 The world is just about to witness a tragic disaster. Millions across the globe have tuned in to watch the first participant of the Teacher in Space programme ascend into space. Excitement is building as the Challenger Space Shuttle is just moments away from launch. The time is 11.38am and it's the 28th of January 1986. The shuttle is just about to lift off the launch pad at Kennedy Space Centre and although initially off to an apparently good start, just 36 seconds later the craft is hit by a strong wind shear. Not long after a small plume of smoke is seen, at 60 seconds post launch Capcom informs Challenger to go up throttle up. Just 5 seconds later the Challenger began disintegrating and quickly after a fireball consumed for shuttle stack. The world had just witnessed the loss of one of NASA's cutting edge in human space travel. Today we're looking at the Challenger Disaster. My name is John and welcome to Plainly Difficult. So this event happened three years before I was born and my first true exposure to it was via one of my favourite films, Koyane Scotsy. Ever since the first time I saw that film back in secondary school in 2001, I'd been fascinated by this disaster. Something as apparently infallible as NASA easily became the victim of its own confidence. Our story today would even lead to a new term, Normalised Deviance, which probably can be applied to a lot of subjects on this YouTube channel. Right, let's get cracking with a little bit of background. NASA during the design phase of the Apollo missions sought out a more cost-effective reusable heavy spacecraft for orbital missions. The concept was decided upon in the early 1970s and this design was set in March 1972. The design had the orbiter which housed a crew and payload with two separate reusable solid booster rockets and an external fuel tank. During the mid-1970s the first orbiter named Enterprise was constructed. She couldn't actually go into space but acted more as a test bed for the systems needed for the project. Eventually, over the coming decades, six orbiters will be built but for today's video we will focus on just one shuttle, Challenger. She was manufactured by Rockwell International, originally being attended as a structural test article to be completed in 1978, after which she was sent to Lockheed for 11 months of vibration tests designed to simulate entire shuttle flights from launch to landing. We'll pause with the Challenger story just briefly to talk about how the orbiter actually gets into space. So to get into orbit, the orbiter's engines are first to fire up and a few seconds later the solid booster rockets also start. This is enough to get the spacecraft off the launch pad. After liftoff, the stack goes inverted. The solid rocket boosters and the shuttle with its external tank separate. This is roughly two minutes after the flight has begun. The solid booster rockets deploy their parachutes, land in the sea and they are recovered, sent back to land and refurbished for reuse later on. So the orbiter and the external tank continue to ascend, with the orbiter's main engine still firing. The external tank is separated from the orbiter. The external tank, after being jettisoned, disintegrates in the Earth's atmosphere. Ok so that was a very basic description of how the orbiter gets to orbit. For more information I'd recommend watching maybe a curious droid video. Apparently people think we're related, we're not. So after its mission the orbiter was designed to re-enter Earth's atmosphere and upon re-entry glide to Earth and land much like a conventional aircraft. Well wasn't that little side tangent exciting? Well let's get back to the history of the Challenger. It was decided that Challenger should have a new lease of life after her experiments, and was to be converted into a full blown orbiter. She had her refit for spaceflight beginning in 1979. Many of her parts were sent back to her manufacturers for reworking. She also even had a new fully functional crew module added. The refit took around three years with Challenger rolling off the production line in July 1982. Her first flight was as STS-6 lifting off on the 4th of April 1983. She was taken to space over her operating life, the first African American, first woman, first Dutch person and be the first night launch and landing. She was used more often than Columbia between 1983 and 1986 making her the go to orbiter amassing 10 flights and over 62 days in orbit. But we'll have to talk about an issue with the shuttle program and it was around those solid booster rockets, the SRB. Those two solid booster rockets were vital to launch as they provided the most amount of thrust at the beginning. They were built by Morton Fire Corps. Each one consisted of multiple sections. Each section was constructed in Utah separately to be put together at the Kennedy Space Center ready for use for blasting an orbiter into the sky. Of course this requires a joint between the sections and this came in the form of a Tang and Cleavish joint. They were free in total for each SRB and they have several vital, especially important for this video components. So the Tang and Cleavish joint works like, hang on with me this is relevant to the disaster, like this. The Tang being the upper segment connecting the two sections by fitting into the lower Cleavish section. There is a retaining pin, clip and band placed to hold the two sections together. The joint is also externally wrapped with fiberglass reinforcement tape. To create the seal between the sections two rubber o-rings seals are employed. They run the entire circumference of the SRB and they are bonded to the case using an adhesive. The seal design was originally considered to be redundant as if the primary first