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ISS with Axiom modules
The International Space Station will gain a set of commercial modules later this decade, a precursor for both commercial space stations and the end of the ISS itself. (credit: Axiom Space)

A dynamic ISS prepares for its future, and its end

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Twenty years ago today, the crew of Expedition 1—Bill Shepherd, Yuri Gidzenko, and Sergei Krikalev—arrived at the International Space Station, kicking off occupation of the station that has continued uninterrupted to this day. NASA and its partners have been celebrating this impending milestone for months, regularly remining the public that there is now a whole generation of people who have no memories of a time when there were not people in orbit.

The milestone, though, is a reminder of something NASA and its partners are a little less eager to talk about: the ISS is closer to its end than to its beginning. While humans have been on the station for the last 20 years, it’s unlikely they will be there for 20 more years. At some point—perhaps a decade from now, or a little longer—the ISS will be retired and, most likely, deorbited.

“The station is in very good condition,” said Sergey Ryzhikov of Roscosmos during a NASA TV media event. Regarding the air leak, he said, “don’t worry.”

NASA has made clear its long-term plan is to eventually retire the station and, rather than build a replacement, shift to using commercial space stations whose development the agency is stimulating (see “Making the transition from the ISS”, The Space Review, September 8, 2020). Doing so, NASA has argued, will allow it to maintain a presence in low Earth orbit as a customer—but not the only customer—of commercial stations, freeing the agency from at least some of the multibillion-dollar annual cost of operating the ISS. That transition, though, depends on having one or more stations ready by the time the ISS reaches the end of its technical or political life.

The policy constraint is probably the lesser of NASA’s concerns. While the agency proposed a couple years ago to end direct federal funding of the ISS in 2025, Congress sharply rejected that proposal and the administration has not pursued it. The ISS is currently formally authorized only through the end of 2024, but members of Congress have proposed extensions of that authorization through 2030.

International partners would likely support an extension of ISS operations to late this decade. That includes Russia, which has largely rejected participating in the NASA-led Artemis program but is willing to continue work with NASA on the ISS. “We and our partners are discussing an option to extend its lifetime to 2028 or even 2030,” Dmitry Rogozin, director general of Roscosmos, said during a panel at the International Astronautical Congress (IAC) October 12. “We are ready to consider any proposal from our partners.”

A bigger concern is technical. Those core ISS modules—Unity, Zarya, and Zvzeda—have now been in orbit for more than two decades, and may be showing signs of their age. In recent weeks the ISS crew spent time tracking down a small but persistent air leak, which required the three-person crew to “camp out” in the Zvezda module over two weekends, sealing off the other modules of the station to track down the leak.

That leak, it turned out, was in Zvezda itself, which a cosmonaut found by watching tea leaves as they followed an air current that led to the leak. That leak has been sealed, but around the same time the station’s Russian segment suffered malfunctions of its oxygen generator and its toilet.

The station’s current crew—like 20 years ago, two Russians and one American—played down the latest problems. “The station is in very good condition,” said Sergey Ryzhikov of Roscosmos during a NASA TV media event October 30. Regarding the air leak, he said, “don’t worry.”

“From all the analysis that’s been done, technically, we can support 2030 and beyond,” said Mulholland.

“If you follow station news, you’ll hear about things breaking all the time. They’re not really breaking,” said NASA’s Kate Rubins in the same event. In many cases, it’s hardware that reaches the end of its service life and be replaced with spare parts on the station, she argued. “So, the toilet breaking? I don’t worry about that. The toilet breaks all the time. We fix it. It’s not a big issue.”

Engineering analyses performed in the last several years have found that the station should be able to operate through at least 2028. “From all the analysis that’s been done, technically, we can support 2030 and beyond,” said John Mulholland, ISS program manager at Boeing, NASA’s prime contractor for the station, during a call with reporters October 13.

He and others see the ISS entering something of a golden age in the coming years. A major reason for that is the introduction of commercial crew services, which not only end reliance on the Soyuz for accessing the station also allows NASA to expand the crew by one, creating significantly more time for ISS research. (In fact, once the SpaceX Crew-1 mission arrives at the ISS, there will be five astronauts in the US segment of the station, counting both the four NASA and JAXA astronauts on Crew-1 as well as Rubins.)

