SpaceX Dragon 2 Updates and Discussion - Thread 3

[sdsds]

Is use of the hard capture passive hooks really required for a useful emergency rescue capability? The soft capture subsystem also has three latches of its own. With two Dragons each in free drift could these conceivably be strong enough to allow emergency (in vacuum) transfers of personnel?

[Robotbeat]

Is use of the hard capture passive hooks really required for a useful emergency rescue capability? The soft capture subsystem also has three latches of its own. With two Dragons each in free drift could these conceivably be strong enough to allow emergency (in vacuum) transfers of personnel?

I had the same thought. In principle, you don't even need a soft dock... An astronaut in an EVA suit could *grab* the other spacecraft if they were in free float. https://www.airspacemag.com/videos/category/space-exploration/intelsat-rescue/

[Cherokee43v6]

Is use of the hard capture passive hooks really required for a useful emergency rescue capability? The soft capture subsystem also has three latches of its own. With two Dragons each in free drift could these conceivably be strong enough to allow emergency (in vacuum) transfers of personnel?

The other question I would have regards if the two mechanisms will interact correctly so that the nose cones don't get frisky with each other.

[eriblo]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie Let me know if I have missed anything make any technical mistakes, I am basing most of this on the previous two flights and this paper: Development of the Crew Dragon ECLSS.

Scenario: Crew-2 launches to ISS for a direct handover. An extremely unlikely event actually occurs stranding the Dragon en route (or, equivalently, docking goes well and the problem occurs during Crew-1 departure). This event could for example be a complete loss of pressure in the propellant system despite all redundancies or some equivalently crippling massive electrical fault in the propulsion system. The requirements are that they can not go anywhere but are left in a state that does not immediately impact the crew or ECLSS (including excessive rotation).

Some or all of the other crew gets into their Dragon, chucks out any non-essential cargo, undocks, chases after the stricken one and catches up with it. It would be easier with only the pilot and commander but that would involve at least temporarily stranding the other two on the ISS. Which might be the safer option considering the rest of the scenario

Now what. If the IDSS was fully implemented they could simply dock and transfer the crew, but it is not. They can most likely soft dock manually although they might have to jettison the nose cones. Now to the tricky part. They depressurize the cabins and open the forward hatches. It looks like that this takes only a minute or so normally and that it should be possible for a crew member to reach it by twisting out of their seat - but it is not going to be easy in a pressurized suit. If the suit umbilicals do not allow them to reach the hatch one or more crew member(s) will have to take turns and disconnect their umbilical and work on it.

This requires that the unbilicals can be disconnected and reconnected in vacuum, either at the leg port, at the seat or both. We know they easily disconnect at the leg in the unpressurized state and the ECLS paper states:

The suit fluid module which feeds the umbilical is a small valve tray mounted inside the seat structure shell containing the main components of the suit fluid management system: a solenoid isolation valve with manual override, a regulator, flow control orifice, suit air check valve, and buddy breathe quick disconnect. The buddy breathe functionality permits a crew member in a seat with a  malfunctioning solenoid valve or regulator to receive gas from an adjacent seat.

I interpret this as the possibility to disconnect an umbilical and connect it to the set next to you (and not a completely separate hose simply connecting the seats). This would involve working during brief periods without external suit air. As they can breath pure oxygen and have a bit extra in the suit they should be good for a few minutes at a time (wonder if the CO2 or the heat becomes a problem first).

With the hatches open the really tricky part starts. The stricken crew will have to disconnect and transfer over one by one which will likely be hard work navigating past  the hatches and other crew members with the suits likely being quite stiff in a seated posture (although the opening itself should be big enough at 80 cm).

Once in the other Dragon they could connect to any free seats or to the buddy connections on the occupied seats. If this is not possible they would have to alternate using the umbilical with a seat occupant. Then would come the hatch closure in an even more crowded capsule before re-pressurizing. Now it is just a question of unlatching the soft capture and deciding whether they should return to the ISS (dv allowing) or go for a reentry which might be broken-bones-uncomfortable but hopefully survivable for the extra crew now strapped to the floor.

