NASA Uses Visual Simulation System
to Condition Astronauts for Maneuvering Within Spacecraft

IMAGES Spring 1989

By Gregory F. Gustin

NASA's PAT (Preflight Adaption Trainer) provides an interesting study of how realtime visual simulation systems are being employed for new applications beyond traditional out-the-window displays for pilot training.

People throughout the world have viewed scenes of American astronauts acting like space gymnasts, tumbling and spinning inside their spacecraft. But very few viewers probably ever realize that these activities induce serious illness in the astronauts.

The eyes of the space gymnasts see the world tumbling about. But, apparently due to the weightlessness of space, the inner ear does not sense the physical motion. The brain therefore receives conflicting signals, recognizes that something is out of sync, and concludes that the probable cause is the ingestion of a poisonous substance. The brain then signals the body to rid itself of the poison. This reaction is very similar to someone who overindulges in alcohol: the classic first symptom is dizziness followed by a short period of illness - that is, the body automatically reacts to rid itself of the poison.

Adaption Can Be Trained
NASA has deduced through experimentation that adaptation to this subconscious mechanism associated with weightlessness can be trained; the eye and ear can learn to experience a discontinuity without adverse effects. Such training requires the astronaut be exposed to an environment very similar to that associated with an orbiting space capsule. The astronaut obviously cannot experience weightlessness on earth for any practical period of time. Several studies have shown, however, that by restricting head and body movement, positive adaptive training results can be achieved.

Alternative To Model-Board
PAT first surfaced as an alternative component to NASA's model-board and camera approach to the shuttle simulation problem. Honeywell's Systems and Research Center became interested in the training requirement and was instrumental in getting NASA to re-examine the model-board approach to training. The entire program was eventually turned away from model-boards to CGI (Computer Generated Imagery). Honeywell then selected Paragon to produce the realtime image generators for the resulting PAT visual system.

In the PAT, the subject is placed in a vacuum bean bag that conforms to the body. This provides a comfortable platform that inhibits (but does not prohibit) body motion. The trainee also wears a helmet attached to a force transducer that prohibits head motion. The entire mechanism is then placed on a seat that rotates about the vertical axis inside a six-foot radius dome.

A two-channel PARAGON computer image generator illuminates the surface of the dome with an image of the Space Lab interior bay. Hand pressures on force plates and head pressures inside the helmet combine to propel the subject within the lab. This creates a training scenario in which the eyes "see movement, but the body does not feel movement.

To accentuate the situation, the chair is commanded to rotate in one direction providing a slight stimulation to the inner ear, while the visual system is commanded to make the room appear to be spinning in the opposite direction, or even to tumble.

The realtime CIG system from Paragon proved to be a more cost effective solution than the previously considered model-board approach, and its power and flexibility provided additional benefit. Not only is it extremely impractical to fabricate a camera lens pick-up with 6-degrees-of-freedom, but the raster shaping of the required image has never been accomplished at this magnitude (i.e., a six-foot radius dome).

The PARAGON displays a highly detailed scene at realtime update rates, yet its most impressive capability relevant to this particular application is the generation of the distortion correction algorithms that allow fitting the image into such a small dome. Although PARAGON is one of the new "low cost" computer image generator systems, a capability such as this illustrates that low cost no longer must necessarily mean compromises in features and/or performance.