# What expansion ratio is the best for mars surface level engines?

What expansion ratio is the best for mars surface level engines?

For launches from Earth, first stage nozzles are much shorter than second stage nozzles because of Earth's high sea-level pressure. For more on that see Wikipedia's Rocket engine nozzle; Atmospheric use.

There are several futuristic proposals to launch from Mars, presumably tourists and professional astronauts on their return flight home, and the first of presumably many robotic sample return missions from Mars is expected in a few years. More on that at What kind of rocket will ESA(?) launch from Mars? Who will build it?

Since Mars has an atmosphere and so is not analogous to launching from the Moon, but it's low pressure so ot analogous to launching from Earth, I'd like to ask What expansion ratio is the best for mars surface level engines?

• I think your question was closed because it is very ambiguous: There is no current Mars sea level. There is only a Mars surface level. You could ask about the expansion ratio for that level, or about a hypothetical past/future Mars sea level. Note that an atmosphere allowing a liquid water sea level to exist would need a higher atmospheric pressure, so the optimum expansion ratio for that surface level would be different from the current, dry one. Consider editing your question in that direction, and the question should reopen. May 27 '21 at 18:22
• When in doubt, 42
– uhoh
May 27 '21 at 23:43
• @AtmosphericPrisonEscape changed it thank you for the comment Jun 1 '21 at 13:11
• A vacuum rated engine would probably be able to manage liftoff at <0.01bar. A bigger problem might be the size of the engine nozzles and the proximity to the surface. Jun 1 '21 at 13:14
• +1 for a good question! I see your edit, but I've further edited your question to better address the concerns raised in comments and the close votes, and now voted to reopen.
– uhoh
Jun 2 '21 at 3:27