The first commercial space station, Haven-1, is now undergoing assembly for launch

"We have a very strong incentive to send a crew as quickly as we can safely do so."

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[EllPeaTea]

Your modules are as spacious as your launch vehicle can support. ISS has 4m wide modules, because that's what they could launch on STS. Skylab was 6.6m wide because that's what you could launch on Saturn V. Same with the length. If you are launching a single module station with Falcon 9, it's going to be less spacious than a single module station launched on NewGlenn, or a multi modular station launched on Starship.

Casey Handmer wrote some stuff on this a few years back. He reckoned it might be cheaper to actually build a launch system that can handle the bigger modules, than to persist with the current system.
https://caseyhandmer.wordpress.com/2019/06/26/are-modular-space-stations-cost-effective/

 

[EllPeaTea]

Are docking collars standardized or does everyone have their own version?

There are 2 main families. The Soyuz one, and the APAS family.
Soyuz one is used when Soyuz and Progress docks with the ISS.
APAS-89 was originally designed by the Russians for Buran to dock with MIR. That then developed into APAS-95, which the Shuttle used with ISS. That then further developed into LIDS, which was further developed into IDSS (Inernational Docking System Standard). Dragon/Starliner/Orion/Starship are all using implementations of IDSS.

Confusingly, there is also a hybrid of Soyuz and APAS used between the Russian modules on the ISS - it has the Soyuz capture system, but the wider collar from APAS.

China is using an APAS variant, but it’s unclear if it’s IDSS compatible.

There is also the CBM (common berthing mechanism), used between modules on the US side of ISS, and by some visiting cargo vehicles (Cygnus and HTV). This is much wider than IDSS, but needs a robotic arm to join the modules/vehicles together.

 

[EllPeaTea]

It might not be the cheapest option, but wouldn't the simplest (and safest) way of doing this be to buy an uncrewed dragon mission from Space-X and have it dock to prove it is capable and safe before sending a crewed mission to try?

If the Dragon can't dock, then the crew can just come back home. If the life-support doesn’t work, they can just come back home. I don’t see what sending up an uncrewed dragon proves that a crewed one couldn’t do safely.

 

[EllPeaTea]

What happened to Axiom? They gave the impression that they were going to be up by now. They must have their modules delivered by Thales Alenia by now.

I think the first module has been or is about to be shipped from Italy. They are also looking to repurpose one of the MLPMs. Eric has previously expressed some doubt about their financial viability on the twitters.
They also have had to rejig their assembly schedule, as the US deorbit vehicle will be using the forward port that Axiom were going to use.

Edit: tweet from Eric late last year after CEO quit.

Bhatia was an excellent fundraiser. Which the company really needs to survive (and pay its bills). Where Axiom goes from here is not clear. Spacesuit business survives because it is mission critical for NASA. Station side of the business faces more questions.

 

[EllPeaTea]

So a little over one mission per year? How does that in any way make financial sense for Vast?

I it doesn’t by itself. But it lets them demonstrate capabilities to NASA that improves their chances of getting a CLD contract. That gets them money from NASA, and also make them a more appealing investment. Which lets them launch Haven-2, and that’s where they start making money.

 

[EllPeaTea]

I was thinking of potential catastrophic failures, not routine failures. Stuff like being unable to undock for some reason. Or worse.

IDSS is a well understood system by now, so I don’t see that being a problem. And I’m not aware of anybody ever having trouble undocking before. First time docking of new systems, yes. But never when separating.

 

[EllPeaTea]

The advantages of a modular system, though, is that each module or group of modules can have their own life-support subsystems. This will allow the station to scale up or down and, more critically, provide redundancy. Depending on station layout/design, you could also then jettison older modules or modules with failing damage. You can then "ship of Theseus" your station indefinitely, which is much less wasteful in the long run and allows for a more continuous presence in space - just keep cranking out modules instead of having to design a whole new $$$ station every decade.

