Author Topic: NASA class MMOD as primary threat to commercial crew vehicles  (Read 14022 times)

Offline Chris Bergin

ASAP talking about MMOD. More interesting as it's related to the past (Shuttle), but also a hat tip to launch and landing being safer, and CCP and ASAP seem rather happy with things. Also shows NASA requirements versus Commercial and so on and I do find LOV/C interesting as much as it's one of those impossible things.

So tried to write it up in an article and added a bunch of cool Nathan L2 renders to make it pretty.

https://www.nasaspaceflight.com/2016/08/nasa-mmod-primary-threat-crew-vehicles/

Offline rcoppola

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The article mentions information gained from Cargo Dragon and MMODs. I'm curious as to the percentage (If any) of hits/close calls, in the vicinity of the SDs that surround and help inform the new OML.
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Offline Robotbeat

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What's an SD and what's an OML.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Lar

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OML is Outer Mold Line I think

I thought SD was SuperDraco but that didn't fit.
« Last Edit: 08/23/2016 02:32 AM by Lar »
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Offline jgoldader

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You can't assure safety even while walking across the street.  1/270 is the standard, if I understood the article, because that's what Orion is supposed to have.  That the CC contractors apparently haven't met that 1/270 PBRA is causing concern.  But NASA has dumped truckloads of money into Orion, more than Boeing and SpaceX combined have spent on their vehicles (I wonder how the expenditures on Orion/MPCV compare to what SpaceX has spent in its entire existence as a company).  It strikes me as odd to expect SpaceX and Boeing to meet a standard set by NASA's own, better-funded, safety-first vehicle. 

And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.  Admittedly, the statistical tools used have come a long way from those described in Feynman's appendix to the 51-L accident investigation, but there will always be known-unknowns and unknown-unknowns, no matter how smart the people who draw up the PBRAs.

I'm not foolhardy, and frequently tell my own children that life is basically one big risk-benefits analysis.  Either traveling to orbit is worth assuming a 0.5-1% or so risk of death, or it isn't.  It will be a long time before we demonstrate space travel as being much safer than that.
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Offline woods170

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You can't assure safety even while walking across the street.  1/270 is the standard, if I understood the article, because that's what Orion is supposed to have.  That the CC contractors apparently haven't met that 1/270 PBRA is causing concern.  But NASA has dumped truckloads of money into Orion, more than Boeing and SpaceX combined have spent on their vehicles (I wonder how the expenditures on Orion/MPCV compare to what SpaceX has spent in its entire existence as a company).  It strikes me as odd to expect SpaceX and Boeing to meet a standard set by NASA's own, better-funded, safety-first vehicle. 

And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.  Admittedly, the statistical tools used have come a long way from those described in Feynman's appendix to the 51-L accident investigation, but there will always be known-unknowns and unknown-unknowns, no matter how smart the people who draw up the PBRAs.

I'm not foolhardy, and frequently tell my own children that life is basically one big risk-benefits analysis.  Either traveling to orbit is worth assuming a 0.5-1% or so risk of death, or it isn't.  It will be a long time before we demonstrate space travel as being much safer than that.
When Boeing and SpaceX were contracted for CCP the full set of requirements was not complete. The PBRA is just one example. SpaceX and Boeing were both fully informed about this before they signed the contracts.
So, both knew that additional (and tighter) requirements could (and would) be forthcoming. Both agreed to CCP anyway. That's just the nature of the business. NASA is trying something new and it is unrealistic to expect that every little detail was fully known and understood in advance. Much like COTS once was, CCP is a learning school for both industry and NASA.

ASAP in my opinion is just making things a lot harder by being afraid of having the first unforeseen (as opposed to avoidable) LOC during the run of the program. So they try to terminate every little identified risk. Trouble is however, there will always be unknown unknowns. Those one generally cannot guard against very well.

Offline su27k

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This may be a naive question, but why don't they stick some hi-def cameras around the heat shield and check for MMOD damage visually?

Offline jgoldader

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This may be a naive question, but why don't they stick some hi-def cameras around the heat shield and check for MMOD damage visually?

