Moho approach

[Colmath]

Hi!

I just sent my first probe to Moho as kind of an exploratory move for future (kerbaled?) missions. It started out with about 10000 m/s deltaV, and with my limited experience in interplanetary travel I managed to establish an encounter with the planet with a periapse of 40 km, so I can use the most of the Oberth-effect. But when I created the node for a braking maneuver at PE I was shocked: it required 5500 m/s deltaV!!!!

Is this normal being in the inner kerbol system, and I came in at the fastest part of my orbit around Kerbol, so orbital mechanics say I should be pretty fast, which I was: not much inside Moho's SOI I was flying at around 6100 m/s.

But still 5500 m/s seems harsh. Am I doing something wrong, or such braking maneuvers are to be expected when visiting Moho?

[Mr.Rocket]

This is actuallly completely normal. I think i saw there are advanced methods of doing it to save alot of delta-v, but i don't know where i saw this. You could slow down at Eve somehow, but otherwise 6100 is normal for this to happen. This is coming from someone who made the same mistake. I got a pe of about 7 km, and i flew by that planet in about 10 seconds, barely had enough time to take pictures.

[Taki117]

Not sure if this is the Exact Video I'm looking for, but I think it will get the job done.

[MaverickSawyer]

Yep. the Kerbin-Moho run has one of the highest dV requirements, just because of your high speed upon arrival without any chance of aerocapture. So, since you picked up all that speed on the way downhill, you have to dispose of it somehow...

[TheDarkStar]

Moho is the hardest place to get to. The only way I can think of to lower requirements is to do what Mr. Rocket said and aerobrake at Eve a bit, but this will likely only remove about 1000 dv off your total amount.

[Dave Kerbin]

I've been there twice now (crashed once). There are two things I've figure out so far to help reduce your delta-v requirements.

The first is common to any planet and it looks like you did it, which is try to get your PE as low as you can before you even enter Moho's SOI. With tweakables you can lower your engine output to as little as 5.5% (this can be changed in flight, not just in the VAB) which gives you the fine control to adjust your PE while still days or weeks away.

The second thing which will probably shave about 1000 - 1500 m/s off the capture is to try and get your inclination matched up to Moho's for your encounter. If you do it during your mid course correction it will probably only cost 200-300 m/s, though you might need an extra orbit before the encounter. Basically think of it like docking, when you reach Moho you're going to need to zero out the relative velocity and make your orbit match Moho. Now you'll get an assist from Moho's gravity but the ratio of that assist compared to your very high orbital velocity will be much less then you get with other planets farther out. Coming in on an incline means you'll have to cancel out all of that 'vertical' velocity, and your velocity being so high the vertical portion will be high too.

[capi3101]

Go maccollo!!! - A post from a couple of months ago, with instructions on how to get to Moho for just 4,000 m/s of delta-V. No cheats involved, just a matter of rethinking how you do that particular transfer.

[canuckster]

I'm currently on my first mission there and I'm sending "rescue" ships to refuel. My first wave of ships included a tug with a lander, a crew ship and a refuel ship. I miscalculated so the tug with the lander didn't have enough dv so I had to use the landers fuel to complete moho capture. Because of this I had to improvise and use all of the refuel ship fuel to fuel the lander, my crew ship is on fumes and needs fuel to get home. I've assembled a monster in orbit so that I can have a full orange tank by the time I get to moho.

[DMagic]

High dV requirements are normal for Moho, but 6000 m/s just for the capture burn is a bit on the high end. You should be able to get from Kerbin orbit to Moho orbit for around 5000 m/s without too much trouble.

The best advice I have is to completely ignore Moho's position relative to Kerbin's. Just start the transfer burn from Kerbin so that you touch Moho's orbit near its closest approach to the sun. Then treat the encounter like a docking rendezvous. It might take a few orbits to get everything lined up, but this way you can ensure that you get an ideal encounter with Moho, one where your solar periapsis matches Moho's and you meet at that point.

[technion]

The transport I took to Moho was built for my Jolean tour. It carried five landers, including landers for Tylo and Laythe, and a science module for each of them, to all the moons of Jool, and then returned. The same transport just barely carried a small lander to Moho.

[Colmath]

Thanks for all the answers guys, I think I learned some things here, useful things. For example I've never thought to do the inclination change in Kerbin's SOI, I never even tried it was so obvious for me to do it in interplanetary space.

I don't think I'll go back to Moho in a while, this mission was only put together because when I returned my mission for Dres I saw on Protractor that I was really close to a Moho launch window, so I sent my Joolian system explorer out to test the waters. As I've said it has about 10000 deltaV, and I managed to get to Jool, and procedurally visit all its moons one after the other with it with plenty of fuel remaining, so I was confident. Turns out, I still need to learn a lot about interplanetary travel.

BTW why is it that this guide says 800 m/s for plane change? however I did it I could not create a node under 1300.... Maybe this launch window I chose was the worst possible one there is?

[Kasuha]

For classic transfer from Kerbin to Moho, use Alexmoon's calculator. Then you'll make it under 4000 m/s.

Gravity slingshot around Eve is possible and can reduce needed dv dramatically - after a lot of trying I was able to transfer to Moho from HKO for about 2700 m/s. But it is very tricky to set up manually.

[radonek]

For classic transfer from Kerbin to Moho, use Alexmoon's calculator. Then you'll make it under 4000 m/s.

This sounds too good to be true… are you sure it works? Like, really works? Or just "oh, and bring along couple of mainsails for that 3000m/s-in-twenty-seconds burn" kind of works?

[Kasuha]

This sounds too good to be true… are you sure it works? Like, really works? Or just "oh, and bring along couple of mainsails for that 3000m/s-in-twenty-seconds burn" kind of works?

Okay I'll correct myself - it's not "under 4000 m/s", it's "around 4000 m/s". Apart of that, it works. I have successfully used it a few times particularly for Moho. Yes, there is a 1500-3000 m/s braking burn but I found it manageable even with LV-Ns if you correct your trajectory to go sufficiently close to Moho surface. To my recent surprise, Moho's Oberth effect is not as insignificant as I thought it to be.

[maccollo]

You can consistently go from low kirbin orbit to low moho orbit for 4000 m/s every time.

You just have to know how to do it right. I wrote a guide on how to guide on how to do it properly, which I've linked below.

http://forum.kerbalspaceprogram.com/threads/61478-Oh-bugger-Injection-burn-at-Moho?p=835667&viewfull=1#post835667

Edited January 22, 2014 by maccollo

[radonek]

It spew 4877m/s total on me. Still, with my first and last attempt at direct hohmann to moho ending at 5500m/s for orbital insertion alone, this IS impressive. Too bad my current Moho expedition is already underway :-(

[Kasuha]

It spew 4877m/s total on me. Still, with my first and last attempt at direct hohmann to moho ending at 5500m/s for orbital insertion alone, this IS impressive. Too bad my current Moho expedition is already underway :-(

You can get lower numbers if you extend the lookup interval. About one of five launch windows is significantly better than the rest.

Of course, maccollo's approach is cheaper than that, and takes longer time.

Using Eve gravity assist is probably cheapest (if you do it right), most laborous and takes the longest. Although if we had a calculator which takes that gravity assist as an option, it would not take significantly longer than standard transfer. It's the orbit matching part which takes the most of the time.