Author Topic: Should Crew Dragon have ability to use SuperDracos for landing emergency?  (Read 56934 times)

Offline Comga

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No high definition altimeter (radar/lidar) for judging when to fire the superdracos and when to shut them off.

If there is no altimeter how does it decide when to fire the chutes?

That would not be needed for a splashdown. GPS + barometric altimeter would be enough for a water landing.

The goal would not be to make a perfect landing with 0 damage, the goal would be to limit impact G-forces to prevent pressure vessel rupture and to give the crew a survival chance in the event of a catastrophic parachute failure.

This doesnt need an exact altitude estimate, it would be enough to limit vertical speed to max 5m/s for any altitude under 50m above sea level. Well within the abilities of available sensors ( including auto-activation if the capsule is in freefall at that stage ). And engine shutdown on impact will be easy too. At those speeds the splashdown will have a clear signal to noise ratio.

You would not need to certify such a contingency program, only the decision tree that makes sure it never ever gets activated under normal conditions.

You would not want to rely on it, ever. But if the parachutes do fail, it might save lives.

It has been confirmed that there is a camera in the window to the astronaut's right of the side hatch.
Time to impact can be determined by image recognition even if altitude cannot.
(Musk does have people working on camera based navigation for Tesla.)
But CorvusCorax's suggestion of GPS should be sufficient, particularly for a water landing.


What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Alexphysics

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I only wish some reporter to ask this on the post-splashdown conference so some SpaceX official could close that damn discussion that's been going around for years even after the cancellation of propulsive landings.

Not helped by articles like this.

Quote
Crew Dragon will remain latched to the ISS until Thursday, when it will embark on a journey back to Earth. It's expected to land on a SpaceX drone ship in the Atlantic ocean, close to Kennedy Space Center.

https://www.popularmechanics.com/space/rockets/a26625114/spacex-manned-mission-iss/

Precisely for that I'm sure some reporter will ask about that. You can imagine why I think that.

Offline Comga

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I only wish some reporter to ask this on the post-splashdown conference so some SpaceX official could close that damn discussion that's been going around for years even after the cancellation of propulsive landings.

Not helped by articles like this.

Quote
Crew Dragon will remain latched to the ISS until Thursday, when it will embark on a journey back to Earth. It's expected to land on a SpaceX drone ship in the Atlantic ocean, close to Kennedy Space Center.

https://www.popularmechanics.com/space/rockets/a26625114/spacex-manned-mission-iss/

Precisely for that I'm sure some reporter will ask about that. You can imagine why I think that.

That line about landing on the ASDS has been corrected to read
Quote
Crew Dragon will remain latched to the ISS until Thursday, when it will embark on a journey back to Earth. It's expected to make a splashdown landing in the Atlantic ocean, close to Kennedy Space Center.


However the question about Super Draco assisted landing remains valid.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Star One

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I only wish some reporter to ask this on the post-splashdown conference so some SpaceX official could close that damn discussion that's been going around for years even after the cancellation of propulsive landings.

Not helped by articles like this.

Quote
Crew Dragon will remain latched to the ISS until Thursday, when it will embark on a journey back to Earth. It's expected to land on a SpaceX drone ship in the Atlantic ocean, close to Kennedy Space Center.

https://www.popularmechanics.com/space/rockets/a26625114/spacex-manned-mission-iss/

Precisely for that I'm sure some reporter will ask about that. You can imagine why I think that.

That line about landing on the ASDS has been corrected to read
Quote
Crew Dragon will remain latched to the ISS until Thursday, when it will embark on a journey back to Earth. It's expected to make a splashdown landing in the Atlantic ocean, close to Kennedy Space Center.


However the question about Super Draco assisted landing remains valid.

No it doesn’t. Stop trying to flog a dead horse. People come here as a resource and all this prolonged discussion does is confuse those viewers.

Offline GregTheGrumpy

Now that this is in its own thread, I see no reason that this discussion shouldn't be had.  It's no more or less germane than many a thread I see here.  If you don't want to participate, don't comment and it will fade away.