There are some technical assumptions in here and it is certainly at a "throw out the checklists, volunteers only, medals guaranteed" risk level but I would watch the heck out of any coverage and the all star movie sure to follow

[Robotbeat]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie ...

...of course, Apollo 13 happened in real life...

It's worth considering such scenarios as it shows you situations where a small change could significantly improve survivability in one of these unlikely scenarios.

Also:
A space shuttle rescue ball (91cm diameter) might barely fit through the Dragon side hatch if you kicked it.

[Robotbeat]

Have there been tests of the spacex suits in vacuum where they try to operate some of the controls?

[woods170]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie ...

...of course, Apollo 13 happened in real life...

It's worth considering such scenarios as it shows you situations where a small change could significantly improve survivability in one of these unlikely scenarios.

Crew Dragon was designed in such a way that a repeat of Apollo 13 is not possible.

Apollo had a major design problem in that all 3 fuel cells and the associated oxygen tanks were all situated in the same segment of the service module.

Crew Dragon on the other hand has redundant tank sets (oxygen, propellants) in four different quadrants of its service section. None of them directly connected to another one. Same for the batteries and power control and suppyl electronics and a whole bunch of other stuff.

There is higher level of redundancy on Crew Dragon then there ever was on Apollo.

So, imagine a repeat of Apollo 13 on Crew Dragon: an oxygen tank blows it top. That will at the very worst affect two quads, but not all four. Thus leaving two quads operational. Crew Dragon can safely deorbit with just two of four quads being functional.

Just about the only SPOF item on Crew Dragon is the primary heatshield. But that applies to every entry-capable manned spacecraft.

[rsnellenberger]

Crew Dragon on the other hand has redundant tank sets (oxygen, propellants) in four different quadrants of its service section. None of them directly connected to another one. Same for the batteries and power control and suppyl electronics and a whole bunch of other stuff.

There is higher level of redundancy on Crew Dragon then there ever was on Apollo.

So, imagine a repeat of Apollo 13 on Crew Dragon: an oxygen tank blows it top. That will at the very worst affect two quads, but not all four. Thus leaving two quads operational. Crew Dragon can safely deorbit with just two of four quads being functional.

Just about the only SPOF item on Crew Dragon is the primary heatshield. But that applies to every entry-capable manned spacecraft.

In that event, how would the O2 be vented from the quadrant with the failed tank - are there controlled blowout panels or high capacity vents built into the hull, or would a section of the unpressurized volume’s paneling (and heat shield) be blown off as happened with Apollo 13? Would Dragon 2 be able to re-enter with an opening (of some sort) in the equipment bays in the base of the capsule - right above the edge of the heat shield?

The astronauts might still have breathing air due to the redundant tanks - but that might be the least of their worries...

[eriblo]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie ...

...of course, Apollo 13 happened in real life...

It's worth considering such scenarios as it shows you situations where a small change could significantly improve survivability in one of these unlikely scenarios.

Crew Dragon was designed in such a way that a repeat of Apollo 13 is not possible.

Apollo had a major design problem in that all 3 fuel cells and the associated oxygen tanks were all situated in the same segment of the service module.

Crew Dragon on the other hand has redundant tank sets (oxygen, propellants) in four different quadrants of its service section. None of them directly connected to another one. Same for the batteries and power control and suppyl electronics and a whole bunch of other stuff.

There is higher level of redundancy on Crew Dragon then there ever was on Apollo.

So, imagine a repeat of Apollo 13 on Crew Dragon: an oxygen tank blows it top. That will at the very worst affect two quads, but not all four. Thus leaving two quads operational. Crew Dragon can safely deorbit with just two of four quads being functional.

Just about the only SPOF item on Crew Dragon is the primary heatshield. But that applies to every entry-capable manned spacecraft.

