What is the acceptable failure rate for a manned spacecraft?

[llivinglarge]

1 in 1000?

 

[steve82]

I'm guessing "acceptable" in our society would be a chance of a fatal accident no higher than the chances of getting in a fatal car acident.

 

[llivinglarge]

Loss of mission critical functionality. Something along the lines of Apollo 13.

 

[rocketwatcher2001]

1 in 100, maybe a little less. I don't think we'll see space exploration/exploitation as safe as driving to the corner store anytime soon. Still, I want the space program to continue boldly. I think we've become too afraid of taking risks, which is bad for a growing society. <div class="Discussion_UserSignature"> </div>

 

[askold]

Acceptable failure rate?<br /><br />One more fatality.

 

[SpaceKiwi]

Assuming human spaceflight.<br /><br />Perhaps I am reading industry progress wrong but, with the evolution of the multiple redundency concept, I'd expect the probability of an <i>Apollo 13</i>-style 'slow-burn' failure to be fairly low. Certainly 1 in several thousands, if not even better than that.<br /><br />I think Challenger/Columbia-style 'instantaneous' failures, whereby the moment a problem is detected it is already too late, will continue to be statistically significant in the forseeable future. Maybe one in 50 or thereabouts. While no loss of life is ever palatable, I personally view such a rate as acceptable, given that the 'nigh-on-impossible' is being attempted each time humans are shot into space.<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><em><font size="2" color="#ff0000">Who is this superhero?  Henry, the mild-mannered janitor ... could be!</font></em></p><p><em><font size="2">-------------------------------------------------------------------------------------------</font></em></p><p><font size="5">Bring Back The Black!</font></p> </div>

 

[mlorrey]

CLV loss of crew risk is supposed to be somewhere between 1:1500 - 1:3000 flights. Given a six man crew, that is a statistical risk of one death in 250-500 flights.<br /><br />This would be a significant improvement over STS. We've lost I believe 14 crewmembers over 114 flights, a risk of one death every 8 flights. The CLV should, therefore be an improvement of 30-60 times more safety than the STS.<br /><br />This being said, STS was supposed to be a lot safer than it turned out being. The O-ring problem we can blame on Nixon, who fired the first SRB selection committee (which rated Thiokol's 4 segment SRB dead last out of four contestants) and appointed one that awarded the contract to Thiokol. The first committees recommended selection was an Aerojet booster that was of monolithic construction: ergo, no segments, no o-rings.<br /><br />The foam risk is another issue. Foam on STS seems to be much thicker than that on the Saturn V's 2nd and 3rd stages, and while official NASA drooges deny it, I have it on good authority from the Lockheed engineers who did the studies, that when Freon was banned by the CFC treaty, they had to stop using it to clean the tank surfaces prior to foam application, and switched to a less effective surface cleaner. It was at this point that the severe foam loss problems are said to have started, according to these engineers. Improperly cleaned aluminum tank surfaces means poorly adhered foam, and thus easier for the foam to delaminate due to tank stretching and allow air to freeze on the tank surface under the foam.<br /><br />So there is plenty of blame to go around on the risk factors in the shuttle program. If we assume these sorts of things are par for the course in any politically dominated contracting system, we can expect similar politically inspired risk factors to creep into the CLV design over time and increase over and above the estimated risks...

 

[radarredux]

> <i><font color="yellow">1 in 1000?</font>/i><br /><br />Depends who is paying, what is "loss", and what is the crew expected to achieve.<br /><br />If the mission is privately launched, the public is willing to accept a higher loss rate than one sponsored by the government.<br /><br />If the crew is pushing the frontier and can potentially achieve fame and fortune, the public will accept a higher loss rate. One of the criticisms of the Columbia loss is the widely held view that they died do nothing new -- going endlessly round and round in Low Earth Orbit. Meanwhile, the public was excited by the 2nd and 3rd launches of Scaled Composites even though it was only Suborbital and the first two launches showed the vehicle to be very dangerous.<br /><br />If the mission is funded privately, then any loss other than loss of life probably doesn't matter. If it is the government, then it "depends". Three examples: (1) Shuttle experiences an engine out during ascent, so it cannot reach ISS but it can return safely (loss of mission); (2) Shuttle experiences damage during ascent but the crew can safely abort to ISS (loss of vehicle); (3) Shuttle is destroyed during ascent or return (loss of life). Because the Shuttle has been end of lifed (EOL), certainly (2) and (3) and maybe even (1) would result in the Shuttle program being shutdown. For CEV/CLV, (2) and (3) and probably even (1) would be accepted.</i>

 

[trailrider]

"Loss of mission critical functionality. Something along the lines of Apollo 13."<br /><br />Given the statistically small number of missions on any program, any individual failure that results in the mission being dramatically incomplete...a la Apollo 13...will be "unacceptably high", percentage-wise. Even if the crew is successfully recovered, major failures will still draw sharp criticism in Congress, and the public.<br /><br />So far as fatal accidents are concerned, THERE IS NO "ACCEPTABLE" RATE! FAILURE IS NOT AN OPTION! Or to quote Walt Williams, "You don't get medals for on-time failures!"<br /><br />Will there be fatalities? Yes, there will. That is a fact of life in exploration. The point is to MINIMIZE such catastrophies as much as humanly possible by careful planning and by listening to the opinions of the true experts in their various fields! That does NOT mean we must get ourselves into being completely risk adverse. But the risks must be worth the consequences! The turtle progresses only when he sticks his neck out...granting that he may get his head cut off sometimes. <br /><br />When the late Gus Grissom was asked to say a few words at the Martin-Marietta plant where the Titan II-Gemini was being built, he simply said, "Do good work." Or, to put it another way...if you are packing parachutes, pack them like you were going to jump with each and every one!<br /><br />Ad Luna! Ad Ares! Ad Astra!

