I am never going back to Moho.

[herbal space program]

On ‎11‎/‎26‎/‎2015‎ ‎11‎:‎36‎:‎05‎, TyrannoFan said:

Every time I try to go to Moho, I get random and bizarre Kraken attacks. Sometimes, two crafts are controlled simultaneously, other times my crafts completely change their orbits by spinning, occasionally my camera drifts off by a few kilometers, and once in a while my crafts receive random acceleration from no identifiable source. As a result of the frustrations thanks to these Kraken attacks, I try to avoid Moho.

D'ohh!! No sooner did you invoke the Kraken than it appeared to devour my mission in Moho's hood. It was a strange one too, that made my ship disappear in the orbital view instead of the staging view. When I went back to the tracking station, everything  was gone. Unfortunately my quicksave was corrupted as well, and my last named save was ages before between Kerbin ejection burns. Sigh. Anyway, I mention it not because I'm  aggrieved but because it happened just as I think I figured out how to cheaply zero in on Moho from an Apoapsis encounter, and I want to communicate that before this thread dies. So:

 Your Moho relative speed is much worse if you initially hit Moho's orbit at its high point, but there are also factors that work in your favor if you do it that way. One is that you can hit Moho's orbit there with very low inclination using just one Eve gravity assist, while it takes either lots of burn or two (very tedious) Eve assists to get you all the way down to Moho's Pe for your initial encounter. IIRC, Metaphor spent 1300+ dV to get to that first Moho encounter, while I'm doing it for about 1150. From there, you need to bleed off a lot less total dV to get captured from a Pe encounter than from an Ap one, but as I think I've figured out, the penalty for using gravity assists to do that is quite significantly less starting from an Ap-tangent orbit than from a Pe-tangent one. The key issue is that every time you use a Moho gravity assist to lower your Ap, you will lower your Pe some amount as well. If the planets are moving counterclockwise, swinging around Moho to lower your Ap moves your Pe a little bit  in and a little bit clockwise each time. If you start from an orbit that is tangent to Moho's lowest point, this Pe lowering is a pure penalty, because both the inward and clockwise movement of your Pe put it further inside Moho's orbit. If OTOH you start from an orbit that's tangent to Moho's Ap, this lowering and pivoting of your new Pe follows the lowering of Moho's orbit as it goes toward its Pe, significantly reducing how far below Moho's orbit each successive grav assist pushes you.  Moreover, if you do just a small prograde burn at around 15 degrees before your solar Ap, you can push your Pe back out and clockwise even more for just a few m/s, also making your next encounter point earlier and closer to Moho's Pe. In this way, I believe that if you can both find a really good path between the resonant energy levels and optimally correct your Pe on each successive orbit, you can shimmy on down and around to a really cheap Moho capture. Anyway, that's my plan and I'm sticking to it...

Edited December 3, 2015 by herbal space program

[Francois424]

Oh right, I knew I had forgotten something....   I wanted to try going there again (for the second time only since 0.22) and forgot.
I need to start putting an expedition and send something there,

I don't remember having a hard time with an Ion probe in 0.25, but then again I never landed.
I don't even know if Moho is Tidally locked.  Does it have a rotation like Mercury in RL ?

[Warzouz]

I don't think if it's tidally lock, but rotation is very slow

[PLAD]

Herbal space program, that is brilliant. I had looked at the first encounter speeds for a Moho periapsis arrival versus an apoapsis arrival, found periapsis looked lower, and left it at that. Your realization that the periapsis decrease resulting from a flyby follows Moho's decreasing distance from the sun... that is freaking brilliant. That does make it sound like the apoapsis arrival is better. You might have to do more flybys of Moho to slow down enough, but if you are saving 20m/s or so per correction it could add up to the superior solution, especially when the lower departure-from-Kerbin speed is added in. I am sorry about your Kraken attack, I look forward to seeing your final results!

Francois424 and Warzouz, I think Moho's sidereal rotation period is 52 Kdays, but since it's year is only about 102 Kdays long the solar day from a point on Moho's surface is longer than it's year, about 123 Kdays. (Kday=6 hours)

[NecroBones]

4 hours ago, Warzouz said:

I don't think if it's tidally lock, but rotation is very slow

I think it's similar to Mercury, with a 2:3 ratio.

[herbal space program]

Thanks so much  for  the encouragement PLAD. It will go a long way towards keeping me from losing heart through this endless process of optimization. This may take a while, but stay tuned...

[pandaman]

Yeah, I find Moho a bit of a challenge too.  Managed to plant a flag at the south pole (eventually, after many failed attempts to encounter and orbit), then the lander ran out of fuel descending to plant a flag next to the mohole at the north pole.  Fortunately Thomfurt Kerman had the wits to bale out and use his jetpack to slow his descent, had he not landed in the hole he would have hit the surface far too fast, but he was able to slow down enough to avoid going 'poof' at the bottom.  Then he got trapped at the bottom and glitched out, crashing the game whenever I switched to him and I had to terminate in the control centre,  RIP Thomfurt.

[ManEatingApe]

Even though Moho doesn't get much love, one small silver lining is the insanely strong solar flux that means photovoltaic panels produce 5x the output compared to that of Kerbin's orbit. This makes it ideal ion territory, no need to drag around Gigantors when a regular 1x6 panel will produce ~90% of the power needed for a single engine.

I was curious to see if a ion only lander with minimal battery was possible for a lightweight "flags and footprint" style mission. Without traumatising Jeb too much, managed to land this on the equator:

as part of this mission: Gallery: Moho on a budget (+ craft file)

Edited December 6, 2015 by ManEatingApe
Added craft file

[Aethon]

Is that 2 ions?  Will it go back to orbit?  Do you think one would?

[technion]

2 hours ago, ManEatingApe said:

Even though Moho doesn't get much love, one small silver lining is the insanely strong solar flux that means photovoltaic panels produce 5x the output compared to that of Kerbin's orbit. This makes it ideal ion territory, no need to drag around Gigantors when a regular 1x6 panel will produce ~90% of the power needed for a single engine.

I was curious to see if a ion only lander with minimal battery was possible for a lightweight "flags and footprint" style mission. Without traumatising Jeb too much, managed to land this on the equator:

as part of this mission: Moho on a budget

Incredibly well done. I always thought it was an established fact that ions couldn't manage the TWR to land on moho.

[ManEatingApe]

21 minutes ago, Aethon said:

Is that 2 ions?  Will it go back to orbit?  Do you think one would?

Never fear!  Jeb made orbit again and rendezvoused with a mothership for a return to Kerbin.

20 minutes ago, technion said:

I always thought it was an established fact that ions couldn't manage the TWR to land on moho.

A back of the envelope F = ma, gives m = 4 / (0.275 * 9.81) = 1.48 tons equilibrium weight for a lander with 2 ions. This weighed 0.88 (lander) + 0.09 (Jeb) = 0.97 total.

Theoretical dV was ~ 3000 m/s, but with 2/3 of the thrust just counteracting gravity there was considerable inefficiency. Still enough to make it down and back (just) which is all that mattered.