You also need a modular approach because micrometeorite or orbital debris damage to single module will allow crew to escape to other spaces. This is only currently feasible to do my making a bunch of smaller self-contained modules and not a single large module with.

Space stations will always be tight because open air is wasted space and mass. It looks cramped but this is the norm on ships, submarines, aircraft, and other such places where mass and energy have a very high cost and human comfort has to be compromised. This has been well understood for hundreds of years. If you've ever go to "tall ship" below decks, you'll see incredibly cramped spaces, no privacy, and most space is "mixed use" - the gun deck is also your mess hall, for example, so you toss the benches into the center of the ship to clear space to roll in the guns to load them.

You could send up a big module and fit out the inside of it with “decks” to avoid having dead space in the middle.

 

[EllPeaTea]

For Dragon, I wonder if the hatch could close in that case.

The hatch isn’t part of the docking system. So it would be unaffected by an inability to undock normally. I would assume the emergency undock process would be:
Close hatch.
Fire emergency separator (which might leave part of the dragon's capture ring behind).

 

[EllPeaTea]

If the nose cone isn't able to close then it can be jettisoned. That likely requires substantial repair work before the Dragon can fly again, but blowing the emergency release probably has the same result so it's a wash. From what I understand the bigger concern is that it would leave the ship's soft capture ring attached to the station, preventing any other spacecraft from docking.

Do we know for sure that bits would be left behind? When I said that earlier it was pretty much uninformed speculation.
But if the docking ring had gotten to a state where it couldn’t undock, I’m not sure I’d want to try again, even if the emergency separation system is designed to leave the adapter in a usable state.

 

[EllPeaTea]

A quick search doesn't turn up specific documentation but I recall seeing specific statements that it uses an explosive mechanism and that it leaves the port unusable afterwards. It was in context of the ISS jettisoning a dead spacecraft, so permanent damage to the passive port was a given, but I can't see how it would be different from the active side. There are twelve latches around the perimeter and three latches on the soft-capture system and any one of them failing to release would prevent undocking. It might be possible to force the ring latches without leaving chunks in the opposing slots, but severing the capture ring would leave it firmly attached to the other port. The worst case scenario is finding yourself stuck in a half-docked position where you can neither complete the hard-dock nor release the soft-dock. The Soviets nearly lost Soyuz 10 that way.

If the soft capture ring wasn’t disengaging, that’s accessible from inside the docking tunnel, so you could hit that with a hammer, then close hatches and release the hard capture hooks. You could probably even do it in such a way that only your soft capture ring takes any damage.

 

[EllPeaTea]

I guess if you require the crew to wear space suits the entire time, then it's less of an issue (although if they survived the immediate issue they may still be stuck in space with no ride home and only hours of oxygen).

I know the depiction of the 'imperfect lock' from Interstellar is likely not exactly how it works, but something catastrophic happening after dock is complete and astronauts have entered the station while the Dragon is docked and taken off their helmets is what I would be worried about. Some kind of unknown issue that occurs only after being docked for a period of time.

If we look at the history of maiden dockings to stations to US ports, the breakdown is as follows.

• Skylab - first docking was by the crewed Skylab 2
• Mir Kristall - first docking was by the crewed Soyuz TM-16 (yes, this port was intended for Buran, but this was a test run for the Shuttle)
• Mir docking module - module was berthed to the shuttle with the Canadarm, Shuttle then undocked from the module after docking the module to Kristall.
• PMA-2 - similar to previous, Unity was berthed to the Shuttle, Shuttle then undocked after docking Unity to Zarya.
• PMA-3 - first docking by the Shuttle.
• IDA-2 - first docking by uncrewed Dragon Demo-2
• IDA-3 - first docking by uncrewed CRS-21.

So we get 3 where first docking was with a crew, and 2 with no crew. And then 2 weird ones with undocking after berthing (but subsequent first dockings) done with crews.