Need help flying to Moho

[OptiSTR]

Hey guys

So i researched the Nuclear engines and made a probe with 3 FL-T800 fuel tanks and 3 Nuclear Engines.

Im using MechJeb, so at first i ordered MechJeb to create Hohman Transferee to to target (Moho), after the maneuver i noticed that I used half of my fuel.

Then I ordered MechJeb to align orbits inclination with Moho, after it was done, i was left with about 1/4 fuel tank.

Then I ordered MechJeb to "transfer to target" but it looks as if nothing is happening.. MehcJeb just doing nothing, not even a maneuver node..

Anyways my question is...

1. How much fuel do i need to fly from a high orbit around the Sun, to lower orbit + catching Moho and landing on it, and then returning to Kerbin?

2. Why MechJeb doesnt make a maneuver node to catch Moho?

Cheers

[r4pt0r]

protip: try playing with the maneuver node on your own. it will improve your ability as a player

Edit: this isnt an anti MJ slam or anything, but try placing a node and dragging the dials. you will learn from it.

[Link]

Why is mechjeb not doing the 'transfer to target'? Well, you already did that, first thing! A holmann transfer is a transfer to your target. Best way I've going with mechjeb is to start in your orbit around kerbin, and use the maneuver planner to 'transfer to another planet'. After leaving kerbins SoI, do a 'fine tune closest approach' to make sure you get an encounter. Then just go about your normal routine!

The person above talking about making your own maneuver node is definitely good advice. A lot of times, I find I can set up a maneuver node that spends less dV than mechjeb, but still use mechjeb to execute the maneuver.

So yea, plain and simple, you already did your transfer

Edit: in order to use mechjebs Holman transfer ability, you must be in same SoI. Aka to holmann transfer to moho with mechjeb, gotta be orbiting kerbol. It'll come up with a nice error message if you do it wrong

Edited May 31, 2014 by Link
moar info

[Kasuha]

Third best way to transfer to Moho: use Alexmoon's calculator and do what it tells you.

Second best way to transfer to Moho: launch when Kerbin is at Moho's inclination point opposite to Moho's periapsis. Lower your Sun periapsis to just touch Moho's orbit (you should get the nearest approach marker exactly where the inclination marker is). Place a braking maneuver at the place where the two orbits cross and brake a little to get Moho encounter. Make sure you pass Moho as low as possible (20 km or so). Then circularize at that point.

Best way to transfer to Moho: use gravity slingshot off Eve.

[Rickenbacker]

MechJeb isn't very good at finding transfer nodes, unless you're at the perfect launch window. Try getting to the launch window (using Kerbal Alarm Clock f ex) and playing around with your own node. You should be able to get an encounter eventually, and then you'll know how to do it. You can always use MechJeb to adjust your approach along the way, or do that manually as well.

[Pecan]

You don't say what core and what else you have on the probe but assuming an Okto 2, z-200 battery, tri-coupler and (because I'm in symmetry-3) 3xOX-STAT solar panels I get 6,928m/s deltaV from those tanks and engines. That should be fine for a Moho intercept and establishing orbit (6,640m/s), although it doesn't have a lot of margin for error. Should you decide to redesign I'd suggest losing two engines and putting core, battery, tanks and engines all in a single stack (11,176m/s, enough to come back again too, with efficient flying and good aerobraking). Multiple engines of the same type (the LV-Ns) will make your burns quicker but they reduce the available deltaV because the whole vehicle is heavier by their extra mass.

[OptiSTR]

Hello again, first of im using MechJeb just to learn, most of the time i do my own maneuver nodes, and pretty good once too.

Thing with Moho is that its orbit is not the same as Kerbin, which makes it difficult, mostly because im spending lots of dV to leave Kerbin gravity pool,

and then even more dV to fit my orbit to that of Moho. And then EVEN MORE dV to make an encounter, in total its about 5k dV (if not more).

Ill try to remove 2 engines from my probe (leave just 1), and instead ill add more fuel, hopefully it will be enough.

Can someone please upload an image of a probe design that is good to fly to Moho and back including landing?

[Cmdr. Arn1e]

People compare Moho and Eeloo for good reason; it takes about as much to get to one as it does the other!

