Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 3  (Read 860080 times)

Online FutureSpaceTourist

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #780 on: 09/18/2019 05:51 pm »


Quote
NASAKennedy
Crew Dragon parachutes successfully deploy during latest development test that simulated a pad abort, where the vehicle is tumbling at low altitude before parachute deploy, validating SpaceX’s parachute models and margins.

Edit to add: Youtube version

« Last Edit: 09/19/2019 06:15 pm by FutureSpaceTourist »

Offline JAFO

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #781 on: 09/18/2019 07:31 pm »
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Offline thirtyone

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #782 on: 09/18/2019 10:53 pm »
If anyone else is interested into getting into the technical details of human rating a parachute, what asymmetric loading is, and how critical all the weird parachute bouncing and inflation events are, turns out there's a lot of open literature from the Orion capsule that might help understand what issues SpaceX (and Boeing) might be having with their parachute deploy systems. They talk about load asymmetry on parachutes, and probability of failure and various other events. If you've watched the Crew Dragon Test videos (search on YouTube - inserting link breaks the post), I think the little cylinders attached on each parachute main rope (maybe some suspension lines, too) are strain gauges which allow them to measure individual loads. They even look at what happens when parachutes collide, which I believe occurred during the Crew Dragon demo.

Load Asymmetry Observed During Orion Main Parachute Inflation


Human rating the orion parachute system

Edit:
Even better, a presentation from NASA about revisiting asymmetric loading, and discussed in the conclusion of the above paper, in the context of the current commercial crew program:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20190026550.pdf

It shows you pictures of the "asymmetric loading" events they're looking at.

From the presentation
Quote
The industry-wide asymmetry value of 1.1 is insufficient for accurately assessing the structural margins of highly reefed parachutes operating in a cluster

Both Crew Dragon and Starliner use (highly?) reefed parachutes. The question is what the exact numeric margins are, and there's probably not much public info that will tell us whether they've both made the new margins. My understanding is that this "asymmetry" is basically when the parachute does not inflate perfectly circularly, so some of the lines to each parachute see much more load than other lines. If the parachute opening is oval, then there is significant asymmetric loading, as I understand it. I don't want to go too off topic from the Crew Dragon here, but you can look for released videos for the Starliner, Crew Dragon, and Orion, to get a sense of how much asymmetry each vehicle has. Some are old, and I'd imagine they must have either gotten better with parachute asymmetry, or have just increased strength to account for the larger peak loads.
« Last Edit: 09/18/2019 11:45 pm by thirtyone »

Offline thirtyone

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #783 on: 09/18/2019 11:56 pm »
Quote
Do you know if they considered (for example) dumping the landing fuel after reaching orbit. That might have reduced weight sufficiently to stick with the three parachute setup. Be interesting to know how the trades went.

I actually thought about this the other day. Of course the hypergolics are toxic, so you wouldn't want to toss the fuel when you're below the atmosphere. And then I remembered that half the point of having crew dragon is to have an abort that works *before* you've made it out of the atmosphere, and in all of those situations you cannot dump the fuel at all.
« Last Edit: 09/18/2019 11:57 pm by thirtyone »

Offline guckyfan

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #784 on: 09/19/2019 07:42 am »
Quote
Do you know if they considered (for example) dumping the landing fuel after reaching orbit. That might have reduced weight sufficiently to stick with the three parachute setup. Be interesting to know how the trades went.

I actually thought about this the other day. Of course the hypergolics are toxic, so you wouldn't want to toss the fuel when you're below the atmosphere. And then I remembered that half the point of having crew dragon is to have an abort that works *before* you've made it out of the atmosphere, and in all of those situations you cannot dump the fuel at all.

The fuel could be dumped after leaving the ISS, after the deorbit burn, before atmospheric reentry.

Offline speedevil

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #785 on: 09/19/2019 11:25 am »
Quote
Do you know if they considered (for example) dumping the landing fuel after reaching orbit. That might have reduced weight sufficiently to stick with the three parachute setup. Be interesting to know how the trades went.

I actually thought about this the other day. Of course the hypergolics are toxic, so you wouldn't want to toss the fuel when you're below the atmosphere. And then I remembered that half the point of having crew dragon is to have an abort that works *before* you've made it out of the atmosphere, and in all of those situations you cannot dump the fuel at all.

The fuel could be dumped after leaving the ISS, after the deorbit burn, before atmospheric reentry.
Are the SuperDracos connected to the same tanks as the Dracos?
If so, non-propulsive ignition of a set of thrusters could quite easily burn much of it off over a short time period before it gets in range of ISS, leaving little more than required to get deorbit.

Offline woods170

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #786 on: 09/19/2019 01:54 pm »
Quote
Do you know if they considered (for example) dumping the landing fuel after reaching orbit. That might have reduced weight sufficiently to stick with the three parachute setup. Be interesting to know how the trades went.

I actually thought about this the other day. Of course the hypergolics are toxic, so you wouldn't want to toss the fuel when you're below the atmosphere. And then I remembered that half the point of having crew dragon is to have an abort that works *before* you've made it out of the atmosphere, and in all of those situations you cannot dump the fuel at all.

The fuel could be dumped after leaving the ISS, after the deorbit burn, before atmospheric reentry.

