Lowest Delta-v to Moho

[Guest]

Almost everyone here would agree that Moho is just plain hard. I say almost, because there are a few here that make it look like another walk in the park. This challenge will hopefully find the best path to take to keep the fuel budget under control. I don't want to limit creativity here so I want you to use whatever means necessary to get to Moho with these things in mind :

1. One ship. No docking. The idea here is to find the optimal path.

2. Mechjeb is encouraged, mainly for the delta-v recorder. If you have another way of recording expended delta-v at all times, go for it. I want to see expended delta-v in each screenshot or video.

3. FAR entries will have a separate leaderboard because of the atmospheric changes on Kerbin.

So with that in mind, the ultimate goal here is to find the optimal path to Moho. Your score is your expended delta-v at Moho landing. Post your screenshots or videos showing launch from Kerbin with expended delta-v at 0, landing at Moho with your total expended delta-v, and anything you think is relevant in between that will help others follow your path. Lowest delta-v from Kerbin launch to Moho landing wins! Good Luck!

Leaderboard :

1. metaphor - 7,217 m/s

2. PLAD - 7,444 m/s

3. Jasonden - 10,851

4. Otis - 10,926 m/s

New Category : Moho return missions

1. Jasonden - ?

FAR Leaderboard :

none yet

- - - Updated - - -

Otis's entry : I think my departure date was year 1 day 76 according to Kerbal Alarm Clock.

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Edited April 13, 2014 by Otis

[PLAD]

A very useful challenge. My first time to Moho I was using an Ion motor so I'd have lot's of spare dV, and then I discovered I couldn't kill enough speed while in Moho's SOI and flew right on by, thrusting the whole way! F5/F9 and I ultimately had to break for 80 minutes (real-time!), adjusting the aim every few minutes. I try to avoid the direct route now.

So flying by Eve to lower both your start boost and Moho approach speed is the obvious approach. Here's how that went:

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Ever since Jasonden's Inspiration Kerbal challenge I've been trying to figure out flybys. I've made a spreadsheet to convince myself I understand the math before writing a program, but I can't execute the burn from low Kerbin orbit accurately enough to follow a path that has a small margin of error. (KSP Trajectory Optimization Tool nails this!) At least it shows me roughly where to look. In the first year UT I think there are two windows, one leaving Kerbin around day 138-144 and arriving at Eve around day 160-170; and one leaving Kerbin around day 310-320 and arriving at Eve around day 350-360. The first window doesn't have any quick routes to Moho (multiple sun orbits are required) but the second window theoretically has one that I show in the last frame. It also aims you nearer to Moho's Apoapsis. If you want to keep the total dV lower than a direct flight I think these are the only windows in the first year.

[Kasuha]

Someone posted this (and return) some time ago on Reddit. From Kerbin orbit to Moho low orbit it was 3213 m/s so the whole transfer took somewhere around 7000 m/s surface to surface. I guess to save a bit more one could also use Mun slingshot.

The point is, human guesswork has no chance against automated tools in this challenge. In the end it is not about who is better but who has better tools.

[Guest]

That's outstanding PLAD and exactly what I'm looking for.

Kashua, I wanted a place everyone who uses this forum could go and get ideas for Moho missions, a one stop shop for planning transfers, a general guide for Moho. I see alot of folks having the same problems I did. I am not a big fan of Reddit for reasons. This is not about piloting skills, there are already plenty of challenges for that. This is about finding the best path to Moho. PLAD showed that DV can be saved over mine. I want others to beat PLAD, and show how they did it, so others can follow along.

[Kasuha]

I wanted a place everyone who uses this forum could go and get ideas for Moho missions, a one stop shop for planning transfers, a general guide for Moho.

You posted in wrong forum, then. If you want to provide such info, you should use the Tutorials section. If you want to figure out how, you should post in the Questions section. This is Challenges section. People come here to show off their skill. Except that I don't think it involves a lot of skill to just run an automated tool which will do substantial part of the work for you.

I would post my attempt but I can't meet your requirement on recording dv because I don't (and am not going to) use any mods. And there's no point in preparing an entry just to get it disqualified.

