Low Moho Orbit?

[Right]

Why do delta-v maps use 50km as low Moho orbit? It's got no atmosphere, and its highest peaks appear to be ~6km. So why not use 16km as low orbit?

[worir4]

I think it depends on the radius of the body not the atmosphere or peaks.

[UmbralRaptor]

Because ÃŽâ€V maps are ultimately simplifications of a complex process. And if they're old enough, they might date from when Moho had an atmosphere.

[Right]

And if they're old enough, they might date from when Moho had an atmosphere.

I think this is probably it. They aren't as old as 0.17, but I'm not sure anyone noticed.

[Tank Buddy]

This DV Map specifies that low orbit is "10Km above atmosphere or clear of obstacles". You should include a few hundred m/s buffer between what the Map says and what your ship has to leave room for error and maneuvers.

[Taki117]

This DV Map specifies that low orbit is "10Km above atmosphere or clear of obstacles". You should include a few hundred m/s buffer between what the Map says and what your ship has to leave room for error and maneuvers.

Even then it lists low orbit as 50km.

[smjjames]

Actually, isn't that about the boundary between what's considered high orbit and low orbit for science? Then again, the Mun and Minmus have it down to 15 and 10km respectively, but you don't need to go that low for it to be considered low orbit.

[Empiro]

What's the minimum altitude for 50x time acceleration at Moho? I had assumed that the DV maps used that altitude. It doesn't really matter too much though -- the difference in Delta-V between a 20km and 50km orbit is pretty low.

[OhioBob]

Actually, isn't that about the boundary between what's considered high orbit and low orbit for science?

For Moho the boundary is 80 km.

What's the minimum altitude for 50x time acceleration at Moho?

The minimum for 50X is 30 km. 50 km is minimum for 100X.

[smjjames]

Hm, *checks wiki*.

For the Mun, the min for 50x is 10km and for 100x is 25km.

For minmus, it's 6km and 12km respectively.

A 'low orbit' of 15 and 10km would put them between those two minimums, haven't looked at the other 'low orbits'.

[Right]

the difference in Delta-V between a 20km and 50km orbit is pretty low.

Low yes, but bigger when you combine lost Oberth effect for the return Hohmann, especially considering that a safe orbit can be as low as 8k.

[smjjames]

You lost me at the 'lost Oberth effect'.

[Right]

You lost me at the 'lost Oberth effect'.

The faster your going, the more efficient your fuel is. Lower orbit means faster orbital speed.

[Kryxal]

Height above surface is energy ... speed is energy squared. Do most of your slowing down when you're lowest and fastest, and you spend less delta-v to reduce more energy. It matters less for lighter celestial objects, but it's always there to some extent.

[Mesklin]

The faster your going, the more efficient your fuel is. Lower orbit means faster orbital speed.

Not faster, burn fuel as low as possible, it is main rule of fuel economy. Usually at the lowest point of trajectory or orbit craft has maximum speed, it is source of common delusion about Oberth's law.

[Renegrade]

Low yes, but bigger when you combine lost Oberth effect for the return Hohmann, especially considering that a safe orbit can be as low as 8k.

According to http://alexmoon.github.io/ksp/, the first return window from Moho, the return cost trips are:

8km: 3,491 (save 21)

20km: 3,497 (save 15)

50km: 3,512 (baseline)

The difference in Oberth effect between these orbits is also low. Heck an orbit of 1500km altitude has a cost of 3,711, or a difference of +220. Moho is a little space potato~

(The cost to transfer between 50 and 20 would be about 40.5(~20 for just PE), and from 50 to 8 would be 58.6 (28.8 for just PE), in case anybody is curious. Orbits are reversible, so to go from 8 to 50 is also 58.6 etc. So if you're stuck in a 50km orbit, probably best to NOT change to the 8km one)