SpaceX’s Crew Dragon spacecraft static fire anomaly - THREAD 3

[Wudizzle]

SpaceX just seems to have more spectacular failures when they do it, which may be what draws everyone to their test campaigns.

Do they? Or do they just tend to do their testing in the public eye? They also have spectacular successes doing things no one else is, which tends to draw everyone to their barrier-breaking test campaigns to see what's next.

Tomato, tomato.

[envy887]

Dragon has also been highly successful to date.

Well this is a thread about Crew Dragon and the only Crew Dragon vehicle to fly is currently in pieces (albeit during a test that did identify an issue that can be resolved).

DM-1 was quite successful, largely because D2 builds on a lot of Cargo Dragon heritage.

And SpaceX isn't going to stop ground testing because one ground test found a problem. Rather the opposite, I should think. That's the whole point of ground testing.

Most things are successful until they are not.  Past performance does not guarantee future success.  Testing is always important.  All engineering firms do it.  SpaceX just seems to have more spectacular failures when they do it, which may be what draws everyone to their test campaigns.

SpaceX does more all-up hotfire tests than most, though. Which is why I expect they will continue firing Dragon abort systems, even if they have to service the burst disks.

[Kabloona]

Burst disk: $100

Pre-flight functional verification of abort system: priceless

[vulture4]

Leaking hypergolic propellant valves have been a recurrent problem since the early days of the space program. Often the Shuttle landed with leaking thruster valves. The underlying problem is that almost all valves utilize an elastomeric material to maintain a seal between the valve seat and the movable valve, and hypergolic propellants are quite corrosive and over time degrade most elastomers. Check valves, because the seal pressure is only maintained by a spring (and the vapor pressure of the propellant), may be more susceptible to corrosive degradation than valves with elecrtromechanical actuators. Bolted flanges such as would be used with a burst disk are not particularly susceptible to this problem because gaskets are static and under much higher compressive pressure than valve seals and the seal can be a single-use deformable metal rather than an elastomer.

In this case one might speculate that the system remained fueled for a longer period than on previous ground tests because of the prior flight, and this allowed more time for degradation of the check valve seal. However if SpaceX is going to rate the Crew Dragon for six month storage on the ISS the normal Draco thruster valves which are used during the rendezvous are also going to have to be tested for reliability during prolonged exposure to propellants.

[dondar]

*snip*
Dragon 2 crafts will be used only ones, i.e. only ONE TIME as passenger vehicles. Superdracos and corresponding plumbing most probably will be removed afterwards in order to free space and weight for cargo missions. Even otherwise the burst discs will be used only in superdracos plumbing and are irrelevant in normal operations. They will be used only in the case of abort mission which would automatically write vehicle off and make it unsuitable for further missions.

Firstly, there is no change to the propulsion systems for the Cargo Dragon v2. SuperDracos are mounted external to the PV so removing them would not free up any space inside.

Secondly, there is nothing preventing SpaceX from using a Dragon v2 to fly people a second time, for example, if Bigelow buys a crew launch to their B330 space station. Or should the ISS be extended out to 2030, it's entirely possible NASA would give the OK to fly their astronauts on one again.

B330 is programmed to fly on Vulcan. NET is 2022.
 If Bigelow suddenly will become a real provider of the space estate SpaceX will be happy to keep Dragon 2 production line even up to 2022 and build more capsules. Conditional When is so far away in SpaceX calendar it is useless to talk about.

To return to SpaceX: as it was stated by SpaceX Dragon 2 Crew capsules are not designed to be reusable. Period.
Probably if paid for to satisfy sufficient commercial interest SpaceX  will redesign the vehicle.

The last time SpaceX mentioned that Dragon 2 cargo won't have superdracos (abortion system of the crew variant) was on SRS-18 Pre-launch conference (specifically at 37m14s Jessica's answer to Jeff Foust question).

More of it as you see even on your diagram life-support system which consist pressurized volume cocoon is also modified for Cargo variant. Probably they will use extra space for the weight redistribution system (cargo variants will have extensive rack system), or they are just saving weight. It doesn't matter really.

[gongora]

To return to SpaceX: as it was stated by SpaceX Dragon 2 Crew capsules are not designed to be reusable. Period.

They have not said that.

[envy887]

To return to SpaceX: as it was stated by SpaceX Dragon 2 Crew capsules are not designed to be reusable. Period.

They have not said that.

Indeed. They only said that CRS2 cargo Dragons will be new vehicles, and that Dragons flown with crew won't be reused fro that purpose. This doesn't exclude reusing Crew Dragons for more crew launches.

