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Could the SLS block 1 reach orbit without solid rocket boosters, and if so, how much payload could it lift?

If it couldn't reach orbit in the block 1 config, could it do so with the Exploration Upper Stage?

I know the Atlas V and Delta IV can reach orbit with a single liquid first stage engine, so it doesn't seem like there'd be any problem with the SLS, which has 4.

Russell Borogove
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Eoin O'Kelly
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1 Answers1

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Could the SLS block 1 reach orbit without solid rocket boosters, and if so, how much payload could it lift?

Fully fueled, the first stage alone has only an 0.77:1 thrust-to-weight ratio; it can't even get off the ground without help from the boosters, which produce more than 4x as much thrust as the core.

If it couldn't reach orbit in the block 1 config, could it do so with the Exploration Upper Stage?

EUS actually makes this problem worse, because it's a heavier upper stage -- all the delta-v in the world doesn't do any good if you don't have enough thrust to get off the pad.

According to some spreadsheet estimating, I believe that with the ICPS and an underloading of first-stage propellant -- say, 500 tons instead of its usual 894 tons of hydrogen and LOX -- it could get off the ground and reach LEO with about 22 tons of payload, which is no more than some Atlas V or Delta IV configurations can do. This would be wasteful, since it would be hauling propellant tanks that were nearly half empty at liftoff.

A shortened version of the SLS core would be less wasteful for no-boosters configurations; I'd estimate something like 31 tons to LEO for a 550 ton first stage + ICPS, or 40 tons to LEO for a 440 ton first stage + EUS. Those stages would be pretty stubby, around half the length of the SLS core.

These estimates could be off by as much as +/- 7% in payload.

I know the Atlas V and Delta IV can reach orbit with a single liquid first stage engine, so it doesn't seem like there'd be any problem with the SLS, which has 4.

All stages and engines are not created equal; the empty weight of the SLS core stage is four times that of the Atlas V and three times that of the Delta IV cores.

Russell Borogove
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  • thank u for your answer. follow up q: what would the necessary specs be for a sls-like rocket with only rs-25s and nothing else in the first stage? – Eoin O'Kelly Jan 05 '19 at 10:47
  • If you shortened the SLS core stage to reduce weight, kept the 4 RS-25s, left off the boosters, and used ICPS as the upper stage, it'd be about 31 tons to LEO. Core would be 50t dry, 500t fuel. About 612 tons total at liftoff including payload. Compare to Atlas V and Delta IV Medium which both wind up around 350 tons depending on payload and booster configuration, or the Falcon 9 at 550 tons. With EUS you'd want an even lighter first stage (otherwise it doesn't have enough thrust to lift off safely); 400+40 tons core stage and 40 tons to LEO. – Russell Borogove Jan 05 '19 at 23:35