Lowest Delta-V to Eeloo

[GoSlash27]

PLAD,

 I'm too busy to participate, but I would just like to point out:

Given the Isp of the engine used, it is possible to verify the DV expended by comparing ship mass at start and finish. DV=9.807*ln(M1/M2) where M1=mass in LKO and M2= mass at Eeloo.

Best,
-Slashy

[herbal space program]

I kind of need to work on this for my Ultimate Challenge goal, so I might participate (although you guys have pretty much plastered this one already IMO).  However, I was also hoping I could show calculated dV based on screenshots of dry mass and resource levels, as @GoSlash27 suggested, rather than needing to install MechJeb. Would you consider a well-documented submission of that nature?

Edited July 15, 2016 by herbal space program

[PLAD]

On 7/13/2016 at 1:06 AM, specialopsdave said:

Wait a sec... I'm fairly new to this gravity assist thing, but... Would it theoretically be possible to, when using the Mun as an assist, somehow assist on Minmus directly afterwards to reduce the amount of passes you have to make? I'm not sure if it works that way, but I think it might work.

It would theoretically be possible, but in practice it would be so difficult to set up and the gains from the Minmus flyby would be so small that I don't think it would be worth it. Minmus orbits way out of the plane of Mun and the planets and is almost never where it would need to be to be used for a flyby. I'd guess the maximum gain from a flyby of it would be <10m/s, and course corrections would eat that up. It would be an ultimate in panache though to fly by both moons on the way out from Kerbin...

Edited July 15, 2016 by PLAD

[PLAD]

13 hours ago, herbal space program said:

I kind of need to work on this for my Ultimate Challenge goal, so I might participate (although you guys have pretty much plastered this one already IMO).  However, I was also hoping I could show calculated dV based on screenshots of dry mass and resource levels, as @GoSlash27 suggested, rather than needing to install MechJeb. Would you consider a well-documented submission of that nature?

This is something of a necro thread, I started it two years ago, but heck, I'd still enjoy seeing and scoring entries so I declare it is still open. It is a very difficult challenge and so I never got a formal entry other than mine (though I did get Vector's spectacular method for using a Mun multi-flyby to enormously cut dV used) Now to your and Slashy's question- it is possible to use the rocket equation to compute dV expended once we know the start and end fuel masses of the craft, assuming no other mass change occurs on the ship. We have to be careful about RCS expenditures in particular- since Monoprop's Isp doesn't match the main engine's fuel we'll get distortions every time you tap the fine controls. On the other hand that will increase the apparent dV used so I'd say it can be ignored. Hmmm... I guess if only one specified kind of motor is used for the large maneuvers so we don't have mixed Isps, and we are careful to record masses before and after staging events then it is acceptable to not use Mechjeb or KER to record dV.

     And in the two years since my last entry I did manage to get from LKO to Jool for 914m/s using Vector's trick, so clearly someone could beat my 1934m/s entry here by about 100m/s, but it would not be easy .

[herbal space program]

1 hour ago, PLAD said:

  And in the two years since my last entry I did manage to get from LKO to Jool for 914m/s using Vector's trick, so clearly someone could beat my 1934m/s entry here by about 100m/s, but it would not be easy .

Thanks for filling me in and thanks for the dispensation to use the rocket equation if properly documented. I did not notice how old the OP was, and I'm not sure I have the patience to try to beat what you posted using a combination of your KEKKJ route and Vector's strategy either, but I may try to submit something in the vein of "simpler but not quite as cheap" as part of my Ultimate Challenge planning. I recently managed to get from LKO to Jool for just under 1300m/s using nothing but DSMs and Kerbin assists except for the initial ejection, for which I used Mun. This is of course no great shakes in the "lowest dV" category, but it has the distinct advantage of requiring only the correct Jool-Kerbin phase angle at the outset:

 

You basically eject prograde then use retrograde burns at Ap to set up oblique Kerbin re-enconters which boost you to first a 3:2 and then a 2:1 resonant orbit. I never tried to use Mun on any of those subsequent Kerbin encounters, but I have a hunch that if I used it to bend my orbit inward as I swing around Kerbin, I might be able to eliminate or greatly reduce the dV I'll need for my solar  Ap  DSMs. Those basically consisted of pulling in my PE at solar Ap so that I'd be coming at Kerbin from the inside on the next pass, so I guess I could in principle use Mun to do some or all of that for me. I have already independently worked out how to use Mun to initially eject inward and prograde so that I can gain energy when re-encountering Kerbin from the inside a bit more than one year later and a bit further along its orbit, but what I found was that I got exactly as much energy back as I would have gotten ejecting prograde around Mun in the first place. This cooled my enthusiasm for the idea, but it never occurred to me at the time that I could use Mun again on the second encounter. It seems to me now that if I set it up so that my initial ejection is prograde and inward, I can re-encounter Kerbin one year plus a few days later, and instead of harvesting all that energy to eject prograde, I can add just a little prograde velocity and relatively more inward velocity, so that I'll encounter Kerbin again a little more than a year later a little further on its orbit. I can repeat this cycle multiple times, increasing my radial velocity significantly but my orbital period only slightly until I accumulate enough radial velocity relative to Kerbin that I can eventually hop up to the 3:2 orbit by swinging close around it rather than the Mun. If I can do that for the first resonant level, I should be able to do it again for the next one, and then finally to get to a Jool transfer orbit. I'm pretty certain I won't be able to get to Jool for 941m/s that way, but I might be able to do almost as well as your KEKKJ route without having to use Eve at all, which would be a worthwhile  accomplishment in itself since it greatly increases the frequency of usable transfer windows. Anyway, hopefully it won't take me so long to get around to trying this that I'll be necro-posting the result again....

