ESA's Mars Express orbiter is getting a major software upgrade that will extend its service life for years to come. On Sunday, the space agency uploaded the update into the veteran deep space probe's computers where it will remain stored in memory until a scheduled restart on April 16. If successful, it will take some of the burden off the aging gyroscopes used to keep the unmanned spacecraft's vital high-gain radio antenna pointed at Earth.
As anyone who regularly uses digital devices can tell you, software updates are a way of life. It turns out that Mars orbiting spacecraft are no exception, with aging electronics that need new instructions to deal with worn out components after years of heavy use.
Mars Express is one of the oldest still-functioning missions to the Red Planet. Launched on June 2, 2003 atop a Soyuz-FG rocket from the Baikonur Cosmodrome, the orbiter arrived at Mars on December 25 of that year. Since then, it has spent 14 years revolving about Mars taking photographs and gathering a mountain of scientific data to send back to mission control in Darmstadt, Germany.
According to ESA, Mars Express is still in remarkably good shape, but that doesn't count for much because the six gyroscopes that are used to keep the spacecraft properly orientated so it remains in radio contact with Earth aren't what they once were. In fact, four of them are close to failing. If that should happen, then the orbiter might as well be a lump of dead iron.
To delay this threat for as long as possible, ESA is turning to the Express' two star trackers. These simple cameras calculate the angles of a number of bright reference stars to determine the orientation of the spacecraft to within a few seconds of arc. This information, combined with that of the gyros, keeps the antenna on target. It also gave a warning to ESA engineers that something was wrong.
"After looking at variations in the intensity of the gyros' internal lasers, we realized last year that, with our current usage, four of the six gyros were trending towards failure," says spacecraft operations manager James Godfrey. "Mars Express was never designed to fly without its gyros continuously available, so we could foresee a certain end to the mission sometime between January and June 2019."
To prevent this from happening, the engineers used their experience of gyroscopes on other missions to come up with a workaround that would extend the life of the gyros by relying more on the star trackers. This would allow the gyros to be switched off and saved for when they're really needed. It's a fix similar to the one used on NASA's Mars Reconnaissance Orbiter (MRO), which is suffering from the same problem.
The snag was that this meant rewriting a large part of the Mars Express' software, then uploading it to the spacecraft. Fortunately, they were helped by reusing code originally written for the Rosetta comet orbiter. However, the task still took months and the engineers weren't even certain that it would be possible.
In the end, several months of coding and testing resulted in the upload of the software into the orbiter's spare memory banks and the final approval to proceed with the upgrade, which was given on Tuesday. If the April 16 restart goes as planned, it will be followed by weeks of testing and reconfiguration.
"Similar, but much smaller fixes, have been developed in the past for other missions with old gyros, such as Rosetta, but this is certainly the most complex and extensive software rewrite we've done in recent memory," says mission manager Patrick Martin. "Thanks to the skill of ESA's teams, Mars Express will fly well into the 2020s, depending on fuel supply, and continue delivering excellent science for many years yet. I look forward to seeing continued joint science campaigns between Mars Express and other Mars missions like ESA's Trace Gas Orbiter and incoming rover missions."
The video below shows a flyover of Mawrth Vallis made from images collected by Mars Express.
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