Quote from: TheRadicalModerate on 07/02/2023 07:49 pmQuote from: Robotbeat on 07/02/2023 06:01 pmI want to point out that the risk that SpaceX would achieve by flying Starship over 100 times in a row without failure first will be lower than the 1:75 threshold NASA has for Artemis 3, and likely would be in line with the 1:150-270 standard for commercial crew missions.Just because you keep asserting this doesn't make it any truer.100/100 reliability:95% CI Adjusted Wald Interval: 96.83% - 100.00%. Best estimate: 99.02%. Empirically, that would be pLOC=1:125 pLOC=1:102 If failures are random and independent, then the probability of 100 consecutive successes is 51% if the true failure rate is 1:143. This is the "more likely than not" confidence level, and any higher confidence level is double dipping.What confidence level does NASA use for reliability estimates?
Quote from: Robotbeat on 07/02/2023 06:01 pmI want to point out that the risk that SpaceX would achieve by flying Starship over 100 times in a row without failure first will be lower than the 1:75 threshold NASA has for Artemis 3, and likely would be in line with the 1:150-270 standard for commercial crew missions.Just because you keep asserting this doesn't make it any truer.100/100 reliability:95% CI Adjusted Wald Interval: 96.83% - 100.00%. Best estimate: 99.02%. Empirically, that would be pLOC=1:125 pLOC=1:102
I want to point out that the risk that SpaceX would achieve by flying Starship over 100 times in a row without failure first will be lower than the 1:75 threshold NASA has for Artemis 3, and likely would be in line with the 1:150-270 standard for commercial crew missions.
Quote from: Coastal Ron on 07/02/2023 06:56 pmThe Titan/Oceangate accident may represent a failure ratio that we hope SpaceX never accepts, but it does represent how much risk "normal" people will accept in pursuit of unique experiences.You're assuming that the normal people were well-informed, and the information they received was accurate.
The Titan/Oceangate accident may represent a failure ratio that we hope SpaceX never accepts, but it does represent how much risk "normal" people will accept in pursuit of unique experiences.
It's weird to have a "confidence level for a confidence (reliability) level." Trying to reach a 95% confidence interval is, to me, just navel-gazing about probability distributions, and the same resources would be better spent improving (reducing) the expectation value for the fatality rate.
In fact, because "confidence interval" is talking about spread of the data, it's actually possible for a MUCH improved number to REDUCE the 95% CI reliability.For instance, if I have a population of 91, 89, 91, 89, 90, the mean will be 90, but the 95% CI lower bound will be 89.123, but if I instead have a population of 91, 89, 91, 89, 99, then the mean will be higher (91., BUT the 95% CI lower bound will be WORSE at 88.165. So purely by adding a much better value in the population (and making NOTHING worse), you can make the 95% CI look worse simply because the spread is greater! That's why I think it's wrong to use 95% CI and instead you should use the expected value (the mean). Don't let navel gazing about how tight your probability distribution is get in the way of improving the actual expected value. It sounds good and conservative to use 95% CI, but everyone is much better served to simply use a more conservative expected reliability threshold instead.
QuoteYou're assuming that the normal people were well-informed, and the information they received was accurate.Adventure-seeking billionaires are not capable of being "well-informed"?
You're assuming that the normal people were well-informed, and the information they received was accurate.
Look, we all know that liability release forms will be signed before getting into a Starship, so I'm not talking about financial risk to SpaceX. What I'm saying is that people are allowed to assume risk that is above what "normal" people would assume, and that is not against the law. It is not even immoral as long as the person going has been allowed to access the internet and see for themselves the history of SpaceX test flights.It would be the rare person today that was not aware of the potential risks to flying to space, on any form of transportation, much less one that is so completely different.People have the "freedom" to make risky decisions. We have whole industries that promote and extoll risky behavior, and spaceflight is just one small category of them. Let's keep some perspective here...
