How do you read the Delta-V cheat sheet on the wiki?

[Name Lips]

I'm in orbit of Mun, and want to know if I have enough delta-V left to land, take off, and get back to Kerbin.

It seems what I need is a Delta-V map like the one on the wiki:

It seems like what it's saying is that if I want to get to Mun, I need to add up the numbers from Kerbin to Mun. 4550+860+210+640 = 6210 Delta V.

That seems to make sense. But if I'm in a low Mun orbit already, can I just start adding from there? 640 to land, another 640 to get back up, then 210 and 860, then into Kerbin's atmosphere. That totals 2350 Delta V. That seems like a lot. I seem to remember, before I discoverd MechJeb, I managed to land a rocket on Mun. It was almost out of fuel, but I just took straight off and escaped Mun's gravity fairly quickly, and from there I had just enough Delta V to shrink my orbit until I hit Kerbin.

It seems like the cheat sheet is not useful for this purpose because it assumes I'm slowing into a nice circular orbit between each maneuver. Is that right? Or will it really take my orbiting lander 2350 Delta-V to land and return home?

Edited January 26, 2014 by Name Lips

[chemieglennie]

You don't need the 860 to slow down for Kerbin. Just get inside the atmosphere and aerobrake.

The 640 to land on the Mun is optimistic. Make sure you start your slowing down burn late and hard. You basically want the reverse of a launch to be as efficient as possible. Quick save will help here.

[technion]

Although this chart is shown everywhere, be careful reading it. As was pointed out above, some values are optimistic. Some, assume perfect encounters which you are highly unlikely to get. Look at the 12000 recommended for Eve. People exploiting the mountains have done it on nearly half that.

[Superfluous J]

I prefer this chart, which has an even lower Mun estimated burn. Note that none of these specifically say what your "low orbit" height is, though the one I linked to states it's the lowest you can orbit at 50x speed.

I tend to stress optimal burns, so I've not found it to be TOO optimistic. However, I always try to have a 10% margin for error or more. If you're in low munar orbit and have (580+580+230+80)*1.1 = 1470 deltaV or more, I say go for it.

The others pointed out that you can aerobrake, which you know but don't see is on the chart. On your chart, any white triangle means you can aerobrake if going "down" and can ignore the number. On my chart, it's a red arrow.

[ComradeGoat]

You don't need the 860 to slow down for Kerbin. Just get inside the atmosphere and aerobrake..

Yes, important to read the key; note the little arrow, which indicates aerobraking as a possibility. That means that arc is almost free in that direction.

BTW, I'd want at least 1,600 on a Mün lander, just to be sure. I like to have 2,500-3,000 in them, so I can do precision landings and not worry too much about my fuel budget. The figures posted there assume a perfect suicide burn, which is more-or-less how you land on Tylo with a ship of any sensible size, but a Mün lander with 2,500m/s delta-V really isn't very big. Go on, spoil yourself!

[capi3101]

I second the usage of 5thHorseman's chart; it's newer and as an added bonus it has included the delta-V requirements of the inclination burns.

For the original chart - you say you're already in low Münar orbit. So from there, it's:

640 to land

640 to launch to low Münar orbit

210 to escape the Mün's SOI

essentially a free ride for the rest of the trip

TOTAL: 1,490 m/s. If you're an amateur, I'd tack on anywhere from 25-50% of that number as a safety margin. Say 1,875 total for safety sake.

The new chart - 580 to land, 580 to low orbit, 230 to escape Mün's SOI, 80 for the transfer back and the rest is free. None for the inclination burn. 1,470 m/s in total for the return trip, so some savings. I'd still go with 1,875 just to be safe.

[Taki117]

I prefer this one Which includes a range of dV depending on planets position in orbit.

[Name Lips]

Thanks everybody, that clears things up a lot.

[lajoswinkler]

Just use this.

https://play.google.com/store/apps/details?id=ch.bigcube.kspcalculator

[metaphor]

I prefer this chart, which has an even lower Mun estimated burn. Note that none of these specifically say what your "low orbit" height is, though the one I linked to states it's the lowest you can orbit at 50x speed.

Try this one, it's slightly clearer with low orbit values.

[capi3101]

^^^

That's now three (four? five? I've lost count) different recommendations for the new chart...