Does NASA have any rocket options to replace ISS segments?

Question

Roscosmos has announced their ISS partnership will end in 2 years

This might have been seen as an indication that the new administration at Roscosmos was in a more cooperative mood. Any such hopes were dashed on Tuesday, when Borisov announced that Russia would not be renewing its current commitment to the ISS, which ends in 2024. NASA's current plans involve keeping the station occupied through the end of the decade.

It's not clear what their plans are, but the new head of Roscosmos did say this

According to The New York Times, Borisov told Russian President Vladimir Putin that the 2024 date gives his country time as well. “I think that by this time, we will begin to form the Russian orbital station,” he said.

In theory, Russia may want some of its ISS segments back for this "new" Russian space station. That does present a problem, in that we need some of those modules, and a decent chunk of our modules were flown on the now-defunct Space Shuttle.

From a different article in March, it seems like NASA's Cygnus module could be used to replace the Russian boosting capacity. The catch is that the rocket that took it up there (Atlas V) was made with Russian engines and all the ones we still have are spoken for.

Cygnus has previously launched on the American-made Atlas V rocket. But this booster also uses Russian-made engines. Because of that, the Atlas V was already due to be phased out later this decade after completing two dozen more launches. The Atlas V rocket developer, United Launch Alliance, has taken delivery of all the Russian engines it needs for these flights. Although these missions are all booked, one solution may be for Amazon to give back some of the nine Atlas V launches it has reserved for its Project Kuiper satellite constellation. Another scenario involves launching Cygnus on a Falcon 9 rocket, something Northrop and SpaceX would probably agree upon in an emergency situation.

Another potential re-boost solution could come from Boeing's Starliner spacecraft, but this vehicle has not yet demonstrated the ability to dock safely with the International Space Station. And it, too, is reliant upon launching on the Atlas V rocket.

The SLS is still in testing and, given the enormous cost of a heavy lift non-reusable vehicle, it seems unlikely to be used for the ISS.

Could a Falcon Heavy do the trick for another Cygnus, or an entirely new ISS module? Or would any hopes for heavy lift capacity be in rockets not yet built/flown?

Answer 1

The main issue for American providers is that there is no real space tug available off the shelf. The Russians often used a modified propulsion module from Progress (Posik, Pirs, Prichal modules) vehicles, or else built the propulsion system into the module itself (Zarya, Zvezda, Nauka). Rassvet was delivered by the Shuttle.

So while Falcon Heavy clearly has the volume in the fairing they need a system other than the second stage up to the station.

SpaceX has demonstrated the ability to berth (get close, CanadArm2 grabs and docs) and dock (PMA only, so not useful) so they know how to get a vehicle close. And maybe they could adapt a Dragon's Draco system to be standalone for another module.

Similarly the Service Module of the Boeing Starliner might be adaptable. The basic ideas in Cygnus is being used in somewhat of this fashion for the Gateway station so that might be the best bet for NASA.

But the US owns Zarya. They paid for it, way at the beginning of the ISS project. The design of Nauka is to be the base of a new station for Russia. I.e. There is at least a design goal, to be able to separate from the ISS and with the Prichal module, form the core of a new station.

Thus the main need is for altitude and attitude control. They just tested Cygnus recently for some of this purpose. There are technical reasons that are a bit beyond me as to why Cygnus cannot yet fulfill the entirety of this role, but it can do some of it.

Thus the real question is less, is there a way to launch a module, but more about how to get the module to the ISS and attached, and then can it fulfill the roles needed that the current Russian modules fulfill.

Axiom is planning to add new modules to the ISS in the next few years, so they may be already solving some of these issues. They too intend to start with the ISS and eventually detach as the ISS phases out and operate on their own.