Eve Free Return?

[Deathsoul097]

Hi, I want to run a mission past eve, as a manned flyby. Does anyone have an idea of the timeframe and DV requirements of such a mission?

I believe 220+ days is probably way too long, but does anyone know for sure?

My craft currently has about 222 days worth of LS, and just under 8K DV. Is this possible with what I have, or do I need a redesign?

(This is not a question about a mod, this is a question about the stock game. I am simply limiting myself with a mod.)

[Gravitas Shortfall]

Hi, I want to run a mission past eve, as a manned flyby. Does anyone have an idea of the timeframe and DV requirements of such a mission?

I believe 220+ days is probably way too long, but does anyone know for sure?

My craft currently has about 222 days worth of LS, and just under 8K DV. Is this possible with what I have, or do I need a redesign?

(This is not a question about a mod, this is a question about the stock game. I am simply limiting myself with a mod.)

A Kerbin year is far less than 222 days, I believe, and so if you had a trajectory that was more or less completely contained within Kerbin's orbit, it should also take less than 222 days. As for planning such a trajectory, that's a bit more difficult. I suspect that it's possible with 8K DV, but I don't know how feasible it would be to find a workable solution via trial and error. There should be a program floating around this forum that's capable of planning flyby maneuvers. I don't know if it can handle the weird case where your destination planet is also your planet of origin, but it's probably the closest to what you're looking for if you just want to go to Eve and back. The problem gets more complicated if you want to chain together multiple gravity assists, like NASA did with the Voyager missions, and I'm not aware of any existing tools that'll do that for KSP.

[Deathsoul097]

Well, it shouldn't be much in the way of gravity assists, as I just want to do a close pass by eve and then burn to intercept kerbin. I want to do it in such a way that I will get the maximum benefit, and use the least DV. I know that the Olex calculator will give me transfer windows and DV for an ejecion burn, but it won't do hyperbolic orbits, or give me a transfer that will go from eve to kerbin (or kerbin to eve) that isn't in an associated transfer window.

[Kryxal]

It actually WILL give you those numbers, just click on the appropriate spot for transfer time and length. When were you looking to take this trip anyway?

[Gravitas Shortfall]

Here you go: http://alexmoon.github.io/ksp/

You can put restrictions on departure date and travel time. What you have to do is find a transfer from Kerbin to Eve, note the arrival date, and then find a transfer from Eve to Kerbin that leaves the same day. You can add up the required DV for both legs, but that's going to be a big overestimate if you're just doing a flyby, as you'll never need to match velocity with Eve, and you can do an aerocapture when returning to Kerbin. I'd suspect that 8K DV would be more than enough.

[ScottyDoesKnow]

Here you go: http://alexmoon.github.io/ksp/

You can put restrictions on departure date and travel time. What you have to do is find a transfer from Kerbin to Eve, note the arrival date, and then find a transfer from Eve to Kerbin that leaves the same day. You can add up the required DV for both legs, but that's going to be a big overestimate if you're just doing a flyby, as you'll never need to match velocity with Eve, and you can do an aerocapture when returning to Kerbin. I'd suspect that 8K DV would be more than enough.

That's pretty cool, I've seen screenshots of the tool but never tried it myself, so I did it out of curiosity. First time using the tool, so I may have screwed up somewhere.

First window is Year 1, Day 147 for 1061 dV. This looks like a perfect transfer (eve and kerbin in the same plane, even though eve is inclined) which you can't always get without a lot of waiting so I'd add on at least 430 which is the max inclination change requirement based on my dV map. So that's ~1500. Looking at the Eve -> Kerbin transfer on Year 1, Day 196 (the day you arrive), the best is 3353 dV. I would assume this isn't perfect, but I'd add on the inclination change dV anyways for safety. So that's ~3800.

For safety I'd say at least 5500 total dV required, which means your ship has tons of dV if your 8k figure is from LKO, but not enough even for even a perfect situation if you mean 8k on the ground.