 

[rocketman5000]

In the publics eyes the their was no glamour in the mission. When Apollo 1 crew died they were fighting for capitalism and the American way.

 

[mlorrey]

If the motorcycle and the train have the same odds of getting into an accident capable of causing a complete loss of passengers, then yes, a motorcycle would be 200 times saver than riding a train. However, they don't have the same odds. I doubt there has ever been a train that killed all of its passengers in a single accident, while there are many motorcycle accidents that kill everyone on board. So, due to the different risk factors inherent in the two types of vehicles, the motorcycle is not safer than the train.<br /><br />If, instead, you had two trains, one that can carry 1000 passengers with a risk of killing 10% of the passengers every 1 in 10,000 trips, and another that is much faster, which carries 100 passengers, but will kill 50% of its passengers every 1 in 2000 trips, what is the comparative risk of one person being killed on each train?<br /><br />The first would kill one person per 100 trips, and the second would also kill 1 person per 100 trips. That being said, which one would you rather ride on?

 

[rocketman5000]

I personally would want to die with an adrealine rush so let me go in a hurry!!

 

[JonClarke]

"When Apollo 1 crew died they were fighting for capitalism and the American way"<br /><br />If true, what a waste.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[qso1]

True only to a degree. The U.S. Government was fighting for capitalism and the American way in the competition with the Soviet Union. It was the only way we would ever have gotten to the moon.<br /><br />The other reasons were science and exploration which alone would not have been justifiable to most politicians and their constituents. I suspect its science and/or exploration that the Apollo crews were really interested in. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[pathfinder_01]

Mlorey given that there has never been a disaster that killed a few crew members but not the entire crew me thinks your statistics are suspect. Heck using those numbers a 747 would probably be the most unsafe plane in the sky because every time it crashed 200+ people can die. <br /><br />I hope the CLV is an improvement but frankly this is one area that you don’t know until it fails. I also don’t think the CLV will get a break because somehow it is “better” than the shuttle. After the first and second trips to the moon (assuming the politicians fund it which I have my doubts on) the public will view moon flight as mundane and risk free. When in reality it can never be anything but. <br /><br />I like spaceflight but when it comes to loss of life who knows what risk is acceptable. For instance loss on a private tour trip could scare away both customers and investors. The loss would also invite greater government scrutiny which could increase costs. The loss could also increase insurance costs and even if the customers and investors don’t run. And who knows what effect the loss of the vehicle would have on the operations. Are they unable to meet contracts with customers?<br /><br />I don’t know what an acceptable loss of life is. I think it is an irrational thing. People fear elevators and flying but don’t mind driving to work everyday (an activity that is riskier than the both of them). The loss of life in both Vietnam and the current Iraqi war is lower than the loss of life in WWII but both wars generate a lot more protest than WWII. <br /><br />I think people are more than willing to accept loss of mission and they are more than willing to accept loss of vehicle but when human lives are loss the equation changes. I have always wondered how far back the manned program would have gotten if Apollo 13 had resulted in the slow death of the crew from a mysterious cause. <br />

 

[baktothemoon]

I don't think we should focus on the odds of people dying in a spacecraft because there are too many things that could go wrong and planning that people will die is neither good for the program nor the astronauts. I wouldn't want to climb on the shuttle with someone saying, "Warning: there is a 1 in 1000 chance that you will die in this thing, there isn't much we can do, have a happy flight." Saying that people are going to die achieves nothing. All you can do is plan for the biggest risks. Cars crash, so we have airbags. Jet fighters crash, so we have ejection seats. You plan for something going wrong but you shouldn't count on it. That would be like saying to the driver or the pilot, " You probably will crash, so you have an ejection seat or an airbag." Would anyone drive or fly after being told that? No. So we shouldn't say the same thing to the press or the astronauts. All we can do is to do our best at designing the space craft and include safety systems to eliminate the major risks, then we can call it safe because we have planned to elimininate risks, instead of calculating the probability of failure in spite of them. We shouldn't worry about every unlikely hazard. I could be hit by a meteorite in the head and killed as I type here on my computer, but do I keep an eye on the sky to see if one is coming? No, I type, and make sure the smoke alarms all work in case my there is a fire, because that is a fairly common hazard that can be mitigated and because I mitigated it, I don't worry about it. You shouldn't calculate the likelyhood of death, because life itself has a 100% likelyhood of death.<br /><br />"Ask not what your country can do for you, ask what you can do for your country." John F. Kennedy

