[bewaretheirs]

Rockets are not LEGO.

You can't just swap engines without a significant redesign of the rocket and ground support equipment to match.

the RS-25 burns liquid hydrogen and liquid oxygen; the BE-4 and Raptor burn methane and liquid oxygen, but the Raptor uses supercooled densified propellants while the BE4 takes them at closer to their boiling point. Switching between BE-4 and Raptor would require nearly as much work as a switch from RS-25 to either.

The varying density, temperature, and fuel-to-oxidizer ratios mean the propellant tanks would need to change size, and that may have some tricky structural implications with respect to the side boosters of the SLS. And the ground support equipment (launch pad, tower, etc., ) would of course also need to be adjusted to match.

[layer8]

> Rockets are not LEGO.

For a moment there I thought that Low Earth Geostationary Orbit might be a thing.

[zakary]

It could be for a few minutes if your rocket has a LOT of fuel to burn