Author Topic: NASA class MMOD as primary threat to commercial crew vehicles  (Read 33614 times)

Offline SWGlassPit

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On top of that, there are other ways a strike could induce LOC that neither a suit nor a sublimator could help.  LOC need not happen at the same time as the strike. It could be much later.

Offline Brovane

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So how far off are Dragon and CST-100 from the requested 1 in 270 number?

I don't think you're going to find that information publicly available.

Why wouldn't it be publicly available? 
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Offline b0objunior

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So how far off are Dragon and CST-100 from the requested 1 in 270 number?

I don't think you're going to find that information publicly available.

Why wouldn't it be publicly available?

Maybe they don't have to.


Offline woods170

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So how far off are Dragon and CST-100 from the requested 1 in 270 number?

I don't think you're going to find that information publicly available.

Why wouldn't it be publicly available?

Maybe they don't have to.


One word: Proprietary.

Offline SWGlassPit

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One word: Proprietary.

This.  Commercial crew and cargo are a new world.  The companies involved in this aren't going to release technical information publicly unless either they are required to in their contract or they believe it will serve their interests.  These aren't the Shuttle days anymore.

Offline Robotbeat

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If NASA gets uppity about it, say the astronauts have to remain suited the whole time. That'll get approval done for the early missions, then the astronaut corp would get mad and say they don't have to wear the suits.

That only protects against LOC from pressure vessel penetration, other factors could also result in LOC that the suits wouldn't help.
Another major one is loss of coolant. Why did you edit out the sublimator part?

pressure vessel penetration is probably the biggest one, since if that happens, there's not a lot you can do if you're not suited up. With the other things, there are options, provided you're in a somewhat stable orbit (which you will be 99.9% of the time)

Pressure vessel penetration is probably not the biggest one. Pressure vessels tend to be well-protected. Other systems not so much. Spacecraft repair in-orbit is difficult.
...right, but we're talking loss of crew, not just "oh, my spacecraft is stranded, halp."

Please give actual examples not "that's probably not the biggest one."
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Offline abaddon

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This.  Commercial crew and cargo are a new world.  The companies involved in this aren't going to release technical information publicly unless either they are required to in their contract or they believe it will serve their interests.  These aren't the Shuttle days anymore.
You're right, these aren't the Shuttle days, please remind me all of the data that was publicly shared about the detailed LOV statistics that NASA compiled running up to the maiden Shuttle launch again?

Offline srtreadgold

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If NASA gets uppity about it, say the astronauts have to remain suited the whole time. That'll get approval done for the early missions, then the astronaut corp would get mad and say they don't have to wear the suits.

That only protects against LOC from pressure vessel penetration, other factors could also result in LOC that the suits wouldn't help.
Another major one is loss of coolant. Why did you edit out the sublimator part?

pressure vessel penetration is probably the biggest one, since if that happens, there's not a lot you can do if you're not suited up. With the other things, there are options, provided you're in a somewhat stable orbit (which you will be 99.9% of the time)

Pressure vessel penetration is probably not the biggest one. Pressure vessels tend to be well-protected. Other systems not so much. Spacecraft repair in-orbit is difficult.
...right, but we're talking loss of crew, not just "oh, my spacecraft is stranded, halp."

Please give actual examples not "that's probably not the biggest one."

Damage they might not know about until too late. Columbia comes to mind.

Offline Robotbeat

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If NASA gets uppity about it, say the astronauts have to remain suited the whole time. That'll get approval done for the early missions, then the astronaut corp would get mad and say they don't have to wear the suits.

That only protects against LOC from pressure vessel penetration, other factors could also result in LOC that the suits wouldn't help.
Another major one is loss of coolant. Why did you edit out the sublimator part?

pressure vessel penetration is probably the biggest one, since if that happens, there's not a lot you can do if you're not suited up. With the other things, there are options, provided you're in a somewhat stable orbit (which you will be 99.9% of the time)

Pressure vessel penetration is probably not the biggest one. Pressure vessels tend to be well-protected. Other systems not so much. Spacecraft repair in-orbit is difficult.
...right, but we're talking loss of crew, not just "oh, my spacecraft is stranded, halp."

Please give actual examples not "that's probably not the biggest one."

Damage they might not know about until too late. Columbia comes to mind.
Okay, so damage to the heatshield. But the heatshield is protected by the trunk. And before departure (but after undocking), Station can take pictures of the rest of the craft to see if there's a major problem.

