Zero-G Experiments

A man in a jumpsuit and soft helmet floats in an aircraft, looking at the camera. Another man is partially visible behind him, and others are in the background.
Two men in jumpsuits stand on stairs leading into a large U.S. Air Force plane.

Bob Greenmun and Jerald Jordan smiled as they boarded a Convair plane for weightless flights. Painted on the side is “How High The Moon” and the flight maneuver.

1962-1963: Zero-G Experiments

At Wright-Patterson Air Force Base, Dayton, Ohio and Eglin Air Force Base, Eglin, Florida, five of the "LDs" participated in weightlessness tests. Flight maneuvers created 12—30 second sessions of zero gravity for experiments on body orientation and gravitational cues.

"It was like being in outer space and a wonderful feeling (for us LD subjects, anyway)."
-Don Peterson

A drawing of a plane in parabolic flight, pained on the side of an airplane under the words U.S. Air Force. Below is "Sine Gravitate" which is Latin for "Without Gravity."

C-131 flight maneuver printed on the side of a Convair plane.

A color photo of a man in an orange jumpsuit and safety harness moving around a plane. Another man behind him is holding a camera.

Flight Maneuvers:

  • 31B (Convair) Start at 1,200 feet, then make a dive before lifting to increase in altitude and speed to 250 knots. Causes 12-15 seconds of weightlessness before coming back down.
  • C-135 (Boeing 707) Start at 24,000 feet and increase altitude to 33,000 feet for 25-30 seconds of zero-g before coming down to a force of 2 g.


The Boeing 707 had seats up front, a padded interior in the middle, and an area in the back for testing equipment. It had a more reinforced structure than the Convair planes to withstand extreme flight maneuvers. Colloquially known as the “Vomit Comet”, the 707 was infamous for making most of its hearing riders violently sick.

"We were constantly being tested and most of that involving every form of motion that you can imagine.
–David Myers

A color photo of two men in orange flight suits, floating in a plane. One wears a soft helmet and appears to be carrying another piggy-back style. A third man floats in the background.

Myers having fun in Zero-G with Navy aides.

A drawing of a man in a flight suit and soft helmet. He appears to be standing upside down inside a plane. Text: "Figure 2 - Subject standing on overhead of C-131B aircraft in modified parabolic maneuver."

When we were not being tested, we were free to “play” in 0 (zero) G. I remember Jerry Jordan rolling up in a ball and being tossed across the room.
–Peterson

A large metal chair from behind, attached to the floor of an aircraft. Many wires are coming off the chair and the person in it.

This device secured subjects in a Fiberglass mold for tests on body orientation.                        

We performed these tests in many different situations other than in aircraft, including during rotation, when immersed in water, when rotating on a centrifuge.
–Myers                                                                  

On one device, “the subjects' task was to set a dim line of light in the dark to what they regarded as "horizontal" in the weightless phase of the parabola.”
-Graybiel

A camera takes high-resolution images of the irises and overlaps each one with the previous one, using the natural markings on the irises as a point of reference to measure how much the eyeball rotates around the center as the subject tilts. This is called counter rolling, a reaction of the otolithic organs to gravitational pull.

A man sits in a large metal chair attached to the inside of an aircraft. His face is only partially visible behind testing equipment.

There was a doctor sitting facing me while I rode backwards and the pilot did aerobatics.  Nothing happened, of course, except I had a great time.
–Jerald Jordan

"The otolith organs in man are physiologically deafferentiated when he is exposed to hypogravitational environments... normal subjects were responding to sensory information not available to the LD subjects, which must have had its origin in the vestibular apparatus.”
–Dr. Ashton Graybiel

A white man in heavy glasses with short hair is strapped into an aircraft seat. He is looking at equipment with dials and meters.

Hal Domich observes equipment during a flight.

"Whatever sensation an astronaut may experience in space is the result of a complex interpretation of sensory data in perception and depends on which data have priority."
(Mayne 23)

A graph of tilt in degrees, versus counterrolling in minutes of arc. Normal subjects show a broad range, and L-D subjects show a smaller range.

The LD subjects showed significantly reduced patterns of counter rolling.  In some experiments, the sharp awareness of the LD of gravitational illusions or sensations meant that the inner ear organs are not always essential for sensing balance and gravity.

The deaf men reported feeling an inversion illusion, which is the phenomenon of feeling upside-down in hypogravity. So did the hearing subjects, but they behaved differently. The LD subjects “accept the apparent miracle of "standing" on the overhead” -Graybiel. Hearing subjects, however, are vulnerable to gravitational cues from the otolithic organs.

  • Jordan: “no feeling of being upright. The pressure on my feet was too little to cause any postural feeling”
  • Harper: “Negative g only was not enough to give sensation of normal weight”
  • Peterson: “if not for the standard (visual) cues, I couldn’t tell. If my eyes were closed I would feel upright.”
  • Myers: “after about five seconds, I began to feel blood coming to my head, and then I began to feel that I was upside-down.”

 To prepare for space travel, astronauts need to train to shut out the sensation from their inner ears and instead tune in to other senses that tell them otherwise.

Zero-G Experiments