Quote from: Coastal Ron on 07/03/2023 06:39 pmQuoteYou're assuming that the normal people were well-informed, and the information they received was accurate.Adventure-seeking billionaires are not capable of being "well-informed"? It's a two-part predicate I put on there. You can only be well informed if the information you're using is accurate.
I have no doubt whatsoever that SpaceX can find people willing to take large risks to go into space more cheaply. But there are two risks to SpaceX, in allowing them to do so:1) The informed consent release is only good if SpaceX can prove that the information provided in the consent was accurate, and that SpaceX wasn't being reckless with the launch. I'd bet that SpaceX would win that set of lawsuits, but I wouldn't bet overwhelmingly on it. And the PR would be bad.
2) The even worse PR comes from the social media feeding frenzy, which can result in regulatory interference. So, yeah, people have freedom to make risky decisions. And companies have the freedom to decide that their being involved in the risk isn't worth the benefit.
In the Titan accident, I'm not a billionaire (yet!) but even I know that carbon fiber construction is not good at resisting compression, and any billionaire would have access to plenty of professional engineers that could have evaluated the risks ahead of time.
And if they don't, there is no amount of regulation that can fix stupid...
Elon Musk is pretty good about talking publicly about risk, and he has been warning people about the riskiness of going to Mars for many years now, so no one is going to be able to plead ignorance about going to Mars, and somehow they have to get to space first...
Yes, PR will likely be the biggest issue, but not by scaring off potential customers, but in causing the U.S. Government to step in and increase regulation in some way.
Quote from: envy887 on 07/03/2023 11:34 amQuote from: TheRadicalModerate on 07/02/2023 07:49 pmQuote from: Robotbeat on 07/02/2023 06:01 pmI want to point out that the risk that SpaceX would achieve by flying Starship over 100 times in a row without failure first will be lower than the 1:75 threshold NASA has for Artemis 3, and likely would be in line with the 1:150-270 standard for commercial crew missions.Just because you keep asserting this doesn't make it any truer.100/100 reliability:95% CI Adjusted Wald Interval: 96.83% - 100.00%. Best estimate: 99.02%. Empirically, that would be pLOC=1:125 pLOC=1:102 If failures are random and independent, then the probability of 100 consecutive successes is 51% if the true failure rate is 1:143. This is the "more likely than not" confidence level, and any higher confidence level is double dipping.What confidence level does NASA use for reliability estimates?You were the one who had that chart for what SMD required for the launchers used on the various classes of science missions, weren't you? I apparently didn't bookmark that and can't find it any more. That's a really useful chart. Do you still have a pointer to it?IIRC, that was all based on 50% CI confidence level, which made sorta-kinda sense for robotic missions on new launchers. Whether that same reasoning would apply for human spaceflight, I don't know.
Quote from: Coastal Ron on 07/03/2023 08:32 pmIn the Titan accident, I'm not a billionaire (yet!) but even I know that carbon fiber construction is not good at resisting compression, and any billionaire would have access to plenty of professional engineers that could have evaluated the risks ahead of time. Beg pardon, but aren't you making my point for me? An "ordinary" billionaire got "informed" of the risks, which he believed were an accurate representation. I imagine that the litigation that's sure to follow will cause OceanGate to implode faster than the walls of its submersible.I doubt that similar litigation against SpaceX would kill the company. But it sure wouldn't do it any good.
Quote from: Coastal Ron on 07/03/2023 08:32 pmIn the Titan accident, I'm not a billionaire (yet!) but even I know that carbon fiber construction is not good at resisting compression, and any billionaire would have access to plenty of professional engineers that could have evaluated the risks ahead of time. Beg pardon, but aren't you making my point for me? An "ordinary" billionaire got "informed" of the risks, which he believed were an accurate representation.
QuoteAnd if they don't, there is no amount of regulation that can fix stupid... We fix stupid with regulation all the time. What do you think seat belt and motorcycle helmet laws are for?
