The vast expanse between Earth and Mars, typically abuzz with scientific data and commands exchanged among various missions at the Red Planet, is about to experience an unusual hush. For approximately one and a half days this November, communication between Earth and Mars will be momentarily severed as Mars slips behind the Sun, marking the occurrence of a solar conjunction.
Solar conjunctions for Mars happen roughly every 25 months when the Red Planet positions itself on the opposite side of the Sun from Earth. During this period, radio signals used for spacecraft communication can be disrupted by the Sun’s active atmosphere, the solar corona.
This year, the disruption spans from early November to early December, impacting missions like ESA’s Mars Express (MEX) and ExoMars Trace Gas Orbiter (TGO). Mission controllers face the challenge of preparing for limited or no communication during this celestial alignment.
To navigate these communication challenges, critical instructions for the spacecraft’s operation need to be uploaded in advance. For MEX and TGO, this means sending three to four weeks’ worth of commands instead of the usual one-week intervals.
As the Sun’s atmosphere interferes with signals, the amount of data exchanged with MEX and TGO must be reduced. Uplinked data to MEX decreases from 2000 bits per second to 250, and the downlink from MEX to Earth drops to as little as 300 bits per second. The ground stations are set to maximum transmission power to ensure clear communication.
This conjunction holds special significance for Mars Express, celebrating its 20th anniversary this year. While it marks MEX’s tenth solar conjunction and TGO’s third, the 2023 event is unique—the first time Mars passes directly behind the Sun since the arrival of the ESA spacecraft.
During the conjunction, communication limitations pose a challenge, mirroring the potential hurdles faced by future human settlers on Mars. However, the experienced mission teams, including James Godfrey, Spacecraft Operations Manager for Mars Express, and Peter Schmitz, Spacecraft Operations Manager for Trace Gas Orbiter, express confidence in managing these celestial events.
Over the years, advancements in planning and technological adaptations have made dealing with conjunctions a routine process. The teams have learned to continue some instrument operations in a limited capacity, ensuring minimal disruptions.
As Mars briefly disappears behind the Sun on 17–18 November, the teams at ESA stand ready, showcasing the resilience and adaptability required for successful interplanetary communication in the ever-evolving realm of space exploration.