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Sep 19, 2014, 08:58 PM
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Replacing the RD-180


Jeff Bezos has a way of showing up everywhere & where you least expect it. It wouldn't be surprising if the 2016 election happened, everyone voted for either Hillary or Biden & the winner was Bezos.

So after introducing the Kindle Voyage on Tuesday, Bezos was selected to produce the replacement for the RD-180 engine on Wednesday, pending a government contract. The BE-4 engine exists only in drawings, would burn liquid methane & liquid oxygen, & produce 550,000 lbs of thrust. 2 would power the Atlas-6 with slightly more than the RD-180's 933,000lbs.

Methane is now the fuel of choice in rocket engines. Now a rough comparison of the efficiency of the current fuels:

RS-25 LH2:
Isp (SL) 366 s

Raptor (conceptual methane engine):
Isp (SL) 321 s

RD-180 kerosine:
Isp (SL) 311 s

Merlin kerosine:
Isp (SL) 282s

Space shuttle booster:
Isp (SL) 242s

There could be a slight advantage in developing a methane 1st stage engine, depending on the cost of handling cryogenic methane, density, & mixture ratio.

Kerosene density: 810kg/m3
Liquid methane density: 422kg/m3
LH2 density: 71kg/m3

It needs twice the fuel tank size to get 10 more seconds of impulse.

Obviously, the change requires a new rocket, not just strapping on the new engine & putting cryogenic methane in the kerosine tank. It's hard to believe the program won't grow into a new Atlas 6, with a new EELV contract. Once again, what started with importing the RD-180 documents intending to replicate the engine becomes designing a new engine, then designing a whole new system because you might as well.

Of course, the voters could decide Russia isn't a problem & stick with the RD-180. It's going to be impossible to finance a methane 1st stage engine without the government.
Last edited by Jack Crossfire; Sep 19, 2014 at 09:10 PM.
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