Ep 44 Challenger Space Shuttle
Engineering News – Surgical Sticky Tape (2:25)
This week's engineering failure is the Challenger Space Shuttle (6:20). 73 seconds after take off, the Challenger exploded (14:45) on live TV. While ultimately a pair of O rings were to blame (23:55), a full investigation occurred (26:55) and found that there were several procedural issues at play.
Challenger Space Shuttle
Hi and welcome to Failurology; a podcast about engineering failures. I’m your host, Nicole
And I’m Brian. And we’re both from Calgary, AB.
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This week in engineering news, surgical sticky tape to repair the GI tract
Like duct tape to a pipe, except this one actually works
Developed by engineers at MIT
Strong, flexible and biocompatible sticky patches can quickly and easily be applied to tears and wounds in tissue and organs.
Currently these tears are repaired with surgical sutures which can trigger scarring, and allow secondary tears on adjacent tissue. Brian, did you know the leakage rate for GI tract repairs is 20%?!?
The adhesive binds within seconds and can hold for over a month, which is long enough for the tear to heal in most cases
The tape is also flexible and can expand and contract with the organ as it heals
Over time the tape dissolves without causing inflammation and sticking to surrounding tissue
The engineering team started out to create double sided tape, but after consulting with surgeons they thought that single sided would have a larger impact with more applications.
If you want to read more on the surgical sticky tape, check out the links to sources on the web page for this episode at Failurology.ca
Now on to this week’s engineering failure; the Challenger Space Shuttle
We want to mention that there is so much information on this accident. So much! And it is impossible for us to cover every single piece. So we decided to touch on a bit of everything, but focus mostly on the things we thought were interesting and the important takeaways to prevent these types of things from happening again. Which I hope is what you love and expect from us and why you keep coming back for more interesting engineering failures.
Jan 28, 1986
Was originally scheduled for July 1985, then November 1985, then January 22 1986 before finally landing on January 28th.
I have to wonder if the shuttle launched in July or summer weather, would it have exploded?
Space shuttle Challenger broke apart 73 seconds into flight, killing all seven crew members on board and witnessed by millions on TV. including many US children who were viewing the launch in school as part of the Teacher in Space program.
The Challenger Orbiter had:
10 flights - the spacecraft was partially reusable (the orbiter section was the reusable part that was launched vertically and could land as a glider)
Almost 1,500 hours of flight time
Travelled 41.5 million km around Earth
Orbited the Earth 995 times
First flight was on April 4-9 1981
Primary use was to conduct in orbit research and deploy commercial, military and scientific payloads
For this launch, the shuttle consisted of the orbiter (crew and payload), the external tank and two solid rocket boosters. The rocket boosters allowed initial take off, burned for two minutes and then separated and fell into the Atlantic under parachute. The external tank provided fuel to the orbiters smaller orbital manoeuvring system engines
There were two O rings which offered redundancy, and they were noted as Criticality 1R which mean that failure could result in destruction of the shuttle and loss of life
There were 7 crew members on board
Commanded by Francis Scobee
Piloted by Michael Smith
Mission Specialists - Ellison Onizuka, Judith Resnik and Ronald McNair
Payload specialists - Gregory Jarvis and Christa McAuliffe (Christa was supposed to be the first teacher in space)
The intent of the mission was to deploy a communications satellite and study Halley’s Comet
It launched from launch complex 39B Cape Canaveral, Florida at 11:38am eastern and disintegrated into the Atlantic Ocean
I don’t think this necessarily played a factor in the accident, but fun fact, the Challenger had launched from launch complex 39A for its first 9 missions and this was the first launch from 39B.
This is the same launch site as Apollo 1 that we covered in episode 34. Apollo 1 launched from launch complex 34. Launch complex 39 is about 15km north of launch complex 34.
For the first 4 seconds of the launch, 9 puffs of dark grey smoke were recorded escaping from the right hand solid rocket booster near the aft strut attaching the booster to the external tank
The investigation determined that these smoke puffs were caused by the joint rotation. The cold temperature prevented the O rings from creating a seal
At about 59 seconds into the launch, a plume of smoke was seen near the aft attach strut on the right solid rocket booster
A leak began in the liquid hydrogen tank of the external tank at 64 seconds
At 68 seconds flight controllers told the crew to throttle up to 104% thrust. The crew replied with “Roger, go at throttle up” which was the last communication
At 72 seconds, the right solid rocket booster pulled away from the external tank, causing lateral acceleration that was felt by the crew. At the same time, there was a large fireball on the side of the external tank. The pilot said “uh-oh”, this was the last speech recorded by the crew.
At 73 seconds, an explosion occurred and engulfed the external tank and orbiter.
The Challenger was at 14km (46,000ft) elevation at the time and broke up into several large pieces. It was going Mach 1.92 at the time.
After a 3 month search and recovery, they recovered many segments and fragments from the ocean floor
This is really sad and morbid, but…. They believe that several crew members survived the initial breakup of the spacecraft, but not the impact at terminal velocity with the ocean surface. The shuttle had no escape system.
