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GCN Home > 08/25/03 issue

Software to change en route to Mars

By Patricia Daukantas, GCN Staff

As Mars wings closer to Earth than it has in 60,000 years, NASA is tweaking the software forthe two rovers speeding toward the Red Planet.

The twin NASA rovers now heading toward Mars owe more of their brainpower to the successful 1997 Mars Pathfinder than to the doomed missions of 1999.

Software developers at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., reused much of the code that guided Pathfinder and its onboard rover, Sojourner. And they’re taking more time to test the all-important software instructions that will steer the two Exploration Rover spacecraft out of interplanetary trajectory and down to a safe landing.

The developers needed so much time, in fact, that they’re still working on the landing code.

Not until November will NASA transmit a software upgrade in preparation for the Jan. 24 and 25 landings, said Roger Klemm, a technical staff member at JPL.

Klemm works on flight software development for Spirit and Opportunity, the twin spacecraft of the Mars Exploration Rover program. Launched in June and July, they are slated to land on opposite sides of the planet to analyze its surface.

The rovers’ computers must operate “in an environment more hostile than a microwave oven,” said Mike Deliman, a technical staff member at Wind River Systems Inc. of Alameda, Calif.
The Mars Rover
Image:
The Mars Rover
The brain of each spacecraft is a 20-MHz, 32-bit Rad 6000 CPU module, a radiation-hardened version of an early IBM PowerPC processor, now manufactured by BAE Systems of Farnborough, England.

“The smaller the electronics get here on Earth, the more susceptible they become to cosmic radiation,” Klemm said.

In 1995, Wind River ported its real-time VxWorks operating system to the Rad 6000 in preparation for Mars Pathfinder. Deliman said he was part of that team, which worked so well that NASA tried to recreate the team as much as possible.

Although the CPU’s power hasn’t been state-of-the-art since the late 1980s, it is the most radiation-hardened processor available for deep space, Deliman said.

The compiler included with the MULTI development environment from Green Hills Software Inc. of Santa Barbara, Calif., is the only compiler validated to generate proper code for the Rad 6000 chip, Klemm said. JPL engineers are using the Green Hills compiler “for heritage reasons” because they reused so much code verbatim from the successful Mars Pathfinder, he said.

The multitasking OS slices up CPU time “so that no one task will hog it, and everyone can get a little piece of the pie,” Klemm said. JPL designed the architecture to work with VxWorks’ scheduling and interrupt features.

The software developers used Wind River’s Tornado integrated development environment, which incorporates the VxWorks OS and various debugging and visualization tools, Deliman said.

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