Offline Negan

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No it doesn’t. Stop trying to flog a dead horse. People come here as a resource and all this prolonged discussion does is confuse those viewers.

Agreed. IMO SpaceX, NASA, and even ASAP don't see a need for this. This is definitely riding a hobbyhorse needlessly.

Edit: added IMO since CorvusCorax is correct that this is speculation on my part.
« Last Edit: 03/04/2019 09:16 pm by Negan »

Offline CorvusCorax

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No it doesn’t. Stop trying to flog a dead horse. People come here as a resource and all this prolonged discussion does is confuse those viewers.

Agreed. SpaceX, NASA, and even ASAP don't see a need for this. This is definitely riding a hobbyhorse needlessly.

You don't know this, do you? To my knowledge we didn't ever get any first hand knowledge whether or not there is such a mode. It has always been speculation, both from the pro side (arguing mostly that SpaceX tethered propulsive hover tests have progressed enough that they should in theory be able to include that feature, but there was no confirmation) and from the con side (with a number of arguments. Some of which, for example that dragon would potentially dump its abort propellant before landing, have been busted. The main argument still standing is that it - and related control software paths - would not be certified by NASA).

What we do know is that SpaceX abandoned propulsive landing as a primary means of descent, stating excessive overhead for qualification and certification. Instead they put parachutes in combo with watering as primary means of landing and added an extra parachute as redundancy.

AFAIK there has been no explicit statement from either NASA nor SpaceX regarding Propulsive landing as a last resort contingency procedure.

What we do know is that this is not a NASA requirement (while propulsive launch abort and the 4th parachute are)

in fact, it stands to argue, that SpaceX would have had the choice. If landing on chutes, either to land with 3 chutes and using the propulsive fallback in case of emergency - but then propulsive landing would still have needed to be qualified and they could have stayed with propulsive landing as the primary solution in the first place - or add a 4th parachute, such satisfying NASA's demands and no need to qualify the propulsive fallback method.

Whenever this topic is discussed, it almost immediately derails into a flamewar wether or not NASA would be OK with such a non-officially-certified side-path failsafe method beyond the minimum required redundancy or not. Which IMHO is distracting, because everyone makes assumptions what NASA might or might not mostly with no first hand knowledge of the internals. And it misses the point.

The much bigger question is wether Dragon2 would even be capable of descending under powered control, despite SpaceX having abandoned the tethered hover tests in an unknown - but yet relatively early stage. No powered descents or drop tests have ever been done in real life (on the other hand, we know the capsule is aerodynamically stable in freefall, and they have done tons of test stand firings of the superdracos as well as hover tests and the pad abort - which might be enough data in order to feed an accurate model for retropropulsion. In fact if anyone ever had enough data to model retropropulsion of descending spacecraft in atmosphere, then it's SpaceX)

In my opinion, but again this is speculative. (I did do some flight control for UAVs, I know how to program a landing autopilot, so this is at least an educated guess) SpaceX has enough data to make a working fallback software that increases the chance of survival in the case of parachute failure from 0% to above 80%.

They got Falcon heavy right on first try. they got Falcon9 right on first try. Chances are high they would nail this without a test, too. They would also "qualify" it internally, as in run it through simulations. But they don't have to proof their model to NASA, since its not a requirement.

What would be helpful would be some inside info whether they ARE doing it or not. Until there is definite answer, this thread is speculation. I much prefer speculation based on physics, mechanics and hard facts than dissing something based on opinion on what NASA policies on something could be, without knowing for certain.

Offline Negan

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You would not need to certify such a contingency program, only the decision tree that makes sure it never ever gets activated under normal conditions.

I'm going to speculate this has already been done and certified.

Offline Lar

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You would not need to certify such a contingency program, only the decision tree that makes sure it never ever gets activated under normal conditions.

