What is the best way to travel to Eeloo and Moho?

[Michael-92]

Hi, I am currently in the process of planting a flag on every celestial body in the Kerbol system.

I have found travelling to Duna, Eve and Dres to be easy enough. I haven't been to the Jool system yet but I imagine it will not be too hard as its inclination is not too much.

However I cannot find a fuel efficient way to travel to Eeloo and Moho, their highly inclined orbits make me think the standard interplanetary transfer methods won't work.

What is the general consensus for travelling to these planets? Can anyone supply a good video tutorial?

Thanks

[lumpman2]

Generally, you should use an interplanetary tug for Eeloo (use another ship with nukes docked to the main lander). I've never visited Moho before, but I would imagine it's not very hard to get enough fuel to reach it since I had boatloads of fuel left when I was in low Eve orbit, and unfortunately I had to ditch all of it. Inclination is not that big of a deal as long as you can match it up as closely as you want to.

[Johnno]

LV-N (nuclear) engines + plenty of fuel. I use alexmoon's Launch Window Planner, usually with a ballistic trajectory but with course corrections where necessary (after leaving Kerbin's SOI and just before entering target's SOI). Alternatively you can match inclinations at ascending/descending node.

[nimbim]

First of all, Moho needs the most delta v out of the planets, just like Mercury.

To rendezvous with Moho and Eeloo it is indeed easiest to go into a solar orbit and plan your transfer maneuver from there. However, it will be less efficient than 1 direct burn to the target from Kerbin. With enough patience you don't need to adjust your plane very much, but matching Moho's plane will make the rendezvous so much easier.

In short, Eeloo needs lots of patience (distances) and Moho needs lots of delta v.

[Scarecrow88]

I've just put a ship in orbit around Moho for the first time, using a ship that successfully went to Eeloo and back, and it's way underfuelled. I even had to use the lander engine and fuel just to slow down enough to get captured. Needless to say, even though the orbit is stable, my Kerbals don't have enough fuel left to make a landing and definitely not enough to get home again, so I've go to work on putting a refuelling rig together to top up their tanks. At least the fuelling rig will only be making a one way trip.

[dave4002000]

The main thing with Moho is making sure you hit your transfer window exactly. Unlike most of the other planets, there isn't a lot of 'wiggle room' for when you can start your burn and a missed window can mean the difference between a 5,000m/s transfer and a 20,000m/s transfer.

The procedure is basically the same as anywhere else, though. Use the planner than Johnno linked to figure out your launch time. Then use this: http://ksp.olex.biz/ to figure out where you should start the transfer burn while in Kerbin orbit. Match planes by burning normal/anti-normal as you cross the DN/AN mid-transfer.

[SRV Ron]

Try to get a capture window where the orbital plane intercepts your orbital plane. That way, you don't have to expend a lot of fuel matching the orbital plane. Getting that small window for capture may, however, take years in Kerbal time.

[Michael-92]

I am still wasting a lot of fuel making a successful round trip to Eeloo. How much fuel should I take, say compared to a mission to Dres?

[Hannu]

These planets have inclined and eccentric orbits. On the other words, orbit calculators which does not take these things into account can give completely useless results. You should use Alexmoon's one. It is not exact too (actually it may be but KSP's physics engine is not) and typically you can use 10-20 m/s lower values. But I have nearly always got encounter with values it gives. You should notice too, that required delta-v varies tens of percents between launch windows.

There are not any more special with these celestial bodies. Especially Moho needs quite large amount on delta-v, but you can do it with LV-N. Just put enough fuel with you. Roundtrip to low Moho's orbit and back takes about 7500-9000 m/s depending on exact geometry. If a calculator gives bad values, you can check couple of next launch windows and delay launch a month or two, because Moho's orbital period is short. Landing and ascending needs additional 2500-3000 m/s from low orbit. You must be very careful in orbit planning and maneuvers. If you make small mistakes everything can look good until you notice in Moho's SOI, that your relative velocity to planet is 5000 m/s instead of planned 2000-3000 m/s. Check the orbit few times during course (immediately after leaving Kerbin's SOI, on about halfway, 5 days before encounter and immediately before and after Moho's SOI change) and make corrections early. Eeloo is easier than Moho. Transitions need less delta-v and planet has lower gravity which helps orbital maneuvers and landings. But it needs several thousand of meter per second too, if you are going to land.

