Why landing on Moho is damn difficult

[Spatzimaus]

That's of course true, but Moho's Oberth effect is rather weak, much less than on Kerbin.

Correct. The smaller the body, the less savings you get from that sort of optimization. A body as small as Moho just won't have enough of an Oberth effect to speak of. But really, there's a bigger factor to consider: when you're trying to hit something like Moho all the way from Kerbin, the chance of your trajectory passing that close to the body is slim unless you make multiple adjustments along the way (each of which gets less and less efficient to perform). KSP's node system just isn't that precise; even if you want to spend a ton of time fine-tuning the maneuver node arrows to pass as close as possible, you can't snap your craft's heading to match the maneuver, so there's plenty of room for drift. Basically, given the precision level of KSP you won't have much of a problem intersecting the SOI, but chances are your trajectory will only pass through the outer part of the SOI unless you want to spend a prohibitive amount of time fine-tuning. It's like throwing a dart at a dartboard and expecting to hit a bulls-eye; sure, it can happen, but there's a whole lot more area in the outer parts of the board. So realistically, on most trajectories I don't expect to pass close enough to really take advantage of the Oberth Effect for anything smaller than Jool. (And in the case of Jool, my primary fuel depot is at Pol so I don't usually WANT to go that far down into the gravity well.)

Besides, the amount of delta-V you save from maximizing the Oberth Effect is often quickly outweighed by the amount you lose trying to shift into an equatorial orbit (or polar, if that's your preference), which is really important when you're trying to land on a precise location (a must if you use Kethane or want to visit an anomaly/mohole) or intersect a moon's orbit for other planets. While speed changes are best done at periapsis, angle changes are best done where speed is LOWEST, at apoapsis. By entering the SOI further out and circularizing, you guarantee the ability to change orientations at the ascending or descending nodes without wasting a ton of fuel.

And again, if you're using ions (or nukes, on a larger vessel) with enough fuel, you can have tons of delta-V to waste, as long as you have enough thrust to decelerate in a timely fashion. You just don't need to concern yourself with shaving every last bit of delta-V off your intercept, so worrying about something like Oberth is just unnecessary..

[Boris_T_Roach]

Only way I managed to do a Moho mission was to position a refueling tanker in orbit at Moho in order that the manned ship carrying the lander , 2 rovers, and a some lightweight probes could arrive in Moho orbit and pick up the fuel

In reality, what happened was that the tanker burned through 1/2 its fuel, and the manned ship burned through all its fuel, plus drained the lander and the rover landers fuel to make it into an orbit

It was at that point the fuel tankers were re-designed to carry even more fuel, meaning when I do a duna mission , theres enough fuel around to do multiple landing with the same ship.... so long as I remember to repack the parachutes.....

[Stargate525]

There's a reason I have the Kerbol rescue insignia on my badges... n.n

I got to Moho. Didn't have enough juice to land properly (I had, amazingly, UNDERestimated the gravity, expecting it to be closer to the Mun), and so the thing fell over. Didn't have enough to get back anyway.

Sent a rescue craft that got him off the surface and somewhere around Eve before it ran out of juice. Sent ANOTHER rescue mission, and discovered just how big a pain it is to do an orbital rendezvous around Kerbol. Finally got him home.

So I feel your pain. It's very hard to get to, and even worse to get BACK.

[BadManiac]

I built a Moho landing with a separate rover and then return to Kerbin mission. I think my interplanetary transfer stage had 18K dV or something and it damn near didn't make it. If you're transfer is even slightly non-ideal you spend a LOT of dV paying for it. Moho is the hardest place to get in the Kerbol system IMO. Since you're in such a low orbit around the sun everything requires such ridiculous amounts of dV.

[Kasuha]

But really, there's a bigger factor to consider: when you're trying to hit something like Moho all the way from Kerbin, the chance of your trajectory passing that close to the body is slim unless you make multiple adjustments along the way (each of which gets less and less efficient to perform).

Actually, when getting there I can usually adjust my trajectory to within 1 Moho diameter right from Kerbin SOI. That's the error the KSP physics engine gives me, the trajectory jumps around by about that much. And I can set it up to jump right around the Moho globe. Then all I need to do is to pass Kerbin SOI boundary at low time warp, and then perhaps apply correction when I'm about three Moho SOI diameters from the intercept and again after I enter the SOI.

I sometimes even correct for collision with Moho, then dump my empty tanks from ejection burn and only after that correct for near miss.

[Alchemist]

Just landing is easy, no more difficult than landing on mun. It was the landing into Mohole that really killing me.