o-ring failed then the secondary one could also be relied upon. As such the seal was rated as critical but a redundant setup. The gaps between the components were then sealed by zinc putty. The o-ring seals are vital in containing the hot gases produced from the SRB's motors during burning. During operation they would be compressed sealing the surface, thus stopping any unwanted flames out at the side of the boosters, which you know could be a little bit catastrophic but the system design was flawed. Issues were discovered in the early 1970s. This was that the o-ring wouldn't always compress and would instead extrude. NASA thought this was acceptable but the issues didn't end there. In 1977 a test discovered that the Tang and Cleavish joint could bend away from each other. This weakened the compression on the o-ring and thus reduced its seal effectiveness. The outer spec situation then allowed combustion gases to erode and damage the seal causing more gases to escape. The issue was further exacerbated when in lower temperatures as like with everything different materials expand and contract at different rates. This greatly concerned NASA engineers and they requested the redesign of the joint to include a shim to close the gap in 1978. One year later and not having received a response to their 1978 memo a second one was sent continuing to object to fire called solid rocket motor joint seal design. A test in 1980 showed yet again in a Tang-Cleavish relative movement was greater than originally predicted. In May 1980 the verification certification committee recommended that NASA conduct full scale tests to verify the field joint integrity including firing motors at a mean bulk propellant temperature range of between 40 and 90 degrees Fahrenheit. NASA replied NASA specialists have reviewed the field joint design updated with larger o-rings and thicker shims and found the safety factors to be adequate for the current design. Reanalysis of the joint with larger o-rings and thicker shims is being accomplished as part of the lightweight case program. The joint has been sufficiently verified with the testing accomplished to date. The first shuttle mission took place on the 12th of April 1981 all went well but just on the second mission STS-2 o-ring erosion was noticed but was found to be an infrequent problem over the coming years. O-ring was found in March and April 1983 and in February and August of 1984, the latter of which had discovered soot had blown past the primary o-ring. Even though after 1982 the o-ring's designation of redundant was removed and with evidence of blow by shuttle launches still continued, NASA would push the design beyond its temperature limits when in January 1985 the launch of STS-51C being the coldest space shuttle launch to date. The air temperature was 62 degrees Fahrenheit or 17 degrees Celsius and it was estimated that the o-ring temperature was 53 degrees Fahrenheit or 12 degrees Celsius. Surprise surprise both SRBs experienced o-ring erosion and blow by. Morton fire coal determined that the low temperature reduced the elasticity of the o-rings which in turn resulted in the gap not being fully filled which would then in turn lead to blow by of soot and gases. Nearly all of the 1985 launches resulted in o-ring deterioration. This prompted Morton fire coal to redesign the case however it was going to take some time and as such the original design was to be used till the replacement was available. This would cover the missions that would eventually run into the start of 1986. STS-51L So I'm not going to go into too much detail about the background of this mission however it was quite important in terms of boosting the public's opinion of the shuttle program. The orbiter Challenger was mated to her solid rocket boosters and external tank at NASA's Kennedy Space Center in Florida on the 17th of December 1985. The mission had been pushed back to January 22nd 1986 after a number of cancellations beginning in July 1985 then due to payload issues in November 1985. As such NASA really wanted to get Challenger into space she was built and ready to go and her crew were trained and eager to get on with it. One of the crew of STS-51B was the first participant of the teacher in space program, Krista McCulfey. Again the mission found itself delayed in January 1986 and was pushed back to the 28th. However there was an issue the air temperature was forecast to drop to 18 degrees Fahrenheit minus 8 degrees Celsius during the night before the launch date. This would mark a significant drop in lowest temperature the shuttle would ever be launched in. As such this actually caused some concern with Morton Firecalls engineering team. Blow by of the vital o-rings had occurred in warmer temperatures after all. A conference call was set up between NASA and Morton Firecalls engineers. In the call Morton Firecalls employees Robert Lund the vice president of engineering and Joe Kilmenster the vice president of the space booster programs advocated against launching until the temperature was above 50 degrees Fahrenheit or 12 degrees Celsius aka the lowest the shuttle had previously been launched in. But something about the mood had changed in communications between the Marshall Space Center and Morton Firecalls. Usually it would be a case that Morton Firecalls would have to prove that the SRBs were safe to fly. Understandable in an environment of if in any doubt don't risk it. However the Marshall Space Center had moved its position of to prove that the shuttle can't fly almost as if any doubt was no longer acceptable. Robert Lund would later say we had to prove to them that we weren't ready. So we got ourselves in the thought process that we were trying to find some way to prove to them