Even probes will fall short when you first try, and it is advised that you check how much dV you will need before you leave somehow - there are a few ways to do this, including using MechJeb in the VAB to see how much dV your transfer stage has...

[EdFred]

I was going to start a similar thread, but, I'm actually landing and coming back. What I've found is it is nearly impossible to get an encounter with a single burn from Kerbin using Kerbal Alarm Clock or MechJeb. So, what I've found the lowest dV to be for me is wait until Kerbin's orbital plane and Moho's orbital plane intersect to do the transfer burn. I can get plane alignment (within 25-50dV) on my ejection burn and put my periapsis to run tangent to Moho's orbit. When I reach my periapsis around the sun, I bring the apoapsis down a bit inside of Eve's orbit and and wait to get a close approach, I burn at the apoapsis to get an encounter, and then do a bi-elliptical circularization around Moho. Returning to Kerbin always seems easier, for some reason.

[Guest]

People compare Moho and Eeloo for good reason; it takes about as much to get to one as it does the other!

Eeloo is generally easier to get to since the braking delta-V is less; they're not really comparable.

[Pwnstarr]

I've been making my own maneuver modes and letting Mechjeb execute them. It acts funny over long distances. Sometimes it even misses maneuvers by a couple of days at high warp. Also try aligning your planes before doing the transfer, it makes things a bit easier.

I did Moho a lot recently (to send refuel and support to my guys stranded at Moho lol). Typically my dV requirements are approximately:

950 m/s to escape Kerbin from a 100 km orbit.

1100 m/s to align planes at a AN / DN.

2200 - 2600 m/s to transfer

3000+ m/s to brake into orbit

So total delta V is around 7250 m/s to break Kerbin orbit and insert into Moho orbit. I'd leave Kerbin orbit with a ship carrying around 10,000 m/s and plan on sending another ship to refuel later. I use the "launch anytime and make a bigger rocket" method of planning my travels.

[Kasuha]

950 m/s to escape Kerbin from a 100 km orbit.

1100 m/s to align planes at a AN / DN.

2200 - 2600 m/s to transfer

3000+ m/s to brake into orbit

So total delta V is around 7250 m/s to break Kerbin orbit and insert into Moho orbit. I'd leave Kerbin orbit with a ship carrying around 10,000 m/s and plan on sending another ship to refuel later. I use the "launch anytime and make a bigger rocket" method of planning my travels.

That's very inefficient way of getting to Moho.

If you use what the Alexmoon's planner tells you, you can get there usually just above 4000 m/s.

Using gravity slingshots you can get it below 3000 m/s.

Below is my attempt at lowest dv on way to Moho. Major burns were:

1003 m/s Kerbin extraction towards Eve

600 m/s Powered slingshot around Eve

1232 m/s Circularizing at Moho

Beside that there were some 130 m/s corrections.

Javascript is disabled. View full album

Edited May 31, 2014 by Kasuha

[Guest]

If you use what the Alexmoon's planner tells you, you can get there usually just above 4000 m/s.

It actually varies quite a bit from what I've seen, but right around 4km/s is pretty much the most optimal direct transfer (without slingshots) I've seen. In practice, I generally bring about 5km/s or even a bit more if I plan to use one of the less optimal transfers because I will have to make a correction and I will be surprised by the braking delta-V required. I've never tried a slingshot, but I think I'll give that a go next time.

[Kasuha]

Okay I admit transfers from the calculator may go anywhere between 4000 and 5000 m/s if you allow it at least one year of search window, higher if you're in a hurry. The window at year 11 is particularly good with transfer for 4049 m/s.

I also tried to plan the calculator-less method (eject opposite to Moho's periapsis, correct for intercept and brake into orbit) and it was just slightly below 5000 m/s so it's not really better than Alexmoon's calculator.

Edited May 31, 2014 by Kasuha

[EdFred]

I can never get under 3kdV for my orbital burn to Moho.

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions.

[cantab]

One thing you can do, if you find yourself short of delta-V for the Moho orbital insertion, is use the encounter as a gravity assist to lower your solar apoapsis, reducing the delta-V needed for capture next time around. IIRC the real MESSENGER probe made three Mercury flybys, shedding speed relative to the Sun each time, before entering orbit.