Mars Enters Solar Conjunction, Interrupting Interplanetary Communication

The phenomenon known as the solar conjunction of Mars is a recurring event that transpires approximately every 25 months, posing a significant challenge for communication with Mars missions. In the year 2023, Mars will align directly behind the Sun, resulting in a complete blackout of communication that will persist for approximately one and a half days. This occurrence underscores the complexities of interplanetary communication and the imperative for meticulous planning and advanced technology.

The space corridor between Earth and Mars typically resonates with a flurry of scientific data, telemetry, and commands shuttling back and forth among nearly a dozen missions stationed at the Red Planet. However, during a span of roughly one and a half days in November, this crucial communication link will fall eerily silent as Mars momentarily disappears behind the radiant orb of the Sun.

This particular celestial alignment, known as solar conjunction, unfolds about once every 25 months. During this phase, Mars positions itself on the opposite side of the Sun relative to Earth. At this juncture, the radio signals employed to transmit commands from Earth to spacecraft and receive data from them can become susceptible to interference from the Sun’s dynamic atmosphere, the solar corona.

The duration of communication disruption is contingent upon the size and capability of a Mars spacecraft’s communication equipment but typically spans the period during which the angle between the Sun and Mars, as observed from Earth, remains within 3–4 degrees. In 2023, this communication hiatus will extend from early November to early December.

In response to this disruption, mission controllers must take meticulous precautions. The Sun’s corona, during the conjunction season, disrupts the radio signals indispensable for communicating with Mars missions. Consequently, measures such as “uplinking” a comprehensive set of critical instructions to enable the spacecraft to function autonomously during the entire blackout period are undertaken. This entails sending commands for a duration of three to four weeks, in contrast to the usual practice of sending one week’s worth of instructions at a time.

It’s worth noting that these conjunctions are not unique to Mars and impact missions conducted by other space agencies as well. To mitigate the effects of solar interference, data transmission rates between Earth and spacecraft, such as ESA’s Mars Express and ExoMars Trace Gas Orbiter, are drastically reduced during conjunction season. This reduction includes limiting the “uplink” data rate to as low as 250 bits per second and the downlink data rate from the spacecraft to Earth to as little as 300 bits per second. Additionally, ground stations are set to maximum transmission power to ensure robust communication despite the challenges posed by the Sun’s atmosphere.

This limitation in data exchange means that the spacecraft can only transmit essential “housekeeping” data related to health status and telemetry, rendering it incapable of sending scientific data during this period. Any data gathered by the spacecraft’s instruments during the conjunction must be stored in its limited onboard memory until the blackout is lifted.

What sets the 2023 solar conjunction apart is the fact that it will mark the first time Mars will pass directly behind the Sun since the arrival of the two ESA spacecraft, Mars Express and ExoMars Trace Gas Orbiter. During this period, from November 17 to 18, communication with these spacecraft will not merely be limited; it will be rendered impossible. These periods of constrained or nonexistent communication between Earth and Mars pose a formidable challenge for future human missions to the Red Planet.

James Godfrey, Spacecraft Operations Manager for Mars Express, explains, “At the beginning of the mission, the team was very cautious about conjunctions, as something going seriously wrong during this period could be difficult to recover from until it’s over.” Over the years, the mission team has refined their approach, allowing some of the spacecraft’s instruments to be used in a limited capacity as long as all necessary commands are uploaded before the conjunction season begins, and all scientific data are stored onboard until the blackout subsides.

Peter Schmitz, Spacecraft Operations Manager for Trace Gas Orbiter, adds that with its larger communications antenna and data storage capacity, TGO can continue its data relay activities for Mars surface assets throughout the conjunction period, even when Mars is directly behind the Sun. This data can then be downlinked to Earth once it becomes safe to do so.

In summary, the 2023 solar conjunction of Mars presents a unique challenge in interplanetary communication, underscoring the importance of meticulous planning and technology adaptation to ensure the continued success of Mars missions.

Frequently Asked Questions (FAQs) about Interplanetary Communication Challenges

More about Interplanetary Communication Challenges

• NASA’s Solar System Exploration: Mars
• ESA – Mars Express
• ESA – ExoMars Trace Gas Orbiter
• Solar Conjunctions and Their Impact on Mars Missions
• Challenges in Interplanetary Communication