A MMOD hit on the heat shield is not the only place or way damage that would cause LO(M,C,V) could occur.  The pressure vessel itself is not invulnerable.  And as the article noted, a hit on a coolant loop could cause LOM during the shuttle days; fuel cells caused early EOM as well a couple of times. 

I believe the vehicles that visit ISS will be inspected for external damage before departure (or did I imagine seeing that?) but that only helps some of the cases.  And suppose you take a hit on the heat shield after you jettison the service module following the deorbit burn, when no inspection would help.  Welp. 

Woods170 was right.  The complexity of the risk analysis requires it to always be changing, and you would hope that you are able to reduce some of the risks as you gain more knowledge of your vehicle and its environment.  NASA is terribly risk-averse, for understandable reasons; but at some level, the only truly 100% risk-free spaceflight is no spaceflight at all.
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Offline woods170

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This may be a naive question, but why don't they stick some hi-def cameras around the heat shield and check for MMOD damage visually?

A MMOD hit on the heat shield is not the only place or way damage that would cause LO(M,C,V) could occur.  The pressure vessel itself is not invulnerable.  And as the article noted, a hit on a coolant loop could cause LOM during the shuttle days; fuel cells caused early EOM as well a couple of times. 

I believe the vehicles that visit ISS will be inspected for external damage before departure (or did I imagine seeing that?) but that only helps some of the cases.  And suppose you take a hit on the heat shield after you jettison the service module following the deorbit burn, when no inspection would help.  Welp. 

Woods170 was right.  The complexity of the risk analysis requires it to always be changing, and you would hope that you are able to reduce some of the risks as you gain more knowledge of your vehicle and its environment.  NASA is terribly risk-averse, for understandable reasons; but at some level, the only truly 100% risk-free spaceflight is no spaceflight at all.

Emphasis mine.
That's a fact. Let's hope it never comes to that.

IMO it's a good thing to dare to take risks. Let's look for example at one of those projects you once worked on Jeff. At the time of launch of the IRAS observatory the risk of the dewar-cover being stuck to the dewar was not entirely eliminated (stiction due to slightly over-sized O-ring seals in the cover). Some of the engineers wanted to postpone the launch, warm-up the dewar, fix the (potential) issue and do all pre-launch preps all over again. That would have meant a six months delay to the mission.
Fortunately the mission manager-in-charge showed he had guts and had the launch proceed as planned. The mission was a huge success and eventually the engineers didn't even bother to fix the same (potential) problem with the similar COBE dewar. One of NASA's finer moments IMO.
« Last Edit: 08/23/2016 03:15 PM by woods170 »

Offline M_Puckett

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Quote
And suppose you take a hit on the heat shield after you jettison the service module following the deorbit burn, when no inspection would help.  Welp. 

And the time you are discussing is so small it will be measured in minutes.  Not worth considering.

Offline abaddon

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1/270 is the standard, if I understood the article, because that's what Orion is supposed to have.  That the CC contractors apparently haven't met that 1/270 PBRA is causing concern.  But NASA has dumped truckloads of money into Orion, more than Boeing and SpaceX combined have spent on their vehicles (I wonder how the expenditures on Orion/MPCV compare to what SpaceX has spent in its entire existence as a company).  It strikes me as odd to expect SpaceX and Boeing to meet a standard set by NASA's own, better-funded, safety-first vehicle.

And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.
Has Orion in fact met this standard or is it "going" to meet the standard?  (Not to mention the missions are so different that a comparison doesn't make sense, really).

Somehow Soyuz has managed to muddle through things so far.  In fact I don't think they've ever lost a Progress to MMOD.  Between the two that's a lot of flights.  Unless we're saying we can't build a vehicle as safe as a Soyuz I have to think this is all a little bit overblown.
« Last Edit: 08/23/2016 03:14 PM by abaddon »

Offline whitelancer64

If I recall correctly, NASA wanted to lower the risk of LOC / LOV down to something more like 1/500, but then realized that because of the risk of MMOD strikes, it could not get the risk level down that low. The overall risk is high because if a hit occurs on a vital system, the results are catastrophic.

It's the same reason some people are scared of air travel; the risk of something going wrong on any one flight is very low, but when something does go wrong, the risk is high that everybody dies.

