Shuttle engine question

Are the main engines cooled by liquid hydrogen, or by a mixture of water and something else? I am pretty sure that they use hydrogen bled off before injection, but a guy here at work seems to think otherwise.

Camaronat wrote in
:


Are the main engines cooled by liquid hydrogen, or by a mixture of water
and something else? I am pretty sure that they use hydrogen bled off
before injection, but a guy here at work seems to think otherwise.

As with most any liquid fuel rocket engine, the SSME is cooled by
its own propellants before burning them. In this case, liquid hydrogen
is pumped through the wall of tubes that form the exhaust nozzle and
combustion chamber. Because it is a closed cycle design, the warmed
hydrogen carries the removed heat back into the combustion chamber
so no energy is lost.

Kerosene, LOX or hydrazine are used in the same way in other liquid
fuel engine designs. The RS-68 used on the new Delta IV is a bit
different; the nozzle has an 'ablative' lining that burns off, pretty
much like any large solid fuel rocket. But the nozzle throat and
combustion chamber are still cooled by the liquid hydrogen.

Smaller rocket engines that operate at somewhat lower temperatures
can get away with radiation cooling of the nozzle.

A separate cooling system would require a lot of mass of water or
some other coolant that would have to be dumped as it is used. This
would be very heavy to carry along and would waste payload.

--Damon

Originally Posted by Damon Hill

Camaronat wrote in
:


Are the main engines cooled by liquid hydrogen, or by a mixture of water
and something else? I am pretty sure that they use hydrogen bled off
before injection, but a guy here at work seems to think otherwise.

As with most any liquid fuel rocket engine, the SSME is cooled by
its own propellants before burning them. In this case, liquid hydrogen
is pumped through the wall of tubes that form the exhaust nozzle and
combustion chamber. Because it is a closed cycle design, the warmed
hydrogen carries the removed heat back into the combustion chamber
so no energy is lost.

Kerosene, LOX or hydrazine are used in the same way in other liquid
fuel engine designs. The RS-68 used on the new Delta IV is a bit
different; the nozzle has an 'ablative' lining that burns off, pretty
much like any large solid fuel rocket. But the nozzle throat and
combustion chamber are still cooled by the liquid hydrogen.

Smaller rocket engines that operate at somewhat lower temperatures
can get away with radiation cooling of the nozzle.

A separate cooling system would require a lot of mass of water or
some other coolant that would have to be dumped as it is used. This
would be very heavy to carry along and would waste payload.

--Damon

Thanks, that is exactly what I thought. I just wanted to make sure I wasn't going insane.