By Paul Dorian,
Overview
Today marks the 35th anniversary of the Space Shuttle Challenger disaster which occurred on January 28, 1986, when the NASA Space Shuttle orbiter Challenger (mission STS-51-L) broke apart 73 seconds into its flight leading to the deaths of its seven crew members. STS-51-L was the 25th American Space Shuttle Program flight since the program began in 1981.
It was also the first mission to have a civilian on board, American teacher Christa McAuliffe. The spacecraft disintegrated over the Atlantic Ocean, off the coast of Cape Canaveral, Florida at 11:39 EST (16:39 UTC). According to the Report of the Presidential Commission on the Space Shuttle Challenger Accident, weather conditions were likely one of the factors that contributed to the incident. Tests conducted during the subsequent investigation showed that O-rings were much less resilient at lower temperatures, but the extreme cold at the Kennedy Space Center was not the only weather factor involved with this tragedy.
Weather’s role in scheduling changes prior to the actual launch day
Challenger’s launch had originally been scheduled for the afternoon of January 22nd. After a two-day slip related to the previous shuttle mission, bad weather at an emergency landing site in Senegal and problems with an alternate site in Morocco delayed the launch to Sunday, January 26th. Air Force weather forecasters provided a pessimistic Sunday forecast to NASA managers the night before, causing managers to postpone Sunday’s launch in advance. However, as it turned out, the weather was fine on that Sunday morning leading launch director Gene Thomas to say “Sunday morning, the weather was perfect. We got a bad report. It happens.”
The countdown then proceeded towards a launch on Monday, January 27th at 9:37 a.m. After the crew boarded Challenger, a tool used to close the hatch became stuck. The ground crew eventually removed the tool, but by that time crosswinds at the Shuttle Landing Facility rose above the acceptable limit for a Return-To-Launch-Site (RTLS) emergency landing. At 12:35 p.m., the launch was scrubbed for January 27th and rescheduled for Tuesday, January 28th at 9:38 a.m. After Monday’s scrub, weather forecasters briefed managers on the outlook for Tuesday morning, January 28th. Clear skies were forecast, but unseasonably cold weather was expected to sweep through central Florida. The minimum predicted air temperature at the launch pad bottomed out at 22°F for the hours just before dawn on Tuesday, January 28th.
With sub-freezing temperatures predicted, ground crews drained most of the water pipes at the launch pad to minimize ice formation. Those that could not be drained were left running overnight, and strong wind gusts blew water onto pad structures where it subsequently froze. The ice inspection team was sent to the launch pad several times overnight to evaluate conditions at the launch pad. Before each shuttle launch, the ice team would do a review of any potential ice buildup on the external tank caused by the supercooled liquid oxygen and hydrogen in the tank. Ice on the tank and launch pad structure was considered a debris hazard because it could break off and damage the shuttle’s fragile thermal protection tiles (i.e., heat shield). Upon seeing the amount of ice on the pad, the launch team decided to delay the launch to 11:38 a.m. in order to give the sun time to melt some of the ice and minimize the debris risk.
Surface weather map on January 28, 1986 featuring an Arctic air mass in the eastern US and high pressure sitting over Florida which set the stage for very cold temperatures at the launch pad; map courtesy Penn State eWall
Arctic air outbreak
There was indeed a widespread Arctic air outbreak in the eastern U.S. on that late January day in 1986 that pushed record-breaking cold air all the way down into central Florida. Arctic high pressure extended southward into the region during the overnight hours helping to contribute to the record-breaking cold (surface map above). Melbourne, Florida, located about 35 miles from Cape Canaveral, recorded a record low temperature of 26 degrees; the normal low on January 28th is 50 degrees. Likewise, Orlando also had a record low of 26 degrees that morning. Both records still stand, and both locations broke their record lows the following morning as well. As a result of cold and some gusty winds, ice accumulated on the launch pad area in the overnight hours. The ice was removed by crews, and multiple ice checks took place prior to launch. According to the investigation report, the ambient air temperature at the time of launch, 11:38 a.m. EST, was measured at 36 degrees. This measurement was made near ground level by a weather tower 1000 feet from the pad. However, the temperature near the failed Solid Rocket Booster joint – located at a higher altitude – was actually estimated to be 28°F. Not only was the ambient air near the Solid Rocket Booster joint colder than ground level measurements due to altitude differences, but the failed joint was shaded from the sun during the hours prior to liftoff. Joints on the sun-facing side were estimated to be nearly 20 degrees warmer than those on the shaded side at liftoff. Furthermore, the gusty winds created an enhanced cooling effect between the supercooled tank and the O-ring joint region.