I'm going to speculate this has already been done and certified.
That's a radical speculation all right. Sure wish it was true but I'm not betting that way.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline spacenut

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I too think it is a good idea to use Super Dracos if there was a parachute failure.  It happened once with the Russians.  Hopefully it would never happen.  But if Super Dracos are not fired for launch escape, the fuel is there to land if they needed it.  This would increase the survival options to better than the Russians and CTS 100 on landings. 

Offline Negan

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You would not need to certify such a contingency program, only the decision tree that makes sure it never ever gets activated under normal conditions.

I'm going to speculate this has already been done and certified.
That's a radical speculation all right. Sure wish it was true but I'm not betting that way.

I was referring to LES system in general. For example Superdracos igniting unintentionally while connected to ISS. Seems likely to me this has been certified to not be able to happen. Maybe it's unrelated to this kind of contingency.


Edit: My guess would be the whole mission process of activation and deactivation of the LES system has been highly scrutinized by NASA and the other ISS partners. Modifying that system with a non-certified feature might not be so cut and dry.
« Last Edit: 03/05/2019 05:16 am by Negan »

Offline Alexphysics

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I too think it is a good idea to use Super Dracos if there was a parachute failure.  It happened once with the Russians.  Hopefully it would never happen.  But if Super Dracos are not fired for launch escape, the fuel is there to land if they needed it.  This would increase the survival options to better than the Russians and CTS 100 on landings.

The difference is that Russians use just a single parachute (although they have an emergency parachute) while Dragon 2 has FOUR. The chance of a total parachute failiure is very very low

Offline jpfulton314

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While we don't know if they have this done and set up, I would suggest that they probably have or at least should.

Hypothetical (unlikely, hopefully never going to happen) scenario:

Parachutes fail, Crew Dragon hits water at high speed and the crew is lost. Superdracos are never fired because there was no option, no manual override, nothing. They were dumb pieces of metal as soon as launch escape system was disarmed.

What would be the first "WTF?" question afterwards once everyone realizes that the capsule had 8 high power thrusters and a ton of propellant for them that could have slowed down that plunge and possibly saved the crew?

How would NASA and SpaceX survive the fallout from the unavoidable public outcry? "Who was the bureaucrat that decided it was a great idea to not be able to even try to do emergency water landing with the thrusters if chutes fail?"

You can explain away not doing certification & testing and not making the superdracos the primary landing method. You cannot explain away a decision to basically make it impossible to try in an emergency if primary (chutes) fail.

So, an educated guess: They do have some kind of procedure for trying to pull of a decisively uncertified maybe-survivable emergency landing with the thrusters. Based on above hypothetical scenario alone. If they do not, they are betting the farm, literally, on parachutes never failing - because the public opinion would crucify everyone involved if it ever happened.


Well, the SES level folk and political types would take the heat.  The GS' below them would melt away into the woodwork, as non-existent.  Heads would roll within SpaceX, especially if there was a Richard Feynman-type out there to stick the o-Ring into the ice-water, so to speak.

Offline ulm_atms

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I would be shocked if the SuperDracos were not in the loop somewhere.

Not having a simple code line that states "if rocket blows up, please use chutes to attempt to save dragon" bit them in the butt already.  You really think they missed this glaring hole in D2?

You have a means of not killing the crew if a catastrophic chute issue happens...I don't see them getting bit again.

Isn't the biggest pain of all the development of these systems the LOC ratio required?  How could having the SuperDracos as the backup of the backup of the backup not help that ratio they they were struggling to reach in the first place?

Chutes fail (ask any skydiver)....but you carried a system capable of keeping you alive if the chutes do fail....why would anyone say no to that as a last resort?  Not to mention the PR disaster for both NASA and SpaceX if the chutes did fail.....man that would be messy.

My speculation is that the ability is there and active, but it's not in NASA's requirement list for CCP, so not externally documented.  We all see this as a big missed hole....the chances that NASA and SpaceX missed it seems....slim...

my $0.02

Offline TrevorMonty

I too think it is a good idea to use Super Dracos if there was a parachute failure.  It happened once with the Russians.  Hopefully it would never happen.  But if Super Dracos are not fired for launch escape, the fuel is there to land if they needed it.  This would increase the survival options to better than the Russians and CTS 100 on landings.