Apollo 13 was not an example of a failure mode but of an all out "Failure is not an option" scenario. There is the anecdote of a response comment to the movie test preview complaining that it had a completely unrealistic typically Hollywood feel-good ending.

A question: What is the oxygen in the service section used for? Dragon does not have fuel cells and as I understand it all ECLSS gases are stored in the 6 COPVs under the floor.

[Robotbeat]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie ...

...of course, Apollo 13 happened in real life...

It's worth considering such scenarios as it shows you situations where a small change could significantly improve survivability in one of these unlikely scenarios.

Crew Dragon was designed in such a way that a repeat of Apollo 13 is not possible.

Apollo had a major design problem in that all 3 fuel cells and the associated oxygen tanks were all situated in the same segment of the service module.

Crew Dragon on the other hand has redundant tank sets (oxygen, propellants) in four different quadrants of its service section. None of them directly connected to another one. Same for the batteries and power control and suppyl electronics and a whole bunch of other stuff.

There is higher level of redundancy on Crew Dragon then there ever was on Apollo.

So, imagine a repeat of Apollo 13 on Crew Dragon: an oxygen tank blows it top. That will at the very worst affect two quads, but not all four. Thus leaving two quads operational. Crew Dragon can safely deorbit with just two of four quads being functional.

Just about the only SPOF item on Crew Dragon is the primary heatshield. But that applies to every entry-capable manned spacecraft.

Apollo 13's failure was due to an unknown unknown. What you're describing is a known known or maybe a known unknown. The whole point about unknown unknowns is you don't know precisely what to mitigate ahead of time, just allow robust overall recovery capabilities. That's why you have pressure suits in the first place...

[Johnnyhinbos]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie ...

...of course, Apollo 13 happened in real life...

It's worth considering such scenarios as it shows you situations where a small change could significantly improve survivability in one of these unlikely scenarios.

Crew Dragon was designed in such a way that a repeat of Apollo 13 is not possible.

Apollo had a major design problem in that all 3 fuel cells and the associated oxygen tanks were all situated in the same segment of the service module.

Crew Dragon on the other hand has redundant tank sets (oxygen, propellants) in four different quadrants of its service section. None of them directly connected to another one. Same for the batteries and power control and suppyl electronics and a whole bunch of other stuff.

There is higher level of redundancy on Crew Dragon then there ever was on Apollo.

So, imagine a repeat of Apollo 13 on Crew Dragon: an oxygen tank blows it top. That will at the very worst affect two quads, but not all four. Thus leaving two quads operational. Crew Dragon can safely deorbit with just two of four quads being functional.

Just about the only SPOF item on Crew Dragon is the primary heatshield. But that applies to every entry-capable manned spacecraft.

Apollo 13's failure was due to an unknown unknown. What you're describing is a known known or maybe a known unknown. The whole point about unknown unknowns is you don't know precisely what to mitigate ahead of time, just allow robust overall recovery capabilities. That's why you have pressure suits in the first place...

Kinda like a leaky check valve that causes entire capsule to blow up...

[Lars-J]

On a lighter note, to distract from yet another rehash of the "can a Dragon dock with and rescue a Dragon" discussion:

For those who missed it on the Crew 1 mission thread, we saw the first pictures of the (parts of) the Dragon toilet:

I'm also attaching a useful close-up created by @Aaron_Space: https://forum.nasaspaceflight.com/index.php?topic=50525.msg2155696#msg2155696

Yes, note the poop symbol/emoji on the toilet. 

[Jcc]

I was wondering about what the crew feels during an orbit raising burn with dracos. Its got to be very slight, but obviously cause any lose objects to collect in the “rear” of Dragon, including crew if they don’t hold onto something. Probably no need to be in their seats, but  good idea anyway. What do you think?