The wind barbs (circled region on right) on this sounding plot at Cape Kennedy on the morning of the launch featured a noticeable change of wind speed and wind direction with height. This “wind shear” was an important contributing factor to the Space Shuttle Challenger disaster. Map courtesy University of Wyoming.
The contributing factor of wind shear
In addition to the extreme cold, wind shear (change of wind direction and speed with altitude) played a vital role in the Challenger disaster as it contributed to the failing of the O-rings on the Solid Rocket Booster. The first hint of trouble occurred at liftoff, but was not noticed until film was developed after the accident. Several puffs of smoke were seen emanating from the right Solid Rocket Booster aft field joint. Challenger encountered several bouts of wind shear (see sounding plot above) starting around 37 seconds into the flight and lasting through just after one minute after liftoff. About one minute after liftoff, a flame plume becomes visible on the right Solid Rocket Booster. The plume originates from around the aft field joint – the same area as the smoke puff seen at liftoff. The plume grew and was pushed by aerodynamic forces toward the external tank. The first evidence of external tank failure is the interaction of the plume with liquid hydrogen leaking from the external tank about 65 seconds into the flight. The plume also began to burn the strut connecting the right solid rocket booster and external tank. The tank structure failed approximately 73 seconds after liftoff, causing the liquid hydrogen and oxygen to vaporize with local combustion. Challenger itself did not explode, but was torn apart by extreme aerodynamic forces. Several large components of Challenger, including the right wing and crew compartment, are visible in photographs and film after the breakup.
Tests conducted during the Rogers Commission investigation showed that O-rings were much less resilient at lower temperatures. As a result, they “would not be able to expand along with the Solid Rocket Boosters case motion, and may not seal the joint properly”. This is what happened with the sub-freezing O-rings in Challenger’s right Solid Rocket Boosters aft field joint. The shuttle was designed to handle a certain amount of structural load with margin built in. During the shuttle’s 8 1/2 minute ride to orbit, on-board computers steered the shuttle along a preplanned trajectory.
Before launch, upper level winds were typically monitored by series of balloons and other devices. Engineers used the wind data to optimize the shuttle’s trajectory to minimize load caused by upper level winds. If the predicted structure load was outside of the acceptable limits, the launch would be scrubbed. In general, wind shear is more important for structural load than just the wind speed by itself. The structural loads seen during Challenger’s ascent were among the largest in the history of the shuttle program. However, the Rogers Commission determined they were not outside of the design limits and therefore did not themselves cause the accident. Some experts believe, however, that the O-ring failure – and as a result the Challenger accident – would not have occurred without the high wind shear.
On September 29th, 1988 – thirty-two months later – the Space Shuttle Discovery launched successfully with its five man crew and the United States had returned to flight.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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I was home from work with the flu and watched this live. The fireball was quite impressive, but various structural elements were thrown out of the fireball, so the hope that the crew capsule was clear dominated the talk for awhile. The retired Space Shuttle Atlantis is on display at the Kennedy Space Center, at Cape Canaveral, Florida. Anytime anyone is nearby they should see this exhibit, take the Atlas rocket trip and finish with the Atlantis program, I guarantee you will never forget it.
Here too, but I was at work, working for a major broadcaster at the time. Years earlier toured the huge building where it might have been assembled. Tour guide said as far as I recollect the volume of it is 4 or 5 million cubic meters , so huge that sometime cloud formed internally?!