[Guest]

Look, Kashua, I'm not trying to exclude you from anything. I wasn't trying to ruffle your feathers. I was trying to explain the point of the challenge. You don't have to use mechjeb or any other mod. I said in the OP that I don't want to limit creativity, and I mean it. Anyway that you can document your Moho mission is fine with me. But, the point of the challenge is to find the cheapest route to Moho in terms of total delta-v expended, so feel free to use any method you can come up with. Your input and opinions are important to me too.

[Jasonden]

A prosaic attempt -- I didn't go for the grav-assists, but tried for a good direct approach. Not totally direct, though -- I waited until a mutual node between Moho's orbit and Kerbin's, launched into an inclined orbit, and injected directly into Moho's orbital plane to avoid plane change maneuvers.

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10851 m/s dV.

[Guest]

Another great entry, Jasonden, thank you. I updated the leaderboard and added another category for return missions as they are important too for getting those science points. If you can still get a delta-v budget for the whole thing I'll put that up in the OP.

[donfede]

...I would post my attempt but I can't meet your requirement on recording dv because I don't (and am not going to) use any mods. And there's no point in preparing an entry just to get it disqualified.

Kasuha - you are sharp. Those of us that choose not to use mods such as mechjeb and ker, can simply take screenshots of mass (map view with expanded craft info) at key points. Calculating and presenting the math is simple (PM me if you'd like a sample libreoffice SS, but I've no doubt you can create a better one ).

[Jasonden]

Another great entry, Jasonden, thank you. I updated the leaderboard and added another category for return missions as they are important too for getting those science points. If you can still get a delta-v budget for the whole thing I'll put that up in the OP.

Ack -- I didn't save the dV on the way back! The return trip was doing double-duty for max science/$. At any rate, the return's dV wasn't as good as I'd have done for a low dV challenge anyway

[PLAD]

That Reddit post that Kashua pointed to really opened this up for me. I had done a 2-dimensional calculation of the minimum speed you can arrive at Moho with if you take a Hohmann path to it from Eve. I came up with about 2200 m/s if you went from Eve's periapsis to Moho's apiapsis, ignoring plane changes and the fact that those 2 apsis aren't 180 degrees apart. Close enough, I thought. Then I saw the Reddit post enter Moho's SOI at 1700 m/s. Another beautiful theory shot down by an ugly fact. So I ran Alex Moon's pork chop plotter and discovered that the Moho approach speed for Eve-Moho can be as low as 1100 m/s! Further study showed that this only happens when you leave Eve when Eve is near it's furthest point below the ecliptic plane, and arrive at Moho when it is near it's highest point above the ecliptic plane. The Eve position is much more important, so you must leave it within a day or so of day 144, 210, 276, etc. (keep adding 65.5 days).

There are 2 problems with this- it costs a lot of dV from Kerbin to arrive at Eve while it's so low, and it is not possible for Eve to change your approach from Kerbin enough to head to Moho. The flyby would have to be at about 550km below Eve's surface.

But doing 2 Eve flybys can solve that!

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The first flyby adjusts the inclination to match Moho's, and the 2nd lowers the periapsis. 8373 m/s total from surface to surface. I had to find a flight from Kerbin to Eve that arrived 65.5 days before a good window from Eve to Moho. It was fun. Note I only made small course corrections after leaving Kerbin, a first for me.

I only looked in the first year. This can clearly be beat, I think the theoretical minimum is about 750m/s less. (Double dare ya!)

[Guest]

That's looking good PLAD. The bar is set pretty high now. I'm currently playing with career mode and trying out some new ideas with the new parts introduced in .23.5. I want to get back to Moho and try out some of what you have showed us soon though.

[Naten]

You posted in wrong forum, then. If you want to provide such info, you should use the Tutorials section. If you want to figure out how, you should post in the Questions section. This is Challenges section. People come here to show off their skill. Except that I don't think it involves a lot of skill to just run an automated tool which will do substantial part of the work for you.

I would post my attempt but I can't meet your requirement on recording dv because I don't (and am not going to) use any mods. And there's no point in preparing an entry just to get it disqualified.