[aero]

Indeed. They only said that CRS2 cargo Dragons will be new vehicles, and that Dragons flown with crew won't be reused fro that purpose. This doesn't exclude reusing Crew Dragons for more crew launches.

That is confusing.
 CRS2 cargo Dragons will be new vehicles New as in a new design or new as in freshly built?
 Dragons flown with crew won't be reused fro that purpose Crew will fly on CRS2 as well as crew Dragon?
 reusing Crew Dragons for more crew launches Crew Dragons can be re-used unless they are CRS2 vehicles.

[ChrisWilson68]

Will the burst disks be expended when the LES is activated ahead of launch or only when it would actually be fired?

We know from the Dragon test failure that system pressurization occurs just before firing (IIRC, it was about 100 msec prior to firing). So the burst disk would remain intact until an abort is commanded and the helium valve is opened to pressurize the NTO tank.

Would they need inspecting after each flight even when not used?

They might want to take a look at the disks after the first few flights just to make sure there weren't any adverse effects from vibration, etc. But the disk environment should be pretty benign. No pressure (just 1 atm) on the helium side, and relatively modest vapor pressure on the NTO side.

I would think that after they do a few post-flight inspections and see no ill effects on the disks, they would feel confident enough to leave them alone after future flights.

I'd expect a preflight (or possibly postflight) test firing of the abort system on every Dragon, so the burst disks would need to be replaced after that.

Would that be something NASA would require of them? If it was does that mean on non-NASA flights they wouldn’t feel the need too?

There's never going to be a non-NASA flight of Dragon.  Starship/Superheavy is much farther along than any potential commercial space station that could possibly ever need its services, so by the time a non-NASA station could be ready, Starship/Superheavy will be in business.  And the one non-NASA customer ever booked for Dragon (Dear Moon) has already been switched over to Starship.

[dglow]

Indeed. They only said that CRS2 cargo Dragons will be new vehicles, and that Dragons flown with crew won't be reused fro that purpose. This doesn't exclude reusing Crew Dragons for more crew launches.

That is confusing.
CRS2 cargo Dragons will be new vehicles New as in a new design or new as in freshly built?

Newly constructed / freshly built.

Dragons flown with crew won't be reused for that purpose Crew will fly on CRS2 as well as crew Dragon?

No. CRS2's 'cargo' Dragons won't include the SuperDraco abort system.

Reusing Crew Dragons for more crew launches Crew Dragons can be re-used unless they are CRS2 vehicles.

Presumably cargo-configured Dragon 2s will be reused for cargo missions, just as done with Dragon 1s.

This implies (speculation) we'll see a vehicle flow where new Dragon 2s are built with the abort system in place then flown for a single crewed mission. Following this the abort engines will be removed and the Dragon subsequently flown for resupply flights in its (now) cargo-only configuration.

[gongora]

This implies (speculation) we'll see a vehicle flow where new Dragon 2s are built with the abort system in place then flown for a single crewed mission. Following this the abort engines will be removed and the Dragon subsequently flown for resupply flights in its (now) cargo-only configuration.

Crew Dragon is not being reused for (Cargo) Dragon 2.  At the CRS-18 press conference it was explicitly said they are different vehicles.  Each Commercial Crew flight will be a new Crew Dragon.  It's possible those could be refurbished for other customers if there is demand for it (such as the Bigelow missions).  Initially each CRS2 flight will be a new Dragon 2 until SpaceX gets a reuse plan in place and approved by NASA.

[dglow]

This implies (speculation) we'll see a vehicle flow where new Dragon 2s are built with the abort system in place then flown for a single crewed mission. Following this the abort engines will be removed and the Dragon subsequently flown for resupply flights in its (now) cargo-only configuration.

Crew Dragon is not being reused for (Cargo) Dragon 2.

That's too bad. I'd picked up (via NSF) that recycling crew vehicles into cargo was the goal. Original POR, but since changed?

At the CRS-18 press conference it was explicitly said they are different vehicles.  Each Commercial Crew flight will be a new Crew Dragon.  It's possible those could be refurbished for other customers if there is demand for it (such as the Bigelow missions).  Initially each CRS2 flight will be a new Dragon 2 until SpaceX gets a reuse plan in place and approved by NASA.

Re: need to (re-)qualify Dragon 2 for reuse, that makes sense. NASA wants to ensure major new components (docking mechanism, for instance) still hold up following reentry.

Will be interested to see how long this takes. How many CRS missions flew before the first reused Dragon?

[dondar]

To return to SpaceX: as it was stated by SpaceX Dragon 2 Crew capsules are not designed to be reusable. Period.