I watched the launch on live TV … To what’s left of my mind Challenger is inextricably linked to Richard Feynman
So, they actually used polymer (plastic) O rings to contain burning stuff (powdered aluminium) that:
a) Destroyed the Hindenburg
b) Is or certainly was, used for welding railways tracks together
Both, all three cases incl Shuttle engines being variations on the Thermit Reaction.
Massive and totally uncontrollable once you’ve lit the fuse, heat/energy you get coming off burning, in Oxygen, Aluminium
In railway welding, to try moderate it somewhat, they use the Oxygen provided by Iron Oxide
aka Rust
Yet in Shuttle they used an as strong as an Oxidiser as they could find!
Then put people on top of it
Yet it was The Weather that brought the thing down???
The Weather???!!!!!????
<facepalm>
And NASA now thinks they know how Climate/Weather works and thus how we might control it.
Jeezus wept, What A Mess We Are In Here
The paint covering the fabric of the Hindenburg may have come close to the composition of thermite, but I don’t think it reasonable to blame the choice of a neoprene O-ring for the leak, had it been within the temperature range for which the design called.
The Shuttle SRB O-rings were Viton, not neoprene. Viton is a fluoropolymer elastomer, while neoprene is a chloroprene polymer. The SRB Prime Item Development Specification called out 25 F as the lower temperature limit for operation, so the boosters were ostensibly qualified to that lower limit (i.e. had been fired at something less than that temperature). Given that the ambient temperature the morning of the launch was outside of the qual limit, it’s inexcusable that the launch went ahead. I was working on development of the Peacekeeper (nee MX) ICBM at the time. We would never have launched a Peacekeeper development test missile outside of its qual environmental limits.
How many successful launches did they have prior to this with good weather? And you want us to believe this one launch with cold weather was a problem because of the powdered aluminium instead?
Four cognizant engineers at the time fought to delay the launch until warmer weather. They were brow-beaten into signing off on the launch. They signed under duress. The O-Rings were not subjected to excessive temperatures as long as they kept the gap sealed. It was only when they could not seal that hot gases passed over them.
It was not bad engineering, nor was it JUST weather. Management (of which I was a member but not in that chain) failed the program.
As I recall from that time (which may be wrong; it was a long time ago) the scheduled experiments were of dubious value. It was primarily a public relations flight.
Still it was a sad day for all aboard and their families.
Congress killed the crew. The design was for a single piece SRB but those would need to be delivered by barge and Morton Thiokol didn’t have that option. Thus the politically directed switch to segmented SRBs shippable by train so that M-T could “win” the contract.
I was arriving at a mile-deep exploration portal when I heard of the Challenger explosion on radio, visiting an underground diamond drill program that I was supervising on a gold property in the West Kootenay area of BC. I remember telling the drillers when I arrived at the drills that the space shuttle had just exploded and disintegrated shortly after lift-off, and was simply, flatly…not believed, it seemed just too crazy a concept, such was the reputation by that time of the shuttle.
I’ve read that 85% of Americans surveyed heard of the explosion within an hour of it happening. Imagine–a crew of diamond drillers a mile underground in an adit in south central British Columbia heard of it within 15 minutes.
You just made an excellent case against the internet and social media. If back in the “stone age” of the 1980’s such news could reach so many people so quickly, what exactly are we wasting trillions of dollars and years of our lives with the internet? The internet, social media, online news, all are actually not aimed at information dissemination but rather putting us all to sleep.
And quite frankly, this post offers nothing new that wasn’t known back then. We did not need the internet even for this “story” or Post or whatever they call news articles these days.
Gawd the world is a mess today. I thought it was bad back then, but wow, we’re probably not going to survive 2021.
Back to my hole now…
The old media is designed to disseminate only that information that the people who own the media believe you should know.
The internet allows people to seek out what they are interested in.
That a lot of people use the internet to look up things you find worthless is not the fault of the internet.
