Orbiting the Sun: The ISS at Mercury

How High Would the ISS Orbit About Mercury?

Introduction: Considering a hypothetical scenario where the International Space Station (ISS) is repurposed for a 12-year mission around the planet Mercury, this article explores the optimal orbit altitude and the practical challenges involved. Unlike the ISS's current role as a research laboratory, a mission to Mercury would necessitate different considerations, especially given the planet's unique characteristics.

Understanding Mercury

Mercury, the closest planet to the Sun, is known for its extreme conditions and minimal atmosphere. With virtually no atmosphere, Mercury's surface pressure is a mere~5 x 10^-15 bar, roughly 0.005 picobars. The average temperature on the sunward side of Mercury can reach up to 725 K (452°C), making the planet inhospitable for human life. Despite these harsh conditions, the exploration of Mercury is relatively sparse, with only a few missions having visited the planet so far.

Historical Missions to Mercury

Key missions to Mercury include:

Mariner 10

The Mariner 10 spacecraft made three flybys of Mercury between 1974 and 1975. It was able to capture photographs and gather data despite the extreme conditions. The second flyby, in September 1974, occurred at an altitude of about 48,000 km, while the third and final flyby, in March 1975, took place at an altitude of just 327 km.

MESSENGER

The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission, operated by NASA from 2004 to 2015, played a crucial role in understanding Mercury's composition and environment. MESSENGER entered orbit around Mercury in March 2011 and continued to gather data until April 2015 when it was allowed to crash into the planet.

Spacecraft Orbits in Mercury's Neighborhood

The upcoming joint European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA) mission, BepiColombo, is scheduled to launch in February 2017 and enter orbit around Mercury in February 2024. BepiColombo's mission is expected to last for one or possibly two years, collecting vital scientific data about the planet.

ISS at Mercury: Practical Considerations

From a practical standpoint, sending the ISS to Mercury presents several challenges. The ISS is primarily designed as an orbiting laboratory with regular crew rotations and resupply missions. Due to the extreme temperatures and the lack of a substantial atmosphere, continuous crew support and resupply would be logistically difficult and resource-intensive. These challenges are amplified when considering the journey to and from Mercury, which would take about 7 years round trip using minimum fuel.

Optimal Orbit Altitude

Given the harsh environment, a practical orbit altitude for the ISS would need to be carefully considered. A minimum altitude above the surface of 200 km might be a reasonable choice, as suggested by previous missions like MESSENGER. This altitude allows the ISS to avoid potential hazards while still being close enough to conduct valuable scientific studies. However, such a high orbit could also be influenced by solar perturbations, which would necessitate periodic adjustments to maintain the orbit.

Alternatives to Human Missions

In lieu of a human mission, robotic probes like MESSENGER and BepiColombo are better suited for deep-space missions. These probes do not require crew support, reducing the logistical challenges and allowing for more focused scientific research. The upcoming Mercury-P lander mission, set for launch in 2031, will provide further insights into Mercury's surface and internal composition.

Conclusion

While the idea of using the ISS for a 12-year mission to Mercury is intriguing, practical constraints and the unique characteristics of Mercury itself suggest that a more specialized spacecraft, such as BepiColombo, would be more appropriate for long-term missions. The 200 km orbit altitude remains a viable and practical choice for any future exploratory mission to Mercury.