Moho Encounter

[Mmmmyum]

What's the best way to plan a Moho encounter? I just did a direct hohmann transfer to it and barely had enough delta-v to get into a orbit (Rocket started with 11k delta-v on the launchpad). Is there a better way of transferring so that you enter at a lower velocity, rather than trying to slow down from 3.3km/s?

[aNewHope]

I had the same problem with my Moho - probe. Right when I came in, I realized, that you need insane amounts of ∆V to circularize.

The only way to make it easier, I can imagine, would be a gravity assist from Eve on your way to Moho.

PS.: The points achieved by a flyby are not bad either.

[numerobis]

Fly by Eve for a gravity assist? That can drop your aphelion down to Eve. Iirc the powered assist is not worth it, so you need exquisite timing to use this opportunity.

[Kasuha]

EVE gravity assist is probably the best option to reduce delta-v needed to brake at Moho. If you're really good, you can slingshot from Eve towards Sun and do some braking there, bring your apoapsis down to Moho orbit and get the encounter - this way you would be actually slower than Moho. But gravity assists aside, the best you can do is to meet Moho at your interplanetary periapsis, make sure your Moho periapsis is as low as possible and just brake there.

[Stochasty]

An Eve gravity assist is definitely the most efficient way. I used one during my SSTO Moho trip (imgur gallery) to save delta-v; total cost from LKO to Moho orbit was about 3.5 km/s.

I should note a couple of things about this. First, you will have to use two Eve encounters to pull this off; the course correction required to get from Kerbin down to Moho is too extreme for a single Eve encounter to manage. The second is that a minimum-energy transfer from Kerbin to Eve is not sufficient to get you all the way down to Moho intercept post encounter; you will need to make another burn during Eve flyby to get there.

Lastly, the most important thing to remember when you do this is that it is important to get your transfer from Eve down to Moho exactly right; you want to be as close to tangential with Moho's orbit when you get there as you can manage. Even minor mistakes can cost over a thousand km/s delta-v, so getting this part right will save you more fuel than anything else.

[Mmmmyum]

Ah, so Eve it is. I just had a really interesting Jool slingshot at the inner system with one of my probes (it would have cost me very little delta-v to go anywhere, but that's another story). Guess I'll increase the conic's drawn and mess with maneuver nodes

[TheReaper]

you can always ignore eve, bring a litlte more fuel than you think you have for security protocols, try to get an encounter with lowest periaps as posible, also always do "moving with the planet" simply achived by entering the SOI from behind the orbital bodies trajectory, this way as the planet rotates you will go with it, and will give a much more slow down due to climbing up after periapsis, if you get encounter from ahead of the bodies trajectory, it is usualy a slingshot to a different location, not the best idea

[maccollo]

Even if you go with an Eve slingshot, the most important thing is that you get a good you encounter, which means you must encounter Moho at it's periapsis.. If you encounter it at it's apoapsis the capture burn will require absurd amounts of delta V.

If you're launching directly to Moho from Kirbin that means you leave when Kirbin is on the opposite side of Moho's periapsis. You then burn down to Moho and orbit until you get a close encounter. If you go with Eve that means you launch from the same side.

The other important thing is to match your inclination before the encounter. If you don't do this you will also get absurd capture burns, because at the encounter you will be moving at speeds over 20 km/h around Kerbol. Now it just so happens that the ascending and descending nodes line up perfectly with the apoptosis, so you can do it where it is most efficient. This also means you can slingshot around Kirbin or Eve to change your inclination.

[Mmmmyum]

I can't bring more fuel. Literally my LV-N with 4 of the Service Propulsion Engines (KW Rocketry) radially attached has 6k Delta-V once it gets to LKO. Any more fuel and it's inefficient. My last shot at it was good enough to only require 3.5km/s delta-v in the capture/circularisation burn at 30km. Shame that because of the burn time I smashed straight into it (tend to fly in map view/minimised with mechjeb) as I wasn't watching the orbit.

Edited October 21, 2013 by Mmmmyum

[rhoark]

Live dangerously; graze Eve's atmo.

[r_loewe]

Spoiler

also line up the ascending or descending node with kerbin so you can match inclinations without having to waste 1 km/s of delta v matching orbital planes.

intercept it at perihelion this is why.

your ships relative velocity is 20 km/s at the interception and moho's relative velocity is 18 km/s do the math

V, your ships velocity

X, body's relative speed.

Z, insertion delta v.

v-x=z

20-18=2

=2 km/s of insertion

now

intercept at aphelion

16-12=4

=4 km/s of insertion.

see, now this will save you about 1 km/s of delta v.

you'd be thinking why not 2 km/s because insertion is 1 km/s more than the second way.

but still saves delta v.

also your periapsis must be adjacent to moho's periapsis.

Edited June 7, 2016 by r_loewe