How A Gold Bullet Almost Destroyed A Space Shuttle

oh it's Scott Manley here and today is a story of how a golden bullet almost destroyed a space shuttle the year was 1999 the flight sts9 teeth wreath a 90 v launch of the space shuttle program this would be the first one commanded by women Eileen Collins who had previously flown a couple of times and she would be trusted with the heaviest payload ever launched on a space shuttle the Chandra x-ray Observatory and its inertial upper stage required to inject into its target orbit this would be 20 tons of hardware and no other payload would be as heavy in part because of the heavy payload the crew was smaller than usual only five were onboard and carrying all of this would be Columbia NASA's oldest orbiter and it had been showing its age it had you know short got a bit of wear and tear there were a few things that were a little iffy with it and yours really important to keep in mind that for a launch of any rocket to be successful 100 things have to go right but for a failure only one thing has to go wrong the Space Shuttle Orbiter is propelled by three rs.25 engines and they are still considered to be exceptionally good engines the plumbing is pretty complicated roughly speaking what happens is the liquid hydrogen is first fed and through the engine through cooling channels throughout the structure in particular the walls of the combustion chamber and the nozzle have a liquid hydrogen flowing through them and the heat of the combustion will vaporize this now the vaporized hydrogen is then passed back through a turbine where it's combined with a small amount of oxygen to create energy that then drives the pumps finally these hot exhaust gases are then passed through to the main combustion chamber where they flow through an injection system where the rest of the oxygen is added and that is there where you get your thrust now in this final mixing stage the oxygen has to run down a series of small pipes where the hot hydrogen gases run over the top and that heats the oxygen these pipes are called oxygen inject reports and there would be about 600 of these in every engine these inject reports we have to be inspected after every single flight and any if any of them looked like they might be showing some fatigue they would have to be disabled and rendered inoperative an engine could operate just fine with a few of these posts disabled and over the lifetime of the shuttle program over 200 would be modified in this way if a post would break off during the engine firing it would be catastrophic and it would almost certainly lead to the destruction of the engine and probably the loss of the shuttle and crew so engineers would disable these posts by wedging a gold pin into the root of the post in the case of STS 93 one of the engines had a disabled post and when the engine started that gold pin came free and was forced down the post by the pressure of the gas behind it it would have emerged with great speed and energy into the combustion chamber like a bullet but the fury of that contained explosion ins in there just deflect this chunk of metal around like it was a leaf on the wind it curved through the throat and impacted on the inside of the nozzle extension if you remember I mentioned that the hydrogen is first running through the walls of the nozzle the nozzle isn't just a simple sheet of metal it's actually over 1,080 loops of metal tubes all welded together and just think about this for a moment this video is your 1080p that's 1080 pixels now imagine welding every row of pixels together these pipes carry the liquid hydrogen to cool everything and always one side the engine Bell is so called that ice will form while on the interior the exhaust is hot enough to boil iron supposedly the engineers looked into failures and they determined that if five of these adjacent pipes were damaged then the loss in cooling in that spot would quickly result in a burn through and the destruction of the engine loss of the orbiter loss of the spacecraft and the crew that gold pinned when it impacted tore open you can actually see in this image where the hydrogen was leaking out into the exhaust naively you might think that this would lead to fuel being used up faster and the engine being at risk of running out of hydrogen before it reached orbit and this would be very bad hydraluxe engines all run fuel-rich because unburned hydrogen is very light and it makes the engine more efficient but also having the reaction being non-stoichiometric that is not the perfect ratio keeps the air reaction burning cooler if the fuel ratio actually changes to include more oxygen it'll get hotter so this can be very bad for example if the fuel supply starts to tail off and the oxygen continues to flow at full speed that will slide your mixture ratio toward stoichiometric things will overheat there'll be no cooling and all that excess oxygen will start to attack the engine so when loading the Space Shuttle they always made sure the fuel tank would have extra oxygen compared to the hydrogen to make sure the oxygen would always be the thing that would burn out first of course the rs.25 engines were controlled by computers with an array of sensors that would make sure the engine was running correctly they could sense something was wrong however because the hydrogen flow sensors were all located upstream from the leak it couldn't see that