, The Associated Press 2004-01-23
Whether on a desktop on Earth or roving about Mars, modern computers share the basic building blocks -- and can run into the same problems.
But glitches are much easier to diagnose and repair on Earth than on another planet. It's a challenge now faced by NASA engineers as they try to find out why the Mars rover Spirit has rebooted its computer 60 times and sent back irregular communications since Wednesday.On Earth, problems can be fixed by hitting the power button or, at most, replacing a bad part. In space, it's not so easy: Remotely hitting the reset button is possible but swapping out hardware is out of the question.
The systems aboard the Mars rovers are specially designed for the rigors of space, from launch to landing and beyond. Software is built so updates can be remotely beamed from Earth.
The rovers' computers don't run Microsoft Windows. They rely on an operating system called VxWorks from Alameda, Calif.-based Wind River Systems Inc., which has provided the software brains for Mars Pathfinder, Deep Space One and other spacecraft.
"The space community in general is very conservative and wants to make sure that their $500 million mission is not jeopardized by software that hasn't gone through the rigors of space qualification," said Vic Scuderi, manager of space programs at BAE Systems in Manassas, Va.
At the heart of each Mars rover is a computer on a single board called the RAD6000. Its circuits are hardened to absorb radiation and qualified for space flight. Otherwise, charged particles would quickly ruin the sensitive hardware.
The system built by BAE has been used in other spacecraft, including Pathfinder, the Mars Odyssey orbiter and Stardust, which earlier this month successfully swooped past the comet Wild 2.
In fact, there are 145 RAD6000s running on 77 satellites in space.
"It's quite a well-heeled computer to be used in spacecraft," Scuderi said.
The microprocessor belongs to the PowerPC family, a version of which is still used today in Apple Computer Inc.'s Macintosh computers as well as corporate servers and workstations.
The chip was designed in the early 1990s by International Business Machines Corp., when the BAE unit was part of IBM's Federal Systems Co. The IBM division, working with the Air Force Research Lab, developed the radiation-hardened version.
Compared to today's Earth-bound PCs, the RAD6000 seems like an underperformer. Its 1.1 million-transistor processor runs as fast as 25 megahertz, compared to 3.2 gigahertz for today's top Intel Pentium 4, which has 55 million transistors.
But the RAD6000 had 10 times better performance over previous processors qualified for space. It reduced the number of boards from five to one. And it reduced the weight and power required for the computer by five fold.
The RAD6000 has no moving parts, so there's no hard drive for storage. Instead, data are kept in 128 megabytes of random access memory.
Another sign that the RAD6000 is not meant for home computers: Each costs between $200,000 and $300,000.