A Graceful Exit, Part 2: What Comes After ISS?

The end of the International Space Station will mark a tectonic shift in human spaceflight. The ISS program united the efforts of fifteen nations, including a landmark union between the United States and Russia, and citizens from eight other countries have since visited the orbiting laboratory. Since its inception, the ISS has delivered new opportunities for nations without domestic access to space. Countless people all over the world owe their livelihoods to the program, their academic careers to research hosted by its facilities.

The station is of particular pride to the United States, which has maintained a continuous, uninterrupted human presence in space aboard the ISS for over twenty-three years. The laboratory has long been a powerful symbol of America’s global leadership in science and technology, which makes its impending loss all the more consequential.

Other world powers are now on the rise: China has begun to assemble a coalition of nations for its International Lunar Research Station, and its Tiangong Space Station now maintains a new human presence in space. India is poised to achieve independent crew access to space in the near future, with its own far-reaching ambitions taking shape on the horizon, including reusable launch vehicles, a domestic space station, and its own Moon landing program.

In its Moon to Mars Architecture, NASA has identified National Posture as a core tenet of its goals in space, a firm assertion of the United States’ continued global leadership. But carrying on the legacy of science and influence left by the ISS will require more than just modules and solar arrays—it will demand that we rethink how to coordinate research in space, and the role of both commercial and international partners in a new space ecosystem. As we prepare the ISS for its graceful exit, how do we fill the void it leaves behind?

Continuing a Legacy

Before we start drawing plans for future space stations, it is critical to understand what we are trying to accomplish. What, really, is the legacy of the ISS?

First, an ISS replacement must, of course, support NASA’s basic needs. Future platforms in LEO must enable continued microgravity research, especially into human and biological sciences, should support technology demonstrations, and must accommodate crew habitation and training. Of the functions provided by the ISS today, these are perhaps the most crucial to provide as its retirement draws ever nearer. Research proposals already face tough competition for extremely limited payload space. Future LEO stations will need to collectively surpass the current capacity of the ISS if they hope to allow real growth of the industry. Research payloads also demand the most technical requirements for an ISS replacement—problems to be solved by payload racks and power systems, crew quarters and living spaces.

But the ISS has always been more than just a laboratory. The ISS program was born of a tumultuous era in world politics; the United States and Russia, diametrically opposed throughout the Cold War, each found themselves struggling to save their own floundering space station programs. Braving backchannels to unite their efforts, their unlikely alliance opened the door for much greater access to space than could have been provided by any single party. Since then, the ISS has uplifted and empowered diverse communities throughout the world, providing an equitable and accessible pathway for people to fly their work into space. Academic institutions, students and educators, and nonprofit organizations all benefit from this spirit of opportunity. These partnerships must continue if future platforms are to truly preserve the legacy of the ISS.

The Commercial Model

Commercialization of space is a fundamental part of NASA’s vision for the future. NASA believes that a commercial space economy will be a key enabler for both a sustained presence in low Earth orbit (LEO) and the exploration of more distant destinations, like the Moon and Mars. While government-funded activities will typically lead the way, commercial enterprise can follow behind the frontier to fill in the gaps and establish more permanent activity.

This is the angle NASA is taking to replace the ISS. The agency’s Commercial LEO Development Program is funding the establishment of several Commercial LEO Destinations, or CLDs—independent, commercially owned and operated space stations. NASA will provide some funding and technical expertise, but CLD providers must pick up the slack. Though NASA will remain a major customer, it is expected that CLD providers will find or create additional business to support their platforms, so that NASA need not support the entire operation. For an agency hoping to send humans to the Moon and Mars in the coming decades, the ability to acquire ISS capabilities without paying for ISS operations is an attractive promise.

However, a key drawback of this approach is that it requires CLDs to become more than just replacements for the ISS, demanding instead that they cater to business cases which do not yet exist. For CLD providers, achieving commercial viability and providing ISS-equivalent capabilities may come into direct conflict with one another. In managing the CLD Program, NASA must strike a delicate balance between supporting its future vision and meeting its urgent need for an ISS replacement. Furthermore, the CLD Program is, fundamentally, a product of the United States and its industry. While international collaboration is not prohibited, the initiative to extend the olive branch of opportunity must come from individual providers.

Meeting in the Middle

The ISS leaves behind a legacy of groundbreaking science and accessible cooperation, yet its designated successors are tasked with building a commercially viable economy. How best to walk this line?

NASA’s Office of Technology, Policy, and Strategy (OTPS) is responsible for studying consequential problems like these. In a study published last November, OTPS analyzed several models which NASA might pursue to balance its needs with the commercial success of future LEO destinations. Without recommending any one model, OTPS highlighted a few key strategies that can help reconcile these disparate aims.

