What Happens During a Last Second Shuttle Launch Abort

Holy Moly! Not to wish anything like this for Saturday’s launch, but I came across this video of the STS-68 launch attempt in 1994 that was aborted at the very last second. Watching it is enough to make your heart stop. Everyone involved must have experienced a tremendous rush followed by extreme let-down! The main engines had lit, but were shut down 1.9 seconds before liftoff when on-board computers detected higher than acceptable readings in a sensor monitoring the discharge temperature of the high pressure oxidizer turbopump in main engine #3. In the history of the shuttle program, five launch attempts were aborted under five seconds from the planned launch. STS-68 came the closest to hauling the mail before being aborted.

The main engines light at six seconds before launch, and within that time, the on board computer decides from hundreds of inputs and constraints if it’s safe for the three liquid fueled engines to keep burning and whether to light the two solid rocket boosters. Once the solids light, there’s no turning them off.
In STS-68’s case, the computers noted the anomaly and shut everything down in about four seconds of time.

Endeavour had to be brought back to the Vehicle Assembly Building to be outfitted with three replacement engines. A test firing of the original engines confirmed that a slight drift in a fuel flow meter in the engine caused a slight increase in the turbopump’s temperature. The test firing also confirmed a slightly slower start for main engine #3 during the pad abort, which could have contributed to the higher temperatures.

The other launches that aborted under five seconds were STS-41 D in June of 1984 which went down to 4 seconds before launch before calling it quits, and these three were stopped at 3 seconds before launch: STS-51 F in July, 1985; STS-55 in March 1993, STS-51 in August 1993.

Here’s a link to a video with a compilation of all five launch aborts, (and includes STS-93 which aborted with 7 seconds to go) and here’s a link to an article that describes what a crew would have to do if they were forced to bail out of the shuttle before launch because of an expected explosion. Yowza!

Hat tip to SpaceKiwi and DrLucyRogers on Twitter!

8 Replies to “What Happens During a Last Second Shuttle Launch Abort”

  1. Interesting that, it appears from the video compilation, it wasn’t until STS 51 in 1993 that the water spray around the main nozzles was used after a main engine cutoff on the pad. I suppose these things get added as extra safety features over time.

  2. Luckily all these aborts preceeded the SRB ignition or we’d be talking a whole new scenario here 🙂

  3. Scary and amazing that they have this procedure.

    What’s also scary is that the shuttle is swaying back and forth for quite a while. When the abort system kicks a bright light is lit up and it’s visible edge of the fuel tank. As the whole thing sways back and forth the tank partially blocks the light, diming and brightening.

    Starting at the 2:15 marker, moving the slider back and forth will show the swaying.

  4. Bummer: NASA just concluded a 1:45 AM ET news conference (on NASA TV June 13th) saying todays’ launch is scrubbed until next Saturday, at earliest, due to a leaking external hydrogen fueling connector. NASA says it needs to effect repairs in the VAB and then move it back to the pad with an expected 4 day turnaround . As if this was not bad enough, the Shuttle team must wait until LRO/LCROSS launches (in a very small launch window) on June 17th. This would push the next earliest Shuttle launch attempt towards a June 20th date 🙁

  5. @ND: Watching the many replays and views of the launch (on NASA TV) from both the ground and external cameras on the SRBs and the main fuel tank, it is quite noticeable that the entire vehicle sways back and forth on the pad until the SRBs ignite and launch locks are released. My favorite views of the ‘swaying’ shuttle come from cameras mounted on the launch tower (particularly near the top of the shuttle) . Also, the camera in the astronaut entry platform usually shows some of that shaking going on, just before it is rotated away from the Shuttle . It was quite a surprise to me to see the amount of sway in this massive vehicle prior to clearing the tower 🙂

  6. Jon,

    Yes indeed. And the swaying is the greatest at the top where the astronauts sit 🙂 ugh. I don’t think I could handle that let alone blast off into space. Would love to be weightless tho.

    The SRB videos are great. I downloaded one that’s a complete, uninterupted shot from launch to splashdown from a camera looking down.

  7. Then of course we had Gemini 6’s launch abort, which still stops my heart every time I see it on film. After films of V2 failures, and particularly the explosion of the X-15’s XLR-99 engine in a manned ground test (see Scott Crossfield, “Always Another Dawn”), I’m still conditioned to an unexpected shutdown being followed by an explosion.

    The worst case of the ‘rock’ was STS-1, where the stack nearly fell over. You can see it very clearly in the IMAX ‘The Dream Is Alive’.

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