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.
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?
Quote from: su27k on 08/23/2016 02:11 pmThis 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.
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.
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.
Quote from: jgoldader on 08/23/2016 11:32 am1/270 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.
Quote from: jgoldader on 08/23/2016 11:32 amAnd 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?
And the 1/270 is a paper standard for a vehicle that has flown once, in what was more or less a boilerplate configuration.
Quote from: abaddon on 08/23/2016 03:13 pmQuote from: jgoldader on 08/23/2016 11:32 am1/270 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 6Voskhod 2Soyuz 130Mercury 6Gemini 10Apollo 15Shuttle 135Shenzhou 5Total 304 flightsThere has been 0 losses due to MMOD. But let's add the robotic crafts:Progress 150Dragon 11TKS 9Cygnus 6ATV 5Total 181HTV 5Also 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.