NASA's O-Ring Problem and the Challenger Disaster

In January 1986 the world watched in shock as the Challenger Space Shuttle, on its way to carry the first civilian to space, exploded just two minutes after lift-off. A presidential commission later determined that an O-ring failure in the Solid Rocket Booster (SRB) caused the disaster. This was not a new problem, there's a long history of issues with the O-rings leading up to Challenger's loss.

Before the Space Shuttle was declared operational, it performed four test flights to space and back. The first O-ring anomaly occurred on the second test flight, named STS-2 (November 1981). After each flight Thiokol, the company in charge of manufacturing the SRBs, sent a team of engineers to inspect the retrieved boosters. The engineers found that the primary O-ring had eroded by 0.053 ''. The secondary O-ring, which serves as a back-up for the primary O-ring, showed no signs of erosion. On further inspection the engineers also discovered that the putty protecting the O-rings from the hot gas inside the SRB had blow-holes.

Luckily, the O-rings sealed the SRB despite the erosion. Simulations done by engineers after the STS-2 O-ring anomaly showed that even with 0.095 '' erosion the primary O-ring would perform its duty up to a pressure of 3000 psi (the pressure inside the SRB only goes up to about 1000 psi ). And if the erosion was even stronger, the second O-ring could still finish the job. So neither Thiokol nor NASA, neither engineers nor managers considered the problem to be critical. After the putty composition was slightly altered to prevent blow-holes from forming, the problem was considered solved. The fact that no erosion occurred on the following flights seemed to confirm this.

On STS-41-B (February 1984), the tenth Space Shuttle mission including the four test flights, the anomaly surfaced again. This time two primary O-rings were affected and there were again blow-holes in the putty. However, the erosion was within the experience base (the 0.053 '' that occurred on STS-2) and within the safety margin (the 0.095 '' resulting from simulations). So neither Thiokol nor NASA was alarmed over this.

Engineers realized that it was the leak check that caused the blow-holes in the putty. The leak check was an important tool to confirm that the O-rings are properly positioned. This was done by injecting pressurized air in the space between the primary and secondary O-ring. Initially a pressure of 50 psi was used, but this was increased to 200 psi prior to STS-41-B to make the test more reliable. After this change, O-ring erosion occurred more frequently and became a normal aspect of Space Shuttle flights.

On STS-41-C (April 1984), the eleventh overall mission, there was again primary O-ring erosion within the experience base and safety margin. The same was true for STS-41-D (August 1984), the mission following STS-41-C. This time however a new problem accompanied the known erosion anomaly. Engineers found a small amount of soot behind the primary O-ring, meaning that hot gas was able to get through before the O-ring sealed. There was no impact on the secondary O-ring. This blow-by was determined to be an acceptable risk and the flights continued.

The second case of blow-by occurred on STS-51-C (January 1985), the fifteenth mission. There was erosion and blow-by on two primary O-rings and the blow-by was worse than before. It was the first time that hot gas had reached the secondary O-ring, luckily without causing any erosion. It was also the first time that temperature was discussed as a factor. STS-51-C was launched at 66 ° F and the night before the temperature dropped to an unusually low 20 ° F. So the Space Shuttle and its components was even colder than the 66 ° F air temperature.

Estimates by Thiokol engineers put the O-ring temperature at launch at around 53 ° F. Since rubber gets harder at low temperatures, low temperatures might reduce the O-rings sealing capabilities. But there was no hard data to back this conclusion up.

Despite the escalation of O-ring anomalies, the risk was again determined to be acceptable, by Thiokol as well as by NASA. The rationale behind this decision was:

– Experience Base: All primary O-ring erosions that occurred after STS-2 were within the 0.053 '' experience base.

– Safety Margin: Even with 0.095 '' erosion the primary O-ring would seal.

– Redundancy: If the primary O-ring failed, the secondary O-ring would seal.

The following missions saw more escalation of the problem. On STS-51-D (early April 1985), carrying the first politician to space, primary O-ring erosion reached an unprecedented 0.068 ''. This was outside the experience base, but still within the safety margin. And on STS-51-B (late April 1985) a primary O-ring eroded by 0.171 '', significantly outside experience base and safety margin. Practically burned through. On top of that, the Space Shuttle saw its first case of secondary O-ring erosion (0.032 '').

Post-flight analysis showed that the burnt-through primary O-ring on STS-51-B was not properly positioned, which led to changes in the leak check procedure. Simulations showed that O-ring erosion could go up to 0.125 '' before the ability to seal would be lost and that under worst case conditions the secondary O-ring would erode by no more than 0.075 ''. So it seemed impossible that the secondary O-ring could fail and the risk again was declared acceptable. Also, the fact that the O-ring temperature at STS-51-B's launch was 75 ° F seemed to contradict the temperature effect.

Despite these reassurances, concerns escalated and O-ring task forces were established at Thiokol and Marshall (responsible for the Solid Rocket Motor). Space Shuttle missions continued while engineers were looking for short- and long-term solutions.

On the day of STS-51-L's launch (January 1986), the twenty-fifth Space Shuttle mission, the temperature was expected to drop to the low 20s. Prior to launch a telephone conference was organized to discuss the effects of low temperatures on O-ring sealing. Present at the conference were engineers and managers from Thiokol, Marshall and NASA. Thiokol engineers raised concerns that the seal might fail, but were not able to present any conclusive data. Despite that, Thiokol management went along with the engineer's position and decided not to recommend launch for temperatures below 53 ° F.

