missions in a variety of aircraft, including NASA's KC-135, a Caravelle, an Ilyushin IL-76 MDK, and, most recently, an Airbus A300 known as the Zero-G, which is flown out of the Bordeaux-Mérignac airport in France.[12] Since 1997, CNES subsidiary Novespace has handled the management of these flights.[13]
In Russia, commercial flights are offered on the Ilyushin Il-76 jet; several U.S. companies book flights on these jets.[14] The 1999 pornographic film The Uranus Experiment 1 had scenes filmed on such an aircraft; it is notable for containing the first instance of zero-gravity sex caught on film.[15]
In late 2004, the Zero Gravity Corporation became the first company in the United States to offer zero-g flights to the general public, using Boeing 727 jets. Each flight consists of around 15 parabolas, including simulations of the gravity levels of the moon and Mars, as well as complete weightlessness.[16] There is also a company in Oldsmar, Florida called Aurora Aerospace that also offers zero-g flights using a Fuji/Rockwell Commander 700. It is also used to simulate the gravity of the moon and Mars.[17]
According to former Reduced Gravity Research Program director John Yaniec, anxiety contributes most to passengers' airsickness. Yaniec gives a rough estimate of passengers, that "one third [become] violently ill, the next third moderately ill, and the final third not at all." Vomiting is referred to as a "kill".[18]