For more than two decades the International Space Station has been orbiting Earth. In that time, it has helped NASA among other agencies have consistent access to low Earth orbit, but it has also cost them quite a bit. It’s estimated that the floating laboratory costs the agency around $3 billion every year, which accounts for roughly a third of the total human spaceflight budget.
With that in mind, NASA has also been working toward its eventual decommissioning, which is expected to happen in 2030, where they purposely deorbit the station, burning up in the atmosphere. Just today however we finally learned what company will be helping in that unique process with a specially designed vehicle. Here I will go more in-depth into the agency picking SpaceX, what type of de-orbit vehicle we can expect, future replacements, and more.
NASA Picks SpaceX
In early 2023, NASA first asked companies for proposals for a space tug that could be used to deorbit the ISS. Some of the companies included SpaceX, and most notably Northrop Grumman, among a few others. Earlier today however the agency finally reaseled its decision to the public. In a quote, they said, “NASA announced SpaceX has been selected to develop and deliver the U.S. Deorbit Vehicle that will provide the capability to deorbit the space station and ensure avoidance of risk to populated areas.”
They went on to say, “While the company will develop the deorbit spacecraft, NASA will take ownership after development and operate it throughout its mission. Along with the space station, it is expected to destructively breakup as part of the re-entry process.” In other words, whatever SpaceX sends up to the station will end up being destroyed as well, likely staying attached throughout the entire process. In terms of the price, the single-award contract has a total potential value of $843 million. They clarified that the launch service for the U.S. Deorbit Vehicle will be a future procurement.”
With all this in mind, one of the first questions is what type of vehicle will SpaceX send for this process. The first thought that comes to mind is an altered Dragon spacecraft. Importantly, there are a few possible stipulations and ideas which the company might take into account. For one, the agency plans to dock the vehicle to the ISS Node 2 Forward port around 1 year prior to reentry. This is meant to ensure the deorbit vehicle arrives prior to the ISS dropping below a reasonably maintainable altitude.
As far as specific vehicle requirements, in an industry day presentation held back in late 2022, the agency laid out a few thoughts. Here they mentioned that the vehicle would need to operate independently of the ISS for 4 days during the deorbit sequence. It would also need to function during and after exposure to ISS environments for at least 1 year. Importantly, regarding thrust, it obviously would need enough to deorbit the station but limit loading from attitude control and translational maneuvers such that it doesn’t cause ISS components to exceed limit loads. In this case, SpaceX will have to work closely with the agency to make sure the structure can handle various burns.
In another instance, the agency was quoted saying, “it will be a new spacecraft design or modification to an existing spacecraft that must function on its first flight and have sufficient redundant and anomaly recovery capability to continue the critical deorbit burn” they said.
Obviously, the entire process is quite high stakes. The International Space Station is primarily made up of a combination of truss elements, modules, solar arrays, and radiators. The truss acts as the backbone of the station, providing physical support for the solar arrays, radiators, and modules. The various modules provide pressurized volume for the many microgravity experiments, a habitable area for crew, and ports for visiting spacecraft to dock and undock. The solar arrays and radiators provide power generation and thermal control for station hardware. Related to the burn itself, NASA said, “Based on behavior observed during the re-entry of other large structures such as Mir and Skylab, NASA engineers expect breakup to occur as a sequence of three events: solar array and radiator separation first, followed by breakup and separation of intact modules and the truss segment, and finally individual module fragmentation and loss of structural integrity of the truss.”
At that point, as the debris continues to re-enter the atmosphere, the external skin of the modules is expected to melt away and expose internal hardware to rapid heating and melting. Most station hardware is expected to burn up or vaporize during the intense heating associated with atmospheric re-entry, whereas some denser or heat-resistant components like truss sections are expected to survive re-entry and splash down within an uninhabited region of the ocean. Thanks to the size of the station, some parts are expected to make it through reentry which is why a controlled deorbit is so important.
While SpaceX’s deorbit vehicle will be needed, NASA wants to naturally lower the station over time as well. The chosen approach for safe decommissioning is a combination of natural orbital decay, intentionally lowering the altitude of the station likely using current propulsive elements, and then execution of a re-entry maneuver for final targeting and to control the debris footprint. They highlight that “This final maneuver is expected to require a new or modified spacecraft using a large amount of propellant.”
Due to the high propellant requirement of this final maneuver, the Earth’s natural atmospheric drag will be used as much as possible to lower station’s altitude while setting up deorbit. Once all crew have safely returned to Earth, and after performing small maneuvers to line up the final target ground track and debris footprint over an uninhabited region of the ocean, space station operators will command a large re-entry burn, providing the final push ensure safe atmospheric entry into the target footprint.
Focusing back on today’s decision, the associate administrator for Space Operations Mission Directorate at NASA said, “Selecting a U.S. Deorbit Vehicle for the International Space Station will help NASA and its international partners ensure a safe and responsible transition in low Earth orbit at the end of station operations. This decision also supports NASA’s plans for future commercial destinations and allows for the continued use of space near Earth. The orbital laboratory remains a blueprint for science, exploration, and partnerships in space for the benefit of all.”
All the way since 1998, five space agencies, CSA (Canadian Space Agency), ESA (European Space Agency), JAXA (Japan Aerospace Exploration Agency), NASA (National Aeronautics and Space Administration), and Roscosmos, have operated the International Space Station with each agency responsible for managing and controlling the hardware it provides. The station was designed to be interdependent and relies on contributions from across the partnership to function. The United States, Japan, Canada, and the participating countries of ESA have committed to operating the station through 2030. Russia has committed to continued station operations through at least 2028.
In terms of other options like boosting the station to a higher orbit to extend its life, the agency decided it wasn’t the best choice. Here they mentioned, “With current capability, it would be possible to raise the station’s altitude enough to slightly extend the orbital lifetime, but not escape low Earth orbit. This disposal method carries a high risk to future operations in low Earth orbit since the station could not be refueled for debris avoidance maneuvers. A debris strike on a space station poses critical risk to astronauts, could render the station uncontrollable, or create additional debris that would present a risk to other missions. Alternative propulsive methods to escape Earth’s gravitational pull have been explored, but these options would require new hardware, a large amount of additional propellants, and would impose large additional cost burdens for the development, test, and deployment of these methods. Ultimately, this decommissioning strategy would only increase risk of the station being struck by orbital debris and delay the uncontrolled re-entry of the space station to a later date” they said.
The goal going forward would be to utilize commercial space stations being built by companies like Axiom Space or Blue Origin. The first Axiom module for example is almost ready to be sent to Texas for final assembly and testing. The Axiom president was quoted saying, “The pressure vessel will arrive in Houston next year, and then we’ll do all the final outfitting at our spaceport facility. And in the 50-year history of human space flight at Houston it will be the first human-rated spacecraft built in Houston” he pointed out. From there Axiom would complete the initial module before launching it in 2026 to be attached to the ISS. This initial module is named Axiom Hab 1, or Ax-H1. It will be outfitted with crew quarters, and will feature both research and manufacturing capabilities. Over the next few years, they would continue to launch modules to the station before undocking from the ISS before its retirement and deorbit.
Unfortunately, besides some of the mission requirements, NASA didn’t release any information on SpaceX’s design or even a rough estimate. In the future, we can hope to hear more from the company as they begin working on a vehicle meant to go to space and never return, at least in one piece.
Conclusion
SpaceX was just selected by NASA to provide a space tug capable of deorbiting the International Space Station. By the end of this decade, they plan to have the station burn up in Earth’s atmosphere with the help of SpaceX. We will have to wait and see how it progresses and the impact it has on the space industry.