And to take Soyuz as an example, the capsule lands ~3 hours after undocking. The odds that dozens of Soyuzes have had no life-threatening MMOD after each spent like 6 months in orbit but that a Dragon has a significant chance of getting a life-threatening hit in just 3 hours after undocking seems very small... You're talking like 1/100,000. More like 1:million because something bad enough to severely damage the capsule but remain undetected is even smaller, especially since the trunk protects the heatshield.

This is why I think the main dangers are from things we haven't fully quantified, yet. MMOD LOC not due to pressure vessel rupture or loss of coolant seems remote. But spaceflight is NOT that safe. So the danger is probably something we haven't fully quantified.
« Last Edit: 08/26/2016 04:11 PM by Robotbeat »
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Offline SWGlassPit

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...right, but we're talking loss of crew, not just "oh, my spacecraft is stranded, halp."

Please give actual examples not "that's probably not the biggest one."

A few examples, not based on any particular specific vehicles or scenarios:

Crew pressure vessel penetrations of sufficient size to prevent successful emergency countermeasures (e.g., donning of pressure suits).

Damage to heat shields that allow sufficient hot gas intrusion during reentry to result in structural failure.

Damage to propulsion systems (including thrusters, propellant tanks, valves, feedlines, and control hardware) that could result in any of the following: inability to deorbit, inability to control attitude during reentry, leakage of thruster exhaust into spacecraft structure, leakage of unreacted propellant into structure (including potential for hypergolic propellants to mix in places they really shouldnt), bursting of propellant tanks.

Damage to reentry power systems (including batteries, cables, and control equipment) that results in any number of failures, including loss of reentry control and loss of recovery systems.

Damage to spacecraft command and data handling hardware that results in loss of control or loss of recovery systems.

Damage to recovery system hardware that prevents initiation of both primary and backup recovery system deployment.

Damage to cooling systems that results in coolant being released into crew pressure vessel, creating a toxic atmosphere.

There are no doubt several others I haven't thought of for this post.  Not all of these are immediately detectable.  Not all of those that are detectable are correctable after the fact.

Offline Rocket Science

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This is my take from the "self licking ice cream cone" ASAP.  The only reason it is an issue is that the vehicles will say Boeing or SpaceX on the side and not NASA... ???
"The laws of physics are unforgiving"
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Offline Brovane

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One word: Proprietary.

This.  Commercial crew and cargo are a new world.  The companies involved in this aren't going to release technical information publicly unless either they are required to in their contract or they believe it will serve their interests.  These aren't the Shuttle days anymore.

Doesn't NASA set the standards for what goes into deriving the LOC number?
"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

Offline SWGlassPit

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Okay, so damage to the heatshield. But the heatshield is protected by the trunk. And before departure (but after undocking), Station can take pictures of the rest of the craft to see if there's a major problem.
There's more to the heat shield than the base heat shield.  The backshell receives a fair amount of heat as well.

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And to take Soyuz as an example, the capsule lands ~3 hours after undocking. The odds that dozens of Soyuzes have had no life-threatening MMOD after each spent like 6 months in orbit but that a Dragon has a significant chance of getting a life-threatening hit in just 3 hours after undocking seems very small... You're talking like 1/100,000. More like 1:million because something bad enough to severely damage the capsule but remain undetected is even smaller, especially since the trunk protects the heatshield.
These are made-up numbers that fall prey to any number of statistical fallacies.  To be clear: there has not yet been enough crewed spaceflight time to provide any statistically significant confirmation of whether the models that drive these risk analyses are overly conservative.  The models are made from the best available data, including space surveillance, breakup modeling, and actual hypervelocity impact testing.  That said, how do you verify whether a calculated 1/270 chance per flight is correct when there haven't been anywhere near that many flights?

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This is why I think the main dangers are from things we haven't fully quantified, yet. MMOD LOC not due to pressure vessel rupture or loss of coolant seems remote. But spaceflight is NOT that safe. So the danger is probably something we haven't fully quantified.
That you haven't thought of it doesn't mean the folks designing and analyzing these spacecraft haven't.
« Last Edit: 08/26/2016 04:28 PM by SWGlassPit »

Offline Robotbeat

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...right, but we're talking loss of crew, not just "oh, my spacecraft is stranded, halp."

