to appear in MacMillan's Space Science Encyclopedia
The earliest human spaceflights were guided by navigational
computers on the ground; there was no onboard computation. But
starting with project Gemini, computers have been an essential part of
every space mission. When the first piloted Gemini flew in 1965, most
computers were the size of a room, and so it was a remarkable
technological achievement to shrink a computer down to a size (2 cubic
feet) that could fit into the small capsule. Onboard computing power
enabled Gemini to carry out tasks such as rendezvous and docking even
though the computer was underpowered by today
The computers used in
spaceflight have always been a mixture of leading and lagging
technology. The fast chips used in desktop and laptop computers on
Earth would never survive in space because cosmic gamma ray radiation
would deposit electrical charges on the chips, and cause data loss or
other failures. Therefore, many chips used in space are
custom-designed with redundant circuitry: three circuits instead of
one so that the three can vote on the correct answer and ignore a
single incorrect result caused by cosmic radiation. In other cases
standard chips can be protected from radiation with special metal
shielding, but even then the onboard chips are typically ten or twenty
times slower than Earth models.
The experience of the National Aeronautics and Space
Administration (NASA) on the Apollo program changed the way people
thought of software as a component in a large system and ultimately
led to great advances in the software development process. In 1966
NASA was concerned that the software might not be ready by the
scheduled launch of Apollo 1. Until that time software had been
thought of as a minor add-on to large projects. Now it appeared
that software development delays were threatening the space race with
the Soviet Union. NASA and its partner, the Massachusetts Institute of
Technology (MIT), were forced to develop better practices of software
requirements analysis, documentation, verification, and
scheduling. Eventually they were successful, and many of the practices
they developed remain in effect. The Software Engineering Laboratory
at NASA Computers are used in spaceflight for three purposes: to reduce
costs, reduce risks, and increase capability. The most significant
form of cost reduction lies in minimizing ground operations. For
example, scientists at NASA The speed and reliability of computers have enabled complex space
missions and maneuvers such as bringing the space shuttle back from
orbit to take place with a reduced risk of failure. However, computers
also play an important role in risk reduction before a mission is even
launched. During the design stage, computer simulations search for
problems and computerized failure analysis techniques estimate the
probability of failure and point out areas to improve.
Computers enable human spaceflight but also diminish the need for
it. When Wernher von Braun first imagined space travel, he thought
that an orbiting space station would be staffed by about eighty
scientists observing the weather and performing other tasks. He did
not foresee that unmanned robotic satellites would perform most of
those tasks more efficiently and less expensively. Astronauts are so
expensive that robots are preferred wherever possible, and are relied
on exclusively for all exploration beyond low Earth orbit and the
Moon.
There are two kinds of robotic control: telerobotic and
autonomous. In telerobotic control a human guides the movements of a
robot in another location via radio signals. A fascinating example is
Robonaut, a human-sized robot with two arms and hands, a head, a
torso, and one leg. Under development at NASA Autonomous control is used when a telerobotic link would be too
slow or too expensive to maintain. For example, Mars is typically
about twenty minutes away from Earth by radio communication, and so
rovers on the Martian surface are designed to have some autonomous
control over their own actions. For more ambitious missions, such as
the Mars sample return mission currently scheduled for 2014, more
capable autonomy using artificial intelligence will be
required. Autonomous robots are also useful as assistants to
humans. An example is the Personal Satellite Asssistant, a
softball-sized robot designed to float in the weightless environment
of the space station. It is designed to propel itself by using ducted
fans, take pictures, analyze temperature and gas levels, and
communicate by voice control. It can check on the status of the
station and assist astronauts in doing experiments, using a
combination of autonomous and telerobotic control.
The best uses of computers combine the three attributes of cutting
costs, reducing risks, and increasing capability. An example is the
Remote Agent program, which controlled the experimental Deep Space 1
mission in 1999. Using technology similar to the space shuttle NASA administrator Dan Goldin has stated: ``When people think of
space, they think of rocket plumes and the space shuttle, but the
future of space is information technology.'' Advanced computer
technology will continue to contribute to this future.
SEE ALSO Humans versus Robots (volume 3); Simulation (volume 3); Telepresence (volume 4).
Peter Norvig
Heppenheimer, T. A. Countdown: A History of Space Flight. New York: John Wiley & Sons, 1997.
Muscettola, Nicola, P. Pandurang Nayak, Barney Pell, and Brian C. Williams. ``Remote Agent: To Boldly Go Where No AI System Has Before.'' Artificial Intelligence 103 (1998):5 Ames Research Center. Personal Satellite Assistant..
Johnson Space Center. Robonaut: The Shape of Things to Come.
Tomayko, James E. Computers in Spaceflight: The NASA Experience. NASA Contractor Report 182505.
Early Spaceflight Computers
The Uses of Computers in Spaceflight
Bibliography
Internet Resources