Lowest orbit

[XerZin]

So where is the limit of every Planet/Moon for the lowest orbit before the gravity takes you and you start to "fall" down towards the surface. I checked the Wiki but I didn't understand exactly what to look for.

Example: Wiki - Says the lowest stable orbit for Kerbin is 70km. So I could make a orbit at 70km but if it would go down to 69km, where the Atmospheric Height is, I would start falling?

This planet has a atmospheric height but not every planet does.

Im confussed... What exatly should I look at on the Wiki? (or if you have the time and feel for it you could post it here )

Edit: Thank you all for the mind explotion 101 physics and thank you Aeshi for this chart:

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

(Highest 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)

Edited June 3, 2013 by XerZin
Thank you!

[SuperFastJellyfish]

The short answer is if there is no atmosphere then you can make a stable orbit as long as you don't hit the ground. The highest peaks on the Mun, for example, are around 3000m tall. So you can orbit the Mun safely at 3001m.

Edit: All an orbit is is constantly falling, but having the horizontal velocity to always miss the ground/atmosphere.

Edited June 3, 2013 by SuperFastJellyfish

[thes50]

So where is the limit of every Planet/Moon for the lowest orbit before the gravity takes you and you start to "fall" down towards the surface. I checked the Wiki but I didn't understand exactly what to look for.

Example: Wiki - Says the lowest stable orbit for Kerbin is 70km. So I could make a orbit at 70km but if it would go down to 69km, where the Atmospheric Height is, I would start falling?

This planet has a atmospheric height but not every planet does.

Im confussed... What exatly should I look at on the Wiki? (or if you have the time and feel for it you could post it here )

If a planet has an atmosphere moving through it will cause drag, this causes your craft to lose energy. This means the craft slows down, as you said the lowest stable orbit for Kerbin is 70km. This is the lowest altitude you can orbit at without passing through the atmosphere. If you lose enough energy your orbit will "collapse" causing your craft to hit the surface of the planet.

In summary, if an object is in orbit and not passing through the atmosphere it will never de-orbit its self. You cannot simply fall to the surface.

Edited June 3, 2013 by thes50

[Pulstar]

The gravity doesn't just "take you" it still works on you when you're in orbit, indeed that is what keeps you from flying straight away into the unknown by keeping you in an orbit.

What gets you down is the atmosphere slowing down your craft as it goes through it thus losing velocity and making you go slower than what you need to stay in orbit. Since in space you have vacuum nothing slows you down and you can orbit forever, as to remain in your orbit you just need to keep going as fast as you already are without adding more speed (in reality it is a bit more complicated and not really forever but in KSP it is basically forever). If there is no atmosphere you can have a stable orbit as low as you like as long as there won't be a nasty hill ruining your day in your way. Hence the limiting factor on those bodies is how high is the terrain over which you will be orbiting.

So essentially the lowest stable orbit is the one where there is no atmospheric gas to slow you down. Mind you, depending how high you're orbiting it may take a while before the spacecraft falls from orbit towards the ground as more pressure=more gas=more drag=more lost velocity. And by a while I mean several orbits.

Edited June 3, 2013 by Pulstar

[Uberick]

Exactly as has been said already; Your orbit can be as low as you want until you hit either atmosphere(which will slow you down), or a mountain(which will slow you down faster) I usually orbit non atmospheric planets at super low altitudes. It looks really cool

[Aeshi]

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)

[SuperFastJellyfish]

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)

Awesome chart! I've been meaning to make one of these for myself. Thanks!

[XerZin]

Yeah I did check the Wiki again I start thinking on the atmospheric height, if there isn't any atmosphere, check the highest terrain. If there is a atmospheric height be above it. Sorry everyone for the stupidity, didn't exatly think straight. 101-physic.

Thank you for the chart! Now I dont need the wiki for that part anymore

Aeshi if you don't mind, I will add that to my first post for anyone that thinks like I did couple mins ago. Thank you Aeshi for the chart and thanks to everyone else that freshed up my mind.

Edited June 3, 2013 by XerZin

[CosmicX1]

Mun: 4 km

(Highest Terrain 3.335 km)

I always thought the highest terrain on the Mün was around 2 km (as I learnt from experience). This knowledge will put a new and terrifying slant on all my future missions to the Mün (especially on the dark side). 0_0

[Aeshi]

Sure, go ahead & use it. That's why I made it after all!

I always thought the highest terrain on the Mün was around 2 km (as I learnt from experience). This knowledge will put a new and terrifying slant on all my future missions to the Mün (especially on the dark side). 0_0

Just about all of the Mun's higher terrain is up at its poles, you only really need to worry if you plan on placing something in a Polar Orbit. The same could probably be said for a few of the other flatter bodies (like Eeloo & Dres), but I haven't checked.

Edited June 3, 2013 by Aeshi

[FadedFlyer]

It says here the lowest safe orbit on mun is 4km

My satellite just crashed on the mun at 5162m. 

 

Photo of my crash site

Edited November 9, 2017 by FadedFlyer

[bewing]

1 hour ago, FadedFlyer said:

It says here the lowest safe orbit on mun is 4km

My satellite just crashed on the mun at 5162m

Welcome to the forums, FadedFlyer.

Yes, this info on this thread is quite out of date. There are two forms of "safety". One is being above the terrain. The current altitude of the highest terrain on the Mun is a little over 7km (near the poles). However, there is also something called the "autodeletion altitude". If you are watching some other vessel X, and vessel Y goes below the autodeletion altitude of any celestial body, then vessel Y will be deleted with a logfile message of "crashed into terrain". Each CB has its own autodeletion altitude. On the Mun it is 8km.

 

Edited November 9, 2017 by bewing

[FleshJeb]

3 hours ago, FadedFlyer said:

It says here the lowest safe orbit on mun is 4km

My satellite just crashed on the mun at 5162m. 

 

Photo of my crash site

https://wiki.kerbalspaceprogram.com/wiki/Mun#Terrain

You may find this useful.