By John McHale
PASADENA, Calif. - NASA officials believe they have pinpointed and solved technical problems that struck the Pathfinder Mars explorer in mid-July, which caused computers aboard the Pathfinder lander to reboot repeatedly and slow the flow of research data to Earth.
A priority glitch in software application code was to blame for continually rebooting computers on the Pathfinder landing craft, says Lloyd Keith, cognizant engineer for the flight computer and operating system for the Mars Pathfinder at the NASA Jet Propulsion Laboratory in Pasadena, Calif.
During exhaustive testing of the Mars lander and rover before the mission to the red planet, all the tasking in the software code was tested at high rates, but not all at once, Keith says. A small low-priority task was unable to complete its function during data flow to Earth when all the high-priority tasks were moving at high rates, he explains.
A fail-safe mechanism in the software, which resets the system automatically when any performance is interrupted, rebooted the system when the glitch occurred, Keith says.
NASA experts solved the problem by raising the priority of the task in question and adjusting the priority of other tasking in the code.
Last month Military & Aerospace Electronics reported that experts at the National Aeronautics and Space Administration (NASA) had virtually ruled out problems with the Pathfinder computer hardware and its operating system, and were concentrating on application software to find a solution to the problem.
They had ruled out the software operating system as the source of the problem, and were concentrating on the spacecraft`s application code, which engineers wrote in the C programming language.
Two positive side-effects to the event - the efficient reaction of the fail-safe mechanism and the flexibility of the software in repairing the problem - enhanced the confidence of NASA engineers in the Pathfinder system, Keith notes.
The Mars Pathfinder is a large collection of commercial off-the-shelf (COTS) technology, ranging from its RAD6000-based mission computer from Lockheed Martin Federal Systems, to its VX Works real-time operating system from Wind River Systems in Alameda, Calif.
Pathfinder`s computer system is a VMEbus open-systems architecture, and features 16-bit COTS dynamic random access memory chips from IBM Corp.
NASA engineers have solved the Mars Pathfinder software problem that caused its computers to reboot repeatedly.
