I gather Russian launches don’t have spoken countdowns. Different traditions, I guess.
If you read some technical books about say the Apollo programme, you will find that the countdown is a very detailed process, mostly automated, where certain things happen at different times, certain aborts can be generated before certain times but not afterwards, etc.
The voice countdown is largely for the media.
Bit of thread drift here but there’s a nice documentary about Saturn V being repeated on the pbs channel at the moment. It covers the combustion instability problem.
An old boy working as a volunteer guide at the Huntsville museum told me an interesting story. He’d been a senior engineer on the F1 engine at the time and said they’d never really understood the instability problem in those days before computer modelling. In the film, there’s a clip of baffles being installed on the injector plate. He said all of this was totally empirical, and they kept on trying until they found a configuration that worked. That meant every flight engine had to be tested live for instability.
The way they did that was to wire an explosive! charge inside the engine and set it off once the thing was running. If the resulting instability subsided, the engine passed for flight. Made me think of the Superior problem referred to elsewhere!
Don’t know if that story is in any of the books that Peter refers to.
Oh, and I believe that the ‘countdown clock’ was originally a sort of mechanical uniselector thing that activated stuff directly, which was why the spoken count was important.
The Russians have them as well as far as I recall.
Whenever time related events and their synchroneous happening are of essence, countdowns are great ideas. I have seen them used in formation flying as well as for other timed events when several people need to trigger an action at the same time.
I also recall that Concorde used a 3 second countdown for applying take off power. Even more amazingly, both the French and Brits did it.
The way they did that was to wire an explosive!
Yes that is correct, though my recollection is that the explosive business was used only during engine development. They had to get the nozzle configuration, the fuel pressures, etc, just right, for stability. The Germans had the same issues on the V2 and solved them adequately there.
was originally a sort of mechanical uniselector thing
Yes; it would certainly not have been a “digital timer” back then.
There is a massive amount of NASA docs out there, for the proper anoraks among us 
Peter wrote:
the explosive business was used only during engine development
He assured me that this was part of the flight qualification process for every individual engine. Another anecdote concerned the winding of the engine bell, which can also be seen in the film I referred to. The bell was entirely formed from wound stainless (or something) tubes which were hand formed as the bell was built up. You can see this in the film, I think. Apparently this was all hand work and there was only one guy who could be trusted to do it – on all the engines! When he retired, so did the F1 engine! Apparently.
PS I seriously recommend that Huntsville museum, if you ever get the chance. The guys there are for real, and they’re not getting any younger…
Timothy wrote:
All the serious answers you read online (there’s a complex sequence of events that have to be done, in order, to launch within a window) are as applicable to launching an airliner, or indeed an MEP.
But usually launching an airliner or an MEP isn’t timing critical – the airport you’re going to isn’t moving relative to you at 7.66 km/s. Launch windows can be quite narrow because you’re trying to meet up with certain objects in orbit or be in a certain place in a certain time without wasting precious delta-V capability. If an airliner launches a minute late it’s no big deal. But a minute late or early can be critical if you’re trying to meet the ISS.
Also due to the tyranny of the rocket equation you don’t have luxuries like carrying huge amounts of extra fuel. Take Apollo 11 for example – the LM landed with less than 30 seconds of fuel in reserve. Timing becomes pretty critical when the margins are that wafer thin, and we are at the limit of our technological capabilities.
Timothy wrote:
All the serious answers you read online (there’s a complex sequence of events that have to be done, in order, to launch within a window) are as applicable to launching an airliner, or indeed an MEP.
Don’t tell me you don’t do a countdown to takeoff? I thought everyone did