[Sauron]

Eloo actually requires less DV to reach than Dres (usually). The skill being tested is transferring to a very inclined and eccentric orbit. Also patience

[Hannu]

I got inspiration to make a Moho trip. I noticed that it was very difficult to get good results even with the Alexmoon's calculator. But when I took Kerbin's finite SOI into account, things started to work. Escape velocity from SOI's surface should be about 290 m/s but the game neglects it. When I subtracted corresponding energy from velocity immediately after burn, it gave exact encounter at exact time. Error of just couple of meters per second are too bad with Moho.

But that was just a theoretical level. Other problem was how to realize that precise delta-v. Values are ideal infinitely short impulses and practically you burn finite time and move tens of thousands of kilometers in varying gravitational potential during that time. I could fix it by making 42 m/s correction immediately after leaving Kerbin's SOI. It would be interesting task for Mechjeb's devs to program a function that makes burns which lead to exact same orbits than ideal values. Do not try to make trans Moho injection from too low altitude. I used 250 km and it gave quite large error. You lose very easily every m/s which Oberth effect saves. And I recommend that you take at least 1000 m/s extra delta v with your first Moho mission. I an sure that that you will need it.

[Stochasty]

The cheapest way to get to Eeloo is to use a Jool gravitational assist to boost your orbit and change your inclination. The conceptually easiest way to manage this is to time your Jool intercept so that Jool is located at either the ascending or descending node (with respect to Eeloo) when you reach it. You can then use a gravity assist to put yourself into an orbit co-planar with Eeloo for free. (For added bonus points, you can use an aerogravity assist, but this is much more difficult.) You probably won't manage an Eeloo intercept directly after the Jool encounter, so I recommend putting your apoapsis out to slightly beyond Eeloo's orbit, and then using a deep-space maneuver at apoapsis to generate your intercept (total cost for this maneuver should be only a couple of hundred delta-v). Because the Jool assist will have substantially raised your periapsis, you encounter velocity at Eeloo with be much lower than it would be on a normal Hohmann transfer, saving you substantial delta-v for your orbital insertion. I've managed a landing on Eeloo with a total delta-v cost on the order of ~3.2km/s using this technique (2km/s for the Jool transfer, ~200m/s for the deep space maneuver, and around ~1km/s for the insertion and landing).

Moho is a lot harder, but you can use a series of Eve/Moho encounters and deep space maneuvers to walk yourself down the gravity well. The goal is not to generate a cheap intercept, but to generate a cheap insertion (since this is where most of your delta-v will be spent). I don't have an exact estimate here, since I haven't flown what I'd consider to be an efficient mission yet; multiple encounters take a lot of patience and planning. Take a look at the flight plan for the NASA MESSENGER mission to give you an idea of the process.

[JiWint]

I did travel to moho with an orange tank + 4 largest FL tanks and 4 LV-N engines.It reached moho with a little fuel remaining (I'm not doing maths so...).

[Jackissimus]

The goal is not to generate a cheap intercept, but to generate a cheap insertion (since this is where most of your delta-v will be spent).

This can't be stressed enough. It costs 2x to 3x times more to insert.

My method? I try to launch a mission to Moho every Moho-year, so about every 30 days. Some Moho-years are just way too expensive so I skip them. I try to aim under about 5200m/s total. I use alexmoon's planner, set to optimal trajectory. It can be done, but you have to be patient. I first set up the correct ejection deltaV and ejection angle (roughly) and then I try to optimize until I get about the correct transfer Apo and Peri. The Apo is usually a bit above Kerbin orbit*. Then I start playing with the Normal+/- marker to move the AN or DN to the opposite side of Moho's orbit (this is where my intercept will be). Then I play sort of with all the markers at the same time until I get an intercept, the resulting dV is usually around what alexmoon's planner predicted.

* I don't really know why is this, although I have some guesses. Can someone explain?

[Moar Boosters]

Yup. And if you screw up the insertion as badly as I did my first time.... you end up lithobraking at around 4km/s.

I didn't find getting the intercept with Moho that difficult and on my second attempt I was able to achieve orbit. The mission went pear-shaped after they landed and re-orbited. They have about 2k delta v remaining, and I couldn't find a return to Kerbin for less than about 3.5k. They're still orbiting moho, waiting for me to send them a big orange tank with a docking adapter on it.