I really would like to see a Picture of it

Behold the rolling probe!

[JiWint]

I don't get why everyone finds getting to moho and landing there difficult

[Surefoot]

Indeed the landing itself is nothing special, Moho is easy. If you want hard, try Tylo. If you want insane, try Eve (i made it though, i should make a post about that maybe).

There is a trap though, that is the orbit insertion. As it's fast moving on a very tilted orbit, approaches are quite expensive, my orbital plane correction cost me over 1300m/s:

Then got my Grand Tour explorer in a very tilted orbit, because the insertion did not happen when Moho was near the ecliptic plane. When you plan such a mission, dont forget to add up delta V for orbital corrections which are needed if you want to get back..

There, nicely in orbit

Then landing was easy, nothing special:

After refuelling thanks to Kethane, took off to meet with the explorer module:

And then went off to Eve (actually Gilly first, to refuel) - that is another story.

[Redshift OTF]

I don't get why everyone finds getting to moho and landing there difficult

That includes coming back? Without Kethane mod?

[jfull]

I'm no pro at KSP, but things went pretty smoothly on my mission to Moho

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The main problems are just getting an efficient transfer orbit, and the massive amounts of fuel needed for capture.

[SpaceSphereOfDeath]

Moho capture (IMO) isn't hard, asparagus stage 8 FL-400 fuel tanks around a centre one with a nuclear engine strapped to it will be enough to get into orbit with about 100-300 Liquid fuel left depending on the payload.

Landing on the dark area's is lake landing on the lakes of minmus

DO NOT GO FOR THE POLES (unless you're amazing and can land IN the moholes, they're the smoothest place there)

Any way, moho isn't hard(-ish).

[CalculusWarrior]

As everyone is saying, actually landing on Moho is not very difficult at all, but actually getting there is. I had a lot of fun when I finally landed; I think the difficulty in getting there added to my enjoyment of the landing.

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[Skyler4856]

You can reduce the delta-v needed with a slingshot off Eve.

All of my "successful" Moho missions have ended with a suicide burn and no chance of returning.

Also, in response to OP, I don't think that NASA or any other space agency has used aero-braking to get to Mars or any other planet. Mercury's lack of atmosphere isn't the obstacle.

http://en.wikipedia.org/wiki/Aerobraking

Hiten-Japan

Magellan-USA

MGS-USA

MRO-USA

Mars Odyssey-USA

[Sof]

http://en.wikipedia.org/wiki/Aerobraking

Hiten-Japan

Magellan-USA

MGS-USA

MRO-USA

Mars Odyssey-USA

I got the terms mixed up a little, but my main point remains true.

What I believe OP meant by no atmosphere is that there is no opportunity to aerocapture around Moho, which otherwise makes orbital rendezvous with planets in KSP much easier. No real mission has yet used aerocapture in the same way, which brings me back to my original point of why the lack of atmosphere on mercury wasn't the reason it had fewer missions.

[Surefoot]

That includes coming back? Without Kethane mod?

With a nuclear engine block attached to your lander for the planetary transfer, it's not so hard. You just need lots of fuel. I got a 10000+ deltaV engine block for that kind of purpose, 8 NERVA's pushing that beast. Can go anywhere and come back without refuelling.

Actually what was hard for me was landing and taking off from .... Gilly ! That's basically just a small dustball, almost no gravity, every manoeuver takes forever since everything has to move so slowwww....

[Kasuha]

I have a one-size-fits-all ship constructed from parts in orbit. It can go anywhere in the system and back, including Moho and Eeloo and there are only three places where it cannot land (Laythe, Tylo, Eve; actually it can land on them, but cannot return after landing).

When going to Duna or Eve, it can even go with just one Jumbo tank instead of three.

[ComradeGoat]

That includes coming back? Without Kethane mod?

From LKO, 1 nuclear engine, one of the biggest grey tanks, 6 of the 720 unit smaller tanks arranged in asparagus fashion, lightweight lander, 3 kerbal command pod. More than enough Delta V to do a Moho mission, landing and back, entirely stock.

[ComradeGoat]

Actually, when getting there I can usually adjust my trajectory to within 1 Moho diameter right from Kerbin SOI. That's the error the KSP physics engine gives me, the trajectory jumps around by about that much. And I can set it up to jump right around the Moho globe. Then all I need to do is to pass Kerbin SOI boundary at low time warp, and then perhaps apply correction when I'm about three Moho SOI diameters from the intercept and again after I enter the SOI.

I sometimes even correct for collision with Moho, then dump my empty tanks from ejection burn and only after that correct for near miss.

