IMAGE: KC-135 Aircraft

IMAGE: KC-135 AircraftReduced Gravity ProgramIMAGE: KC-135 Aircraft


The Reduced-Gravity Program operated by the NASA Lyndon B. Program Johnson Space Center (JSC) in Houston, Texas, provides the unique "weightless" or "zero-g" environment of space flight for test and training purposes on a cost-reimbursable funding basis. With the coming of age of the Space Transportation System and the current plans for the Space Station, this capability is ideal for the development and verification of space hardware prior to launch.

The Reduced-Gravity Program was started in 1959 to investigate human and hardware reactions to operating in a weightless environment. The reduced-gravity environment is obtained with a specially modified KC-1 35A turbojet transport which flies parabolic arcs to produce weightless periods of 20 to 25 seconds. The KC-1 35A can also provide short periods of lunar (1 /6) and Martian (1/3) gravity. Approximately 100,000 parabolas have been flown in support of the Mercury, Gemini, Apollo, Skylab, Space Shuttle, and Space Station programs.

The KC-1 35A cargo bay test area is approximately 60 feet long, 1 0 feet wide, and 7 feet high. The aircraft is equipped with electrical power, and overboard vent system, and photographic lights. Air and nitrogen sources are also available. Ground facilities include a test equipment build-up area, briefing room, and telephones.

A typical mission is 2 to 3 hours long and consists of 30 to 40 parabolas. These parabolas can be flown in succession or with short breaks between maneuvers to reconfigure test equipment. The Reduced-Gravity Office provides scheduling, test coordination, and in-flight direction for the test programs.

For additional information or the initiation of a project, contact:

NASA Lyndon B. Johnson Space Center
Reduced-Gravity Office, Ellington Field
Mail Code: CC43
Houston, TX 77058

Telephone (281) 244-9875

KC-135A Aircraft Trajectory

IMAGE: KC-135A Aircraft Trajectory

The above diagram shows a typical zero-g maneuver. However, the maneuver can be modified to provide any level of g-forces less then one g. Some typical g-levels used on different tests and the corresponding time for each maneuver are as follows:
Negative-g (-0.1g)Approximately 15 seconds
Zero-gApproximately 25 seconds
Lunar-g (one-sixth g)Approximately 30 seconds
Martian-g (one-third g)Approximately 40 seconds

Advantages of Testing in the Controlled Reduced-Gravity Environment of the KC-135A

The Aircraft

Air Force KC-135A: A four-engine turbojet aircraft similar to the commercial Boeing 707
Crew: Pilot, copilot, flight engineer, and two test directors
IMAGE: KC-135 Aircraft

Cabin Cross-Section View
IMAGE: KC-135 Cabin Cross-Section View

Floor Plan
IMAGE: KC-135 Floor Plan

Responsible NASA Official: Dominic Del Rosso (
NASA Technical Monitor: Sharon Beth Halprin (
Webmaster: JSC Custom Applications
Last Updated: 11/07/2012