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What's the most dV savings you can get off of a Mun sling?


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I've used flybys of Mun many times when I was trying to reduce the dV needed to get somewhere to an absolute minimum, normally in a challenge. The dV benefit varies depending on where you're trying to go. Summary follows, note I only give links to the albums  because they are large, I try to give enough detail to allow others to copy what I do. Note that these were done in earlier versions of KSP, but no flight paths outside of Kerbin's atmosphere have changed for any of these.

The most benefit I ever got from one flyby of Mun when traveling from LKO(75x75km orbit) to Eve is 87 m/s. It reduced what I need from 1068m/s to 981 (initial boost) plus 4 m/s of course corrections. The course corrections make an exact number difficult because you need more of them when using Mun but it is hard to get a repeatable number. Here is the album showing that flight. Note how low the Mun flyby was (180m above the surface!), which is why I think this is an absolute maximum gain for one flyby.

http://imgur.com/a/cT18z

On more typical flybys at 10-20km altitude the benefit is more like 80 to 70 m/s (still to Eve), and I've had to make extra corrections of up to 20m/s. If you are going straight to a further planet like Jool then the benefit is smaller because you are going faster and spend less time in Mun's SOI.

You can make multiple passes of Mun to get a larger benefit. In the mission below I used 5 flybys of the Mun to reduce the dV needed to get from LKO to a Duna encounter to 878m/s. Normally this would take about 1050m/s, so about 170m/s savings total.

http://imgur.com/a/cNG8P

You can even use fybys of Mun to get you to a low Munar orbit from LKO for less. Normally going from a 75x75km Kerbin orbit to an 8x8 Mun orbit would take 856m/s+4m/s corrections+273m/s=1133m/s. Using the path in the album linked below I did it for 845+ 15 +209=1069m/s. It's an awful lot of work for a 64m/s savings though. You can follow the path in reverse to get home for the same savings, I do that later in the album.

http://imgur.com/a/wxGvv

You can get from low Minmus orbit to Kerbin for about 110m/s by flying by Mun. Doh... I think it's about 160m/s for a straight shot, but I only have an old note for that.

So those are the savings, the problem with Mun flybys is the high precision required and the extra course corrections that leads to.

 

 

 

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32 minutes ago, PLAD said:

I've used flybys of Mun many times when I was trying to reduce the dV needed to get somewhere to an absolute minimum, normally in a challenge. The dV benefit varies depending on where you're trying to go. Summary follows, note I only give links to the albums  because they are large, I try to give enough detail to allow others to copy what I do. Note that these were done in earlier versions of KSP, but no flight paths outside of Kerbin's atmosphere have changed for any of these.

The most benefit I ever got from one flyby of Mun when traveling from LKO(75x75km orbit) to Eve is 87 m/s. It reduced what I need from 1068m/s to 981 (initial boost) plus 4 m/s of course corrections. The course corrections make an exact number difficult because you need more of them when using Mun but it is hard to get a repeatable number. Here is the album showing that flight. Note how low the Mun flyby was (180m above the surface!), which is why I think this is an absolute maximum gain for one flyby.

http://imgur.com/a/cT18z

On more typical flybys at 10-20km altitude the benefit is more like 80 to 70 m/s (still to Eve), and I've had to make extra corrections of up to 20m/s. If you are going straight to a further planet like Jool then the benefit is smaller because you are going faster and spend less time in Mun's SOI.

You can make multiple passes of Mun to get a larger benefit. In the mission below I used 5 flybys of the Mun to reduce the dV needed to get from LKO to a Duna encounter to 878m/s. Normally this would take about 1050m/s, so about 170m/s savings total.

http://imgur.com/a/cNG8P

You can even use fybys of Mun to get you to a low Munar orbit from LKO for less. Normally going from a 75x75km Kerbin orbit to an 8x8 Mun orbit would take 856m/s+4m/s corrections+273m/s=1133m/s. Using the path in the album linked below I did it for 845+ 15 +209=1069m/s. It's an awful lot of work for a 64m/s savings though. You can follow the path in reverse to get home for the same savings, I do that later in the album.

http://imgur.com/a/wxGvv

You can get from low Minmus orbit to Kerbin for about 110m/s by flying by Mun. Doh... I think it's about 160m/s for a straight shot, but I only have an old note for that.

So those are the savings, the problem with Mun flybys is the high precision required and the extra course corrections that leads to.

 

 

 

Wow. Just... Wow. I just viewed that album. Most impressive. But I must ask: how did you plan these slingshots in the first place? I mean, how did you know that these planets will be in correct positions that many steps ahead, and that required slingshot altitudes won't be below surface/inside atmosphere?

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10 minutes ago, aluc24 said:

Wow. Just... Wow. I just viewed that album. Most impressive. But I must ask: how did you plan these slingshots in the first place? I mean, how did you know that these planets will be in correct positions that many steps ahead, and that required slingshot altitudes won't be below surface/inside atmosphere?

For the planetary paths I use Flyby Finder and the Lambert spreadsheet, both available here (I wrote them). For the stuff with just Mun I winged it because it's relatively easy to flyby something and then come back to it at the same spot. And thanks!:)

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