Please give actual examples not "that's probably not the biggest one."

A few examples, not based on any particular specific vehicles or scenarios:

Crew pressure vessel penetrations of sufficient size to prevent successful emergency countermeasures (e.g., donning of pressure suits).
As I said, just say the astronauts have to wear spacesuits the whole time.

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Damage to heat shields that allow sufficient hot gas intrusion during reentry to result in structural failure.
Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

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Damage to propulsion systems (including thrusters, propellant tanks, valves, feedlines, and control hardware) that could result in any of the following: inability to deorbit, inability to control attitude during reentry, leakage of thruster exhaust into spacecraft structure, leakage of unreacted propellant into structure (including potential for hypergolic propellants to mix in places they really shouldnt), bursting of propellant tanks.
Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

And if the propulsion system is damaged, the spacecraft is stranded, not LOC. And Dragon can actually survive ballistic entry.

Those other things you mention could happen, but are incredibly unlikely. Propellants don't stick around and mix in vacuum. Notice this has never happened on Station or Mir or Salyut or Skylab.

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Damage to reentry power systems (including batteries, cables, and control equipment) that results in any number of failures, including loss of reentry control and loss of recovery systems.
Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

And Dragon can survive ballistic entry and has a manual pull-cord for the chutes.

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Damage to spacecraft command and data handling hardware that results in loss of control or loss of recovery systems.
Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

And Dragon can survive ballistic entry and has a manual pull-cord for the chutes.
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Damage to recovery system hardware that prevents initiation of both primary and backup recovery system deployment.
Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

Corner case of corner cases.

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Damage to cooling systems that results in coolant being released into crew pressure vessel, creating a toxic atmosphere.
Again, I suggested the crew keeps their spacesuits on the whole time.

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There are no doubt several others I haven't thought of for this post.  Not all of these are immediately detectable.  Not all of those that are detectable are correctable after the fact.
Basically they all are detectable. They basically are all correctable (via rescue) as long as you haven't done the deorbit burn yet (in which case you have only minutes of vulnerable time), but still have lots of redundancies even then.

Again, this sounds like corner-cases of corner-cases.

I sincerely, SINCERELY doubt it'll be MMOD that causes the next space disaster.

EDIT:You repeated a lot of the same risks in order to make it sound like a long list. That's why I repeated my responses.
« Last Edit: 08/26/2016 04:33 PM by Robotbeat »
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Offline SWGlassPit

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Doesn't NASA set the standards for what goes into deriving the LOC number?

The situations that need to be considered when determining what contributes to LOC depend heavily on the detailed design of the vehicle.  It's a discussion between NASA and the contractor and would absolutely contain substantial chunks of proprietary information.  NASA handles and respects proprietary information all the time.  Because commercial crew and cargo operate under a wholly different structure, we all are going to have to get used to the idea that a lot of the stuff that NASA used to make public during the shuttle days will be held proprietary under these contracts.  It's part of the price you pay for commercial space.

Offline srtreadgold

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Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

The backshell however is not protected by the trunk/service module and is exposed in a high threat region for long periods of time before reentry, and inspection might not catch the damage.
« Last Edit: 08/26/2016 04:41 PM by srtreadgold »

Offline Robotbeat

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Again, heat shield is protected by the trunk and damage could be spotted from Station shortly after undocking, and the odds of getting hit in the few hours between undocking and landing are ridiculously small.

The backshell however is not protected by the trunk/service module and is exposed in a high threat region for long periods of time before reentry, and inspection might not catch the damage.
Backshell doesn't get that hot. It'd take a large impact (easily detected) to damage it enough.
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Offline SWGlassPit

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--snip--
Basically they all are detectable. They basically are all correctable (via rescue) as long as you haven't done the deorbit burn yet (in which case you have only minutes of vulnerable time), but still have lots of redundancies even then.

Again, this sounds like corner-cases of corner-cases.

I sincerely, SINCERELY doubt it'll be MMOD that causes the next space disaster.

EDIT:You repeated a lot of the same risks in order to make it sound like a long list. That's why I repeated my responses.

A few points:

The base heat shield is not the only heat shield.  The backshell heat shield has no protection.  Zero.  None.  Sufficient penetration of the backshell heat shield is absolutely a LOC event.  That this is easily detected is only your assertion and is not necessarily borne out by facts.  It depends greatly on what structure and infrastructure exists behind the strike.