The fact that there was no conclusive data supporting this new launch criterion, that Thiokol did not raise these concerns before and just three weeks ago recommended launch for STS-61-C at 40 ° F caused outrage at Marshall and NASA. Thiokol then went off-line to discuss the matter and management changed their position despite the warnings of their engineers. After 30 minutes the telcon resumed and Thiokol gave their go to launch Challenger Space Shuttle. Shortly after lift-off the O-rings failed, hot gas leaked out of the SRB and the shuttle broke apart.

2012 And The End Of The World

Whatever you are planning for your future, whether it’s a new house, starting a family or even going on a diet – don’t bother. In four years the world will end and your plans will be ruined. This is the belief of thousands of people across the planet, preparing for the end of the world and death of mankind. So grab your diary and put this date in it – December 21st 2012.

The concept is gaining momentum as many religious texts, historical documents and even NASA have ‘predicted’ that there will be major changes to the Earth in the year 2012. And with the help of celebrity believers including the always-reliable Mel Gibson joining in, 2012 has become the talking point at dinner parties everywhere.

So, where has this cultural phenomenon come from and why do so many people believe? The widespread panic that accompanied the end of the millennium and the whole Y2K debacle seems to have shapeshifted into another end of the world scare. Why should we believe this one when Y2K believers became figures of fun to all those who had mocked them. Well, there are many reasons to listen as 2012 theorists can source ‘facts’ and ‘knowledge’ to support their claims.

The most referenced prediction comes from the Mayan Calendar as believers point to the completion of the B’ak’tun cycle as the signal that a new world order will be upon us. So the Mayans have apparently predicted that the end of the world will occur in 2012 and that the length of the lunar moon is 329.53020 days. They were only thirty seconds out with their lunar moon guess so basically it’s all over for us earthlings. Misinterpretation can make a big difference when translating ancient texts.

If you aren’t convinced yet then take a trip to Yellowstone National Park where the world’s biggest volcano lays dormant. Beneath this US tourist attraction, a volcano with a pattern of erupting every 650,000 years is expected to celebrate its special day with us. So when is the volcano’s anniversary, that’s right – 2012. It is understandable that the volcano is set to erupt in the near future but it would seem unrealistic that it would even wipe out a small section of the American population so are the believers clutching at straws with this one?

Moving on. So the Earth has two magnetic poles, north and south, that help protect the Earth’s surface from the devastating effects of the sun. Well, hold on to your hat, because the protection is about to be rescinded, the poles are shifting and we are all set for the worst case of sunburn in history. So, stock up on some factor 50 sunblock and grab the biggest hat you can find because it is about to get extremely hot.

Scientists have also announced that sunspot activity will reach a massive peak in 2012, resulting in severe solar storms and atmospheric changes. With this predicted sunspot expected to be up to 50 per cent stronger than previous ones, NASA has even began making preparations for the problems that await. But will these events make as big an impact on live as we know it as is suggested?

Cynics will say that all of these theories are based upon false translations and misinterpretations that manipulate people’s faith and need to believe. However ridiculous the claims may seem to non-believers, it is certainly going to be an interesting day when the clock strikes midnight and the 21st December 2012 is upon us.

Tim Cook: Fake news is ‘killing people’s minds’

Technically Incorrect offers a slightly twisted take on the tech that’s taken over our lives.


Apple CEO Tim Cook

Praying for the truth to come through isn’t enough, Cook believes.


Stephen Lam/Getty Images

Fake news has rather dominated the conversation of late. It’s made it very hard to stay in touch with reality.

Why, even the president and his staff insist that CNN, bastion of the middle ground, merely peddles fake news.

Information that’s false, but made to look real online, seems to proliferate daily — and I’m not suggesting CNN is part of that.

Some say fake news affected the election and that Facebook was partially responsible.

Apple CEO Tim Cook believes the fakery is “killing people’s minds in a way.” That’s what he told The Telegraph on Friday during a visit to London.

Cook insisted that the problem is serious across much of the world and everyone needs to be made more aware.

“It has to be ingrained in the schools, it has to be ingrained in the public,” he said. He called for a “massive campaign,” one that speaks to every demographic. But what form might this campaign take?

Cook explained: “We need the modern version of a public service announcement campaign. It can be done quickly if there is a will.”

Whose will, though, would it require? Technology companies might be involved. Cook believes tech firms need to invent tools that weed out fake news.

He likened the need to combat fake news to the way world awareness of global warming was raised. He said it was kids who were first prepared to learn and absorb information about the environment; then those children persuaded their parents to do something about it.

“In some ways kids will be the easiest to educate,” he said. “At least before a certain age, they are very much in listen and understand [mode].”

Somehow, though, I’m not sure public service announcements would work so easily. People have become more keen to believe what they want to believe and more suspicious of anything that runs counter to their beliefs.

They will surely look at any PSA through that subjective prism.

CNET Magazine: Check out a sampling of the stories you’ll find in CNET’s newsstand edition.

Tech Enabled: CNET chronicles tech’s role in providing new kinds of accessibility.

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