Also, just because something bad has turned out ok many times before, doesn't mean the risk is not that big. See: Shuttle and o-ring burn through / insulating foam strikes. It's just a matter of time before a MMOD strike disables a vehicle and / or kills a crew in orbit.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Offline docmordrid

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And 65,000 pedestrians are hit by a car every year just in the US. It's always something, and not even hiding in bed can eliminate risk; gas furnaces and water heaters go boom, you could throw a blood clot, etc.

No one gets out of life alive. Get on with it....
« Last Edit: 08/23/2016 05:10 PM by docmordrid »
DM

Offline baldusi

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1/270 is the standard, if I understood the article, because that's what Orion is supposed to have.  That the CC contractors apparently haven't met that 1/270 PBRA is causing concern.  But NASA has dumped truckloads of money into Orion, more than Boeing and SpaceX combined have spent on their vehicles (I wonder how the expenditures on Orion/MPCV compare to what SpaceX has spent in its entire existence as a company).  It strikes me as odd to expect SpaceX and Boeing to meet a standard set by NASA's own, better-funded, safety-first vehicle.

And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.
Has Orion in fact met this standard or is it "going" to meet the standard?  (Not to mention the missions are so different that a comparison doesn't make sense, really).

Somehow Soyuz has managed to muddle through things so far.  In fact I don't think they've ever lost a Progress to MMOD.  Between the two that's a lot of flights.  Unless we're saying we can't build a vehicle as safe as a Soyuz I have to think this is all a little bit overblown.
Let me see...
After these crewed flights:
Vostok    6
Voskhod    2
Soyuz    130
Mercury    6
Gemini    10
Apollo    15
Shuttle    135
Shenzhou    5
Total         304 flights

There has been 0 losses due to MMOD. But let's add the robotic crafts:

Progress   150
Dragon   11
TKS      9
Cygnus   6
ATV      5
Total      181
HTV      5

Also zero losses due to MMOD.

May be it is because no spacecraft has been in space long enough? Shuttle definitely never stayed too long. But Soyuz and Progress have stayed a lot up, but at 270 flights including short trips and failed launches, they haven't actually done 270 210-day stays. That's 155 years of orbit time, btw.

Offline jgoldader

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And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.
Has Orion in fact met this standard or is it "going" to meet the standard?

Check back after several hundred flights.
Recovering astronomer

Offline whitelancer64

1/270 is the standard, if I understood the article, because that's what Orion is supposed to have.  That the CC contractors apparently haven't met that 1/270 PBRA is causing concern.  But NASA has dumped truckloads of money into Orion, more than Boeing and SpaceX combined have spent on their vehicles (I wonder how the expenditures on Orion/MPCV compare to what SpaceX has spent in its entire existence as a company).  It strikes me as odd to expect SpaceX and Boeing to meet a standard set by NASA's own, better-funded, safety-first vehicle.

And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.
Has Orion in fact met this standard or is it "going" to meet the standard?  (Not to mention the missions are so different that a comparison doesn't make sense, really).

Somehow Soyuz has managed to muddle through things so far.  In fact I don't think they've ever lost a Progress to MMOD.  Between the two that's a lot of flights.  Unless we're saying we can't build a vehicle as safe as a Soyuz I have to think this is all a little bit overblown.
Let me see...
After these crewed flights:
Vostok    6
Voskhod    2
Soyuz    130
Mercury    6
Gemini    10
Apollo    15
Shuttle    135
Shenzhou    5
Total         304 flights

There has been 0 losses due to MMOD. But let's add the robotic crafts:

Progress   150
Dragon   11
TKS      9
Cygnus   6
ATV      5
Total      181
HTV      5

Also zero losses due to MMOD.

May be it is because no spacecraft has been in space long enough? Shuttle definitely never stayed too long. But Soyuz and Progress have stayed a lot up, but at 270 flights including short trips and failed launches, they haven't actually done 270 210-day stays. That's 155 years of orbit time, btw.

