Simulation

Space explorers venture into the unknown. But the support crews of the space explorers do their best to send their imagination, analysis, and scientific knowledge ahead. Simulation has always been an integral part not only of astronaut training but also of testing engineering designs of hardware and software and all the procedures developed for the mission. The hard work of a dedicated simulation and training support team prepares the astronaut crews to successfully deal with emergencies, while mostly avoiding surprises in the mission execution.

Simulation allows the astronauts to become comfortable with the unfamiliar. The astronauts practice on simulators such as a mock-up of the space shuttle's crew compartment. Pilots practice shuttle approaches and landings with the modified Grumman Gulfstream G-2 corporate jet (otherwise known as the Shuttle Training Aircraft), which mimics the different drag and center of rotation of the shuttle. Mission specialists maneuver cargo in the payload bay or practice satellite retrieval on a simulated manipulator arm.

Demanding crew training regimes at the National Aeronautics and Space Administration's (NASA) Johnson Space Center in Houston, Texas, include single-system trainers that simulate specific functions such as propulsion, guidance, navigation, and communications. All of the single-system training comes together in the shuttle mission simulator (SMS) and the shuttle engineering simulator (SES). The SES simulates rendezvous, station keeping, and docking using a domed display for a realistic full-scale perspective of the shuttle cockpit view. The SMS includes a motion-based simulator for ascent and entry training, and a fixed-based simulator for orbit simulations. The SMS simulators imitate the sounds, scenes, and motion of a full shuttle mission—from liftoff to touchdown—to give the astronauts the feel of a real mission.

Every conceivable emergency or malfunction is practiced repeatedly in the simulator. The simulators are also used for problem solving. When theoxygen tank exploded on Apollo 13, for example, ground support teams and backup astronaut crews used the simulator to work solutions and send new procedures to the crew.

Sophisticated for their time, the original simulators were installed in 1962 by the Link company, which pioneered full-flight simulators. But that was the age of room-sized mainframe computers and engineers carrying slide rules in their pockets. Neither the personal computer nor the hand calculator had been developed yet. Tools for mission training are more sophisticated today. The SMS and the SES were upgraded in 1999 with new Silicon Graphics computers and software that increased the display capability by a factor of thirty.

NASA increasingly uses sophisticated interactive virtual-reality simulators to plan and train for space shuttle and International Space Station operations. In the Johnson Science Center's Virtual Reality Laboratory, astronauts wearing virtual-reality helmets see the payload bay, each other, and the object they are handling. They can practice handing off an object to other astronauts. Handholds for the objects are suspended from ceiling wires calibrated to mimic the object's behavior in zero gravity.

Science teams from around the world also use virtual-reality simulations to coordinate, plan, and execute International Space Station and experiment operations. Virtual-reality databases allow distant users to observe diverse system interactions together.

While NASA is now able to employ sophisticated computer technology for simulating space tasks, realism can be simulated with simpler technologies. Astronaut candidates experience weightlessness on a KC-135 airplane flown in a parabolic path that simulates twenty to thirty seconds of floating in space. Known as the "vomit comet" because of the unsettling effect of sudden weightlessness, the KC-135 simulates zero gravity for astronaut training as well as for microgravity experiments.

Tasks involving the manipulation of massive objects for space shuttle operations or space station construction can be simulated in NASA's Neutral Buoyancy Laboratory (NBL) at the Johnson Science Center. (Neutral buoyancy is when an object has an equal tendency to float as sink.) Astronauts suit up and train underwater with backup scuba divers for missions such as the repair of the Hubble Space Telescope. Linked with the SMS and the Mission Control Center, astronauts in the NBL can train on specific mission timelines with flight controllers and astronauts piloting in the cockpit.

To become familiar with a lunar landscape, Apollo astronauts visited volcanic and impact crater sites such as Craters of the Moon National Park and Meteor Crater. They made geological field trips to Alaska, Hawaii, and Iceland. At Sunset Crater Volcano National Monument outside of Flagstaff, Arizona, geologists created a realistic site for operating in a lunar environment by blasting craters in the cinder field, erecting a mockup of the lunar lander, and bringing in a lunar rover for the astronauts to drive.

When it all comes together before a launch, the simulations and training prepare the astronauts to confidently go where no one has gone before—except in the imagination.

Computers, Use of (Volume 3);; International Space Station (Volumes 1 and 3);; Rendezvous (Volume 3);; Space Shuttle (Volume 3).

Benedict, Howard. NASA: A Quarter Century of Space Achievement. The Woodlands, TX: Pioneer Publications, Inc., 1984.

Burrows, William E. The Infinite Journey, ed. Mary Kalamaras. New York: Discovery Books, 2000.

Swanson, Glen E., ed. "Before This Decade Is Out. . . ": Personal Reflections on the Apollo Program. Washington, DC: NASA History Office, 1999.

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