# G forces of Starship 1 when leaving Earth orbit?

Is there a stated estimate of what the G forces an astronaut would experience on Starship 1 when leaving Earth orbit?

In vacuum maneuvers will be taking place with the three vacuum Raptors, target hoped for thrust somewhere around 2500 kN each. For a loaded Starship at around 1000 tonnes F/m=a gives 7.5 m/s2 or just under one G. As the tanks empty this would increase to around 82 m/s2 or just over 6G.

If you use the current actual Raptor thrust around 2000 kN this gets a peak acceleration of 50 m/s2 or 5G.

This puts the forces around those on an Apollo crew, but higher than the 3G peak targeted for the space shuttle, though the same throttle bucket approach may be used.

Actual G forces departing earth depend a lot on final engine thrust, final Starship mass and mission profile (how empty the tanks get during departure).

While less efficient it would be possible to operate all six engines which would close to double the forces, though there are few cases where this would make sense.

• Why use as many as three engines? I would imagine one, throttled fairly well down to give a 1g or so acceleration would be plenty Jan 5, 2020 at 10:45
• @steve Linton, the current info on Starship lists three vacuum engines. I'm assuming to give the thrust to reach LEO. Which makes it less optimal for Mars/Moons missions but many space decisions are not single axis optimal. In practice for a number of reasons would expect a 3G maximum for planned maneuvers, throttling and cutting engines as required. Oberth effect does mean that injections are best done at the highest thrust your vehicle can efficiently achieve. Jan 5, 2020 at 11:59
• @GremlinWranglerI know the engines are there, presumably, as you say, to reach LEO and also to provide redundancy, I'm familiar with the Oberth effect, but I can't believe making am injection of a few km/s in five minutes instead of one will make much difference. You will not be significantly further from Earth at the end of the burn. Jan 5, 2020 at 16:27
• For the Moon and Mars missions outlined, the burn to leave Earth orbit wouldn't come close to emptying tanks, since fuel must be carried for landing and possibly takeoff from the destination. Even using all three engines, I think that keeps acceleration under 4G or so. Jan 5, 2020 at 16:29