“The real value of the International Space Station is going to be the scientific advancement and the scientific discoveries,” Mulholland said, “that are going to pay back the commitment to the International Space Station.”

Having additional crew is giving NASA some flexibility in planning ISS operations. “Crew time has generally been our biggest constraint to executing things on orbit,” said Marybeth Edeen, manager of the ISS research integration office at NASA, during a presentation at an October 15 meeting of the Aeronautics and Space Engineering Board (ASEB). Planning for station operations now has a positive margin: more crew time than allocated tasks. “Never had it before,” she said. “We have crew time that we haven’t exactly figured out how we’re going to use.”

Crew time, though, is not the only factor affecting the utilization of the station. She noted some payloads need no crew time, as they’re operated remotely, but still require power, data, and other resources to operate. There’s also cargo transportation up to the station as well as back down to Earth: upmass and downmass, respectively.

Cargo may be at a premium for ISS activities in the near future, as the station’s crew expands to seven and with the introduction of new cargo vehicles. While the upgraded version of Cygnus is already flying, and the new cargo variant of Crew Dragon is set make its first flight to the station likely in December, there’s the potential for delays for both Sierra Nevada Corporation’s Dream Chaser and HTV-X, the upgraded version of Japan’s HTV cargo vehicle.

Those new vehicles offer “tons of capability,” Edeen said, but their introduction will likely be delayed simply based on the history of past vehicle development efforts. “New vehicles are hard, but everyone forgets that once they’ve been up and running for a while,” she said. “This is what’s driving our worry about cargo shortfalls.”

That cargo shortfall could push back some research payloads. “We are either going to have to slow down how much we can get accomplished on orbit, or somehow get more stuff to orbit,” she said.

Research is fighting for cargo space with crew supplies as well as station hardware. That includes, in the next few years, new solar arrays that will be installed on the station, she said. Those arrays, placed on top of six of the eight existing arrays to take advantage of existing infrastructure, will be one-third the size of the old ones but produce the same amount of power thanks to improvements in solar array efficiency.

“ISS, from the outside, is seen as a static program. It’s been around for 20 years,” Edeen said. “In reality, it is an incredibly dynamic program.”

Another factor is NASA’s low Earth orbit commercialization initiative. That will eventually include a series of commercial modules on the station by Axiom Space but, in the near term, also supports short-duration private astronaut missions by Axiom and possibly others. At the IAC last month, Michael Suffredini, CEO of Axiom, said the company was finalizing the contracts with its customers, and with NASA, for the first such mission on a SpaceX Crew Dragon spacecraft in late 2021—a flight that is rumored to include actor Tom Cruise.

“We’re cautiously optimistic that, by the end of October, we will have everything in place to move forward for a launch in the fourth quarter of 2021,” he said at the conference. (As of November 2, Axiom hadn’t announced that the flight plans had been finalized.)

Adding those private astronaut missions into the mix further complicates the station’s logistical challenges, Edeen said. “If you’re going to fly another three or four crew even for a short mission, they all need food, they all need consumable supplies, they all need clothing,” she said. “This, then, exacerbates our cargo upmass issues if these guys can’t take everything they need with them.”

Edeen added that the ISS program was happy to take on this new challenge of commercial activity on top of the research work on the station, but that it was a challenge nonetheless. “It’s another objective and challenge that we will have to go work on and figure out how we can support them.”

That demand, some ASEB members said, might be a sign that NASA’s commercialization initiative is working: there’s more demand for the ISS than resources available, suggesting there’s a market for a commercial facility. Edeen, though, noted that many ISS users, such as those for the half of NASA’s ISS resources devoted to the ISS National Lab, have much of their costs underwritten by NASA. “If they had to pay for it themselves, how much of that demand would drop off?” she asked.

All that, she said, serves as a counterpoint to the argument that the ISS is a stable, mature program that has overcome the political and technical challenges of being developed and assembled that consumed much of the program’s history. “ISS, from the outside, is seen as a static program. It’s been around for 20 years, everything continues,” she said. “In reality, it is an incredibly dynamic program.”

That dynamic nature may cause a lot of near-term headaches for NASA, but it might be essential to demonstrating there is a market for human spaceflight in LEO after the ISS finally reaches its end, most likely less than 20 years from now.

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