Do you really want to go back to a world where a small handful of people could control what an entire nation was learning?
MarkW
To quote john McEnroe, ” you can not be serious”
Have you seen what the stinkin’ Silly Con valley are doing to the news lately?
How did you respond to this article? How did you get to this article in the first? If you didn’t get there via the internet, please enlighten me.
I believe that I remember that there was an engineer w/ NASA that had serious concerns about the o-rings due to the cold temperatures at the time of launch. Relatively soft rubber like seal becoming rather inflexible and shrinking when cold? Whoda thunk that! Ask any mechanic! And huge o-rings to boot! LISTEN TO THE ENGINEERS and boot the PR people!
Quick search to support my memory from many years ago. An engineer had concerns about the o-rings … https://www.nasa.gov/centers/langley/news/researchernews/rn_Colloquium1012.html
I also remember seeing this NASA article dated 10/5/2012. When the Challenger exploded I was manager of the business unit of a major chemical company that supplied the o-ring lubricant to Thiokol. The seal in question was really the combination of o-ring and the lubricant applied on the o-ring when the seal was installed. To my knowledge we were never brought into the discussion (although attorneys may have been). We supplied the lubricant based on its set of chemical and physical specifications not performance in use.
Here’s another one: https://priceonomics.com/the-space-shuttle-challenger-explosion-and-the-o/
I’ve seen this article before. The author makes the point that NASA wasn’t using all the data it had on the O-rings and therefore made a bad decision. Then he goes on to his wider point:
“Selectively analyzing data like in the case of the Challenger is a pervasive problem, but it’s particularly common in media. For example, the media reports when bad things happen (like a rare terrorist attack) but doesn’t report when it doesn’t happen because the absence of an event isn’t newsworthy. As media consumers, however, we use this coverage to form opinions and make life decisions (like voting, determining personal safety, convincing our friends of certain beliefs), without realizing how selective this coverage is; this distorts how we view the world and leads us to make flawed decisions.”
Sounds like he is describing the major flaw of climate studies.
Let us be clear, in both Challenger and especially Columbia, the judgement of sober NASA engineers did not lead to the deaths of the astronauts, the decisions of ambitious NASA administrators did.
With Columbia, the engineers wanted to ask the military to use their satellites to photograph the underside of the shuttle.
The administrators rejected the idea. Reportedly they were worried about a publicity disaster if the public were to learn that the shuttle was damaged and that NASA had no way to get the astronauts back to earth safely.
Actually, it came down to the lead Flight Director, Linda Ham. She blew off Air Force requests to take pics of Discovery. She was the epitomy of the Houston Flight Director “We know All…Shut up, peon.” creed of that time. She tried to brush it off as no one was to blame, but she personally killed ANY chance at rescue, however remote such rescue may have been…
indeed, my understanding is that through unofficial channels, the requests were already made. But, once Linda and the Shuttle Program Director were aware of them, they pulled the plug and sealed the fate of the crew.
Some say nothing could have been done. But call b.s. on that. If the photos revealed a hole , then the entire apparatus of NASA and it’s private sector contractors would have been harnessed to find a solution. I believe they would have risen to the occasion.
The following link provides a summary of the regression analysis that analyzed the risk of failure versus launch temperature. https://byuistats.github.io/Statistics-Notebook/Analyses/Logistic%20Regression/Examples/challengerLogisticReg.html
The engineers were right in raising alarm. The analysis shows that “… shows that the odds of the o-rings failing for a given launch decreases by a factor of 0.79 for every 1° F increase in temperature. Said differently, the odds of an o-ring failure during launch decrease by 21% (1-0.79) for every 1° F increase in temperature. (Also, from the reverse perspective, every 1° F decrease in temperature increases the odds of a failed o-ring by a factor of exp(0.232) or 1.26.”
The brittle O-Ring theory at ambient slightly below freezing is nonsense, don’t care if Feynman himself thought of it. Millions of O-rings in use world-wide in sub-zero ambient conditions don’t fail. But nobody wanted to admit that it was simply installed incorrectly when there was a supposedly thorough inspection program.