Edited July 15, 2016 by herbal space program

[PLAD]

An impressive and interesting mission! I see what you are doing there, you are spitting  a Juno-style DSM into two, as a result the first DSM is closer to the Sun then a lone one would be, and the 2nd DSM is further from the Sun then a lone one would be. The very interesting question is whether that saves total dV over doing just one DSM and one flyby of Kerbin. The further from the sun you are at your DSM the higher the multiplication effect, so does the higher-efficiency 2nd DSM exceed the loss of the lower efficiency 1st DSM? Using Mun to get to the 1st DSM makes it even more complex, because the slower you are going when you fly by Mun the bigger its addition to your velocity. This will not be simple to analyze.

   You are quite right that a low-dV path that requires nothing but Kerbin and Jool is available much more frequently than any path requiring other planets and so will be used more often.

You have another interesting idea there, so far when doing multiple flybys of Kerbin or Kerbin/Mun we are increasing (or decreasing) the SMA of the ship's solar orbit, but one could instead  keep the solar SMA the same by 'storing' the extra energy in solar orbit eccentricity, you would orbit Kerbol in 1 Kerbin year but you would encounter Kerbin at a high angle relative to its path around the sun, thus giving a higher VSOI at Kerbin. I would be interested to see how that works out, I've avoided it because I fear the final flyby that sends you to your destination would require too much of a turn angle around Kerbin, and that little planet wouldn't be able to swing it (just like it can't do my low-dV KEKKJ with only one K between Eve and Jool). I you're only swinging to a 3:2 orbit then it might be OK.

We're finding all these excellent ways to get to Jool, but if you are going on to Eeloo then the windows are much more restrictive. At some point though someone is going to capture into orbit around Jool and then just wait until an optimal Jool-Eeloo window opens and use Tylo to get flung to Eeloo for free.

 

[DBowman]

On 7/20/2014 at 7:34 AM, PLAD said:

LKO to Eeloo surface: 1934m/s.

Hi @PLAD, I had a go following your 2344 trajectory - amazingly enough I kinda managed it - thanks for the detailed notes.

I think I was not so rigorous to begin with and then had to fudge things at the Jool & Eeloo encounters - still much lower dV than otherwise. I can tighten up on the encounter timing next time I do something like this - I'm working on a low mass Eeloo return. I found myself doing normal 'adjustments' to find the EKJ encounters (I mean an order of magnitude larger than your tweaks). Are these normal anomalies probably due to my timing sloppiness? Should I expect that if the timing is right then the planet will 'just be there'? Is there a rule of thumb re where the Pe should go? equatorial? wherever it causes the next encounter to pop out? Any advice is appreciated.

I've also used your FlyByFinder to find an Eeloo-Jool-Kerbin, and seat of the pants-ed K-K-K to get a cheap K return.

Edited August 5, 2016 by DBowman

[PLAD]

On 8/4/2016 at 6:40 AM, DBowman said:

Hi @PLAD, I had a go following your 2344 trajectory - amazingly enough I kinda managed it - thanks for the detailed notes.

I think I was not so rigorous to begin with and then had to fudge things at the Jool & Eeloo encounters - still much lower dV than otherwise. I can tighten up on the encounter timing next time I do something like this - I'm working on a low mass Eeloo return. I found myself doing normal 'adjustments' to find the EKJ encounters (I mean an order of magnitude larger than your tweaks). Are these normal anomalies probably due to my timing sloppiness? Should I expect that if the timing is right then the planet will 'just be there'? Is there a rule of thumb re where the Pe should go? equatorial? wherever it causes the next encounter to pop out? Any advice is appreciated.

I've also used your FlyByFinder to find an Eeloo-Jool-Kerbin, and seat of the pants-ed K-K-K to get a cheap K return.

Yup, I've found the most important parameters to match are the encounter times and especially the time of the Eve periapsis. Each successive flyby can be a little sloppier but when doing KEKJ or KEKKJ the time of the Kerbal departure and the Eve flyby should be less than +/-6 hours off. If you are outside that window you can still make it but the corrections required start to increase dramatically, as it sounds like you found out. The altitude of the flyby is not so important, just find the altitude and latitude of Pe that will get your ship to the next encounter at the right time. The trick is that you cannot see more than two or so flybys ahead because of the digital limits of precision, so you have to trust that the planets will be where you need them at the right time.

   There was a tool called Slinger that would show you where all the planets would be at a specific time in the future, that was very useful because it could show me where both Kerbin and my ship would be when I needed to be at a future flyby periapsis and it was easy to adjust things to make the two match up. I don't think it has been updated past 1.0.5 though. It really taught me that the encounter time was the most important thing though.