Headed to Moho - - last minute advice?

[mellojoe]

((Update))

We did it!!! Thanks to all your help!!

-----------------------------

I've assembled a craft in orbit around Kerbin. It is currently sitting on 13,000 delta-v.

Will this be sufficient to arrive at Moho, and then return? I think so, but I've never done Moho before. It scares the bejeebus out of me. I have two brave Kerbal men aboard .... Jebediah and Bob. Please tell me they aren't signing up for their last missions.

My game plan:

• Push to Moho when it is at periapsis with Kerbin at its apoapsis.
  
• Orbit sun until encounter.
  
• Encounter Moho orbit, as low as I can get.
  
• Map for Kethane.
  
• Drop a small lander can for Jeb and Bob to explore the surface.
  
• Mine and refine kethane to refuel lander can.
  
• Leave Moho and rendezvous with rest of ship.
  
• Go home.

This is my big plan. Kethane on every planet. Moho is my last stop, and I think I can do it. But out of all of them, Moho scares me the most. We've done Eve successfully. We've done Eeloo succesfully. We've even got a massive mission in Jool, that has been hugely successful. But Moho? Moho? Yeesh. I don't know.

13,000 delta-V in orbit around Kerbin. Enough? Or do I need to rethink my design? Also, any last minute tips?

Edited March 25, 2014 by mellojoe

[Tex]

13k Delta-V is more than enough, I believe. Um... other than that, uh... Take a scenic tour and check out the Moholes!

[maccollo]

I'll just leave this here.

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

You should be able to go to Moho, land, and then return to Kerbin for just about 9 km/s, maybe less if you divide the Kerbin escape burn into 3 segments: Increase apoapsis beyond Mun, make 25 degree inclination change or so at apoapsis, escape when you fall back to periapsis.

[Pecan]

13km/s is plenty to get to and orbit Moho. Since you're going to be mining and refining kethane there do you even need to worry about the fuel to come back?

[mellojoe]

How low can one orbit Moho before things start to crash?

Thanks to you all, I'm successfully in orbit around Moho. Used less than 6k delta-v getting there and adjusting orbit. I'm currently in a low 13,000m orbit, and I think I want to go lower before I detach my lander-can. If I were to sneak down to just 9km, am I going to start bumping into things? Are there mountainous peaks that go very high? I have so much fuel left in my transfer stage, that I want to keep using it as much as possible to make my landing/ascending easier.

[Streetwind]

According to the wiki, the highest elevation on Moho is 6817 meters. Thus, you can make a safe 7km orbit.

You can maximize the usage of your transfer stage by burning retrograde to zero out your velocity, then ditch the stage and use the lander engines only for the short vertical descent. Or heck, use the transfer stage for the landing as well, and only ditch it a few meters before touchdown.

[mellojoe]

Wait ... you are suggesting:

Burn retro into a stall.

Detach lander.

Switch back to main craft.

Burn prograde to get back into safe orbit.

Switch BACK to lander.

Control lander decent.

..... thats crazy .... like Kebal krazy .... so crazy it just might work .....

[Taki117]

Wait ... you are suggesting:

Burn retro into a stall.

Detach lander.

Switch back to main craft.

Burn prograde to get back into safe orbit.

Switch BACK to lander.

Control lander decent.

..... thats crazy .... like Kebal krazy .... so crazy it just might work .....

It's horribly inefficient though. What I would do is use the Transfer Stage to perform the de-orbit burn, detach your lander, circularize the transfer stage and then land the lander. This way you're not burning all that unnecessary dV by completely stopping your orbit.

[FREEFALL1984]

It's horribly inefficient though. What I would do is use the Transfer Stage to perform the de-orbit burn, detach your lander, circularize the transfer stage and then land the lander. This way you're not burning all that unnecessary dV by completely stopping your orbit.

I don't think he means a full complete stop, performing a full stall at that altitude and with all that speed and with (I assume) nuclear engines would take an age, consume thousands of m/s of dV and almost certainly result in a fiery death of the main vessel before he makes it stationary.

[mellojoe]

Correct. I was over-exaggerating for the sake of kerballing. It is interesting to think about putting my main craft into a crashing suborbital trajectory before jettisoning the lander-can, and then re circularize the main craft. I hadn't considered that, honestly.

I think I will drop my main orbit to about 8km or 9km. And I think my lander has sufficentient thrust to handle the rest. But, I will quicksave ... just in case. You know ... in case my first attempt is merely a simulation run on computers before I attempt the "real" landing.

[Streetwind]

Oh, you want to keep your transfer stage? Well yeah, then that's not an ideal maneuver

I guess I'm too used to expendable transfer stages, myself.

[mellojoe]

Thanks to all, we did it!

Using the technique described by maccollo, Jebediah and Bill were easily able to get to Moho. They drove the transfer stage down to a small 8km x 8km orbit at Moho. Took the lander down ... which was the scariest part. My tiny lander + kethane rig needed more fuel. It was basically a suicide burn at the extreme. Not fun. But we did it. When I go back (which I will), I'll redesign my lander. I kept cutting weight, cutting weight, cutting weight to ensure I had enough delta-V to complete the mission, that I think I cut too much. I could have easily used a much larger lander, which I will in future missions. Then, Jeb and Bill refuelled the lander and headed back to the waiting transfer stage. Pushed the whole thing out to a 1000km x 1000km orbit in order to wait for a return window, and to give us enough distance so that the long transfer burn could be done in a single orbit. At the low orbit, the period was only about 30 minutes, and my estimated burn was close to 20. It would have required multiple passes to get anywhere, so making a larger parking orbit ensured I could do the long burn in one shot.

Landed back at the KSC (or close enough). I'll have an image write-up coming soon.

Thanks again to everyone who offered advice. It was HUGELY useful.