The difference is that Russians use just a single parachute (although they have an emergency parachute) while Dragon 2 has FOUR. The chance of a total parachute failiure is very very low
It was failure of drogue parachute that caused main not to deploy on Soyzu1. Modern capsules have redundant drogues and mains.

Offline punder

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I can easily see NASA insisting that SpaceX explicitly delete this capability, based on the perceived risk of an inadvertent SD firing being larger than the risk of parachute failure.

Offline eriblo

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Since we do not know the technical details and probabilities of different failures one can also argue in the other direction*. I too can conceive of a 3-4 parachute failure and a hidden Hail-Mary-McGyver feature saving the day at the last second. But I can also apply that imagination to a system where uncertified code can cut the parachutes at any time or get trigger happy with 500 kN worth of supersonic fire...

I'll also note that it has been established that the propellants are not vented but that does not mean that the system is not safed by depressurizing it or cutting power to the corresponding electrical subsystems. Also, it is likely that the parachute cutting mechanism is currently designed around only ever working when the capsule is safely in the water, no exceptions. Anything that changes hardware or procedures obviously needs to go though certification.

I would think it is a good idea if it is just an extra software module that has been tested not to interfere in any way (not easy) and which will only activate when the best possible outcome is "everyone dies". But I can imagine NASA would at least like to se a few drop tests of C201 once it is done with the in flight abort and SpaceX are not going to add anything without it being signed off.

EDIT: *I agree with punder.
« Last Edit: 03/05/2019 06:47 pm by eriblo »

Offline CorvusCorax

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Redundant main + drogues certainly help in some failure scenarios. Especially if it is hooked up so such any drogue could still pull out all the mains. Or maybe mains can even deploy without drogues. A lot of the specifics depend on the exact implementation of the system. But no matter how redundant you go, almost every system still has a single point of failure somewhere.

It could be even the redundancy that hits you. assume, you went overboard on safety. There are 20 different paths to independently trigger and enforce chute deployment, to make sure your chutes ALWAYS deploy.

One of them failes: It deployes, alright, but while still falling at mach 3. The effect: catastrophic failure of entire chute assembly and attachment point.

Ok, you could have a 2nd independent set of chutes attached somewhere else... but that capsule isn't THAT big

Redundancy is always a double edged sword. It can improve reliability - but also the number of possible failure cases.

Adding thrusters to a capsule as a backup for chutes would be madness. Propellants, weight, tank pressurization,... so many things that can go wrong.

Luckily, Dragon2 already has the thrusters. Under that perspective, making them available is a no brainer.




Offline CorvusCorax

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just a question: why would someone want to cut the chutes when emergency thrusters activate?

Assume, parachutes are deployed but entangled and didnt open. Capsule drops at 10m/s. Thrusters activate at 30m and slow descent to 5 m/s until water impact. No need to cut any chute wires before splashdown. We aren't talking precision landing here, just a reduction of sinkrate ( or freefall worst case)

There would not need to be any coordination between the systems. Parachute trigger by altitude, sinkrate, and maybe a timer for backup. They get detached by a splashdown detector ( probably with a delay to avoid triggering it by air turbulence )

Thrusters would also be triggered by altimeter + sink rate monitoring and only limit sink rate to a survivable level for the last few meters.

If some parachutes are still working, or partially working, perfect. Less work for the thrusters.






Offline abaddon

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Thrusters would also be triggered by altimeter + sink rate monitoring and only limit sink rate to a survivable level for the last few meters.
...and manual activation.  Make absolutely sure it doesn't go off automatically in a borderline zone where it might increase risk relative to current risk.

Seems reasonable, but obviously this would require hardware to be added, procedures, training, etc.

If it's all automatic... that seems like you could be increasing risk in some scenarios, seems iffy.  It should be done right or not at all, I think.
« Last Edit: 03/05/2019 07:14 pm by abaddon »

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