Use a Mainsail cluster hax'd with infinite fuel to get into orbit and then kill all of your speed. Then, undock with a docking port so there's not any noticeable force being sent out on detach, and start burning in one direction after infinite fuel's turned off. Record the speed you were at when you started, and then once all of the fuel's gone from the thing, then record your speed. Subtract the start speed from that speed (the "end speed,") and you've got an approximation of how much dV your ship has.

[Pds314]

Someone posted this (and return) some time ago on Reddit. From Kerbin orbit to Moho low orbit it was 3213 m/s so the whole transfer took somewhere around 7000 m/s surface to surface. I guess to save a bit more one could also use Mun slingshot.

The point is, human guesswork has no chance against automated tools in this challenge. In the end it is not about who is better but who has better tools.

3213 m/s is really amazing. I guess when I did the calculations and gave a minimum of 3600 m/s, I neglected to consider Eve's slingshot effect during the Eve transfer, just the possibility of redirecting or Aerocapture.

Of course, that doesn't mean this is the best possible. Multiple orbits using Eve or Kerbin as a repeated slingshot and/or aerobrake might be able to make it marginally more efficient.

And holy #%$#%#@$@#$%$@#$$%^$%#@ that is a tiny ship.

Too bad we can't use the sun for aerobraking...

[Jasonden]

There are 2 problems with this- it costs a lot of dV from Kerbin to arrive at Eve while it's so low

This is most impressive, and will be hard to beat! One idea for further improvement: you could save maybe up to 400m/s dV leaving Kerbin orbit by launching into an inclined orbit around Kerbin first. Then you wouldn't need all that normal dV.

[PLAD]

Me again, last entry for this challenge I hope, my honey-do list is being neglected.

I pulled out all the stops and put some good ideas others have had to use. I've put as many of the details into the album as possible so anyone can imitate this. The path has some margin from Kerbin to Eve, and Eve to Moho, but the Eve to Eve flyby dates are critical. This is how I'm flying to Moho from now on.

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Lucky timing or a slightly better window in later years might still knock a couple hundred m/s off of this.

Jasonden flew back! I bet with luck you could take this general path back for about 2300 m/s. I'd like to see that.

[Kasuha]

In the end I got curious so I tried at least LKO (100 x 100) to Moho 20 x 20 orbit. Screwed up a little (one too many Eve slingshots and missed Moho inclination somewhat) but I still made it in ~ 2965 m/s.

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[PLAD]

Kasuha has shown another innovation I hadn't considered. By Injecting energy at an Eve periapsis one reduces the boost required at Kerbal and the deboost required at Moho. At first I thought it would all come out even, but Eve is a lot heavier than Kerbal or Moho so the Oberth effect should be greater at Eve. It also adds flexibility to the whole mission as you can compensate for errors, and have wider launch and arrival windows, by adjusting the size of the Eve boost. I think. Can't try it for a few days, alas.

Edited April 9, 2014 by PLAD
Doh!

[Guest]

Life has thrown some curveballs my way and I haven't had much in the way of spare time lately. I see some new entries and I updated the OP. Kashua, can you give me a total DV used from Kerbin launch to Moho landing so I can put you in the OP also?

[Kasuha]

Kashua, can you give me a total DV used from Kerbin launch to Moho landing so I can put you in the OP also?

No I can't. As I wrote before I don't use mods so I have no idea how much dv I used to get to orbit on Kerbin. Also I have not landed on Moho so my entry does not qualify for your challenge.

It would make me more than happy, though, if you do me a favor and spell my name correctly. Thank you.

[metaphor]

Here's a 7217 m/s attempt. About 4400 for launch to LKO, 1700 for LKO to Moho capture, 1200 for Moho capture to landing. I used the same strategy as the MESSENGER spacecraft to Mercury, with 2 Eve gravity assists followed by several Moho gravity assists. It should be possible to go even lower, under 7000 m/s, by optimizing the transfers.

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[Guest]

Wow, metaphor, that's impressive and also shows a level of patience few ever achieve. Leaderboard updated, and I've got a feeling that's going to be really hard to beat without adding even more gravity assists from the Mun or something.

