sdrevik

Single Lander for Tylo, Vall, Pol, Bop [STOCK]

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Even though I have 15,000 excess science.. it's not enough.  I found I had not yet landed on any of the Jool moons.   Bad Kerbals!

 

So, i decided I would take a lab with me, and make a single lander that can hit all the moons except Laythe (requires a specialized design).   Tylo being the biggest challenge, because of its very high gravity/size, it's like landing on Kerbin without an atmosphere.    So I designed a lander with some jettisonable fuel, with the idea I would go to Tylo FIRST, and then wouldn't need those tanks for Vall, Pol, or Bop.   I would bring my lab with me as an undockable section, with its own fuel, RCS, etc.   Unfortunately, I forgot to put a probe controller on it, but that's OK, I'll just have the lander always dock to it.   The small docking ports are for refueling (note that I can't refuel the lander without the lab until I jettison the tanks, but might have been nice to put one on an external tank just in case.).  The lab acts as the big com relay back to Kerbin, if needed.

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And, of course, I need to refuel constantly, so I made a one-piece driller/ISRU/fuel transport, with a small docking port for refueling the lander/lab sections.  Small engine to just handle interplanetary and landing on Pol.

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Checking out the dV for the lander, the DV maps *say* I need about 2280 to land and take off at Tylo, with 4750, I *should* have enough, right?  (more on this later).    It may take a low starting orbit, but on paper, it should work.

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So, first we get up into Kerbin orbit, and head to Minmus to refuel everybody for the long drive to Jool.   Note that I was able to keep the lower booster from Kerbin, so it took two refueling runs, but the landing section would come into Jool with plenty of fuel, while the driller would come into Jool orbit with maybe only 800 dV, probably enough to get to Pol on its own, but this added extra insurance.
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  Turns out I had plenty, transfer, orbit and landing is maybe 500-700.  We refuel everyone at Pol, and head to Tylo.

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Now, I begin to worry- if I start my landing low (say 17km), and get back to a low orbit, can my fuel ship dip down that low to refuel (before landing and after re-orbit), and climb back out the gravity well and get back to Pol and land?   The answer, it turns out, is yes.  I leave about 1000 dV for each run back to Pol.

 

So, we try our first descent from 17km.   We learn two things.  (1) You can't start from 17km because you can't slow down fast enough before gravity sucks you into a mountain.  If you thrust downward enough, you use too much fuel.    

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So we raise the descent to about 30km.  That works well, but we land with only about 2100 dV left, not nearly enough to get back into orbit.   It turns out it takes about 2500 dV to get to a roughly 10km orbit.
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Yep, this looks bad.

 

So, after failed attempts, I realize I need help.  So I built another fuel/engine "top" component to provide more fuel (and the thrust to counter its extra weight).   Note that I added a decoupler to the docking ring, because those BIG docking rings have enough magnetic attraction they don't come loose easily.   I am still granted the proper dV, but I didn't want to have something that might crash on top of me and explode after landing.  With this component and some careful piloting, I'm able to land with about 2561 dV left.   Note that I hit hard when I landed and broke a strut, but I should still be fine for Vall.

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2561 was enough to put us back into a 9kmx20km orbit, with enough dV left to re-dock with the science section.   Then the refueler only had to make one stop!
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So, the major lesson learned is- don't trust the dV maps.  It took about 2600-2800 dV to land and 2300-2400 to reach stable orbit, and that's with optimal piloting.   But other than that, the "two ships, single lander for four moons" project is so far a success, and has passed the toughest test.... Tylo, with only one landing strut as a casualty.

Edited by sdrevik

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