[Gravitas Shortfall]

That's pretty cool, I've seen screenshots of the tool but never tried it myself, so I did it out of curiosity. First time using the tool, so I may have screwed up somewhere.

First window is Year 1, Day 147 for 1061 dV. This looks like a perfect transfer (eve and kerbin in the same plane, even though eve is inclined) which you can't always get without a lot of waiting so I'd add on at least 430 which is the max inclination change requirement based on my dV map. So that's ~1500. Looking at the Eve -> Kerbin transfer on Year 1, Day 196 (the day you arrive), the best is 3353 dV. I would assume this isn't perfect, but I'd add on the inclination change dV anyways for safety. So that's ~3800.

For safety I'd say at least 5500 total dV required, which means your ship has tons of dV if your 8k figure is from LKO, but not enough even for even a perfect situation if you mean 8k on the ground.

Hmm, is the 3353 from Eve assuming you're starting from Eve orbit? If this is just an Eve flyby, then the ship should actually already be on a trajectory to more or less intercept Kerbin's orbit without any burn near Eve. Any burn just needs to adjust that trajectory enough to account for the fact that you aren't actually in an Eve -> Kerbin launch window.

Also, this method is assuming an optimal transfer from Kerbin to Eve, but another thing someone could try is forcing an early or late transfer using the date constraints, and then seeing if you make up that DV with a more favorable return.

[ScottyDoesKnow]

Hmm, is the 3353 from Eve assuming you're starting from Eve orbit? If this is just an Eve flyby, then the ship should actually already be on a trajectory to more or less intercept Kerbin's orbit without any burn near Eve. Any burn just needs to adjust that trajectory enough to account for the fact that you aren't actually in an Eve -> Kerbin launch window.

Also, this method is assuming an optimal transfer from Kerbin to Eve, but another thing someone could try is forcing an early or late transfer using the date constraints, and then seeing if you make up that DV with a more favorable return.

You're right, I didn't consider that. So that could save you 1061 dV right there. I thought about the optimal transfer possibly not being the most optimal transfer-and-return, but honestly it seems like too much of a bother trying out a bunch of different dates.

[Gravitas Shortfall]

edit: weird delayed dup post - disregard.

[Deathsoul097]

Well. I did it. With under 7.3Km/s of DV from kerbin's surface, and got a low flyby over eve. It was essentially, get to orbit, transfer, plane change, low pass and burn at peri, and then another slight plane change/prograde burn to intercept kerbin with a 15km peri. (Meanwhile I was still halfway between eve and kerbin.) Also, total flight time was about 120 days, so I could have probably managed to tag on another kerbal or two, or given myself a bit more DV leeway. Funnily enough, if I had done an extra 100m/s of burn at eve peri, I would have had a suborbital jool encounter. Talk about dumb luck. (It was about 2 years away however, so I looked at it laughed, and said, how's about no.)

Jeb pack your bags, were going on a trip.

*where to?*

Everywhere. (I have never been to dres, ike, bop or pol, and I have only ever landed on duna, eve, jool(?), gilly, mun/minmus (They go without saying really.) eeloo and laythe. I find it funny actually, many people complain about ike and how it's always in the way. I almost never encounter it. I'm either lucky, or Ike likes my kerbals.)

Edited March 2, 2014 by Deathsoul097

[Kryxal]

Try working it backwards, maybe? The return requirements upon Eve arrival are UGLY!

For departure from Eve, there's a nice window at year 1 day 322, about 1400 delta-v with a flight time around 56 days, but you can cut that down a LOT with some extra delta-v: year 1 day 318, 1750 delta-v, 21 days!

With a Kerbin departure at year 1 day 147 for not quite 1100 delta-v, aerocapture at Eve and return via the short route given, you're looking at getting back with about a month to spare (though your Kerbals might not appreciate the 4-month layover) and are under half your delta-v requirements.

In addition, if you come off-window on your departure, you can leave a bit over a month later for an extra 400 delta-v or so. With the delta-v you have, and the ability to aerocapture and wait on the other end AND on return, your windows can be more flexible than most.

Edit: oops, a bit too late...