NASA’s long-lived Mars Odyssey orbiter completed a switch to a backup primary computer earlier this week, cementing the 11-year-old spacecraft’s role as a critical communications relay for the agency’s Curiosity and Opportunity rovers.

The transition from the A to B side primary processor included a critical swap to Odyssey’s backup inertial measurement unit, the navigation subsystem that controls pointing of the orbiter’s antenna, solar array and science instruments. The swap followed several months of troubleshooting that confirmed degradations in the primary (A side) IMU.

The timing of the transition, however, preserves the A side computer and IMU, ensuring they can be reactivated, perhaps for as long as a few months, in case difficulties with the B side systems arise.

“The side swap has gone well,” said Odyssey Project Manager Gaylon McSmith in a Nov. 12 statement from NASA’s Jet Propulsion Laboratory, outlining the transition that began Nov. 5. “All the subsystems that we are using for the first time are performing as intended.”

While monitoring seasonal changes on the red planet, Odyssey shares the rover communications relay duties with NASA’s Mars Reconnaissance Orbiter. Odyssey’s B-side communications relay duties, suspended during the transition, resumed late Nov. 11.

Odyssey was launched on April 7, 2001, one day after the most recent previous activation of the B side IMU. The spacecraft maneuvered into orbit six months later, and in December 2010 claimed the distinction as the longest-working Martian probe.

Curiosity reached Mars’ Gale Crater for a two-year primary mission in early August. Odyssey landed on Meridiani Planum in late January 2004.