Getting the Most out of Mars Express

Mars Express has the distinction of being one of the oldest operational spacecraft at Mars, with over 18 years since its injection into Martian orbit in December 2003. Designed for a nominal mission of one Martian year to survey the red planet, it is currently applying for its 9th mission extension. A recent technical review has concluded that Mars Express was technically fit to continue providing excellent science return for the 2023-25 and 2026-28 extension intervals. The spacecraft subsystems, scientific payload and ground segment are in overall good health, allowing continued smooth mission and science operations. The 3 lifetime-limiting elements of the spacecraft are the gyros, the batteries, and the fuel remaining onboard. The situation of the gyros has been improved by the successful implementation of a gyroless operations mode in May 2018 by the Mars Express teams at ESOC and ESAC. This difficult modification saved the mission and now allows an IMU duty cycle currently reduced to a monthly figure of about 3 to 4 % of the original usage. Mars Express can expect its gyro lifetime to be extended well beyond the 2025 timeframe. Studies performed in 2019 and 2020 have shown the spacecraft batteries to be much less degraded than had previously been assumed. The findings of these studies were substantiated in subsequent eclipse seasons. A new battery power model now used operationally allows for more flexibility in science planning particularly during eclipse seasons. The longest, most challenging eclipses of the mission were passed successfully in 2021. With shorter eclipse durations in the coming years the outlook is very favourable for continuing to operate the batteries well beyond 2030. The fuel situation remains satisfactory based on regularly actualised estimates and on a very low fuel consumption (assuming no safe modes; the last one was in 2011). The estimated ~3kg of usable hydrazine (with high confidence based on the Venus Express experience) left onboard can take the spacecraft mission operations to beyond 2030 with the current load of science operations. Planning and execution of science operations have been improved by upgrades to the mission operations run from the MOC at ESOC and to the Science Ground Segment operations done at ESAC near Madrid. More flexible, rationalised and in some cases even reduced constraints are now in place which enhance the capability of the spacecraft and its payload in performing scientific observations and data taking. Finally, new science opportunities are presenting themselves in the coming years, illustrated recently by the routine implementation of mutual radio occultations between Mars Express and the ExoMars Trace Gas Orbiter. This will greatly expand the number of atmospheric observations in the future. Automated dual-band radio science occultation observations have now been implemented at egress. The MARSIS subsurface radar is implementing two new promising modes of operation, one to investigate the subsurface at a better sampling rate and one to characterise Phobos, the largest Martian moon and future target for Japan’s MMX mission. Another proposed mission capability will be to perform active sounding of the local plasma environment using combined operation of the ASPERA particle detector and the MARSIS radar. MELACOM relay operations have increasingly taken place with regular Mars Surface Laboratory overflights and were also recently upgraded to implement CNSA’s Zhurong rover overflights and prepare for supporting the ExoMars rover mission as well as other NASA landed assets. These are only a limited set of examples of how Mars Express keeps delivering new and exciting science return. Interplanetary missions can operate over many years and learning how to use the technology in ways that were maybe not part of the original operational concept is an incredibly important ability. The above demonstrates that the Mars Express teams have been able throughout the mission’s many years of life to render Mars Express a better spacecraft now than at any time before, with in-flight upgrades that kept the mission flying. Those teams were able to make such changes thanks to: robust in-house control and support of the ESAC-run MAPPS planning software allowing for continuous improvement; Flight Control Team with enough skill and resources to modify and fully test the flight code; instrument teams with enough funding and support to allow for software updates/testing late in the mission. This might help younger and upcoming missions assemble the resources now so that they can attempt life-extending changes later. Combining a special set of payload instruments onboard Mars Express, very resilient spacecraft and payload health and a favourable orbit configuration, this makes for a still unique mission at Mars, very much complementary to newer orbiting elements with different capabilities. ESA is getting the most out of Mars Express and will continue to do so in the coming years, contributing to and enhancing the international cooperation at Mars.