The cabin was made of reinforced aluminium and remained in one piece after the explosion
Three crew members activated their personal egress air packs which provided 6 minutes of breathable air
When the cabin hit the ocean surface it was going 333 kph (207 mph) about 2 minutes and 45 seconds after breakup
Unfortunately, launch escape systems were not considered during shuttle development and NASA thought the expected high reliability of the shuttle meant it didn’t need an escape mechanism. Escape options were also complex, high cost and heavy weight.
Failure of two redundant O-ring seals in a joint of the solid rocket booster
The low temperatures of the launch reduced the elasticity of the rubber O-rings and they could no longer seal the joint
Engineers recommended against launching until the temperature was at least 12C. The forecast for Jan 28th was -8C overnight and -3C by 930am. Overnight measurements of the solid rocket boosters recorded -4C for the left and -13C for the right. Temperature at the time of the launch was 2C.
Not exactly the same, but this is why I have winter tires.
When the seals didn’t seal, there was a breach in the joint shortly after liftoff allowing the pressurised gas within the booster to burn through the walls to the external fuel tank
Ronald Reagan, president at the time, created the Rogers Commission to investigate the Challenger Shuttle accident
Failure of the aft casings joint in the right hand solid rocket booster
NASA’s organisational culture and decision-making processes - we saw similar problems in the Apollo 1 accident 19 years and 1 day earlier. It’s interesting that both of these occurred in January. Although I don’t think the temperature was an issue for Apollo 1 as it was for the Challenger. But it's fascinating how things like winter weather, which we are so used to in Canada, can debilitate an area that doesn’t usually experience those types of conditions. This seems pretty straightforward as I say it out loud, but it always takes me a second to understand places that don’t have winter.
Test data from as early as 1977, 9 years before the accident, showed how big of a design flaw and how big of a risk of failure the O rings were. Despite warnings from NASA engineers, NASA management and the manufacturer found the wide tolerances to be acceptable.
The NASA engineers also warned managers about temperature concerns launching in January, but they didn’t listen. I’m shocked…
Correcting the joint seal problem was possible by redesigning and manufacturing new joints before the accident, but schedules and costs were higher priority than flight safety - good thing that’s not the case anymore… wait… just kidding, this hasn’t changed at all
One important thing to note is that there was no evidence of joint contamination, fracture or other damage contributing to the accident.
With respect to the o-ring specifically, as the joint rotated, the tang and clevis bent away from each other, reduced pressure on the o rings, weakening their seals, allowing the combustion gases to erode the O-ring. The O-ring could no longer contain the burning propellant gases under the range of operating conditions expected during take off and flight, but on top of that, the materials are made from recipes only known by the manufacturer which can be changed without certification or approval. This has hopefully changed with strong specifications and requirements for quality control, but this is huge.
The field joints of the solid rocket booster should have been redesigned to provide the following features and much improved factor of safety
Movement in the joint
Proper spacing between tang and clevis - the two arms that make up both sides of the joint. The tang would be the plug (male) side and the clevis would be the socket (female) side.
Seals that can withstand high and low temperatures as well as all dynamic thermal and structural loadings
The o rings can adequately seal without the use of a putty
Protection against insulation debonding and propellant crackings
The decisions to launch was based on a faulty engineering analysis of the joint seal behaviour
The Shuffle Safety, Reliability and Quality Assurance Program failed to exercise control over the problem tracking systems, didn’t critique the engineering analysis, and didn’t provide an independent perspective during Flight Readiness Reviews
Pressure from management led to the discounting of proper technical concerns and engineering judgement
They decided to launch despite uncertainty represented by ice forming on the Fixed Service Structure and didn’t make a reasonable effort to mitigate avoidable risks to the Shuttle. In fact, the launch shouldn’t have been permitted until the ice was cleared from the platform.
The Launch Director didn’t place safety above all else with regards to launch readiness
There seemed to be differing requirements to define readiness, leading to failures in communication between NASA and its contractors.
The investigation found that the fuel tank itself, while it did explode, did not contribute to the accident in that the forces of the failed solid rocket booster are what ruptured the fuel tank wall and were forces above and beyond reasonable design considerations.
32 month hiatus of the Space Shuttle program
The Endeavour launched in 1992 to replace the Challenger, with redesigned solid rocket boosters. As well, the crew wore pressure suits during take off and landing
The surface recovery efforts reached 12 aircraft and 8 ships by 7pm on the day of the accident and lasted until February 7th
The sub surface recovery efforts reached sixteen ships and got underway on February 8th and lasted until April 29th
So there you have it, two little O rings led to a catastrophic explosion of the Challenger space shuttle 73 seconds after lift off.
For photos, sources and an episode summary from this week’s episode head to Failurology.ca. If you’re enjoying what you’re hearing, please rate, review and subscribe to Failurology, so more people can find it. If you want to chat with us, our Twitter handle is @failurology, you can email us firstname.lastname@example.org, or you can connect with us on Linked In. Check out the show notes for links to all of these. Thanks, everyone for listening. And tune in to the next episode where we’ll talk about Kowloon Walled City, what was once the most densely populated spot on Earth.
Bye everyone, talk soon!