Mars Express: One more extension to foster its legacy

 Mars Express: One more extension to foster its legacyP. Martin, C. Wilson and the Mars Express Science Ground Segment Team and Flight Control TeamMars Express mission technical statusClose to being the oldest operational spacecraft orbiting Mars, Mars Express has reached a lifetime of well over 20 years [1, 2]. The spacecraft platform health continues to be very good, albeit with only three operational gyros, the minimum needed for spacecraft operations. Gyroless routine operations continue running very smoothly as have been since May 2018. Further improvements have been deployed in the current extension cycle (e.g., wheel off-loadings added to the Gyroless Mode functionality), resulting in a drop of the gyro duty cycle to 3.3% or lower. This figure is expected to drop further over time, giving an estimated mission lifetime well beyond 2030. The spacecraft technical lifetime is also limited by fuel availability and battery performance. Latest predictions confirm available fuel for operations until at least 2033, and battery performance compatible with operations until 2042.The technical status of the payload of Mars Express is overall very good to excellent, with all instruments maintaining their full technical capability as needed to support the identified science objectives of the proposed further extension, except for the Planetary Fourier Spectrometer (PFS) which suffers from pendulum laser diode ageing causing intermittent data loss.With VMC and the Melacom telecommunications package being used routinely for science data acquisition, the spacecraft now has onboard two more science instruments than at launch! The mission performance, measured in terms of executed science observations versus the observation plan remains steadily close to 100%. Ground segment operations and systems are running smoothly. A further enhanced mission toward an additional extensionA number of mission elements have been enhanced through the last few years. The reprogrammed MARSIS instrument is now capable, via deployed new sounding mode, of longer and continuous high-sensitivity sounding passes. Also, operational and scientific collaboration with ExoMars TGO has been increased, in particular through MEX-TGO inter-spacecraft radio science occultations. Such new implementations demonstrate that innovation still takes place on this ageing mission.Mars Express continuing operations in the 2027-2029 timeframe would allow covering a full range of observation types. Furthermore, dedicated campaign possibilities are MARSIS South Polar nightside sounding, HRSC mid-latitude dayside imaging, co-located radio occultation with MARSIS soundings, Earth radio occultation high-density sounding, Phobos campaigns with JAXA’s MMX, and solar wind campaigns with NASA’s ESCAPADE.In more detail with respect to international collaboration opportunities, a further extension would allow: coordinated Phobos characterisation observations through MMX phase 3 (sampling) and Mars observations of MMX phase 4; Phobos – solar wind interaction via MEX/ASPERA & MMX/MSA multi-point measurements; Mars atmosphere co-located observations via MEX/MaRS radio occultation soundings which are targets of interest for MMX/MIRS hyperspectral observation sequences, to enable 4-D atmospheric characterisation; MMX-MEX measurement cross-calibration, cross-validation, and sample analyses. Following the well-established MEX/MAVEN scientific scheme, collaboration with ESCAPADE, whose payload is highly complementary to the Mars Express payload, would consist in multipoint measurements, key to plasma and ionospheric science, to disentangle spatial & temporal variations. Fostering Mars Express science return and legacyMars Express continues to be ESA’s most productive mission in planetary science. Its long-duration observational record is unmatched for atmospheric & ionospheric science, and a further extension would sustain the planetary science community until EnVision, JUICE and ExoMars rover arrive in the early 2030s.  In addition to optimising the returned science via the proposed extension, the Mars Express team plans further effort toward enhanced archiving activities, with the aim of leaving a usable data archive as a high priority for mission legacy. Following the example set by Rosetta in 2016, an enhanced archiving phase has been proposed for the 2027-2029 period in order to ensure all mission science teams are up to date with deliveries, adequately staffed to support a final PSA archive review including documentation revisions and reprocessing as necessary, and support higher-level data product deliveries. Focus is therefore being placed on ensuring this long-lived planetary mission has the optimised legacy it deserves. [1] Martin et al., Extending Mars Express gyros for a scientific lifeline, EPSC abstract, 2024.[2] Martin et al., Mars Express: From the launch pad to a 20-year success record at MarsSpace Science Review, Vol. 221, 2025.