Mars Express Updates Software And Extends Its Lifetime Until 2034
Mars Express mission operators at ESOC successfully sent a new software patch that would allow the spacecraft to operate in its third decade.
A space mission is as durable as its most critical subsystems. For ESA’s Mars Express, this subsystem is the ring laser gyroscope – or gyro – which is essential to point instruments and antennas accurately, but which wears out over time.
To overcome this challenge, satellite engineers and flight controllers at ESA’s European Space Operations Centre (ESOC) have devised a way to use input from another equipment – the star trackers – to replace the gyros’ information.
Mars Express has been using this solution for about a third of its 21 years in orbit.
In 2017, the flight control team noticed that four of the spacecraft’s six gyros were aging faster than expected, threatening to end the mission within two years. To save the mission, the solution was implemented and has been regularly updated ever since. Today the last upgrade would allow the spacecraft to function until 2034.
However, this solution was originally supposed to keep the satellite operational until mid-2025. Beyond this date, the gyroscopes would wear out due to their necessary use.
So how did mission control managed to extend the spacecraft in its third decade? By changing the definition of “necessary”.
Minimising opportunities
Over the years, the mission control team at ESOC has strived to minimise the opportunities for using the gyroscopes, when the star trackers are blinded, during orbit correction manoeuvres, or during safe mode.
The largest contribution is during the daily ‘wheel off-loadings’ (WOL). This special manoeuvre involves using a set of wheels spinning inside the spacecraft together with thruster firings to effect a change in momentum, and hence the velocity, of the spacecraft. In about a quarter of the cases, the attitude of the spacecraft required for the off-loading that would blind one or both star trackers and trigger the activation of the gyros.
Updating a satellite designed in the 1990s can seem like software archaeology. Mission operators had to dig up 33-year-old Microsoft 3.1 to figure out which line of code needed to be edited and then work out by hand the changes before installing them to the star tracker’s memory.
“At the start of gyroless operations, we would turn on gyros for all WOLs out of concern for the star trackers’ possible blindness. However, several waves of studies have allowed us to reassess the star trackers’ field of view and reduce the number of times gyros had to be switched on,” says Mars Express Spacecraft Operations Manager James Godfrey.
“This software patch now allows us to detect if one of the star trackers stops tracking during the wheel off-loading and in this case switch on the gyros. This means we can now leave the gyros off during most wheel off-loadings and they will only switch on if they are needed. All in all, when combined with the existing gyroless mode software this whole set of upgrades have allowed us to reduce opportunities to use gyros by 97%”.
MMX in sight
This development is particularly crucial to support the Martian Moon Exploration (MMX) mission. Originally planned to launch in 2024, with an arrival at Mars in 2025 and a Phobos sample return departing Mars in 2028, the JAXA-led mission was supposed to be supported by Mars Express for the entry descent and landing of its rover on Phobos.
Martian Moon Exploration (MMX) mission — ESA
With the mission now postponed until 2026 and all its milestones moved by approximately two years, it is more than ever necessary for keep Mars Express to be up and running until at least 2029.
“With the latest update and the help of the gyro-monitoring machine-learning tools, I am fully confident that the mission control team will successfully keep the mission ready to support MMX,” says James Godfrey.
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