It’s simply not possible to compare the little O-rings used world wide unless you can fine one that fits a cylinder that’s over 12 feet in diameter and subject to forces none of the “world-wide” O-rings encounter and . The o-rings simply were not capable of conforming, in cold weather, to be an effective seal. They used heat resistant putty to “fill in” in those times when the O-rings didn’t provide a tight seal. Basically, the O-rings and putty allowed the solid fuel to burn through the O-rings.
It was a poor design. Engineering rumors on the Cape knew this and proposed solution but were not implemented due to cost concerns. I’d rated that as possibly true. They did change the design to one that included using three O-rings.
Regardless, see the Britannia article on which states:
“The immediate cause of the accident was suspected within days and was fully established within a few weeks. The severe cold reduced the resiliency of two rubber O-rings that sealed the joint between the two lower segments of the right-hand solid rocket booster. (At a commission hearing, Feynman convincingly demonstrated the loss of O-ring resiliency by submerging an O-ring in a glass of ice water.) Under normal circumstances, when the shuttle’s three main engines ignited, they pressed the whole vehicle forward, and the boosters were ignited when the vehicle swung back to centre. On the morning of the accident, an effect called “joint rotation” occurred, which prevented the rings from resealing and opened a path for hot exhaust gas to escape from inside the booster. Puffs of black smoke appeared on the far side of the booster in a spot not visible to most cameras.”
https://www.britannica.com/event/Challenger-disaster
The Presidential Commission: “ln view of the findings, the Commission concluded that the cause of the Challenger accident was the failure of the pressure seal in the aft field joint of the right Solid Rocket Motor. The failure was due to a faulty design unacceptably sensitive to a number of factors. These factors were the effects of temperature, physical dimensions, the character of materials, the effects of reusability, processing, and the reaction of the joint to dynamic loading.”
All in all, it can be argued it was not a “single point of failure” by pointing to the O-rings by themselves but had there been any O-ring material that would have withstood the environment, it didn’t exist in 1986.
Actually Feynman was constantly berated and vilified to begin with for theorising on the (true) cause of the disaster, with a whole band of people in denial who wanted him removed.
Sounds pretty familiar doesn’t it?
I saw a documentary on the Challenger disaster a few months ago. Apparently there was political pressure to not throw too much blame Thiokol’s way.
DMac,
That’s the first I’ve heard of incorrect installation of the O-rings. Please provide reliable links.
O-rings come in a huge variety of shapes, sizes and materials.
Just because one type of 0-ring is capable of handling low temperatures is not proof that all of them can.
On previous low temperature launches, the o-rings showed signs of partial burn through when the boosters were recovered and taken apart.
I just walked in from the unheated shop after using the compressed air for about one minute worth of use. The control trigger did not close reliably as is typical in the winter. Temperature is now 31F. WD-40 works to solve issue so it is not ice. My other ‘nozzle’ has no issues. I think it’s the O-ring because it’s been there a loong time and only an issue in the first cold spell.
Rob Dawg is correct, the root problem was the segmented SRB design that was approved solely to appease a Utah Senator by letting Morton Thiokol “win” the contract. (I remember reading about the proposal to spin up a Fiber Reinforced Plastic booster at Kennedy. Monolithic construction, light weight, rigid, etc) I do wonder why the Pregnant Guppy solution wasn’t chosen to get an SRB from Utah to Florida. (NB the Super Guppy, still in service, was used to transport Saturn V third stages)
And you are correct, there are many O-ring elastomers that could have been used that would not have failed due to a minor temperature swing. But, NASA not only failed on the mechanical assembly checks, they also failed to ensure that the selected O-ring construction would be all weather capable. Although there were plenty of good materials available, they picked one that only worked in a narrow temperature band. Oh yes, and the whole joint design was upside down and inside out.
And NASA launch management failed. Instead of doing the prudent thing of postponing because the engineer was concerned, as they had postponed earlier because of concerning weather forecasts, they instead opted for asking Morton Thiokol to recommend launching. Asking executives if the multimillion dollar product they sold you will work is not due diligence.