[Hannu]

Moho orbit insertion is very sensitive. I tried to use window which open at year 5 day 266 as exactly as I could. I calculated every possible details I could and finally got correct orbit. Insertion to 98 x 99 km orbit took 1864 m/s. Theoretical value to 100 km orbit was 1852 m/s (alexmoon's calculator shows 1855 m/s but I got about 3 m/s free because KSP does not take gravity into account outside SOI). But before I understood the effect of limited SOI, I tried to trans Moho injection with 11 m/s too high velocity. It gave nice encounter, but fortunately I investigated things further. Braking would have needed over 3000 m/s. You can also see sensitivity from dv transfer maps. Launch windows to Moho are very narrow and dv requirements increase very steeply if you deviate from optimal orbit.

But do not worry if you hate mathematics. I have flown to Moho and back with oversized crafts before and wondered why all calculations underestimate MOI so much. If you do not enjoy playing with orbital mechanics, pack 10000 m/s and use good old brute force. It is the most easy solution.

This is my Moho craft. Orbital mass (250 km orbit) is about 70 t.

Edited September 3, 2013 by Hannu
I added image.

[Vanamonde]

I believe the best way to deal with inclination would be to match planes in your Kerbin orbit before setting out, though I confess that I haven't figured out how to match planes, hit the launch window, AND arrive at the right point in the target's orbit so that you are *on* its orbital plane rather than merely parallel to it. (Sorry I can't explain that more clearly, but I don't have the technical terminology for the situation.)

[Hannu]

Yes, it is true and real planet probes use it. But unfortunately KSP and any mod as I know do not have suitable tools to determine all orbital parameters and help to launch at correct time to get correct longitude of ascent node. I launch always equatorial orbit and then calculate prograde and normal components of needed delta v and search correct time by Mechjeb's Maneuver node editor. It does not typically increase delta v more than 100 m/s even with most inclined planets. Inaccuracy due to the long duration of burn is worse thing.

[SRV Ron]

This all stock interplanetary probe rocket made it to Moho using the upper stage LV-N with drop tanks. I first did an orbital plane burn before doing the capture maneuver. It does take long burns for orbital capture unless you can plan for that ideal window of launch and capture where you can eliminate the orbital plane burn.

The interplanetary probe vehicle to anywhere with universal probe lander.

Probe orbiting Moho

[Michael-92]

I finally landed and returned from Eeloo, Alexmoon's calculator really helped. I will try a Moho mission soon and report back how it went.

[Michael-92]

Well, I made it into orbit around Moho, with my mothership having enough fuel to take me home. But I severely underestimated Moho's gravity and didn't have a big enough lander to arrive at the surface then go back into orbit.

Oh well, back to the drawing board I guess.

All the advice in the topic has been sound so far, I would recommend trying the techniques posted in this thread so far for anyone who is struggling to travel to planets with an inclined orbit, as well as people dealing with how to go to Moho.

Thanks

[kurja]

I believe the best way to deal with inclination would be to match planes in your Kerbin orbit before setting out, though I confess that I haven't figured out how to match planes, hit the launch window, AND arrive at the right point in the target's orbit so that you are *on* its orbital plane rather than merely parallel to it. (Sorry I can't explain that more clearly, but I don't have the technical terminology for the situation.)

afaik it is not possible to match inclinations with another body while orbiting kerbin; consider that you are essentially orbiting the Sun alongside kerbin, you can't really have a different inclination without first leaving kerbin's soi. Maybe you could launch and exit kerbin's soi at an angle matching your target body's inclination, but then you'd need to do that an an ascending/descending node which isn't likely to coincide with your launch window :^/

[WafflesToo]

Energetically speaking, Moho is one of the more distant planets from Kerbin. I haven't tried it yet, but I think it might be cheaper to use a bi-eliptic transfer instead of the more traditional Hohman maneuver.

The real trick will be finding out if I'm any good at pulling off a bank-shot

[Vanamonde]

afaik it is not possible to match inclinations with another body while orbiting kerbin

I phrased that poorly. I meant make your Kerbin orbital plane parallel to the target planet's orbital plane so that you don't have to change planes during the transit, though that does have the complications I went on to mention.

[Stochasty]

The way to do what you want, Vanamonde, is to look up the ejection angle and ejection inclination from your preferred launch window planner and use that to set your inclination. You want to launch at the time of day such that your position on Kerbin's surface is below the point in your orbit where you would want to make your ejection burn, and instead of launching due east you launch either north or south by an amount equal to the ejection inclination specified.

Edited December 7, 2013 by Stochasty