NASA shifts vital computer tasks onboard long-running Mars Odyssey satellite

Mars Odyssey has been operating on one side of its redunanadt computer system for 11 years

After 11 years, NASA scientists running the Mars Odyssey Orbiter have decided to switch the machine's redundant computing functions from one side to the other in an attempt to keep the technology serviceable as possible.

Odyssey, which spends its time performing a number of science functions like taking close-up shots  of the Red Planet and relaying information from the Curiosity and Opportunity rovers operating on the surface of the planet, has redundant systems - side A and side B, NASA says.

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"We have been on the A side for more than 11 years. Everything on the A side still works, but the inertial measurement unit on that side has been showing signs of wearing out," said Odyssey Mission Manager Chris Potts at NASA's Jet Propulsion Laboratory, in a release.   "We will swap to the B side on Nov. 5 so that we still have some life available in reserve on the A side. The spare inertial measurement unit is factory new, last operated on the day before launch."

The inertial measurement unit is a gyroscope mechanism senses changes in the spacecraft's orientation, providing important information for control of pointing the antenna, solar arrays and instruments, NASA said.

The side swap will take place on Nov. 5 and will put Odyssey into "safe mode." As the team and the spacecraft verify all systems can operate well over the following several days, the orbiter will return to full operations, conducting its own science observations, as well as serving as a communications relay, NASA  said. The Curiosity and Opportunity rover teams will reduce the amount of data planned for downlinking until Odyssey returns to full capacity after the side swap is complete, and will maintain near-normal tactical operations in the interim, NASA said.

According to NASA Odyssey's website, all of Odyssey's computing functions are performed by the command and data handling subsystem. The heart of this subsystem is a RAD6000 computer, a radiation-hardened version of the PowerPC chip used on most models of Macintosh computers. With 128 megabytes of RAM and three megabytes of non-volatile memory, which allows the system to maintain data even without power, the subsystem runs Odyssey's flight software and controls the spacecraft through interface electronics.

In addition, using three redundant pairs of sensors, the guidance, navigation and control subsystem determines the spacecraft's orientation, or "attitude." A sun sensor is used to detect the position of the sun as a backup to the star camera. A star camera is used to look at star fields. Between star camera updates, a device called the inertial measurement unit collects information on spacecraft orientation.

This system also includes the reaction wheels, gyro-like devices used along with thrusters to control the spacecraft's orientation. Like most spacecraft, Odyssey's orientation is held fixed in relation to space as opposed to being stabilized via spinning. There are a total of four reaction wheels, with three used for primary control and one as a backup, NASA says.

Odyssey launched April 7, 2001, began orbiting Mars on Oct. 24 of that year, began systematic science observations of Mars in early 2002, and broke the previous record for longest-working Mars spacecraft in December 2010.

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