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Landge

[Question] Capturing Orbits, Is there an Optimal Altitude for Airless Planets?

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While working on my Moons of Jool missions I've been trying out different altitudes for capturing orbits around airless moons. Is it as close as you can get without crashing into the surface? Or way out 500k or more any different in fuel efficiency? Does it even matter?

Not using MechJeb or any other mod that might chart stuff like that, It seems like it makes no difference whether you burn more fuel to slow down enough farther out or letting gravity, building up speed, as you get closer to the surface and burn there. What's your take on the subject?

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You want to come in as low as possible but you don't want to create a new crater on the surface so make sure your periapse is above the max terrain height.

Aeshi did a very useful table for this.

I actually did a small table of this for my own Space Program. Here, I've shown what I personally would consider to be the lowest "safe" orbit you could do, along with the height that the terrain/atmosphere begins:

Kerbin: 70 km

(Atmosphere begins at 69.079 km)

Mun: 4 km

(Highest Terrain 3.335 km)

Minimus: 6.25 km

(Highest Terrain 5.725 km)

Duna: 42.5 km

(Atmosphere begins at 41.446 km)

Ike: 13.5 km

(Highest Terrain 12.725 km)

Eve: 97.5 km

(Atmosphere begins at 96.709 km)

Ghilly: 7.5 km

(Highest Terrain 6.4 km)

Dres: 6.5 km

(Highest Terrain 5.67 km)

Moho: 7.5 km

(Highest Terrain 6.753 km)

Eeloo: 4.5 km

(Highes Terrain 3.869 km)

Jool: 139.25 km

(Atmosphere begins at 138.2 km)

Bop: 23 km

(Highest Terrain 21.749 km)

Pol: 6 km

(Highest Terrain 5.585 km)

Tylo: 13.5 km

(Highest Terrain 12.695 km)

Laythe: 56km

(Atmosphere begins at 55,262 km)

Vall: 9km

(Highest Terrain 7.976 km)

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You want to be as close as you can. This works in the way that almost none of your velocity is vertical, making you fight gravity. It works in the same way that coming in low for a Mun or Minmus capture is more efficient than being far away.

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Sweet! I do tend to drop in low more, just to watch the Kerbalnaut's expressions, as that big chunk of rock comes zooming in. :D

My Ultra-Low Orbital Surface Telemetry 1 satellite is currently in a ~15km orbit over Tylo is the lowest sat I have in a stable orbit. The other crashed and burned while attempting a landing there.

Ucgnn7Xl.png

It's now obvious now how I lost my sat over Pol. It was set at ~5km orbit.

Edited by Landge

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I don't have access to the wiki right now. Can someone check the atmosphere height of Jool? That number seems way off to me.

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The wiki says Jool's atmospheric height is 138 155.11 m, so the number in the table is correct

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I don't have access to the wiki right now. Can someone check the atmosphere height of Jool? That number seems way off to me.

KSP Wiki lists the Jool atmosphere as "138 155.11 m" so 138.155km. Aeshi's numbers aren't off enough to really worry about.

EDIT: Ninja'd;.;

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Is Jool a proper gas giant yet or no? It should be ALL atmosphere that just gets thicker and thicker until you implode or start floating lol

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Is Jool a proper gas giant yet or no? It should be ALL atmosphere that just gets thicker and thicker until you implode or start floating lol

If you descend in to the atmo, that's exactly what happens. However, the game engine shows the atmo as only being 138km thick.

@OP:

The oberth effect says getting lower is better, and my experiences seem to back this up, it seems like I get a stable orbit much more quickly if I'm orbiting very low as opposed to trying to stabilize as soon as I enter the system.

Plus, look at it this way: Whatever you don't do with your orbiter, you have to do with your lander, and your lander is (most likely) not as fuel efficient as your orbiter, and it'll cost you dearly in weight.

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I'm kinda honored people still remember that table.

Props for making it, its something everyone will find useful.

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Props for making it, its something everyone will find useful.

+1 Nice work Aeshi!

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