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Early Space Shuttle Flights Riskier Than Estimated
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Early Space Shuttle Flights Riskier Than Estimated


Early Space Shuttle Flights Riskier Than Estimated

Early Space Shuttle Flights Riskier Than Estimated
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A retrospective risk analysis by the Space Shuttle Safety and Mission Assurance Office finds that the first nine shuttle flights had a 1 in 9 chance of catastrophic failure — 10 times the risk of flights today. Teri Hamlin and Mike Canga of NASA's Johnson Space Center discuss the report.


This is SCIENCE FRIDAY. I'm Ira Flatow.

After the Challenger exploded in 1986, President Reagan ordered a commission to investigate the disaster, and one of the participants was the famous physicist Richard Feynman. In his appendix to the presidential report, he wrote that the engineers he surveyed estimated such a disaster could happen roughly one out of 100 launches. Management gave figures like one in 100,000.

And now, 25 years later, a new NASA analysis has pegged those earlier flights as much riskier than even the most conservative estimates at that time, about a one in 10 chance - one in 10 chance - of losing a shuttle and its crew, which means only a 6 percent chance of making it through the first five years of shuttle flights, all the way to the Challenger disaster, without a catastrophe -only 6 percent.

As the shuttle program gears up for its last flights, is this risk worth now taking? Can we apply what we know today about the risks of space flight to whatever replaces the shuttle? That's what we'll be talking about this part of the hour. Our number is 1-800-989-8255. You can tweet us, @scifri, @-S-C-I-F-R-I.

Teri Hamlin is the technical lead of space shuttle probabilistic risk assessment at NASA's Johnson Space Center in Houston. Welcome to SCIENCE FRIDAY, Ms. Hamlin.

Ms. TERI HAMLIN (Technical Lead, Space Shuttle Probabilistic Risk Assessment, Johnson Space Center Houston, NASA): Thank you for having me.

FLATOW: You're welcome. Mike Canga is the space shuttle program risk manager at NASA's Johnson Space Center. Welcome to SCIENCE FRIDAY, Mr. Canga.

Mr. MIKE CANGA (Space Shuttle Program Risk Manager, Johnson Space Center, NASA): Thank you.

FLATOW: Ms. Hamlin, tell us about this new risk review that you folks did. Did they know how risky it was back then? Because I recall - I covered the shuttle from day one - they kept - NASA kept routinely quoting the risk, if I remember, as something like one in 100,000.

Ms. HAMLIN: No, they did not, at that point in time, understand what risks they were accepting at that point in time. They really didn't have a methodology in place to quantify - like we do today - to quantify the risks using complex models.

And also, there was just, you know, at that point in time, we hadn't flown very many flights, and so we weren't - we didn't understand the integrated effects of the space shuttle vehicle at that point in time.

FLATOW: Because right up to the Challenger disaster, the risk in this new assessment is one in 10.

Ms. HAMLIN: Yes, that is correct. That is correct because what we're doing is, we're taking our current knowledge that we have today, and applying that to the configuration of the vehicle back then.

FLATOW: Mike Canga, knowing what we know about the risks today, about the risk to astronauts' lives, if we had known it was one in 10, would you say that the early flights were simply too risky for Christa McAuliffe and civilians like that to have flown?

Mr. CANGA: I'm going to defer a little bit on that. I believe better management would have had to take that into better assessment than they had at the time. I do think we really under-appreciated the amount of risk at the time. And whether or not an individual would have been willing to accept that risk, I think it was incumbent on the agency to try and express it to them as accurately as we could.

Ms. HAMLIN: Can I interject a little bit here?

FLATOW: Sure, please.

Ms. HAMLIN: I would just also say that if we knew at that point in time what the risks were, and therefore had this assessment, knew the dominant risk contributors, we would have been actively pursuing reducing those risks, as we do today - as we've done.

FLATOW: And a good - and a follow-up question to that is: What are the dominant risk contributors?

Ms. HAMLIN: The dominant risk contributors to the early flights?


Ms. HAMLIN: That would, obviously, be the RSRM and the thermal protection system, the solid rocket motor and the thermal protection system, Ascent debris risk that both Columbia and Challenger...

FLATOW: The foam falling off.

Ms. HAMLIN: Yeah, that's correct.


Ms. HAMLIN: And also - the main engine also is a big contributor.

FLATOW: Main engine, would that be hydrogen?

Ms. HAMLIN: That would be the engine parts, the very high-energy turbo pumps that are involved in that operation, that they could have an there is hydrogen involved, but it's the moving parts that can then come apart and explode.

FLATOW: And the number one risk today to the shuttle is, I think, is surprising to most people. What would that be?

Micro meteoroid and orbital debris.

FLATOW: Stuff that's up there already, floating around in space.

Ms. HAMLIN: That's correct. That's correct. And it's not those big pieces of debris that we're talking about. It's the little - tiny, little paint flecks that maybe chip off old satellites that could - that are moving extremely fast, that can cause a critical damage on the vehicle.

