After spending over 12 years studying the Red Planet, NASA's Mars Reconnaissance Orbiter (MRO) is getting some preventative maintenance to allow it to remain in service until the mid-2020s. In one of the changes designed to reduce the wear and tear on the gyroscopes used to orient the unmanned spacecraft, the space agency is looking to the stars to keep it on track over the coming years.

Launched from Cape Canaveral Air Force Station on August 12, 2005 atop an Atlas V rocket, the US$720 million MRO was originally tasked to spend two years conducting orbital reconnaissance and exploration of the Red Planet. However, NASA's tradition of over-engineering has allowed the spacecraft to extend its service life far beyond its official remit.

Despite this success, the MRO is now feeling its age as its attitude control systems grow less reliable. The orbiter uses a set of gyroscopes and accelerometers to make sure its instruments and the radio antenna are always pointing in the right direction by tracking how it shifts and turns as it circles around Mars. The primary system was already switched off a few years ago after it clocked up 58,000 hours of service, and NASA says that the backups have now reached 52,000 hours.

To help extend the life of the gyroscopes, mission control plans to swap over to an alternative system for routine attitude control tracking, while saving the gyroscopes for more important tasks where greater accuracy and precision is needed or while the orbiter is in safe mode. To do this, an "all stellar" software patch was uploaded to the MRO's computers, which allow it to determine its attitude using its star tracking instrument.

This month, NASA engineers will order the MRO to do a full-swapover test, where the star tracker and its backup unit take over completely from the gyroscopes. It will use pattern recognition software to seek out bright reference stars in its field of view by scanning them several times a second, then calculating changes in attitude by the stars' shift in position. If the test goes well, the MRO will shift to "all-stellar" mode in March and remain there indefinitely.

In addition to modifying the attitude control routine, mission control is also working to help the MRO better manage its power supply. Its primary energy source is its 2,000 W solar panels, but the batteries are over 12-years old and are becoming weaker. This is important because not only do the batteries act as a buffer to protect the spacecraft from electrical spikes, but they provide primary power for 40 minutes out of every two hours as the orbiter passes through the shadow of Mars.

To keep the batteries going, the MRO was commanded to put them on a higher charge rate while reducing demand on them. To do this, the spacecraft uses the available solar power to preheat its systems before it passes into darkness, so the batteries have less to do to keep the systems warm. In addition, the probe's Sun-synchronous orbit, which keeps the MRO passing over targets at the same local time each orbit, will be shifted after 2021 so it passes overhead later in the afternoon to reduce the amount of time the spacecraft goes through shadow. This delay in altering its orbit is to allow the MRO to better act as a transmission relay during Mars mission landings this year and in 2021.

"We are counting on Mars Reconnaissance Orbiter remaining in service for many more years," says Michael Meyer, lead scientist of NASA's Mars Exploration Program. "It's not just the communications relay that MRO provides, as important as that is. It's also the science-instrument observations. Those help us understand potential landing sites before they are visited, and interpret how the findings on the surface relate to the planet as a whole."

Source:
NASA