QuoteYes, PR will likely be the biggest issue, but not by scaring off potential customers, but in causing the U.S. Government to step in and increase regulation in some way.Which is exactly what I said, wasn't it?
I have referenced.that document, yes. It is NASA policy directive 8610.7. https://nodis3.gsfc.nasa.gov/displayDir.cfm?t=NPD&c=8610&s=7D50% confidence in 95% reliability (14 consecutive successes) is required for flagship payloads in the absence of any other flight data.The failure rate requirements for crew rating are apparently quite different from those for flagship payloads, judging by NASA's requirement of a 1:270 threshold for commercial crew.
Quote from: steveleach on 06/30/2023 10:27 pmQuote from: Lee Jay on 06/30/2023 06:53 pmI can't believe this claim is serious. One of the things we learned from Shuttle is not to try to make one vehicle do too many things. Did we really forget that lesson already?Of course it is serious. For Starship to be successful (which means delivering huge numbers of people to Mars) it needs to do a whole bunch of things: take off from Earth, refuel, travel to Mars, EDL at Mars, take off from Mars, travel to Earth, EDL at Earth. That's a tall order, no question, but it is the fundamental design goal for the vehicle.But that's a stupid goal. The goal (if you think colonizing Mars is a good idea) should be to do all the things necessary to colonize Mars. It doesn't all have to be done by the same vehicle and, in fact, doing it that way is very inefficient. I have used, for work, vehicles between 62 pounds and 320,000 pounds, each one for a different purpose.To use the 737 analogy, if that's such a good idea, why do we have CRJs, PC12s, and 777s if the 737 fleet can do it all?
Quote from: Lee Jay on 06/30/2023 06:53 pmI can't believe this claim is serious. One of the things we learned from Shuttle is not to try to make one vehicle do too many things. Did we really forget that lesson already?Of course it is serious. For Starship to be successful (which means delivering huge numbers of people to Mars) it needs to do a whole bunch of things: take off from Earth, refuel, travel to Mars, EDL at Mars, take off from Mars, travel to Earth, EDL at Earth. That's a tall order, no question, but it is the fundamental design goal for the vehicle.
I can't believe this claim is serious. One of the things we learned from Shuttle is not to try to make one vehicle do too many things. Did we really forget that lesson already?
STS failed in so many ways, it's hard to say that the main lesson was not to do too many things. I think the main lesson was not to have the design dictated by too many external influencers.
Quote from: meekGee on 07/05/2023 03:17 amSTS failed in so many ways, it's hard to say that the main lesson was not to do too many things. I think the main lesson was not to have the design dictated by too many external influencers.I think the other thing STS failed at was flexibility - there was no reasonable way to change anything about the stack other than the payload inside the orbiter. In the SH/SS architecture, SH is just the worlds largest dumb(?) booster, like Saturn V, Atlas, Vulcan. It doesn't much care what the thing you bolt on top of it looks like. Wanna want to turn it into a three stage rocket? Wanna turn it into an unmanned tanker? A bus carrying 200 passengers? SH is fine with that; the thrust of 33 Raptors will be there and ready for you. You just(?!?) need a new SS design to do what you want.
...As I said above, we have good PRA models for launches, and they map relatively cleanly onto Starship. By mission #100, I'd expect that our handle on ascent reliability would be quite good. ...
Confidence, reliability, and number of consecutive successes are related by the formula:log(confidence)/log(reliability)=successesPlug in 50% and 95%, and the number of successes is 13.51. Since you can't have a fractional success, they would take the next integer. That's where NASA got 14.
Yeah. Starship has a good chance of finding "abort solutions" for well understood failure cases like pad abort or in flight abort in case of booster issues - especially now with the introduction.of hot staging and the planned 9 engine ship variants.
Without knowing the risks, the answer "which risks need to be mitigated by abort systems" cannot really be answered, so the question of "how" becomes kinda moot.
So effectively , we wont know wether starship will need an abort system, nor for what modes, until we have seen 50-100 landings and probably a few more exemplary failures.