Why did NASA want to launch? Because management thought it would be bad PR to cancel again. FAIL!
Pregnant Guppy. One of the oddest looking aircraft I have ever seen.
https://en.wikipedia.org/wiki/Aero_Spacelines_Pregnant_Guppy
I’m astounded by the way you can jump to conclusions without any information. Clearly you are not a rocket scientist. Your approach makes me wonder if you are any kind of scientist.
You put people on top of huge stockpiles of explosive and burning fuels and launch them into space…and then are shocked that one of these blows up. The Space Shuttle was an amazingly complex machine where literally thousands of parts could lead to an eventual catastrophic failure. It is a testament to mankind that we can build these machines and they only occasionally kill their crews.
There are going to be accidents…more of them in the future. The trick is to reduce known risk by as much as possible and then learn from the mistakes. Everything needs to be tested, tested and retested before putting a person on top. Everything needs to be checked, checked again, and then rechecked by different pairs of eyes to ensure mistakes are caught.
This is one reason I no longer belief that manned space-flight is the best near course. You can lose a robot and yeah, it’s expensive but no one died. The complexity (and therefore risk) of getting living people to Mars and back is off the scale…getting a robot their and samples back is very doable.
The Space Shuttle was an amazing piece of engineering, despite how cludgy it worked. The next step is to build an airframe capable of horizontal launch, high orbit capable, and then a glided return. Building reusable rockets is a nice temporary answer but we need true shuttles if we are to ever setup real space stations (Lagrange point orbits, artificial gravity).
Now that this article is published some nut case is going to make the claim that Climate Change killed the astronauts. In truth is was a failure of imagination when designing and then testing the simple O-rings.
“You can lose a robot and yeah, it’s expensive but no one died.”
These were volunteers, engineers, that were aware of the risks. Shouldn’t they be allowed to make the choice as to whether the risk was too great or not?
Challenger was bad…as it had been highly promoted as 1st Teacher in Space.
But, I have also read a large amount of the Columbia Report, and the disregard for human life that took place at NASA while Columbia was orbiting to its doom, was beyond the pale. It was both shocking, and moving.
My advice to any young person wearing NASA gear is to read the Challenger and Columbia reports, you’ll never look at NASA the same way again.
School kids across the country had been gathered by their teachers in order to watch the launch. I can’t imagine trying to explain to a bunch of 2nd and 3rd graders, what had just happened.
Sadly prophetic.
Yes I watched the Columbia launch standing outside in Florida and it was another freezing cold day. Subsequently, on its return I went outside to hear the sonic boom as it went over towards the cape on recovery – and of course did not hear it.
I’ve always thought that “anniversary” was a poor choice of words for an infamous event, such as this, or the attack on Pearl Harbor. I think that “annual remembrance” better conveys the point of publicly recognizing the date.
We might note that there were two SRB’s on that launch. The other booster did not fail.
The other booster was in the sun and was some 20 degrees warmer at the time of launch.
Fair point. It did go through the same wind shear forces though, but certainly possible that there was an absence of an at-launch O-ring failure.
I’ve got it–O-ring warmers! My car has them.
The “acceptance of deviance” underlayed both Challenger and Columbia. The O-rings were not supposed to see the heat of the burning fuel. When they flew STS-2 (the second mission) they started to see erosion into at least one of the primary O-rings. This should have stopped the flights. They rationalized the reason for the deviation, and insisted they had a “backup” secondary O-ring. The fixes they made (procedures, etc) seemed to avoid the problem on future flights, but when erosion reoccurred, they rationalized that, and started comparing the amount of erosion with previous flights, and began to think they understood the problem. But the erosion wasn’t supposed to happen at all. They finessed the deviation, and continued to fly. It finally caught up with them.
