Delta-V for Eve-Moho-Eve path

[SkyFall2489]

For my grand tour mission, I'm wondering how much delta-v I will need to get to Moho and back. I plan to depart from Gilly to Moho, and on the way back swing by Eve on a path to the outer system, maybe stop at gilly again.

My questions:

1. Should I send the main ship over (5-6 km/s), or should I send over a specialized ion vehicle?

2. How much delta-V do I need exactly? Including landing, but if I send the main ship I have ISRU.

[Leganeski]

Moho and Gilly both have significantly eccentric orbits, making a straight Hohmann transfer impossible. The best route I know of involves dropping down to Eve and putting your periapsis at the right longitude so that when you eject from there to Moho, the transfer meets Moho at periapsis. It requires an awkward ejection from Gilly, but saves a lot of fuel at Moho.

• Gilly to Eve: 180 - 680 m/s depending on Gilly's location
• Eve to Moho: 640 - 730 m/s
• Capture / ejection at Moho: 1020 - 1060 m/s
• Landing / takeoff at Moho: 850 - 870 m/s

This adds up to a total cost of 2700 - 3350 m/s in each direction. That isn't enough to require a specialized ion vehicle, especially not if you have ISRU, but Moho's moderate gravity (0.275 g) can be challenging for motherships to land on.

The route I took to Moho in my grand tour mission actually went Minmus-Moho-Mun so that I could use the full gravity assist potential of Eve in both directions. (Technically, it was Moho from stock-scale JNSQ, but it has a very similar size and orbit as stock Moho, and that entire section of the mission would have worked almost identically in the stock system.) I packed 8800 m/s of delta-v because I didn't want to worry, but I only ended up using 4360 m/s to get from Minmus to Moho, and that was with a terrible Moho encounter. With a better placed Eve assist, it could have taken less than 3200 m/s, and the theoretical minimum for that route (in the stock system) is about 2320 m/s.

In summary, getting the mothership to Moho and back is totally doable, but will likely require some careful orbital maneuvering.

[SkyFall2489]

8 hours ago, Leganeski said:

Moho and Gilly both have significantly eccentric orbits, making a straight Hohmann transfer impossible. The best route I know of involves dropping down to Eve and putting your periapsis at the right longitude so that when you eject from there to Moho, the transfer meets Moho at periapsis. It requires an awkward ejection from Gilly, but saves a lot of fuel at Moho.

• Gilly to Eve: 180 - 680 m/s depending on Gilly's location
• Eve to Moho: 640 - 730 m/s
• Capture / ejection at Moho: 1020 - 1060 m/s
• Landing / takeoff at Moho: 850 - 870 m/s

This adds up to a total cost of 2700 - 3350 m/s in each direction. That isn't enough to require a specialized ion vehicle, especially not if you have ISRU, but Moho's moderate gravity (0.275 g) can be challenging for motherships to land on.

The route I took to Moho in my grand tour mission actually went Minmus-Moho-Mun so that I could use the full gravity assist potential of Eve in both directions. (Technically, it was Moho from stock-scale JNSQ, but it has a very similar size and orbit as stock Moho, and that entire section of the mission would have worked almost identically in the stock system.) I packed 8800 m/s of delta-v because I didn't want to worry, but I only ended up using 4360 m/s to get from Minmus to Moho, and that was with a terrible Moho encounter. With a better placed Eve assist, it could have taken less than 3200 m/s, and the theoretical minimum for that route (in the stock system) is about 2320 m/s.

In summary, getting the mothership to Moho and back is totally doable, but will likely require some careful orbital maneuvering.

Thanks!

My mothership has a TWR of 0.46 when full and without its boost module (which I can leave in orbit), so landing should not be a problem. 
Could I maybe leave the boost module at gilly to carry the tylo lander to the outer system on its own, while the mothership goes to Moho and then just slingshots past eve to the outer system? Id lose a little delta v without it, but the boost module was mainly meant to help push the extra weight of the eve lander.

[Leganeski]

30 minutes ago, SkyFall2489 said:

Could I maybe leave the boost module at gilly to carry the tylo lander to the outer system on its own, while the mothership goes to Moho and then just slingshots past eve to the outer system? Id lose a little delta v without it, but the boost module was mainly meant to help push the extra weight of the eve lander.

I don't see why not. As long as the mothership still has enough fuel to reach Moho, the boost module doesn't need that much delta-v to get from Gilly to the outer system (2750 m/s for a direct transfer, or 320 m/s for a Gilly-Eve-Kerbin-Eve-Kerbin-Kerbin-Jool route).

[king of nowhere]

22 hours ago, SkyFall2489 said:

Could I maybe leave the boost module at gilly to carry the tylo lander to the outer system on its own, while the mothership goes to Moho and then just slingshots past eve to the outer system? Id lose a little delta v without it, but the boost module was mainly meant to help push the extra weight of the eve lander.

when i did something similar in one of my grand tours, i rejoined the ships at duna; it's a convenient staging ground.