hydrogen was leaking from the system what it could see was the chamber pressure had dropped so in response it opened the oxygen valves a little more to increase the amount of thrust now this increased the chains of mixture ratio as a result everything got hotter in fact that point 3% leak of hydrogen led to 50% of the safety margin being used up in the engine and after the engines of course there is Mission Control normally Mission Control would be right on top of this kind of thing trying to diagnose the problem but this was not the only problem on this launch hundred copy liftoff [Applause] a booster lost controller done see lost center engine a right engine P looks like something on a c-1 the engineer in the propulsion could console was focused on a big red warning light telling him that one of the Boosters had no hydraulic fluid the Boosters used hydraulics to gimbal the nozzles and steer the launch vehicle without this the shuttle would go out of control and in a worst-case scenario might start heading for a populated area fortunately this fluid indicator was merely the symptom of a cable that had come loose during the first few seconds of launch the astronauts on board they didn't see any of this but what they did see was a warning light telling them that their fuel cell pH was wrong the fuel cells on the space shuttle generate electrical power by reacting hydrogen and oxygen in a controlled manner fuel cell pH indicated that the fuel cell was breaking down and that controlled reaction could quickly become an uncontrolled reaction with explosive consequences again this was a false reading but the real problem was still pretty dramatic an electrical cable was shorting out and phantom electrical signals had triggered the fuel sensor before the circuit breakers had shut it down to isolate the fault the cable had been slowly damaged over 20 years flight because a screw head had a small burr in it probably because some overzealous engineer had tightened it too much during assembly and we that cable represented one of the redundant power buses and when it went offline it also took two of the engine controllers offline of course each engine has two computers and main computer and a backup the center engine was forced to switch to his back up after his primary computer lost power either computer was capable of controlling the engine but the primary computer sent more detailed telemetry submission control lost most of the telemetry for this center engine and another was running way hotter than it should there was also another consequence of the computer failure in the center engine the computers each have their own set of sensors and norm they would average this data in the case of the center engine the backup computers pressure sensor was reading high and when the primary computer shut down the backup choose to slightly throttle down the center engine because it thought it was running too high I've heard that this may actually have been a stroke of luck that reduced the overall oxygen consumption and saved the mission but anyway in the end the flurry of failures didn't cause a mission failure the shuttle squeaked into orbit with the engines shutting down a hundred and fifty milliseconds early due to low oxygen the vehicle was within fifteen feet per second of its target speed and the mission subsequently proceeded as normal with no extra ohms one burn needed to get into orbit after ditching the external tank and running through post launch checklists one of my favorite Mission Control exchanges can be heard as for the crew they didn't have much they could do to remedy the situation the only action they took in response to the situation was to disable the AC bus sensors this would prevent the possibility of any of the other two electrical busses going offline automatically if there were other transient signals or glitches the other thing that astronauts do during the ascent is prepare for abort scenarios many of the calls to Capcom to crew is going down the list changing the modes of the abort system if the orbital under speed had been greater they might have had to burn a lot of ALMS fuel to make up the difference beyond that they might have been forced to abort and land without deploying the payload there's two possibilities that might have come here one would have been a transatlantic abort four they didn't quite make it into orbit they would skim across the Atlantic and land in Africa but if they got into a low orbit that couldn't be sustained there's abort once-around option where they would fly around and land back in the US and for what I can tell Chandra was a very sensitive device had it been returned to Earth in the payload it would have been torn down and rebuilt to ensure that it was still working before it was relaunched but these days it's still working has been going for 19 years of its five-year mission I'm Scott Manley fly safe [Music]

Channel: Scott Manley

Views: 645,238

Rating: 4.9185138 out of 5

Keywords: space shuttle, disaster, rocket, nasa, rocket science, sts-93

Id: u6rJpDPxYGU

Length: 11min 25sec (685 seconds)

Published: Mon Aug 13 2018

Reddit Comments

[u/Triabolical_]

For more on this see Wayne Hale's excellent series of posts. Make sure to read them in chronological order:

https://www.google.com/search?q=wayne+sts-93&rlz=1C1GCEA_enUS762US762&oq=wayne+sts-93&aqs=chrome..69i57.3565j1j7&sourceid=chrome&ie=UTF-8