Yeah, it's really not hard. Just wait a bit, but not too long, and you can do the adjustments a couple of weeks out using RCS.

It's not like you're trying to nail equatorial Jool orbit with a precise periapsis for aerobraking to Laythe from 180 days out (which is perfectly doable in KSP).

IDGI; when I finally plucked up the guts to do a Moho mission after putting it off for ages, it was a non event. Just take a nuke and lots of fuel, and build light. It's, IMO, easier than getting to the Joolian moons.

[Kasuha]

It's, IMO, easier than getting to the Joolian moons.

Since I learned braking in Jool system by gravity slingshots off Tylo and aerobraking on Laythe from any angle, I don't consider travelling Jool system an issue. Moho is IMO the harderst to get to place in the system.

But it clearly depends on individual experience. Things turn easy once you know how to do them.

[Surefoot]

Since I learned braking in Jool system by gravity slingshots off Tylo and aerobraking on Laythe from any angle, I don't consider travelling Jool system an issue.

Then now do it with FAR Totally redefines the aerobraking experience...

[ScallopPotato]

I've beeb able to complete a Moho fly-by in career mode. It just takes a lot of delta-v and I knew I didn't have enough to orbit or land. Yet I still had more than I needed to do a fly-by, so I used the rest of it to get an earlier encounter with Kerbin.

I've found that the best Moho launch window is at the ascending or descending nodes, mostly to avoid inclination changes. When I reach periapsis (at the ascending or descending node), I do a burn to get an encounter on the next pass or two. I like adjusting my encounter to where it intersects the planet. This is because I can't see what side the close approach is on, and it takes a lot less delta-v to raise my periapsis out to the dark side than adjusting from a 1000km light side encounter.

If that makes any sense. I have a second Moho mission waiting in LKO right now. It's a large nuclear transfer vehicle and a small mun-type lander docked in front.

Has anyone tried using an Eve gravity assist to reach Moho? I know MESSENGER and other Mercury probe used Venus flybys to get the encounters. Like, on my latest Eve mission, Kerbal Alarm Clock said Eve was only 1 day away from the Moho window when I had my late encounter.

[Spatzimaus]

Actually, when getting there I can usually adjust my trajectory to within 1 Moho diameter right from Kerbin SOI.

And that's just not close enough for the Oberth effect to have any real impact on your delta-V. You have to be CLOSE for Oberth to change anything, especially since you'll often be braking with a low-TWR, high-ISP engine like a nuke or ions and have to start the actual burn well before you reach periapsis. The point is, there's no real benefit to aiming that close, and quite a few downsides. Barring any Oberth savings (which, as we've said, is negligible for a body as small as Moho) there's no difference between passing close by Moho and decelerating to a close orbit, versus passing through the outer regions of the SOI, decelerating to a circular orbit out there, and then decelerating down to a lower orbit with two small burns. The three-burn setup has a nearly identical delta-V total, and has the added advantage that you can fine-tune your orbit quite a bit easier (especially inclination).

Likewise, as I said before, there's very little difference in delta-V between dropping straight down to Moho from Kerbin, versus dropping to an intermediate circular orbit just outside Moho's orbit and then setting up an intercept from there. The difference is that by splitting these sorts of maneuvers into two parts, you make it far easier to do these sorts of things with a low-TWR engine since you'll need to burn for less time within Moho's SOI, which is really the limiting factor for one that small. You'll be spending most of your deceleration delta-V in a solar orbit, where you have plenty of time to play with, and only need a small amount of thrust to match Moho's vector once you enter its SOI. Then, once you're in there and circularized at whatever distance you entered, you can take your time dropping down to a lower orbit.

[T_Ray_TV]

It's always seemed to me that the deltaV needed to capture and circularize will be similar to the deltaV needed to transfer to the orbital intercept... ignoring inclination.  So if it takes you 6k to get there it will probably take you (very roughly) another 6k to capture and establish a low circular orbit.  And then there's the landing.  The gravity feels like 2 to 3 times that of the Mun.  And based on Ziggy Kerman's vertical leap that seems about right.  My landing spot is too hilly.  I need to find a better area to land.

[James Kerman]

Welcome to the forum, @T_Ray_TV.

This is a pretty old thread and lots of new stuff has been added to the game since the last post.

It might be a good idea to start a fresh thread about landing on Moho to see what the current game has to offer and to witness the amazing adventures of other Moholoians.

[Starhawk]

There are really three big challenges built in to the solar system in stock KSP.

1.  Getting to Moho.
2.  Landing on Tylo.
3.  Ascending from Eve.

Happy landings!