The Final Descent: SpaceX's $843 Million Contract to Deorbit the International Space Station and Lessons from Mir

Introduction

As we approach the end of the International Space Station's operational life, NASA has taken a significant step towards ensuring its safe retirement. On June 26, 2024, NASA awarded SpaceX a contract worth up to $843 million to develop the United States Deorbit Vehicle (USDV), a crucial component in the controlled decommissioning of the ISS.

The USDV Mission

The USDV will play a pivotal role in the final phases of the ISS deorbiting process, scheduled for around 2030. This spacecraft will dock with the ISS and execute a series of precise maneuvers to guide the station into a controlled reentry over a remote ocean region, likely the South Pacific. This approach ensures a safe and responsible transition in low Earth orbit at the end of the station's operational life.

Historical Precedent: The Deorbiting of Mir

Before discussing the ISS deorbiting plan, it's worth examining the precedent set by the Russian space station Mir. Operational from 1986 to 2001, Mir was the first modular space station and held the record for the largest artificial object in orbit until the ISS surpassed it.

Mir's deorbiting operation in March 2001 provides valuable insights:

1. Size comparison: At about 130 metric tons, Mir was significantly smaller than the ISS, which weighs approximately 450 metric tons.
2. Deorbit process: Mir's controlled deorbit involved a series of engine burns to lower its orbit gradually.
3. Final descent: On March 23, 2001, Mir made its final plunge into the South Pacific Ocean, with debris falling into a predetermined area approximately 1,800 miles east of New Zealand.
4. Scale of operation: While challenging, Mir's deorbiting was less complex than what the ISS will require, given the ISS's larger size and international ownership.

The ISS Deorbiting Challenge

The ISS presents a more significant challenge than Mir due to its size and complexity:

1. Massive structure: Often described as "as big as a football field," the ISS requires a more powerful and sophisticated deorbit vehicle.
2. International collaboration: Unlike Mir, which was primarily a Russian project, the ISS involves multiple international partners, complicating the decommissioning process.
3. Controlled reentry: Like Mir, the ISS is planned to be brought down over the South Pacific, far from populated areas.

Technical Challenges and Requirements

1. Reliability: NASA emphasizes the critical nature of the USDV's reliability. The spacecraft must function flawlessly on its first flight and incorporate sufficient redundancy and anomaly recovery capabilities to maintain the critical deorbit burn.
2. Design: While specific details of SpaceX's design remain undisclosed, it's speculated that the USDV may be based on the Dragon spacecraft platform, which has proven its capabilities in cargo and crew transportation.
3. Ownership and Operation: Unlike NASA's commercial cargo and crew services, the USDV will be owned and operated directly by NASA, underscoring the mission's critical nature.

Funding and Timeline

The $843 million contract covers the development of the spacecraft, with a separate procurement planned for its launch. NASA's FY2024 budget request included $180 million for the program, with an additional $109 million sought for FY2025. The total project cost is estimated to be around $1.5 billion.

Exploring Alternatives

NASA's decision to pursue a controlled deorbit came after careful consideration of alternatives:

1. Disassembly and component return: Ruled out due to technical challenges.
2. Repurposing in orbit: Deemed unfeasible.
3. Boosting to a higher orbit: Not practical given the ISS's size and structural considerations.
4. Commercial takeover: Not possible due to the multinational ownership of ISS components.

Flexibility in Planning

While the current plan targets 2030 for deorbiting, NASA has included options to store the USDV on the ground until the mid-2030s. This provides flexibility if the ISS's operational life is extended or if commercial low Earth orbit destinations are not ready to support NASA's ongoing needs by 2030.

Conclusion

As we approach the end of the ISS era, the development of the USDV represents a critical step in responsible space operations and debris mitigation. The lessons learned from Mir's deorbiting inform this more complex operation, ensuring that the ISS's final act will be as carefully managed as its decades of groundbreaking scientific research and international collaboration. The successful deorbiting of the ISS will mark the end of an era in space exploration and set new standards for the responsible management of large space structures.