Wiki mentions “the system designed to pump high-pressure helium from the launch pad into the first stage turbopumps, which would get them spinning in preparation for launch.” These pumps, I assume, are related to the fuel delivery system for the primary rocket motors, and thus must be very high capacity. This would necessitate a lot of horsepower (energy) to drive them.
If so: What is the energy source for these pumps… in flight?
Turbopumps have a pump section which is powered by a gas turbine that extracts power from a hot/pressurized gas stream.
Here’s a schematic for a space shuttle main engine; looks like they use separate pumps for the fuel and LOX, and they send a little bit of LOX over to the fuel pump’s turbine, and a little bit of fuel over to the LOX pump’s turbine. That little bit of combustion (with lots of diluent) provides the power needed to drive the pump, while keeping temps in the turbine low. The big combustion for producing thrust doesn’t happen until you get to the main combustion chamber.
The SSME engine is much more complex than Space-X’s Merlin engine. The Merlin uses a simple gas-generator cycle, where fuel is simply piped to a small combustion chamber and the hot gas that results is used to drive a turbine, which has the pumps on the same shaft. The exhaust gas from the turbine is simply piped away. Staged and combined cycle engines (for instance the SSME) are much more difficult, as they try to make use of the waste gas from the turbine, and inject it into the main combustion chamber to eek out every last bit of energy from the fuel.
The trick with starting an engine up is to note that in many engines the gas generator is fed with pressurised fuel - which is pressurised by the fuel pumps. OK, so how do you get the fuel pumps running if we need them running to feed the gas generator. So you need to work out how to spin the pumps up enough that they can deliver enough fuel to the gas generator to get the entire system to start up. There are many ways of doing this. Really just limited by the imagination of the designers.
Power? Yes, silly power. The SSME has two turbo pumps, one for fuel, one for oxidiser. From memory the fuel pump runs at about 80,000 hp. The F1 engines on the Saturn V had a single turbopump assembly for bot fuel and oxidiser, and needed about 60,000 hp from the turbine.
Missed the edit window.
If you want to see the power involved here is a recent test of an F1 engine gas generator. Remember, this is only going to power the turbine that runs the fuel and oxidiser pumps.
This youtube video by Scott Manley gives an excellent explanation of how different types of rocket engine pumps work.
Very informative answers.
Thank you all very much!
There IS good info in that video but I feel I must warn others that it is 90% some dude on his couch babbling to the camera, which I usually cannot stand. I’d rather just read a transcript. But again, it is good info and my problems with jabbering heads might just be my own.
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