it wouldn't work and we were unable to do that. We couldn't prove absolutely that the motor wouldn't work. He would also continue to say later on well but it's the kind of mode we got ourselves into that evening. It seems like we have always been in the mood in the opposite mode. I should have detected that but I did not but the roles had kind of switched. As such after a 30 minute break in the conference call to confer amongst Morton Firecalls staff management came to the conclusion that flying in low temperatures should in theory cause no more issues than when the shuttle flew at a temperature of 53 degrees Fahrenheit. When the conference call resumed Firecall came back saying that there was substantial margin in the event of failure and gave their final approval for flight on the 28th of January. Measurements overnight recorded lows on the left SRB of 25 degrees Fahrenheit or minus 4 degrees Celsius and the right SRB at 8 degrees Fahrenheit or minus 13 degrees Celsius. Ice had formed all over the fixed service structure. This caused concern with the orbiters manufacturer Rockwell International. They were concerned that ice could damage the orbiters thermal installation. However engineers at Kennedy and Johnson Space Centers advised that there was no issues with the ice. However an hour delay was ordered to allow the temperature to warm up a little bit. The launch was set for just after half 11 in the morning of the 28th of January. At 20 minutes before liftoff ice was seen to be melting and clearance for flights was given for 1138 a.m. The air temperature now was around 36 degrees Fahrenheit or 2 degrees Celsius. Time for liftoff. Six seconds before 1138 a.m. Challenges three main engines ignited. At T minus zero seconds the two solid rocket boosters ignited and challenger started to move. Almost immediately a gray puff of smoke was observed around the right booster's joint near the attachment strut. This was hinted at gas blow by due to the improper sealing of the O-rings. Just two seconds later however the smoke stopped. This was due to some of the solid fuel falling within the booster and temporarily sealing the gap. At 36 seconds post liftoff challenger experienced a severe wind shear. To counteract this the shuttle attempted to correct its trajectory. The change in yaw and pitch dislodged the solid fuel that had been acting as a plug and this was at an altitude of 3,000 meters or 9,800 feet. At around T 58 seconds another plume of smoke appeared around the same spot as before on the right SRB strut. Two seconds later the plume begins to touch the external tank. At 64 seconds a hole could be seen being burned into the tank. This caused a leak of liquid hydrogen fuel. Challenger's computer tried to counter the now lost in thrust from the right SRB. Capcom and the crew aboard the orbiter were still unaware of the unfolding disaster and at 68 seconds the instruction of throttle up was given. At around 72 seconds the crew felt a lateral load. Pilot Michael J Smith was recorded as saying uh oh. The pressure was falling in the external tank and thus was affecting the main engine's performance. At 73 seconds the aft dome of the external tank failed and at around the same point the right SRB rotated away from the strut. Moments later the whole vehicle began to break up. The altitude of Challenger was around now at 47,900 feet. The external tank was now fully disintegrating. Challenger was pushed against the airflow and was hit by aerodynamic forces resulting in a load factor of up to 20g. The orbiter separated from the external tank and continued to fly for another 30 or so seconds. The shuttle stack had been completely separated. In sections of the now disintegrated orbiter flying about in different directions hurdling back towards Earth. The crew compartment remained relatively intact. The force at separation was estimated to be between 12 and 20g but quickly dropped down to 4g and then free fall. It could then be seen falling through the sky. The crew cabin fell for approximately two minutes and 45 seconds after its separation eventually slamming into the Atlantic Ocean. At 89 seconds post launch the video Challenger was seen in mission control and now the full weight of the disaster began to sink in. NASA Public Affairs Officer Steve Nesbit would announce the explosion when just a few moments before he had been reading out stats from the flight data. He would say, We have a report of the flight dynamics officer that the vehicle has exploded. The flight director confirms that. We're looking at checking with recovery forces to see what can be done at this point. Recovery operations were dispatched immediately with the ship's MV Freedom Star and MV Liberty Star heading towards the crash site. However, due to falling debris recovery couldn't begin until 1237. Understandably hopes were held for any survivors but with an estimated impact force of the crew compartment with the sea being 200g it was very unlikely. By 7pm some recovered debris from the orbiter and external tank was found. With surface operations concluding on the 7th of February, subsurface operations ending the next day. However submarines and submersibles would scour the seabed around the impact area for SRB and crew compartment debris the months to come. Pieces of Challenger would continue to wash up ashore even as late as 2022 when a pretty large piece of around 20 feet long was discovered off the coast of Florida. The crew compartment would be found on the 7th of March 1986. The remains of the crew were removed on the 4th of April. However, one of the bodies floated away. This was Gregory Jarvis. His remains were recovered just over a week later. But what the public really needed to know now was how could such a