July 14, 1997 11:15 AM PDT
Low tech, high payoff on Mars
In an effort to reduce costs and development time, NASA used more off-the-shelf, commercial components than any previous missions in creating the "budget" systems now exploring Mars.
The microrover Sojourner, for example, uses a fairly common processor for control and guidance: a modified version of an older Intel 80C85 chip.
Controlling the landing processes and overseeing most of the operation is a radiation-hardened but relatively run-of-the-mill computer based on IBM technology for commercial workstation computers, incorporating a rugged chip built by Lockheed Martin Federal Systems.
The pictures of the martian landscape being sent back from the microrover Sojourner as it trundles across the red planet's sand are being captured by imagers developed by Kodak for applications such as medical and scientific photography--not outer space.
"It was really only the second time in recent memory where we had gone outside for a computer component," said Glen Reeves, flight software manager for the mission. So far, however, performance has been excellent.
According to Reeves, not only did the Pathfinder team save money on hardware using the processor, but they economized on software as well. With the same processor already in use in thousands of workstations, plenty of programmers were already building software for it.
The decision to use off-the-shelf components was made early on. "We were stuck with a very short time span to work in and a very tight budget," Reeves said. "To do these missions efficiently, we knew we were going to have to rely on the expertise of industry."
Some of the Pathfinder communications technology is the most prosaic. Sojourner and the Pathfinder lander communicate by radio using two 9.6-kbps radio modems. And these aren't scientific or military units--they're a pair of commercial grade devices from Motorola. NASA scientists found it easier to buy 30 of the devices, select the eight best and modify them for space flight rather than trying to build radio modems from scratch.
The images from Sojourner and Pathfinder have to be processed when they reach Earth, and for that NASA is using commercially available Silicon Graphics workstations. The computers are used for 2D image processing and storage, as well as 3D simulations.
SGI technology is also being used to guide the microrover across the martian surface. Because of the time delay in transmitting signals from Earth to Mars, maneuvering the rover across the rocky landscape isn't easy--it's like driving a car that responds 20 seconds after you turn the steering wheel.
To compensate for this lag, the scientist driving the microrover uses an interface constructed with SGI's Inventor 3D graphics language, which was developed primarily for use in scientific simulations and other applications.