Sol 446:
Spirit and Opportunity use NASA's Mars Odyssey orbiter as their main communications link between Mars and Earth. On April 2, Odyssey entered "safe mode," which is a protective state a spacecraft automatically enters when onboard fault protection software instructs the spacecraft to disregard its onboard sequence of commands and wait for instructions from the ground. As a result, relay communication with the rovers was suspended, and Spirit did not receive any data from sols 444 and 445. With an unknown status of the rover after its drive, the Spirit team restricted rover operations to remote sensing.
Sol 447:
The Odyssey flight team scrambled to recover the orbiter, but it remained in a safe state, not yet available to support relay communications. Spirit received very little information from its "direct-to-earth" communications link, so the rover team planned another basic remote sensing sol, which generated little data.
Sol 448 (April 7, 2005):
Spirit performed additional remote sensing, including panoramic camera and navigation camera imaging. The Odyssey team brought the orbiter back on-line, the Spirit team received all imaging needed for continuing to drive, and team members are planning to drive on sol 449 with a new appreciation for their orbiting partner! The Odyssey team is investigating the cause behind the fault protection software sending the orbiter into safe mode.