FLATOW: Teri, would you agree that's the number one risk?

Ms. HAMLIN: I would. I would agree.

FLATOW: I'm sorry. Mike, would you agree?

Mr. CANGA: Well, yes, for in-flight risk, that is our top risk based on our estimates. I mean, we spend a lot of time and effort analyzing the things we understand, and we have such a length of time on orbit that that's really where it gets us.

FLATOW: With the shuttle program just about finished, with just maybe a launch left, why are we releasing this data now, and why are we concerned about the risk?

Mr. CANGA: Well, we're releasing the data now because we have it. I mean, the study that we're talking about is one we've done based on all the information we haven't had. We would not have been in a position to do this kind of study a couple of years ago.

I'm sorry, what was the...?

FLATOW: No, I'm just saying: What have we learned about the future?

Ms. HAMLIN: Well, besides trying to understand our past on the shuttle and trying to show that we have made significant progress on reduction of risk, we're trying to maybe show that new programs out there, new vehicles, may not be as safe as they think that they currently are, or the calculated risk is right now - that there may be some unidentified or unknown risks that they'll be facing in the future, just like the shuttle did.

FLATOW: And to be aware that you have to look for the unexpected risks that you might not be thinking about.

Ms. HAMLIN: That's right.

FLATOW: Yeah. One thing that's interesting, looking at your report, is risk did not always go down. You would think, over flight time, the risk would go down. But in some cases, it did not. Why is that?

Ms. HAMLIN: The reason - there are some external events that can happen to us when - in particular, that significantly increased the risk was the EPA banned freon, CFC 11, which was our blowing agent for the external tank foam. And so when we had to go to a new blowing agent, the foam did not adhere as well to the tank, and we got significantly more damages on the vehicle because of that.

And so it was really an external event that occurred to us which increased our risk.

FLATOW: And looking forward: We don't have any manned space flights, after the shuttle, planned. I mean, nothing that's - you know, we talk about it a lot. What can you, you know, do besides say, remember this stuff for the next time?

Mr. CANGA: Well, there are several programs in hand. At Johnson, we're working on a multipurpose crew vehicle. And of course, SpaceX is working on their Dragon vehicle. So actually, the designs are in work now. So now is the time to have this information out for the designers.

FLATOW: So you have been looking, Teri, at the risk of commercial rockets, then?

Ms. HAMLIN: We're going to be - well, I haven't personally, I mean, been looking at it. But we are sharing this information with them. We're planning on -to share this information with them, yes.

FLATOW: Because - I'm sorry, Mike, go ahead.

Mr. CANGA: Oh, no, I didn't say anything.

Ms. HAMLIN: That was me. I was going to continue.

FLATOW: Go ahead, please.

Ms. HAMLIN: I was just - it's still up in the air, with regard to commercial, how the NASA-commercial relationship is going to proceed in the future.

FLATOW: What about international relationships? Have you shared this with the Chinese and the Indians, other people who have active rocket programs?

Ms. HAMLIN: We have not shared this with - it currently has not been released for - outside the United States.

Mr. CANGA: We are...

Ms. HAMLIN: Well, I understand that, but I meant the whole entire - the entire...

Mr. CANGA: Right. We are working on releasing this and publishing this information. So at that point, it would be available. But it still has to go through some approval cycles.

Ms. HAMLIN: What's been released, currently, is just, it's a high-level summary of the study that's been done.

FLATOW: And some interesting timelines on there, showing the risk fluctuating up and down. It's quite interesting. And some of the statistics on the data sheet - like at the bottom, it talks about there was a 6 percent likelihood of making it to flight 25; and a 7 percent likelihood of making it from flight 26, which was the Challenger disaster, to flight 113, which was Columbia, without loss of the crew or the vehicle - using the values on the chart.

Mr. CANGA: To me, it wasn't that - the early flights were a surprise, when we did them. But we're talking about long campaigns. So, you know, we're talking about 26 flights, which is more flights than we had in our previous space flight - manned space flight experience. And then we're talking about the run from flight 26 to 113.

That is - those are long runs of flights with moderate probabilities. So when you look at the entire campaign, things begin to add up. In terms of per flight, these are - I'm probably stepping on Teri here, but these are independent probabilities. So the per-flight basis is really not too far off from either previous programs or - if you look at the failure rates of unmanned launchers, we're actually quite a bit better than those.

FLATOW: We've run out of time. I want to thank you both for taking time to be with us today.

Ms. HAMLIN: Well, thank you.

Mr. CANGA: Thank you.

FLATOW: You're welcome. Teri Hamlin, technical lead of space shuttle probabilistic risk assessment at NASA's Johnson Space Center in Houston. Mike Canga is space shuttle program risk manager at NASA's Johnson Space Center as well.

And if you want to see the summaries of this report and this interesting graphic, go to our website at, and click on the link that'll take you to the NASA site. And you can look at this really interesting graphic of what the actual risks referred now - one in 10, one in nine - for those early space flights.

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