The devices, known as inertial measurement units or IMUs, give the spacecraft data about its orientation vital for maintaining spacecraft attitude and for pointing the orbiter's large antenna and science-observation instruments in the desired direction
The orbiter has two identical copies of this device, dubbed IMU-1 and IMU-2, each containing three gyroscopes and three accelerometers.
"The reason we're doing this [switch] is that one of the gyroscopes on IMU-1 is approaching its end of life, so we want to swap to our redundant unit early enough that we still have some useful life preserved in the first unit," said Mars Reconnaissance Orbiter Mission Manager Reid Thomas of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The swap is expected to take less than two days before the orbiter resumes its normal functions of science observations from orbit and communication relay for Mars rovers, JPL said.
IMU-2 has been used previously, but IMU-1 has seen much more use.
After the swap, IMU-1 will remain available as a backup if needed for short periods, Thomas said.
"To make sure we have a smooth transition, regaining attitude knowledge as quickly as possible, we will power off all instruments, do the IMU swap, maneuver to sun point, do the IMU swap, and then put the spacecraft into safe mode," he said. "The safe-mode process re-initializes the spacecraft's knowledge of its attitude."