Similarly, the tank insulation started falling off in the very early flights. Dings in the orbiter thermal protection system were observed and “accepted” as not a safety-of-flight issue. Some were due to foam shedding, some were due to debris kicked up at landing, and other causes. But they thought they could accept the deviance and not jeopardize the manifest (flight schedule). But tank shedding should not have been accepted at all. But it started as a small annoyance, and there was lots of project momentum to keep flying. It was a fundamental flaw in the design, like the O-rings, but they finessed it, and accepted the deviance. Tragedy awaited again.
The shuttle was an amazing vehicle — it was a launch vehicle, it was an on-orbit space station, and it was a re-entry vehicle and glider at landing. And it was reusable, however costly it was to turnaround and get ready for the next flight. It was always a technology demonstration, never really operational. And the crew were stuck if something major went wrong in the first two minutes. No way to escape until after the SRBs burned out. And even then, there were periods where a single engine failure would require a return to the launch site (involving a powered pitcharound with all three engines burning) which was never tested and was a huge unknown. Two engine failures would lead to water landings in some cases. Bailout wasn’t even an option until after Challenger. It was an amazing machine but its cost meant that two mission failures in 130 or so flights were just not acceptable. Unlike Apollo 13, the engineers on the ground were not able to help with either accident. Fundamental design weaknesses doomed both crew. NASA will never get over it.
I was flying off the coast of Jacksonville, Fl out of Cecil Field. The S-3 was in a training area at time of the launch. We watched from about 15000 feet as the shuttle went up and then formed that now infamous Y shape with exhaust. We radioed in as ready to supply SAR as needed. We were told to stand by. We held off the coast in radio contact for what seemed like forever. We were finally told our services were not needed and returned to home base.
I will never forget seeing that Y shape out of my window. The crew knew and could doing nothing to help even though we were so close.
Several years ago I was in contact with the software engineer who did the analysis on the O-rings when they were being developed. It was known that the rings would become stiff if the temperature dropped below a set temperature and that information was part of the specifications. The real problem for the O-rings was the upper temperature temperature so that was what they were designed to handle.
After the shuttle failure, the engineer felt guilty and went over the entire analysis looking for a possible mistake in the calculations and found none. Nasa had pushed the specification beyond safe limits.
There is more to the story that is personal in nature that I can’t tell but the engineer felt uncomfortable continuing that line of work so the engineer went to medical school and became a doctor,
My first thought when saw the fireball on TV was ,- oh my god, the poor young teacher …
although there were still six other astronauts on board!
Richard Feynman wrote in his book “What Do You Care What Other People Think?” very detailed about his results on the risks of shuttle starts and the causes of the tragic Challenger desaster, his point of view fairly free of political considerations.
It is pathetic that the same ignorance of elastomer properties is a tool in the marketing of so many products – tires’ Glass Transition Temperatures. Did you know that summer tires may break if used in the winter? /sarcasm
It is always the engineers’ fault. One Aww-shoot wipes out many attaboys.
The conspiracy of ignorance masquerades as common sense.
Only a government “scientist” couldn’t figure out how to make a $20 O-ring seal for $450 million.
2 notes to self:
Try not to launch a large caliber solid 30F below the temp one has ever successfully been launched before. Challenger.
When a chunk of the ET falls off, take a look and see if it hit something. Columbia.
Do not forget the piece the EPA had in both accidents, the asbestos ban for Challenger and the CFC ban for the ET SOFI which came up in chunks x10 after the ban than before. Cheers –
Was the capsule with the bodies of the astronauts and teacher brought up out of the ocean? — or are the details of that operation too early to tell?
The reason the tragic Challenger accident occurred was due to Dynamic Overshoot – a start-up transient phenomenon of physics when a sudden load is applied to a flexible structure the effective loads nearly double – which was not accounted for in the original structural loads. It’s a familiar phenomenon – when you step on a bathroom scale the weight on the dial overshoots your actual weight dramatically. We naturally wait until the oscillations stop before we acknowledge the real weight. But the loads on the spring inside the scale really follow the numbers on the dial.
