�v Needed for Eve Mission

[Barefoot Friar]

Right so according to alexmoon's site, I've got an Eve transfer window coming up pretty soon, so I'm thinking about sending a Kerbal. I want to make sure he comes home. I would like to request help with figuring the total ÃŽâ€v I need for the entire mission, point-by-point. I'm not terribly good at math, but I can usually figure formulas out, so feel free to give me whatever you have.

Basically, I'm needing to figure out how much ÃŽâ€v I need for each stage. I've started at the end of the mission and am working backwards, so I have so much for aerocapture and deorbit, so much for return to Kerbin from Eve, so much for Eve orbital maneuvers (which includes releasing a probe, releasing a robot lander, and sending a Kerbal to land on Gilly), and then so much for transfer from Kerbin to Eve. If I can figure those out, I can do the rest.

From what I'm reading, he's calling for a Kerbin ejection of 1039m/s, a course correction burn of 5, and an Eve insertion of 722 for a total of 1766m/s. Then to come home it's 616m/s ejection, 129 correction, and 1071 for Kerbin insertion, totalling 1817m/s. Which would make the mission total, before Eve orbital work and Kerbin deorbit, 3583m/s. How accurate is this, and how close can I cut it? Should I increase my ÃŽâ€v budget by a certain amount for insurance? (Note, I begin in a 100km Kerbin orbit and finish at a 50,000km Eve orbit; I know that's awfully high but it fits my mission parameters better than dropping to a low Eve orbit and then having to ascend again.)

I fiddled around in the VAB this afternoon and came up with a transfer stage with about 8km/s, before adding the aforementioned landers and probe. I was worried it wasn't going to be enough, but this looks like it'll be about double!

Anyway, any tips would be appreciated.

Edited November 4, 2013 by Barefoot Friar

[Specialist290]

Your math sounds about right, but I'd like to add a few notes and caveats:

1. The calculator generally assumes a machine-perfect transfer, which is extremely difficult for a human being to execute manually using stock-only tools, so I'd definitely include a little extra buffer fuel, just to be on the safe side. Usually about 25-50% extra delta-v (which doesn't exactly correlate to 25-50% extra fuel mass, but that's a whole different topic of discussion) for your transfer stage is a safe estimate.

2. On the other hand, you've got an atmosphere at both of your destinations, meaning you can reduce the delta-v for insertion considerably using a technique called "aerobraking" -- basically, you dip partway into your target planet's atmosphere to let air drag slow your craft down, allowing you to save fuel. That means that you can effectively almost zero out the insertion requirements if you perform your aerobraking correctly, although it's probably a good idea to carry a little bit of reserve fuel (or use your leftover maneuver reserve) anyway, just in case you need it (for instance, for correcting your trajectory after reloading your quicksave upon discovering that your first aerobraking pass takes you straight into Eve's surface ).

3. Since you're releasing both a probe and a robot lander (and possibly a separate manned lander, if that's a different vehicle from the Kerbin return vehicle you're using), your final vehicle is going to be lighter leaving Eve than it was arriving. Thus, you can probably cut your Kerbin return delta-v estimates a little closer than you would for just a single there-and-back craft, since your engines won't have nearly as much mass to push back to Kerbin.

That being said, an 8k transfer stage should definitely be enough to make it to Eve and back, even if your piloting gets a bit sloppy.

Hope this helps

[Barefoot Friar]

Awesome, thanks! This really helps.

I've read about aerobraking, but I've not tried it yet. This seems like the perfect opportunity to learn how.

[kahlzun]

it depends if you are planning to land the kerb on Eve surface: getting him back needs a LOT of extra dV...

[Barefoot Friar]

No, Kermit is landing on Gilly, which is no sweat. I'm sending a robot on a one-way to Eve's surface. I'll try a manned Eve landing later, after I've learned how to do a few more things.

[numerobis]

If you're up for a fly-by (and thus not landing on Gilly), you can get away with just the delta-V to get there, plus a little bit for course corrections.

[SaturnV]

Aerobaking is awesome for planet that has thick atmosphere, for your mission, it can save you 8000 dV of your oneway lander. If you don‘t managed to get back, I think 5000 m/s final stage ismore than enough