Bit of a specific one here but, I was looking at the Wikipedia article on the timeline of STS-51-L (Challenger disaster) today and I couldn’t figure out what one of the events meant.
A point came during the vehicle breakup when the high pressure fuel turbopumps were approaching their redlines. This I understand. The next event seems to be the final communication from the number two engine: “Channel A votes shutdown, two strikes on channel B”.
What the hell does this mean?
In: Engineering
the shuttle had 2 computers, which were both running the same code. the idea was that the two computers would cast votes on important decisions, and that normally they’d agree, but if one of them had an error (a glitch really) then the voting outcomes would be different and the error could be caught and an overruling decision would be made by the astronaut. From what you’ve written, it looks like computer A wanted to shutdown the engine. Not sure about 2 strikes on channel B, maybe astronaut slang for saying that channel B agreed with A?
Edit: Apparently the shuttle used a triple-redundant avionics computer, so there would be a majority vote on decisions ie: 2:1 against or for.
Edit edit: But the main engine controller was dual redundant
Hi, retired Shuttle engineer here/manager of Atlantis OPF post Columbia. I coukd explain more about Columbia as I worked on the reconstruction committee, but will try to keep your question as EILI5 as possible.
The space shuttle had several types of computers, and buses, all in control of different things, yet they could all over ride each other in the main scheme of things.
The final data bits your referring to are broken bits, and not reliable. They are part of a “redline” shut down. As the ET broke up from aerodynamic forces after the top of the booster swung into it, it disrupted fuel flow to the engines. But they still had fuel in the system. We redid the shutdown codes after bad sensors caused an abort to orbit on 51-f.
As the first tank ruptured, the engines began running rich for a few Microsoft seconds, so they tried to compensate, but couldn’t. The vehicle at this point was breaking up, and the engines were pushing through the afternoon of the cargo Bay.
Now is where your question comes in. The engines new something was wrong, and we’re attempting not only to fix their fuel flow rate, but we’re still gimbling trying to keep the shuttle on course, but by now their was no shuttle and full breakup had occurred. The 3 APUs (Auxiliary Power Units) were now destroyed or cut off, so any power or transmissions past this point are unreliable, and most likely static garble. But most likely, it was the engines signaling that they were getting ready to drop out from low fuel pressure.
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