Above all else, future LEO operations must embrace flexibility and adaptability. In an ideal LEO ecosystem, multiple CLDs are present and interchangeable, with both NASA and other customers able to seamlessly operate across any available platforms. The study suggests the incorporation of more transient spacecraft—such as SpaceX’s Dragon or Sierra Space’s Dream Chaser—to conduct shorter “sortie” flights, docking at CLDs only when the mission requires additional amenities. Interoperability and standardized interfaces like docking ports will be critical to the functionality of this model, preventing conflicts due to exclusivity. Scalable platforms could also enable infrastructure to respond to the changing needs of the market. Such flexibility would enable a diverse range of activities to be conducted in space simultaneously, ensuring that all users receive equal opportunity to meet their needs.

The OTPS study also suggests that NASA may take on a managerial role in LEO, acting as a broker to connect users to platforms like CLDs. Extending the legacy of the ISS as a tool for empowerment, NASA may continue to drive research interests, providing funding and resources to vetted proposals and helping researchers understand which platforms will best suit their needs. If NASA-sponsored activities receive a guaranteed proportion of space aboard flights, or perhaps an autonomous region aboard a CLD, the agency’s interests would be all the better protected amidst a crowded market of commercial activities.

The Current Landscape

NASA’s CLD Program is currently supporting three funded LEO destinations: Axiom Station, Orbital Reef, and Starlab. While none of them individually matches the current capacity of the ISS, each promises to bring its own unique strengths to the developing commercial ecosystem.

Axiom Station

Axiom Station is being developed primarily by Axiom Space, a relatively new yet well-established player. Axiom plans to use the ISS like a shipyard, building their station from the forward port of the Harmony module. Once a minimum capability has been reached, their segment will detach and become a free-flying station. However, this dependency on the ISS places pressure on the company to have their modules ready before the station is decommissioned. To compensate, Axiom recently reorganized their construction plan to fast-track an independent configuration, allowing them to separate from the ISS with just two modules. The first, Habitat One, is currently under construction by Thales Alenia Space in Italy, and recently passed its critical design review. The company has also tested orbital maneuvering thrusters in recent months, which will enable their modules to reach the ISS independently after launch. Axiom maintains a 2026 launch target for Habitat One, though later milestones, including separation from the ISS, remain unclear.

Axiom Space has built a strong history of commercial and international partnerships, particularly through its private astronaut missions to the ISS. Three missions have flown so far, using SpaceX’s Dragon spacecraft to carry astronauts from a wide variety of countries, including Canada, Israel, Italy, Saudi Arabia, Spain, and Turkey. The most recent, Ax-3, marked the first all-European commercial flight to the station. Axiom has also signed agreements with partners such as the Canadian Space Agency, the European Space Agency, Italy, and South Korea’s Boryung Corporation; each of these will study commercial business opportunities aboard Axiom Station, and could lead to future human spaceflights for these partners. Furthermore, partnerships such as one with the Wake Forest Institute for Regenerative Medicine, recipient of a National Science Foundation grant, indicate Axiom’s desire to support the broader American research community and non-NASA government agencies.

Orbital Reef

Orbital Reef is led by a partnership between Blue Origin and Sierra Space, with the support of numerous other contractors. Orbital Reef leverages the 7-meter fairing of Blue Origin’s New Glenn launch vehicle to provide much larger modules than are present on the ISS, including inflatable segments provided by Sierra Space. This dependency is not without risk, although New Glenn has been tracking steadily towards its first operational flight later this year. The station is designed to be expanded over time using a series of repeating modules, enabling fairly straightforward growth as demand requires. Updates on Orbital Reef have been sparse; Sierra Space has completed several burst tests of its inflatable LIFE modules, while Blue Origin recently passed NASA milestones in the development of its life support system. Blue Origin has referenced a 2027 target for Orbital Reef to be “operational,” though this date lacks detail about other milestones such as launches.

While Blue Origin has kept fairly quiet about Orbital Reef, its suborbital spaceflights with New Shepard offer some insight into the company’s attitude towards accessibility and collaboration. New Shepard has so far completed seven suborbital tourism flights carrying passengers from a diverse array of backgrounds and nationalities, including Mexico, Portugal, the Netherlands, Egypt, and the United Kingdom. New Shepard has also carried research payloads for non-NASA customers including universities and other research institutions. These ventures highlight Blue Origin’s experience engaging with commercial and international customers, which the company is likely to leverage for Orbital Reef. Similarly, Sierra Space has partnered with the space agencies and industry of Japan, Germany, Turkey, and the United Kingdom to study opportunities for future business in space, aboard both free-flying Dream Chaser spacecraft as well as its LIFE modules. Notably, Japan will provide the docking system for LIFE modules, which will directly contribute to the construction of Orbital Reef.

Starlab

Starlab is the product of a joint venture between Voyager Space, Europe’s Airbus, Japan’s Mitsubishi Corporation, and Canada’s MDA Space. A key selling point of Starlab is that it will be launched as a single, monolithic unit, requiring minimal outfitting once in space. Starlab’s pressurized volume is provided by one large metallic pressure vessel, rather than the modular designs employed by other stations. This strategy will require the 8-meter fairing volume of SpaceX’s Starship launch vehicle; Starship has completed several test flights so far, though some time remains before it is capable of deploying such a large payload. This announcement lacked a launch date, though the station is intended to fly before the ISS is decommissioned in 2031.