tragedy happen to NASA of all organizations? Finding the cause. Now I'll say straight away as this video outline has hinted at that we know what the cause was. It was the poor decision to launch in cold weather but have reduced the effectiveness of the o-ring seal. But in January 1986 that wasn't exactly obvious. After all blow by had occurred several times before and the orbiter had completed many successful missions. The shuttle had over 2.5 million parts and it was the world's most complex flying machine. The investigation would be no small task. The presidential commission on the space shuttle Challenger accident was set up in February 1986 and it was tasked with sifting through thousands of documents photographs and statements. Although the failing o-rings was a big contender they did have to look at every potential avenue for disaster. The board included Chairman William P Rogers Vice-Chairman Neil Armstrong and then David Aikerson Eugene Covert Richard Feynman Robert Holtz Donald Kutcher Sally Ride Robert Rummel Joseph Sutter Arthur Walker Abbott Whelan and Chuck Yeager. The investigation would gain the name the Rogers commission after its chairman. The committee was split into four panels the accident analysis panel development and production panel prelaunch activities panel and the mission planning and operations panel. Each panel will contribute to over 160 total interviews over 35 sessions and would involve over 6000 employees from NASA and its main contractors over a period of four months. They were zero in violent extensive footage of the launch on the cause of the plume of hot gases that appeared on the right SRB next to the strut. The evidence was pretty damning of an instance of blow by. On the 11th of February during a televised hearing board member Richard Feynman produced a sample of SRB O-ring and placed it in a cold glass of water. Oh I took the stuff that I got out of your seal and I put it in ice water and I discovered that when you put some pressure on it for a while and then undo it it maintains it doesn't stretch back it stays the same dimension in other words for a few seconds at least and more seconds than that there's no resilience in this particular material when it's at a temperature of 32 degrees. This memorable moment helps solidify in the public's mind of the poor oversight that NASA had demonstrated. Feynman had been at odds with other members of the commission including his chair Rogers due to his harsher approach to investigating the evidence. He was much more critical of NASA management and their apparent lack of understanding of the risks that they had taken with not only the O-rings but other parts of the shuttle program. NASA's standards had seemingly dropped in order to keep up the busy schedule of orbit emissions which fostered a management culture of quantity over safety where blatant red flags were ignored. We can see this in Robert Lund's statements after the disaster. I mentioned earlier that he felt the culture had changed from prove safe to prove it won't be safe. Feynman's criticisms and investigation would appear in the report's appendix F. His conclusions were pretty harsh. Feynman would say if a reasonable launch schedule is to be maintained engineering often can't be done fast enough to keep up with the expectations of originally conservative certification criteria designed to guarantee a very safe vehicle. In these situations in these situations subtly and often with apparently logical arguments the criteria are altered so that flights may still be certified in time. They therefore fly in a relatively unsafe condition with a chance of failure of the order of a percent. It was a clear case as of what sociologist Diane Vaughan would coin of normalised deviance which is the normalisation of clearly unsafe practices. Exactly what happened with the first case of O-rings blow by. Just because it didn't cause a disaster doesn't mean it was safe but NASA a molten fire call carried on regardless. The disaster would result in the redesign of the SRB where the joint's tang would have a reduced risk of rotation. NASA also reevaluated other parts of the shuttle project which wouldn't have saved the Challenger's crew but would overall improve safety of future crews in a multitude of different events. And now for the slightly grim part of when did the crew perish. Although the exact moment isn't known it's likely some survived post separation as some switches have been operated that couldn't have been done so by the impact. The crew were failed that day by a culture of safety ignorance. Of course space travel can't be 100% safe but Challenger really shouldn't have flown that day. Feynman in his conclusion to appendix F would rather eloquently say I think it best describes the situation. For a successful technology reality must take precedence over public relations for nature cannot be fooled. Pretty poetic if you ask me I definitely recommend reading the full Feynman appendix F section as he was obviously a genius. So that's it my video on the Challenger disaster. Although it is a little bit longer than my usual videos I still feel as if I've barely even scratched the surface. I highly recommend reading the Challenger launch decision book by Dianne Vaughn. I'll put an Amazon affiliate link in the description if you decide to buy it it helps out the channel with a little kickback. So if you want me to cover the Columbia disaster let me know in the comments but I do also fear that it will be quite a larger video. Please feel free to comment like and subscribe hit the bell and all that jazz I'm really trying to push for a million subscribers because why the hell not. And all I have to say is thank you for watching and Mr Music place out please.