Orbiting Mars since 2001, Odyssey has carried out extensive studies of the Red Planet as well as serving as a communications relay between Earth and surface missions. Before switching into safe mode, the satellite was relaying data to-and-from the Mars Exploration Rover (MER) Opportunity.
Since Odyssey has been out of commission, science activities of Opportunity have been delayed.
NASA has worked out that Odyssey detected "unexpected performance" from the electronic encoder that controls a gimbal - a pivoted support that controls the rotation of an object (in this case, Odyssey's solar array) around a single axis - prompting on board computers to switch into standby until a fix could be found by mission control.
The spacecraft automatically switched from using its high-gain antenna to transmitting via its slower low-gain antenna. Scientists have since switched it back.
All space missions are rigged with fail-safe systems to prevent small glitches from triggering mission failure. Mars rovers and landers switch themselves into "Lazarus" mode when solar energy gets scarce and satellites are equipped with software designed to protect the whole system from cosmic ray impacts.
The need for these systems was highlighted recently when the 30-year-old Voyager 2 probe suddenly transmitted gibberish data. Although the mission continues to live far long than anyone ever dreamed, its aging computer "flipped a bit" of data for an unknown reason.
I speculated that a cosmic ray might have been the culprit, others believed aliens hijacked the probe. Which ever theory floats your boat, I suppose.
Unfortunately, fail-safe systems don't always go to plan. In May, I reported that a communications satellite in geosynchronous orbit had been hit by a solar storm, frying its brain. The satellite was turned into a "zombiesat." Unfortunately, even modern satellite fail-safe systems will be rendered useless if the onslaught of solar particles completely overwhelm the spacecraft.
Image credit: NASA/JPL