 

[mlorrey]

The statistics aren't suspect, your understanding of them is. When a stat like "1 in 1000" is used, that doesn't meant one person will die every crash. It is a rate.<br /><br />There have certainly been many high speed vehicles fail with only partial crew loss, and airliners certainly crash all the time with only part of the crew and passengers being killed.<br /><br />The CLV will be an improvement, and while YOU won't know its risks until something fails, engineers generally have a very good idea of how things fail and how frequently. Failure analysis is a whole branch of engineering that can analyse exactly how many things are likely to fail. However, no engineer is perfect, things do get overlooked or misestimated. Things also fail improbably, and assumptions about the quality of materials don't always hold without NDI of materials and construction methods.<br /><br />The space tourism rules today are pretty explicit in requiring that space tourists be made aware of the risks and that they accept them as a condition of flight. So, while the media may decide one accident is too many, there will always be people who consider any risks acceptable. If there weren't there would be no market for bungee jumping, base jumping, skydiving, hangliding, rockclimbing, scuba diving, etc. That there is such markets means you are quite obviously wrong.

 

[trailrider]

There is also a matter of perception here. When TWA Flight 800 took off from New York, the people on board had "every expectation" of arriving safely. Why? Because people fly B747's every day and nothing ever happens. (Let us assume that the cause of the explosion WAS the fuel/air mixture and the frayed wiring in the centerline tank. There IS strong evidence that this was the cause, so please do NOT get into other potential causes!) Why did the passengers make that assumption? It certainly was NOT because there were NEVER crashes of 747's or airplanes prior to this. So they must have considered the risks "acceptable", as do most of us.<br /><br />The difference certainly IS one of PERCEPTION! Not a single 747 was grounded while they found and fixed the problem. In fact, I'm not even sure ALL 747's have been modified to reduce the likelihood of such a problem...yet.<br /><br />If you are the one KIA'd, the "odds" are 100 percent! The point is public perception of what constitutes a risk. Maybe, if we could persuade NASA and the media to do so, they ought to post the statistical probabilities of the next mission along with the potential for a fatal accident in a scheduled airliner (you can bet the airlines would NOT like that!) and in an automobile.<br /><br />So far as feeling like "safety systems" should give you a feeling of confidence in life, airbags DO save lives...but they have also killed small adults and children. Ejection seats do save the lives of fighter and SOME bomber crewmembers. BUT...(and I don't have any recent statistics...just ones from the 1980's)...as of that point in time, dating from the beginning of the use of ejection systems (seats, capsules, etc.), the rate of saves was only 50 percent, and that did NOT included those seriously injured (almost ANY ejection from the old Viet Nam-era F-4 seats resulted in compression fractures of the vertibrae), even if they survived.<br /><br />Educating the public is tough, because modern technology is

 

[baktothemoon]

My point was that we have to accept some risks and mitigate manageable risks in order to continue space exploration, my point also was that risk and probability of disaster being the main focus achieves nothing if we have already tried to make the vehicle safe. Do you agree or disagree?<br /><br />"Ask not what your country can do for you, ask what you can do for your country." John F. Kennedy

 

[tplank]

I'm thinking something more like one in ten is "acceptable"...but really, it isn't up to me to measure. The only relevant measurement is whether those taking the risk are comfortable with the risk they are assuming. I realize we are talking about public support here, but that is part of my point. We should not yeild this ground on the safety thing. There are noble aims here and people who believe in them.<br /><br />Perhaps we have become too weak (risk adverse) as a society to undertand this. Test pilots undergo enormous risk behind the stick with far less potential rewards. The risk of colonization of North America was not very favorable but the colonists came anyway. Fortunately there was no public opinon sitting there telling them they were nuts.<br /><br />Perhaps we should send folks of various seperatist movements: libertarians, the IRA, Kurds...ect... I say this tounge firmly in cheek, but really it is profitable to think of the big picture: there are people for which these risks are quite acceptable.<br /><br />And who chickens such as you and I to qubble when those succesful folk are flirting with the temporal version of immoratility? <div class="Discussion_UserSignature"> <p>The Disenfranchised Curmudgeon</p><p>http://tonyplank.blogspot.com/ </p> </div>

 

[hk8900]

In my opinion, for fatal accidents, the acceptable rate is around 0.5%<br />Of course lower is better, but spaceflights are hard<br />Currently, the vehicle with lowest accident rate is the Soyuz<br />With a crew of 3 lost in the 1960s<br />(We cannot take Shenzhou[0%] into account as it has only conducted 2 manned launches)<br /><br />However, space exploration MUST continue<br />Remember, the fatal accident rate in the early days of intercontiental sailing in 1600s and 1700s is higher than 50%

 

[no_way]

one point in this discussion is not yet mentioned. all destinations and even all human lives are not equal in context of a mission. a military crew heading to rendezvous with a killer asteroid to deflect it from collison course with earth will definitely accept higher risk of death than couple of billionaires wanting to go on lunar vacation. i believe some people would accept 1 in 2 chance of getting killed just to be a first person to set foot on Mars as well.