The Starlab project has seen a rapid accumulation of partnerships in 2024; Voyager Space’s joint venture with Airbus was only finalized earlier this year, while Mitsubishi and MDA Space joined shortly thereafter. In addition to providing technical expertise—MDA space will provide robotic arms to the station—these agreements help forge deeper connections with international customers. Like the other CLD providers, Starlab has studied possible business opportunities and human spaceflights with other nations, including the Canadian Space Agency and the Indian Space Research Organization. In particular, Starlab’s alignments with Airbus and ESA are expressly intended to provide an avenue for European customers to access space after the ISS, enabling Europe to invest in domestic industry rather than paying American companies. This symbiosis is already bearing fruit: in May, Starlab procured three cargo flights from The Exploration Company, a European provider developing its own cargo transportation spacecraft to service commercial stations. This striking arrangement provides a glimpse into what the commercial LEO landscape may look like in the coming decade.

Other Players

In addition to these three funded destinations, the CLD Program is also supporting unfunded partnerships with several other companies, which receive NASA expertise to develop specific capabilities in support of the broader CLD effort. Notable among them is Vast, a company which is aggressively pursuing the development of its own station, Haven-1. Vast hopes to launch this small, single-module platform as early as 2025, potentially ahead of any funded CLDs, though its capabilities would be comparatively limited. While not affiliated with the CLD Program, other companies have expressed interest in contributing to station hardware, such as Gravitics, which recently partnered with Axiom to develop a utility spacecraft to service their station. Both Vast and Gravitics plan to build larger station modules exploiting Starship’s payload capacity in the future, though these concepts have not been incorporated into any current CLD as of writing.

Evaluating Our Prospects 

There is little doubt that each of these CLD providers is technically capable of building a functional station in LEO. However, the success of any of these platforms is contingent upon their ability to balance commercial viability with NASA’s needs. A survey of this landscape makes one thing clear: collaboration is the key to meaningfully replacing the ISS.

There is clear international interest in continued access to space after the retirement of the ISS, and each CLD provider has already leapt at the opportunity to court these users, offering both payload space and seats for astronauts. The more tangible the agreement, the better; Axiom’s private astronaut mission model needs only to substitute Axiom Station for the ISS, while Starlab is the first to have cargo flights publicly booked. Orbital Reef has dealt primarily in studies for now, but Blue Origin’s experience with New Shepard suggests an interest in helping underserved populations access space all the same. All three CLDs will include internationally sourced hardware, boosting economies around the world while future business cases take shape.

All three providers are also well aware of the demand for flexible and adaptable payload space, even before the ISS is decommissioned. Representatives from each CLD provider attended NASA’s Human Research Program Investigators’ Workshop earlier this year to advertise their capabilities to the community, including members of academia and institutions alike. Sierra Space offers payload space aboard its free-flying Dream Chaser spacecraft, lending the Orbital Reef team a degree of flexibility as recommended by the OTPS report. SpaceX has advertised similar space aboard its Dragon spacecraft, a capability their close partner, Axiom, may prove keen to take advantage of. Of the three CLDs, Orbital Reef seems best suited to future expansion along its roadmap, whereas Starlab’s monolithic design renders additional modules an open question.

Yet the timeline for each provider represents the biggest uncertainty of all. Only Axiom can fly its modules aboard a currently operational launch vehicle, SpaceX’s Falcon family, though New Glenn and Starship are not far behind. Axiom Station is the first to have produced major flight hardware, but its ISS-dependent assembly strategy may temper this advantage. Axiom Station is also furthest in the design process, with Habitat One passing critical design review this year. Updates from NASA’s Human Exploration and Operations Committee show a preliminary design review for Starlab sometime in 2024, while Orbital Reef may not meet this milestone until next year, if not later.

Despite the paucity of updates from the companies themselves, NASA has held firm on its intent to retire the ISS in 2031. NASA administrator Senator Bill Nelson has suggested the ISS could “technically” be kept operational if CLD providers are not ready in time to prevent an American station gap. Yet it is important to note that, even if a gap is avoided, it will take time for CLDs to grow to a capability matching that of the ISS. If only a single or incomplete CLD is available when the ISS is deorbited, the United States will still suffer a significant loss of capability until future destinations come online, which could have major consequences for the research community.

Closing Thoughts

There will never be another station like the International Space Station, nor a program to match its unique circumstances. No matter what low Earth orbit looks like in 2031, the paradigm will have forever changed. There is thus one more question to answer: will this change be for the better? Despite the tension between government and commercial use cases, NASA’s CLD Program seems well on its way to procuring stations that will continue an American presence in space. But it is the partnerships being forged today that will determine whether CLDs can truly replace the legacy of empowerment and accessibility that the ISS will leave behind. If timelines fall behind and agreements unravel, the United States and its partners may find themselves in second place for the foreseeable future, seeking other avenues for access to space. But, should these destinations flourish, the end of the ISS could instead herald new beginnings, as the veteran laboratory makes a graceful exit and a new generation of opportunity is born.

Edited by Nik Alexander, Scarlet Dominik and Emily B.