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The only serious alternatives I have seen reported for the current Soyuz coolant problem are to either use the existing Soyuz, hopefully patching and testing it enough while attached to ISS to be able to safely use it to transport the crew back to Earth or to send up a an unmanned replacement Soyuz.

Crew Dragon was originally designed to handle up to 7 people, but the current design only supports 4. From this article:

[Changing the specification for the crew seat angle] meant SpaceX had to do away with the company’s original seven-seat design for the Crew Dragon.

"With this change and the angle of the seats, we could not get seven anymore," Shotwell said. "So now we only have four seats. That was kind of a big change for us."

While I suspect it could be redesigned for 7 people, getting NASA to certify it would be an extensive and time-consuming process, so I will assume that is not a realistic option. Neither is sending up Starship - it will be a while before it is human-rated.

However, while Soyuz requires custom seat liners for each astronaut, Crew Dragon does not. Since Cargo Dragon can fly without any crew, why can't NASA and SpaceX send up a Crew Dragon with one astronaut (i.e., as Crew Dragon is designed for hands-on controls in an emergency) and a set of appropriately sized flight suits for the 3 stranded Soyuz crew members. Dump the broken Soyuz. Stranded crew comes back to Earth in Dragon. Russia gets to continue with the original plans for the Soyuz that is currently being considered as a rush replacement.

Alternatively, if Russia determines that the damaged Soyuz is a viable craft, could NASA tell astronaut Frank Rubio to wait on ISS, then send the next Crew Dragon up with only 3 crew members instead of 4, providing him with a possibly safer trip home?

Just saw this article NASA, Russia's space agency probing cause of Soyuz leak so maybe my idea isn't so wild after all.

NASA is exploring whether SpaceX's Crew Dragon spacecraft can potentially offer an alternative ride home for some crew members of the International Space Station after a Russian capsule sprang a coolant leak while docked to the orbital lab.

Another report: NASA asks SpaceX about International Space Station rescue options

Update - Soyuz and Dragon

The current plan is to send up Soyuz empty so that it can bring back all 3 crew members. However, in case of emergency, NASA has determined that Crew Dragon could safely carry an astronaut back home in the cargo area.

https://wccftech.com/nasa-strapped-astronaut-with-cargo-strap-on-spacexs-ship-floor-as-emergency-measure/

NASA actually indicated they could take up to 3 additional crew members - 7 total - as Crew Dragon was originally designed for 7 crew members. However, the current plan is that in an emergency the 2 cosmonauts would return on the damaged Soyuz as Roscosmos has determined that the damaged Soyuz is capable of safe reentry with 2 crew members instead of the usual 3.

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    $\begingroup$ I'm not sure that it's true that a seven-seat Crew Dragon would require a design recertification. That was the originally documented design, and my impression is that the back bench space was instead swapped out for more interior cargo room. I don't have any documentation at hand to back up the idea that the seven seats could still be mounted, though. $\endgroup$
    – Erin Anne
    Dec 20, 2022 at 4:17
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    $\begingroup$ thanks for the link. Hope you don't mind I'm going to edit the blockquote a little to include what the change was. $\endgroup$
    – Erin Anne
    Dec 20, 2022 at 5:59
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    $\begingroup$ @TrySCE2AUX Space is fine. Life support is fine - Crew Dragon can support 4 people for several days, so 7 for 1 day should be easy. The problem is apparently the seat angle for a safe (for puny humans) reentry. $\endgroup$ Dec 20, 2022 at 15:07
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    $\begingroup$ @manassehkatz-Moving2Codidact just because a Lifesupport system can support 4 people for several days doesen't mean that it can support almost double the people for a shorter timespan. Also, I don't know if they installed a smaller version to save on weight on the dragons used as taxis to and from the ISS. $\endgroup$
    – TrySCE2AUX
    Dec 21, 2022 at 5:46
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    $\begingroup$ @user3528438 aside from politics, which would already rule it out, China originally got its units from Russia in the 90s, making their 1st generation docking units compatible with APAS-89. They're on at least 2nd generation now, with power and refueling interfaces that removes them from that compatibility. With NDA's on all ISS PMA's that also removes that level of compatibly, so no to Shenzhou. The main problem with Dragon or anything as a lifeboat is.. no one wants to pay for it (remembers ACRV..). With the ISS perceived EOL on the horizon this is even less likely to change. $\endgroup$ Dec 29, 2022 at 21:16

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Nobody here came up with an answer, but NASA did! One of my original ideas was:

Alternatively, if Russia determines that the damaged Soyuz is a viable craft, could NASA tell astronaut Frank Rubio to wait on ISS, then send the next Crew Dragon up with only 3 crew members instead of 4, providing him with a possibly safer trip home?

According to:

https://tlpnetwork.com/news/2023/01/crew-rescue-missions-scheduled-following-ms22-leak

that is mostly what is currently planned. The next Crew Dragon will be sent with only 3 crew members instead of 4, leaving behind a cosmonaut originally scheduled for the mission, and sending up a flight suit for Frank Rubio so that he can return in the Crew Dragon at the end of that mission.

Meanwhile, Russia will do a similar thing with a Soyuz, sending up a new Soyuz with only 1 cosmonaut instead of 3, who will return home with the 2 currently stranded cosmonauts at the end of that mission.

There will be some follow-on adjustments to get crew rotations back to original plans, but this takes care of the current problem, as long as there is no need to evacuate the ISS in the next two months. There has never been a need to evacuate the ISS, but there have been times when the crew has gone into their spacecraft for safety, and that is currently not an option for the "stranded" crew.

But according to:

https://futurism.com/the-byte/russia-slaps-down-plan-spacex-rescue-cosmonauts

this plan is not yet finalized.

The latest plan is to send up a Soyuz empty and use it for all 3 stranded crew members:

https://www.theguardian.com/science/2023/jan/11/russia-to-launch-rescue-ship-to-space-station-after-meteoroid-hit

But now NASA is back to Dragon as a Lifeboat:

https://www.space.com/nasa-equipping-spacex-dragon-iss-lifeboat

This is currently only in case Soyuz MS-22 has to be used in an emergency, as having only two cosmonauts on board will reduce the cooling load and Dragon can handle another passenger. I'm not sure how they'll attach the seat liner to Dragon without a real seat. Duct tape?

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