The sizing of hardware is only as good as the loads analyzed; if the real loads are nearly 2X those analyzed for and the factor safety is 1.5, there will be problems. Yale Jay Lubkin, writing in the May 1988 issue of Defense Science covered things reasonably well. He reported that Mr. Ali AbuTaha investigated the accident on his own and concluded dynamic overshoot was the cause. Initially when Mr. AbuTaha presented his findings they were dismissed by NASA. But after further review they redesigned the affected structure to the ~2X loads due to dynamic overshoot. NASA has since required that dynamic overshoot loads be incorporated in new designs. https://www.flightglobal.com/dynamic-overshoot/11898.article
NASA has a copy of Ali AbuTaha’s report on their website. https://www.nasa.gov/pdf/382045main_19%20-%2020090730.11.STS%20Problem%202003.pdf
Yale Jay Lubkin’s article addressed some of the questions associated with the accident, including shuttle solid rocket booster (SRB) design with multiple segments and O-rings, cold temperatures, refurbishment and reuse of SRBs, twang loads, launch delay timing, and wind shear. If wind shear was such a problem why was the Y shaped smoke trail largely intact for several minutes after the launch without the characteristic distortion expected from wind shear?
Titan III & IV missiles used similar segmented SRB’s (from a different supplier) with a single O-ring in the joints between the segments (Shuttle used 2 O-rings for redundancy). Titan SRB’s were tested in colder temperatures than the Challenger launch experienced without a problem. It turns out the reason is that O-rings aren’t even necessary, since the way the fuel in the SRB is shaped the gap between the segments is only present for the first 1.5 seconds, after which the thermal expansion of the solid fuel closes the gap. And 1.5 seconds isn’t enough time to burn the O-rings or structure. Shuttle SRB O-rings were found with scorch marks (but not burned through) on many launches, even ones at 70F temps.
Videos of the launch show a puff of black smoke at the instant of the SRB ignition at the location where the strut connects the orbiter to the SRB. Clearly there was insufficient time for any burning of O-rings but also the puff shot out radially from the barrel. If the O-ring was leaking then the puff would go along the vertical direction, not radially. This is true because the puff resulted from the failure of the SRB barrel through the O-ring groove; due to the loads on the strut from the main engine thrust (twang loads) plus the pressure load resulting from SRB ignition.
Why did the SRB fail? This was one of the first SRB barrels that was previously flown and refurbished. When a SRB barrel is refurbished, the shape is checked to make sure it is within specifications for uniform diameter. This one was out-of-spec and they used a hydraulic jack to get it back to spec. But the max load on the jack allowed per spec was not sufficient to bring it fully to round. So instead of scrapping the discrepant barrel they added a mechanical jack along with the hydraulic one to force it within tolerance. (The spec didn’t say they couldn’t do that.) So what we had here was an SRB barrel which was overloaded at the strut connection due to dynamic overshoot on the first launch, followed by overloading to get back to round, and a 3rd overload on the Challenger launch. So the barrel substantially exceeded design limits 3 times and broke through the O-ring groove – the thinnest section of the barrel – which is coincidentally adjacent to the orbiter connecting strut attach clevis.
With the crack in the barrel wall the flow of hot gases continued to erode the opening as the flight progressed. This radial flow generated lateral thrust which pushed the shuttle off course, so the gimbals deflected the rocket nozzles to correct the trajectory. This gimbaling was executed as if the cause was due to something temporary, like a gust. But the gimbaling put bending on the SRB barrel which somewhat closed the crack, which reduced the lateral thrust for a few seconds. When you look at the video there are a series of puffs from the leaking crack as the flight control repeatedly applied correcting gimbal commands. After a time the hot gases/flames (they were still flowing radially) kept widening the crack and impinged on the external tank, until it burned through and triggered the explosion.
Many early rocket launches since the 1950’s experienced explosions right at lift-off. The cause was not initially understood, but the hardware was strengthened until it was 2X stronger than it started and the failures stopped. Dynamic Overshoot has been the cause of many problems in the rocket age.