Would have required the addition of a new fuel dump system that wasn't previously on the Crew Dragon design. That was considered to be more of a risk (both in terms of added complexity and added cost) than adding a fourth parachute.

Offline whitelancer64

Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #787 on: 09/19/2019 02:26 pm »
Are the SuperDracos connected to the same tanks as the Dracos?
If so, non-propulsive ignition of a set of thrusters could quite easily burn much of it off over a short time period before it gets in range of ISS, leaving little more than required to get deorbit.

Yes, both SDs and Dracos use the same fuel / oxidizer tanks.
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Offline Barley

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #788 on: 09/19/2019 03:46 pm »
Quote
And then I remembered that half the point of having crew dragon is to have an abort that works *before* you've made it out of the atmosphere, and in all of those situations you cannot dump the fuel at all.
I don't understand this.  Doesn't abort in the atmosphere use the fuel?  Is there an in atmosphere abort mode that doesn't fire the super dracos as long and hard as they can to get away from a malfunctioning stage?

Online FutureSpaceTourist

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #789 on: 09/21/2019 05:41 am »
https://twitter.com/elonmusk/status/1175259405832589312

Quote
Great work by SpaceX parachute engineering! The Crew Dragon parachutes are way more difficult than they may seem. The Apollo program found them to be so hard that it became a notable morale problem!

Offline gongora

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #790 on: 10/01/2019 08:31 pm »
[The Atlantic] How NASA Works With Elon Musk

Quote
Koren: Musk said this weekend that SpaceX would be ready to fly NASA astronauts within three to four months. Does that sound realistic to you?

Bridenstine: No. They have redesigned their launch-abort system, and with that redesign, [the system] has to be qualified. We are lucky that the explosion happened when it exploded during a test. If that wouldn’t have happened, we would be taking a lot more risk than we would not be aware of right now. But now that we have a new design, it needs to be tested, it needs to be qualified.

And that’s not the hardest problem. The hardest problem is the parachutes. We do not have the margin of safety [that NASA requires] in the parachutes, and that’s going to take probably more time to resolve than the launch-abort system.
« Last Edit: 10/01/2019 08:32 pm by gongora »

Offline rockets4life97

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #791 on: 10/01/2019 11:44 pm »
How many parachutes does Soyuz have? How were they modeled? Oh wait...

Offline HeartofGold2030

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #792 on: 10/01/2019 11:49 pm »
How many parachutes does Soyuz have? How were they modeled? Oh wait...

Soyuz hasn’t had a parachute failure since 1967, Crew Dragon on the other hand...I guess more isn’t always better...

Offline gongora

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #793 on: 10/02/2019 12:03 am »
How many parachutes does Soyuz have? How were they modeled? Oh wait...

Crew Dragon is several times heavier than the Soyuz descent module.

Offline drnscr

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #794 on: 10/02/2019 12:16 am »
How many parachutes does Soyuz have? How were they modeled? Oh wait...

Soyuz hasn’t had a parachute failure since 1967, Crew Dragon on the other hand...I guess more isn’t always better...

What failure in the parachute system was there during DM-1?

Offline gongora

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #795 on: 10/02/2019 12:22 am »
How many parachutes does Soyuz have? How were they modeled? Oh wait...

Soyuz hasn’t had a parachute failure since 1967, Crew Dragon on the other hand...I guess more isn’t always better...

What failure in the parachute system was there during DM-1?

There have been failures in other Crew Dragon parachute tests.

Offline drnscr

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #796 on: 10/02/2019 01:18 am »
Thank you, I made a bad assumption NASA was bitching about the ‘chute that draped over Crew Dragon 1 after splashdown... I apologize

Offline exilon

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #797 on: 10/02/2019 08:55 am »
Would having propulsive landing even shorten the timeline?

SpaceX would've had to test the bejeezers out of the nominal landing sequence and test the backup parachute method which requires the capsule to land with a full load of propellant. More parachutes needed so that a parachute failure doesn't turn the capsule into a impact-fused bomb. Parachute modeling issue discovered here, leading to more testing.

Not to mention during one of the nominal landing tests, the capsule straight up explodes in the air due to the check valve issue.

I just don't see how the original plan could've made this test campaign faster.

Offline ValmirGP

Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #798 on: 10/02/2019 10:02 am »
Going by the mantra "the best part is no part" and the conviction of the worst error an engineer can make is "try to perfect something that is not needed" recently expressed by Mr. Musk, I believe the simplest solution is to revert to the tried and tested three chute design and dump the hipergolic fuels prior to landing to get rid of the excess mass.

Offline eeergo

Re: SpaceX Dragon 2 Updates and Discussion - Thread 3
« Reply #799 on: 10/02/2019 10:06 am »
Going by the mantra "the best part is no part" and the conviction of the worst error an engineer can make is "try to perfect something that is not needed" recently expressed by Mr. Musk, I believe the simplest solution is to revert to the tried and tested three chute design and dump the hipergolic fuels prior to landing to get rid of the excess mass.

Then you have awesome amounts of fresh hypergol contamination on the capsule's surface just prior to landing. Without taking into account the non-negligible risk that system doesn't work (or works at the wrong time) and you end up overweight under 3 chutes.
-DaviD-

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