On 18/04/2016 at 7:32 AM, Nich said:
For a challenge 100 DV can be the difference between 1st and 5th place. Although I have to agree minimus first is cheaper based off my gut feeling. You have to account for the entire trip and burning to minimus first takes more advantage of oberith saving more DV then the transfer back cost from the mun. I also have no idea what cost more transfer from mun to minimus or minimus to mun. It may also depend on the mission landing vsorbit vs flyby. Without building each mission and totaling all the burns I just can't say.
Well, let's try to do it. I have some empiric results. We'll ignore landings and ascendings, because the values are the same, no matter which route is taken.
1a) Mun then Minmus
- Kerbin to Mun : 860 m/s
- Mun insertion burn : 275 m/s
- Mun to Minmus : 210 m/s
- Minmus insertion burn : 90 m/s
- Minmus to Kerbin : 165 m/s
- TOTAL : 1600 m/s
2a) Minmus then Mun
- Kerbin to Minmus : 930 m/s
- Minmus insertion burn : 155 m/s
- Minmus to Mun : 85 m/s
- Mun insertion burn : 205 m/s
- Mun to Kerbin : 275 m/s
- TOTAL : 1650 m/s
So the Mun then Minmus route still wins with a small advantage. But also note that I did not take into account the low Kerbin orbit, which is more expensive for the "Minmus then Mun" route, since you have to launch in an inclined orbit. This loss is however accounted in the Mun to Minmus burn, but it's almost negligible due to the Mun's rotation speed being low (~10 m/s).
On 18/04/2016 at 5:19 PM, 5thHorseman said:
If you're going for a challenge and totally minimizing dV expenditure, then you shouldn't be going from Minmus to Kerbin. You should be going from Minmus to Mun for a gravity assist to slow you down to encounter Kerbin. Likewise, you shouldn't burn up to Minmus from Kerbin but use a Mun assist to get there.
It'll only save a few dozen m/s of dV but if you care about 100...
You can't benefit from both gravity assist, because you have to stop at Mun at some point. But you can still get one, and I mentioned it earlier. Problem is, I'm really bad at gravity assist, despite having read a lot of topics about this.
While getting a Mun gravity assist back to Kerbin is quite easy (it cost about 90 m/s), getting a Mun gravity assist that kicks you to a 10 km Minmus encounter AND correct your inclination (from 0° to 6°) is not something I'm able to do. If someone can do it, please send pictures and parameters.
Despite that, I can easily simulate it by placing a ship at Minmus's inclination, periapsis at Mun's orbit and apoapsis at Minmus's orbit. This would result in a Minmus capture of about 80 m/s.
So let's rebuild our two roads :
1b) Mun then Minmus
- Kerbin to Mun : 860 m/s
- Mun insertion burn : 275 m/s
- Mun to Minmus : 210 m/s
- Minmus insertion burn : 90 m/s
- Minmus to Mun gravity assist : 90 m/s
- TOTAL : 1525 m/s
2b) Minmus then Mun
- Kerbin to Mun gravity assist : 860 m/s
- Minmus insertion burn : 90 m/s
- Minmus to Mun : 85 m/s
- Mun insertion burn : 205 m/s
- Mun to Kerbin : 275 m/s
- TOTAL : 1515 m/s
So, in this particular case, the Minmus then Mun route wins, by almost nothing.
However, please note that all those results are empiric results. It means that I had lot of fun with Hyperedit, created a lot of maneuver node and look at them. I would say that each result have an uncertainty of 5 m/s, and therefore each total have an uncertainty of 25 m/s.
So, while in the no gravity assist case, the Mun then Minmus road wins ; if you start playing with gravity assist, you can't really say which route is better. (but maybe Slashy could come with his awesome math skills and clear this out for us 
).
On 18/04/2016 at 11:24 AM, Plusck said:
I've found exactly this technique works wonders for Moho. The correct launch angle from Kerbin is a lot less than this (and it has to be the opposite angle to Moho's inclination, since this'll reverse as you leave Kerbin's SOI), but if you get it right it can save hundreds to escape at AN/DN and match Moho's inclination.
Oh yeah, Moho is on my to-do list, but I intend to try the route of PLAD who made an awesome double Eve gravity assist. You still have to launch in an inclined orbit though.
Edited by Tatonf