They have not said that.

I couldn't find quickly the direct quote, but somewhere in the second half of 2018 a SpaceX representative (I think not Hans because I would remember that) answered why SpaceX does not implement Crew Dragon re-usability even if NASA are ready to pay for that. He/She told that  the number of the Crew Dragon contracted by NASA is smaller than the number of flights necessary to study and certify Crew Dragon life support system reuse so they simplly didn't bother with design re-usability.

[ZChris13]

as a amazing people but otherwise nothing special, I have heard these public statements from SpaceX:
1. Crew Dragon is designed to be reusable (specifically, that Dragon 2 has a bunch of changes that make it easier and faster to reuse than Dragon 1)
2. Crew Dragon will not be reused (I don't know if there are any qualifiers on this statement)
3. Cargo Dragon 2 has differences from Crew Dragon

I think this implies that Cargo Dragon 2 might be reused like Dragon 1 is, but I have not heard much talk about Cargo Dragon 2 at all before the CRS-18 press conference.

[dglow]

Crew Dragon is not being reused for (Cargo) Dragon 2.  At the CRS-18 press conference it was explicitly said they are different vehicles.

Thanks again for this clarification. Going back to the CRS-18 pre-launch conference the relevant Q&A begins at 41:02:

Question:
"What I mean is they'll never be used for crew Dragon, they're just dedicated for cargo?"

Jessica Jensen, SpaceX:
"Correct, yes. As soon as we build the weldment there are slight differences. So while a lot of the subsystems are the same they really are – they will be different vehicles. We won't interchange between cargo and crew vehicles."

Initially each CRS2 flight will be a new Dragon 2 until SpaceX gets a reuse plan in place and approved by NASA.

At 36:29:

Jessica Jensen, SpaceX:
"Then the Dragon 1 fleet is retired and we switch over to the CRS2 contract, where we then fly the Dragon 2 vehicle which is a modified version of the Commercial Crew vehicle. That one we are going to certify up-front to be qualified for up to five flights."

[theinternetftw]

Going back to the CRS-18 pre-launch conference the relevant Q&A begins at 41:02:

For future reference, a full transcript is here:
https://gist.github.com/theinternetftw/6afa42cd7803101ddfa7222968deca4d

[OxCartMark]

Leaking hypergolic propellant valves have been a recurrent problem since the early days of the space program. Often the Shuttle landed with leaking thruster valves. The underlying problem is that almost all valves utilize an elastomeric material to maintain a seal between the valve seat and the movable valve, and hypergolic propellants are quite corrosive and over time degrade most elastomers. Check valves, because the seal pressure is only maintained by a spring (and the vapor pressure of the propellant), may be more susceptible to corrosive degradation than valves with elecrtromechanical actuators.

Not metal on metal?

[vulture4]

Leaking hypergolic propellant valves have been a recurrent problem since the early days of the space program. Often the Shuttle landed with leaking thruster valves. The underlying problem is that almost all valves utilize an elastomeric material to maintain a seal between the valve seat and the movable valve, and hypergolic propellants are quite corrosive and over time degrade most elastomers. Check valves, because the seal pressure is only maintained by a spring (and the vapor pressure of the propellant), may be more susceptible to corrosive degradation than valves with elecrtromechanical actuators.

Not metal on metal?

Metal on metal valves have also been used but with hard surfaced valves even small amounts of particulates in the propellant can prevent the valve from sealing. I am not sure of the construction of the valve that failed but I seem to recall a similar failure on a planetary probe years ago.

[DistantTemple]

Leaking hypergolic propellant valves have been a recurrent problem since the early days of the space program. Often the Shuttle landed with leaking thruster valves. The underlying problem is that almost all valves utilize an elastomeric material to maintain a seal between the valve seat and the movable valve, and hypergolic propellants are quite corrosive and over time degrade most elastomers. Check valves, because the seal pressure is only maintained by a spring (and the vapor pressure of the propellant), may be more susceptible to corrosive degradation than valves with elecrtromechanical actuators.

Not metal on metal?

Metal on metal valves have also been used but with hard surfaced valves even small amounts of particulates in the propellant can prevent the valve from sealing. I am not sure of the construction of the valve that failed but I seem to recall a similar failure on a planetary probe years ago.

In the discussion of burst disks there are comments, that seem obvious that a "soft" metal element can form the seal where the burst disk is clamped tightly in a bolted flange, instead of using any "gasket" material at all.

[DAZ]

Will SpaceX ever find/announce the root cause or will SpaceX settle for the proximal cause of the anomaly and move on using the burst disks?