General Question XR2 SCRAM engine on mars...

[SpaceCowboyJoe]

I've just landed on Mars with the XR2 and...

Well I'm just considering that most likely SCRAM should not work in a 0.13% Oxigen atmosphere, not even considering the tremendously low pressure.

I guess the way home should cost a lot of fuel.

 

[Enjo]

I like how scrams work on Mars, so that I can cruise with a constant speed and enjoy the view.

 

[SpaceCowboyJoe]

I like how scrams work on Mars, so that I can cruise with a constant speed and enjoy the view.

I didn't really attempt as once i get there I had no scram fuel available and I didn't refuel...
In any case, unless I totally misunderstood, with such a low quantity of oxigen in mars atmosphere I think there's no way a jet engine could work.

 

[dbeachy1]

Orbiter does not model Oxygen content in an atmosphere, and so XR SCRAM performance depends only on atmospheric density and ship velocity. In any case, the Mars atmosphere is so thin that I wouldn't expect much thrust from the SCRAMs on Mars.

 

[SpaceCowboyJoe]

Orbiter does not model Oxygen content in an atmosphere, and so XR SCRAM performance depends only on atmospheric density and ship velocity. In any case, the Mars atmosphere is so thin that I wouldn't expect much thrust from the SCRAMs on Mars.

Exactly! It's kinda a nice glitch.
Considering mars atmosphere being so thin the speed to have a scram engine working should be enormous.... probably bigger than the 4 kmps er second that allow you to get to the orbit

 

[Linguofreak]

Orbiter does not model Oxygen content in an atmosphere, and so XR SCRAM performance depends only on atmospheric density and ship velocity. In any case, the Mars atmosphere is so thin that I wouldn't expect much thrust from the SCRAMs on Mars.

Surface pressures on Mars are equivalent to about 30-50 km on Earth, so really actually right in the middle of the SCRAM operating range (24-60 km from the checklist in the XR Operations manual).

And realism-wise, it's not even that bad for the SCRAMs to be able to operate on Mars. Assuming chemical propulsion (lower main engine ISP settings in the config file), the XR could be assumed to carry oxidizer for the SCRAMs on no-oxygen worlds, which would reduce fuel efficiency but still be better than rocket propulsion at equivalent exhaust velocity (because we're using atmospheric air for propellant). Assuming nuclear propulsion (higher main engine ISP settings), there's no need for the XR to carry SCRAM fuel at all, the incoming airstream can just be heated from the reactor, regardless of composition.