Every flight to space has had MMOD strikes. The Shuttle has had damaged systems from MMOD strikes. STS-7 had a window so badly damaged from a strike that it had to be replaced. The Shuttle's radiators have had several large MMOD strikes, some just barely missing the main cooling loops, if those were damaged, mission control would have considered aborting.

Again, just because there haven't been catastrophic failures doesn't mean there is no risk.

The overall risk level is still high because a MMOD strike to a critical system could easily cause loss of crew or vehicle.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline whitelancer64

For those who don't know, the way engineers assess risk is with Risk Priority Number spreadsheets. Basically the risk is broken down into 3 parts: the possible Severity of the risk, the Frequency or Occurrence of the risk, and the ability to Detect or Prevent the risk. Each part is given a number between 1 and 10, one being the least and 10 the most. These numbers are then multiplied together, with the final number assessing the risk on a scale of 1-1000. Then risks with the highest numbers are given the highest priority for correction or reduction.

We already know that the potential severity of a MMOD strike is that it could cause loss of vehicle or the crew, so that's a 10. We know that MMOD strikes occur on every spaceflight, so that's also a 10. The ability to detect MMOD strikes or prevent them from causing catastrophic failure is the key here. The Shuttle, for example, had multiple coolant loops in its radiators, so if one was damaged it could be shut down. NASA also installed additional layers of shielding over the main coolant loops to prevent or reduce damage in the event of a direct hit. However, even though the risk of damage is reduced, it still hasn't been eliminated, so it will always be higher than 1. I would say it can't be less than 5, which would be a moderate likelihood that current MMOD mitigation will prevent catastrophic damage. So based on the numbers 10, 10, and 5, the overall Risk Priority Number is 500. A high risk, and that's being generous, I'd guess that NASA has assigned an even higher risk level than this.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline darkenfast

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I can see Loss of Mission, but I think that they are being overly pessimistic on Loss of Crew.  It would take an awful lot of bad luck for the crew to die from an impact that would otherwise cause a mission to be aborted, either through re-entry or staying/return to ISS.  Something like a window being blown out because of damage.  All life support taken out, including the seat loops.  Heat shield with a hole big enough to let plasma enter and destroy the craft (remember, the shield already has holes in it).  Something big enough to penetrate the hull and a crew-member (or secondary projectiles from such a hit). That sort of thing.   

Offline Robotbeat

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No mission has ever been lost due to MMOD. ISS and MIR both huge, neither had major accident due to MMOD. I bet you could reduce this risk to very low levels if you blocked up the windows.
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Offline M_Puckett

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1/270 is the standard, if I understood the article, because that's what Orion is supposed to have.  That the CC contractors apparently haven't met that 1/270 PBRA is causing concern.  But NASA has dumped truckloads of money into Orion, more than Boeing and SpaceX combined have spent on their vehicles (I wonder how the expenditures on Orion/MPCV compare to what SpaceX has spent in its entire existence as a company).  It strikes me as odd to expect SpaceX and Boeing to meet a standard set by NASA's own, better-funded, safety-first vehicle.

And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.
Has Orion in fact met this standard or is it "going" to meet the standard?  (Not to mention the missions are so different that a comparison doesn't make sense, really).

Somehow Soyuz has managed to muddle through things so far.  In fact I don't think they've ever lost a Progress to MMOD.  Between the two that's a lot of flights.  Unless we're saying we can't build a vehicle as safe as a Soyuz I have to think this is all a little bit overblown.
Let me see...
After these crewed flights:
Vostok    6
Voskhod    2
Soyuz    130
Mercury    6
Gemini    10
Apollo    15
Shuttle    135
Shenzhou    5
Total         304 flights

There has been 0 losses due to MMOD. But let's add the robotic crafts:

Progress   150
Dragon   11
TKS      9
Cygnus   6
ATV      5
Total      181
HTV      5

Also zero losses due to MMOD.

May be it is because no spacecraft has been in space long enough? Shuttle definitely never stayed too long. But Soyuz and Progress have stayed a lot up, but at 270 flights including short trips and failed launches, they haven't actually done 270 210-day stays. That's 155 years of orbit time, btw.

Let's not forget the X-37B staying up for two years at a time with a TPS similar to the shuttle.

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