Thrust ratio on Kerbin to Mun?

[HSV Guy]

Quick question, what is the 'trust ratio' on Mun compared to Kerbin?

For example, I want to be able to put some RCS thrusters on the top of my craft to allow me to tilt it from vertical to horizontal and back again on Mun. Rather than going to Mun and trying to work this out I figure if I find that on Kerbin I need a thrust of x and the ratio of thrust on Mun to Kerbin is 5 to 1, to do the same on Mun I'd need a thrust of x/5.

Edited September 22, 2015 by HSV Guy

[Red Iron Crown]

Moving this over to Gameplay Questions.

The ratio is 6.02. So a Mun craft only needs about 1/6 the thrust of a Kerbin craft.

[Tatonf]

If you want to know how to find it by yourself, go to the tracking station, select the body you're interested to land on and check the parameters on the right.

What you're looking for is "ASL gravity", which, in the case of the Mun, is 0.166 g.

Then divide 1 by this value and you'll get your ratio.

1/0.166 = 6.02

[Padishar]

Also bear in mind that the RCS thrusters have pretty bad Isp in atmosphere so their thrust is severely reduced compared to in a vacuum. If you give yourself 1/6th of what it needs on Kerbin then you will have more than double what you need on the Mun.

[HSV Guy]

Thanks for the replies. Exactly what I was after.

[nekogod]

RCS thrusters put out 0.42kn at sea level on Kerbin and 1kn in a vacuum.

Knowing this means a TWR of 1.1 on the Mun is equivalent to a TWR of 0.08 at sea level on Kerbin.

[nekogod]

I'm pretty certain that you have adjusted that the wrong way...

How so?

A TWR of 1 at sea level with RCS thrusters is equivalent to a TWR of 2.4 in a vacuum whilst under kerbin gravity, the mun has 0.166 the gravity so you multiply the TWR by another 6.02 and you come up with a mun vacuum TWR of 14.448

So to work out what a TWR of 1 on the mun is on kerbin you simply divide by 14.448. Which is 0.07

By which I mean is if on mechjeb or KER it states your kerbin atmospheric TWR is 0.07 then on the mun you will have a TWR of 1.

[Red Iron Crown]

If you're using KER or Mechjeb this whole question is moot, just set the body to the Mun and let it calculate for you.

[Padishar]

How so?

Sorry, I had a brain freeze due to a 4.5 hour work conference call. Your numbers are fine. I thought I'd deleted my post about 2 minutes after posting it but it appears it didn't take...

[nekogod]

If you're using KER or Mechjeb this whole question is moot, just set the body to the Mun and let it calculate for you.

Aye, but where's the fun in that!?

Sorry, I had a brain freeze due to a 4.5 hour work conference call. Your numbers are fine. I thought I'd deleted my post about 2 minutes after posting it but it appears it didn't take...

no worries

[MarvinKitFox]

Quick question, what is the 'trust ratio' on Mun compared to Kerbin?

Don't Trust the Mun, I hear he is jealous of MinMus.

Oh, tHrust?

You want to know how much RCS is needed to tilt a vehicle, on Mun as opposed to Kerbin?

If you are not fighting gravity, it will be the same, as mass and thus inertia remains constant.

If you *are* fighting gravity, figure 6X the gravity force to fight on Kerbin. Mun is not very grabbity.

If your Kerbin vehicle is at sealevel, you are already operating at a massive 60% penalty due to air pressure. RCS does not operate well in air.

So in the end, your answer is that on Mun you need somewhere between 1 and 0.07 as much RCS as on Kerbin. Most likely never more than 0.17 as much