My apologies to Kasuha, no offense intended. My eyes and my brain aren't always on the same page.

[donfede]

A very useful challenge. My first time to Moho I was using an Ion motor so I'd have lot's of spare dV, and then I discovered I couldn't kill enough speed while in Moho's SOI and flew right on by, thrusting the whole way! F5/F9 and I ultimately had to break for 80 minutes (real-time!), adjusting the aim every few minutes. I try to avoid the direct route now.

So flying by Eve to lower both your start boost and Moho approach speed is the obvious approach. Here's how that went:

http://imgur.com/a/IKeHM

Ever since Jasonden's Inspiration Kerbal challenge I've been trying to figure out flybys. I've made a spreadsheet to convince myself I understand the math before writing a program, but I can't execute the burn from low Kerbin orbit accurately enough to follow a path that has a small margin of error. (KSP Trajectory Optimization Tool nails this!) ...

Nice pics and flight PLAD. Is your spreadsheet available? What were you thinking per program-wise? Had you considered forking/patching alexmoons coffeescript?

[donfede]

Here's a 7217 m/s attempt. About 4400 for launch to LKO, 1700 for LKO to Moho capture, 1200 for Moho capture to landing. I used the same strategy as the MESSENGER spacecraft to Mercury, with 2 Eve gravity assists followed by several Moho gravity assists. It should be possible to go even lower, under 7000 m/s, by optimizing the transfers.

Can you elaborate Metaphor on your technique of sending a probe to equatorial orbit with a maneuver node? Looks like it's to save the step (and dv) of establishing LKO before burning for Eve. Did you use it for any inclination changes?

Also, can you share how you identified the launch windows, or should this approach be repeatable for several Eve->Moho encounters?

Edit: relevant link to this thread/discussion - describing gravity assists (including leveraging Eve's inclination) http://www.reddit.com/r/KerbalAcademy/comments/1or0d8/psa_how_to_gravity/

Edited April 10, 2014 by donfede
link to gravity assist doc

[metaphor]

Can you elaborate Metaphor on your technique of sending a probe to equatorial orbit with a maneuver node? Looks like it's to save the step (and dv) of establishing LKO before burning for Eve. Did you use it for any inclination changes?

Also, can you share how you identified the launch windows, or should this approach be repeatable for several Eve->Moho encounters?

Edit: relevant link to this thread/discussion - describing gravity assists (including leveraging Eve's inclination) http://www.reddit.com/r/KerbalAcademy/comments/1or0d8/psa_how_to_gravity/

Yeah, so first I sent a test probe into equatorial low Kerbin orbit, then made a maneuver node from that probe to get to Eve. I had to cross Eve's orbit at an ascending/descending node (so that I would actually intersect Eve's orbit instead of going below/above it). So I added a liberal amount of inclination change to the maneuver node to make sure that happened. As you can see from the picture, it's going about 30 degrees towards the south (that node had about 1200 m/s prograde component and 1600 m/s southward component, for a total of 2000 m/s (Pythagorean theorem)). But it's inefficient to do such a huge inclination change when you're already in orbit. Much more efficient to do it during launch. So I waited until the KSC was right under the maneuver node and I launched the ship into an orbit inclined 30 degrees to the south of an equatorial orbit. It doesn't cost much delta-v to launch into an inclined orbit rather than an equatorial one, you lose maybe 50 m/s from not taking full advantage of Kerbin's rotation. But now, if you remake that same maneuver node in the new orbit, you don't have to add any inclination change, you can burn straight prograde to get the same effect, for only ~1200 m/s. Ships do this all the time in reality, when they need to go to an interplanetary destination where they need an inclination change, they first launch into an inclined orbit around Earth to save delta-v.

The only real planning I did for this mission was to identify the Moho-Eve ascending/descending nodes, so that I could get gravity assists from Eve at a node. That way, I could burn from Kerbin and meet Eve at one of those nodes, so that Eve gravity assists could eventually cancel out all my Moho-relative inclination. With more planning, you could look for windows such that you always have less than one or two orbits between gravity assists, but I just waited in solar orbit for a few orbits each time until the planets happened to line up, since flight duration wasn't a factor.