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So who on the crew will perform the spacewalk?
“We’d say all four of us are doing it — there’s no airlock and it’s being vented down to vacuum” inside the spacecraft, Isaacman said.
Interesting choice. Some sort of airlock module attached to the hatch seems like a better idea, but maybe that isn't possible. Hope those EVA suits work well since there's a 4x chance for failure with all 4 of them facing the harshness of space. Same goes for the internal capsule controls/modules/computers.
Gemini and Apollo both did spacewalks by venting the crew capsule. Hardening the electronics for vacuum is also really helpful in case of an emergency depressurization. I have no idea if Dragon was originally designed with that in mind, but Orion was. The flexibility to spacewalk in the same suits and without an extra airlock could also come in handy for future planned or emergency servicing missions.
Yes, but Gemini and Apollo were 50+ years ago. Airlocks are likely safer for everyone since ISS and shuttle spacewalks all used them. I think the ISS one also allows prebreathing in the hours before spacewalks to minimize chances of the bends.
And good point about hardening the electronics and equipment. That has to be a requirement regardless I guess since a depressurization could happen on any flight. But depressurizing then repressurizing them during flight increases the risk of something happening compared to not doing it.
If I recall correctly, there will be a several hour long prebreathing phase then several more hours for depressurization phase during this spacewalk.
As far as electronics are concerned, I think Dragon uses redundant consumer grade computers with consensus algorithms. That might not be enough for high radiation environments like high earth orbit though. I’d be curious to hear official word on if that’s still the case.
as in, depressurization will take several hours? That seems extreme.
I believe that’s correct. This allows the astronauts to adjust to the pressure changes (they operate far, far below 1 atm) as well as abort if anything goes wrong with the suits. This is the first test of these suits after all.
It makes sense that the astronauts would need time to adapt to the pressure difference, but...
This is the first test of these suits after all.
Surely they've been tested on earth before launch???
Yes, but the microgravity plus radiation environment makes for a fundamentally different thing than testing in a lab!
That has to be a requirement regardless I guess since a depressurization could happen on any flight.
Yes, this has been pointed out by the crew (IIRC) in an interview about the mission. (Not to suggest that no work was needed on the issue, just less work than people might expect. Obviously it can be the case that taking an unlikely contingency scenario and making it a deliberate part of a mission, raises the level of assurance needed.)
Some sort of airlock module attached to the hatch seems like a better idea
Did you imagine the airlock would be mounted on the outside or the inside of the capsule? If it's on the outside, it seems like it could mess with the aerodynamics on ascent. If it's on the inside, it seems like it would cut into usable living space.
Same goes for the internal capsule controls/modules/computers.
This is something I wish was discussed in more detail. Did they need to swap out any components to withstand vacuum?
I was thinking outside; external module. Apollo could "store" external modules for launch in the fairing, then dock with them in space (ie, moon lander/moon ascent). That's enormously complex of course though.
Why not an inflatable airlock? It worked* for Voskhod.
*
*I mean it didn't kill the crew...
there aren't a lot of scenarios where having fewer people in vacuum will help save someone. You'd have to have an event where someone has an emergency that's bad enough they're not able to return, but slow enough that there's time for a second person to come get them through an airlock cycle.