Coming Back from the Mun

[Mango]

I've been experimenting with different designs to get to the Mun and back.
However, the best I can make ends up on the surface without enough fuel to even get back into orbit around it.
Has anyone else had better luck with this? I can't seem to get it right...

[Just Jim]

http://steamcommunity.com/sharedfiles/filedetails/?id=451121684

I've had this lander to the Mun and back several times. As long as I don't waste fuel landing her, she can make a breakaway orbit back to Kerbin easily.

[Surimi]

Try putting external fuel tanks on the lander, then when you land transfer the fuel into your main tanks and jettison the external ones before taking off.

[Woody]

Install Engineer or MechJeb to get DV calculations. The other options is to do the math yourself or just learn from experience of how much fuel to carry for the payload and engines being used.

If you choose to do the math yourself just google to get the formula. There is also some Delta-V maps to give you an idea how much you need to get to places and back.

[jhendriks87]

If you havent already, you should look at getting either mechjeb or kerbal engineer mods. Both of these will give you the Dv that you have in total and it also breaks it up into your stages as well. Using the mod you can change your design to make sure you have the correct amount of Dv.

[Mango]

I've got Kerbal Engineer already, and I already had a Delta-v map on hand, but it doesn't seem to be quite right. How much Dv is usually required to go there and back?

[jhendriks87]

That depends on alot of things including how efficiently you get to an LKO and do your subsequent burns, also depends on weight etc, and also how effiecient your landing is. If everything went exactly to plan you would need around 7500Dv but that is with exact burns and the best gravity turn to LKO. Once landed on the mun it takes around 580m/s to get back to a Low munar orbit and then a further 250-350m/s for your ejection burn from munar orbit and leave you with a kerbin PE of around 20km. Just plan to have more than 7500 aim for around 10000 to allow for mess ups.

[kbmodigity]

From the surface of the mun to orbit you have to figure about 400-500 D/V, that will put you in roughly a 10 km orbit. Then at best efficiency you have to figure about another 300-400 DV burn to end up in an orbit that hits Kerbin at a 30 km height which should bring you safely down to the surface.

This all depends on the weight of the vessel and all as well. KER should tell you though as to what you have left depending on your weight.

Always plan on at least 900 D/V minimum to make it home from the Mun from a landed position. Might be a little too much, but then again, would you rather have a little too much D/V or too little?

[koimeiji]

If I'm remembering right, a rocket needs a total of about 4.5 km/s delta V to get from the launchpad to the Munar surface and back. +-1 km/s delta V for maneuver efficiency.

[kbmodigity]

Originally posted by 東方 Koishi Komeiji 303:

If I'm remembering right, a rocket needs a total of about 4.5 km/s delta V to get from the launchpad to the Munar surface and back. +-1 km/s delta V for maneuver efficiency.

No, the charts say an average of 4500 d/v just to reach orbit of kerbin. Those numbers are a bit high depending on how efficient you can do your gravity turn.

After orbit you have to figure about 825 D/V to get to the mun. Then another 100-200 to acheive orbit. Figure another 600 to land, and then another 900 to get home.

These numbers are high and leave alot of room for error and adjustment, but a good rule of thumb.

[Woody]

Here is the DV I plan on using when going to the Mun:

To LKO(80K): 4K
Encounter Mun: 1K
Orbit Mun: 400
Land: 750
Orbit Mun(10K): 850
Return: 400

Total: 7400 DV

This is almost 1K more DV then needed but accounts for mistakes and ineffient burns.

[Rogue]

I always skip the Mun orbit stage on the way back. Just point up and go until I'm out of the Mun's SOI. Probably a terribly inefficient way of doing it but there's always fuel to spare. *shrug*

[Woody]

Originally posted by Rogue:

I always skip the Mun orbit stage on the way back. Just point up and go until I'm out of the Mun's SOI. Probably a terribly inefficient way of doing it but there's always fuel to spare. *shrug*

If you do it at the right time it is not inefficient. if you take off a little behind where you would burn in orbit it works out basically the same DV.

[Rickenbacker]

Originally posted by Deep Hurting:

Try putting external fuel tanks on the lander, then when you land transfer the fuel into your main tanks and jettison the external ones before taking off.

This works well for small landers. Even better, place fuel lines (if you have them) from the drop tanks to the main tank, then just get rid of the drop tanks when they're empty.

[The_Mell]

Originally posted by Rickenbacker:

Originally posted by Deep Hurting:

Try putting external fuel tanks on the lander, then when you land transfer the fuel into your main tanks and jettison the external ones before taking off.

This works well for small landers. Even better, place fuel lines (if you have them) from the drop tanks to the main tank, then just get rid of the drop tanks when they're empty.

The whole drop tank thing can be quite interesting if done in the right dimension but the smaller the tank the less efficient it is because you need a decoupler, too, and in the end it's all about deltaV, right? That and the overall complication of a rocket - sometimes simple is good enough.
I use a drop tank for my transfer to Mun&Minmus and usually most of the descent:
http://steamcommunity.com/sharedfiles/filedetails/?id=442180047

[Surimi]

Originally posted by Rogue:

Probably a terribly inefficient way of doing it but there's always fuel to spare. *shrug*

Actually, it depends where you are on the Mun. If you're on the opposite side to the direction the Mun itself is travelling (as it orbits Kerbin) and you burn straight up, you're burning retrograde relative to Kerbin and will be half-way home by the time you leave Mun's SOI.

The reverse is also true, however. If you're on the "front" side of the mun as it orbits, you will probably end up flying off into space and wasting a bit of delta v.