[Asteroza]

On a lighter note, to distract from yet another rehash of the "can a Dragon dock with and rescue a Dragon" discussion:

For those who missed it on the Crew 1 mission thread, we saw the first pictures of the (parts of) the Dragon toilet:

I'm also attaching a useful close-up created by @Aaron_Space: https://forum.nasaspaceflight.com/index.php?topic=50525.msg2155696#msg2155696

Yes, note the poop symbol/emoji on the toilet. 

Uh, why is it in the ceiling edge? I suppose since it's near their feet when in their seats, I suppose it won't be an issue on splashdown...

[woods170]

It is always interesting to consider these Apollo 13 movie type scenarios where everything within the capacity of the equipment, materials and crew goes - the actual probability of the events do not matter since otherwise you would not have a movie ...

...of course, Apollo 13 happened in real life...

It's worth considering such scenarios as it shows you situations where a small change could significantly improve survivability in one of these unlikely scenarios.

Crew Dragon was designed in such a way that a repeat of Apollo 13 is not possible.

Apollo had a major design problem in that all 3 fuel cells and the associated oxygen tanks were all situated in the same segment of the service module.

Crew Dragon on the other hand has redundant tank sets (oxygen, propellants) in four different quadrants of its service section. None of them directly connected to another one. Same for the batteries and power control and suppyl electronics and a whole bunch of other stuff.

There is higher level of redundancy on Crew Dragon then there ever was on Apollo.

So, imagine a repeat of Apollo 13 on Crew Dragon: an oxygen tank blows it top. That will at the very worst affect two quads, but not all four. Thus leaving two quads operational. Crew Dragon can safely deorbit with just two of four quads being functional.

Just about the only SPOF item on Crew Dragon is the primary heatshield. But that applies to every entry-capable manned spacecraft.

Apollo 13's failure was due to an unknown unknown. What you're describing is a known known or maybe a known unknown. The whole point about unknown unknowns is you don't know precisely what to mitigate ahead of time, just allow robust overall recovery capabilities. That's why you have pressure suits in the first place...

Kinda like a leaky check valve that causes entire capsule to blow up...

Again: unrealistic once in orbit. The leaky check valve did not trigger anything until the abort system was rapidly presurrized for firing the SuperDracos.
SuperDracos are disabled when in orbit.
The only scenario where a leaky check valve would have blown up the entire capsule - in flight - would have been an abort during ascent. As in: the capsule is not even in orbit yet.

And the entire on-going discussion is about a Crew Dragon getting stranded IN ORBIT.

[ZChris13]

woods, the leaky check valve was an example of an unknown unknown, the same sort of mishap that endangered the Apollo 13 crew. They exist. This is all an excuse to delve into the land of make-believe and what-if, you don't need to get worked up about how exactly this hypothetical excuse to play space rescue with our toy dragon capsules came about.

[woods170]

woods, the leaky check valve was an example of an unknown unknown, the same sort of mishap that endangered the Apollo 13 crew. They exist. This is all an excuse to delve into the land of make-believe and what-if, you don't need to get worked up about how exactly this hypothetical excuse to play space rescue with our toy dragon capsules came about.

Emphasis mine.

Sorry, but NO. The cause of the Apollo 13 mishap is an example of a KNOWN unknown. It was known that the SM Oxygen systems had to be able to run on both 65V and 28V. It was also known that documentation for this redesign effort was whoefully incomplete.

So, NASA personnel and contractor personnel knew that their paper trail of the redesign efforts were incomplete, but failed to act on it. And thus it remained unknown that the thermostat switches had been overlooked in the redesign effort.

Thus it was known that it was unknown if all parts of the oxygen system had been properly redesigned.

[baldusi]

Wasn't the initiating cause the fact that one of the tanks suffered a hit (it was dropped, IIRC), and it was impossible to inspect inside at that stage so they only did an external inspection and shipped it without making enough notes on the paper trail?

[Vettedrmr]

Wasn't impossible, IIRC, but they chose not to.

[zubenelgenubi]

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