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Vomit Comet is a nickname for any airplane 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's Reduced Gravity Research Program since 1973, where the nickname originated. NASA prefers the nickname Weightless Wonder for public relations reasons.

Contents 1 Operating principles 2 History 3 Commercial flights 4 Airsickness 5 Other uses of the term 6 See also 7 Notes 8 References 9 External links

Main article: Weightlessness

The airplane produces weightlessness by following a parabolic vertical flight path. A parabolic flight path is the same path that would be taken by an object in free fall, such as a cannonball fired into the air. As a result, the aircraft does not exert any G force on its contents, so the contents have zero apparent weight relative to the aircraft.

The aircraft heads upward at an angle of 45 degrees. As soon as the pilot begins the rotation into the parabolic trajectory, weightlessness is achieved. This lasts all the way "up-and-over the hump", until the craft reaches a declined angle of 30 degrees. At this point, the craft has lost a significant amount of altitude, and must begin to pull into a hard upward turn. 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 half way up its upward trajectory, and the pilot again initiates the zero-g parabola. ^[1]

In general this aircraft is used to train astronauts in zero-g maneuvers, giving them about 25 seconds of weightlessness out of 65 seconds of flight. This often produces nausea due to airsickness, especially in novices, giving the plane its nickname. Astronauts training for the Moon missions practiced walking with 1/6 of their weight to simulate the level of gravity on the Moon.

NASA has flown parabolic 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".^[2]

Twin KC-135 Stratotankers were used until December 2004 and 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 airplane was retired in 2000 and is now on display at Ellington Field, near the Johnson Space Center. It's 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 airplane with a McDonnell Douglas C-9B Skytrain II that was formerly owned by KLM Airlines and the United States Navy [1]. The same year, the Zero-Gravity Corporation, a commercial parabolic flight operator which offers parabolic flight to both researchers and adventure tourists, began flying parabolic flights for NASA with Boeing 727 jets.

Since 1984, the ESA and the CNES have flown similar reduced-gravity missions in a variety of airplanes, 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.^[3]

In late 2004, Zero Gravity Corporation became the first and only company in the United States to offer parabolic weightlessness flights to the general public. Each flight consists of around 15 parabolas, including simulations of the gravity levels of the Moon and Mars, as well as complete weightlessness.^[4]

According to Reduced Gravity Research Program director John Yaniec, anxiety contributes most to passengers' airsickness. Yaniec gives a rough estimate that of passengers, "one third [become] violently ill, the next third moderately ill, and the final third not at all." Vomiting is referred to as a "kill." ^[5]

Commercial operator ZeroG Corp claims their tourist rides with up to 15 parabolas are much less traumatic compared to the typical research flight with from 40 up to 80 parabolas.^[6]

Vomit comet may also refer to any other form of transportation on which riders are said to become nauseated or seasick, such as a bus that transports late-night revelers ^{[7] [8]} or a fast boat such as a high speed catamaran. ^{[9] [10]}.

In Sim City the "Vomit Comet" is a fairground attraction.

• Microgravity
• Space tourism

• Haber, Fritz and Haber, Heinz: Possible Methods of Producing the Gravity-Free State for Medical Research, Journal of Aviation Medecine XXI (1950)
• Easton, Pam (Oct. 30, 2004). NASA's weightless aircraft is retired. Associated Press.
• Glen Golightly (May. 15, 2000). Vomit Comet finds a home. Space.com Houston Bureau.
• Dennis Overbye (March 1, 2007), Stephen Hawking plans prelude to the ride of his life, New York Times

• Reduced Gravity Research Program
• Interview with John Yaniec
• About the NASA Reduced Gravity Research Program
• "ATLAS aerospace" is a Russian company that offers reduced gravity flights in an "IL-76 MDK" wide-body airplane.
• Virtual tour of the Airbus A-300 Zero-G
• C-135 Variants Part 6 - includes scale drawing of NASA 930
• Reduced Gravity Experiment in a Nasa´s KC-135A