Not all failures are immediately detectable.  This is undisputable fact, despite your assertions to the contrary.

Nobody is saying that MMOD is the cause of the next space disaster; that is a strawman argument.

Your impression that I simply repeated redundant items belies your failure to understand what I wrote and nothing more.  The only thing that I repeated was that there was a strike.  Where the strike is, how big it is, and what it hits changes the game completely.

The analyses cover as many corner cases as they can, including the likelihood of loss of redundant systems.

Offline Robotbeat

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--snip--
Basically they all are detectable. They basically are all correctable (via rescue) as long as you haven't done the deorbit burn yet (in which case you have only minutes of vulnerable time), but still have lots of redundancies even then.

Again, this sounds like corner-cases of corner-cases.

I sincerely, SINCERELY doubt it'll be MMOD that causes the next space disaster.

EDIT:You repeated a lot of the same risks in order to make it sound like a long list. That's why I repeated my responses.

A few points:

The base heat shield is not the only heat shield.  The backshell heat shield has no protection.  Zero.  None.
Sure it does. There's a bunch of spam on it.
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Sufficient penetration of the backshell heat shield is absolutely a LOC event.
"Sufficient" meaning a very big hole. Remember, the backshell does not get very hot. And even if it was "penetrated," that's not sufficient to say it'd cause a big problem. What heat is brought in is dissipated by the aluminum structure. Even if you had an actual small burn-through of the aluminum (exceedingly unlikely, even with damage of the backshell enough to be visible), the backshell has such low temperatures (compared to the front) that it's not even necessarily a LOC event because the crew would be wearing pressure suits and there are no wings to fall off.
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That this is easily detected is only your assertion and is not necessarily borne out by facts.
Yeah, it is. Dragon is white and has much smaller area than Shuttle did. And the portion in question is actually facing Station already and much of it can be seen clearly out the window even while docked. 
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It depends greatly on what structure and infrastructure exists behind the strike.
The whole surface is painted white. High resolution pictures are already taken of Dragon on departure. Regardless of what's "behind" the strike, a strike large enough to cause the sort of damage you're talking about is most likely to be quite visible.
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Not all failures are immediately detectable.  This is undisputable fact, despite your assertions to the contrary.
What assertions? I never said all failures. I said: strikes big enough to do the sort of damage you're talking about are going to leave a mark. MMOD leaves visible craters when it impacts.

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Nobody is saying that MMOD is the cause of the next space disaster; that is a strawman argument.
Did I say that? I wasn't just saying it wouldn't be the cause, I am saying that the probability that it's the cause (and let me clarify here: on a reentry capsule such as Dragon... ISS is a much bigger target) is actually low, thus not only do I not think it's the likely cause, but I'd take a significant handicap on those odds. And the thread title says "NASA class MMOD as primary threat to commercial crew vehicles." So my argument most certainly is not a strawman.

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Your impression that I simply repeated redundant items belies your failure to understand what I wrote and nothing more.  The only thing that I repeated was that there was a strike.
Many of the things you stated overlap.

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The analyses cover as many corner cases as they can, including the likelihood of loss of redundant systems.
Sure, but we're talking about significant probabilities that can add up to MMOD being the "primary threat." I find that unlikely.

Primary threat, as long as you take the countermeasures I mentioned, is probably something not fully considered. And I stand by that.
« Last Edit: 08/26/2016 05:54 PM by Robotbeat »
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Offline SWGlassPit

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Portions of the backshell get hot enough to create a problem.

Imagery is not infallible.  Impacts that appear small on the entry face can create large amounts of damage farther in -- that cannot be discovered on orbit as they would require disassembly of the hardware.  White hardware actually makes identification of strikes in imagery more difficult as it creates difficulties in controlling the image exposure; against the dark background of space, white surfaces tend to get blown out to the point that impact features are difficult to distinguish from other artifacts -- the ISS radiators have the same problem.  This is, of course, assuming that the images are of sufficient resolution and perfectly in focus -- not always a valid assumption.

If you read the ASAP report that drove this article, the total mention of MMOD amounts to less than a paragraph.  This thread is getting wrapped around the axle on assumptions and incomplete/outdated information.  That something is the "primary" threat does not mean the threat is "large."  It just means that other identified and controlled threats are "smaller".

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