Fun with sepratrons on Duna lander

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So, just a silly little mission designed around fulfilling a contract that ended up way cooler than I expected.  :)

The situation:  I was strapped for cash, but then a lucrative contract came along for "Test 10m heat shield landed at Duna."  Was worth a ton of funds.  So I grabbed it, and since I hadn't been to Duna yet in this career, decided to make it a science lander, as well.


The interesting design challenge was this:

  • I wanted to use the heat shield as a heat shield, even though Duna reentry doesn't usually need it (because I had a crappy transfer window and was coming in hot), meaning that I needed to inflate it before hitting atmosphere.
  • On the other hand, I couldn't keep it on the lander after landing, since it completely overshadowed all my solar panels and such, so the lander would go dead pretty soon if I kept it that way.
  • But I couldn't jettison it before landing, because then I couldn't do the "run test while landed" thing.

So this made for an interesting problem:  how to get the darn heat shield off the lander, after landing, without harming the lander?


So, what I settled on was to mount the heat shield on an inverted decoupler atop the lander, then mount a couple of sepratrons to it.  The sepratrons were mounted symmetrically, but they weren't actually a symmetry group.  This allowed me to give one sepratron a thrust-limiter setting just a smidgeon higher than the other one.  The idea was that the slightly asymmetric thrust would make the heat shield curve off to one side as it lifts off the lander, so it would be flung clear and wouldn't come back down on top of it.

Seemed like a sound idea, the math worked out... but of course one never knows in KSP how something will turn out until one tries it.  :)


n6xvOrg.png ended up looking way cooler than I expected, and worked perfectly.  :)  Did exactly what I wanted it to.

The sepratrons were tuned to roughly 50% thrust, so they burned for a while and accelerated smoothly as the heat shield arced away from the lander.  It was awesome, felt just like it was one of the NASA Mars rover landings.


It turns out that a couple of sepratrons have got a surprising amount of muscle, on Duna.  They flung the heat shield half a kilometer into the sky.


Up, up, and away!

(If you're thinking "gee, Ike looks funny," you're not seeing things.  That's Pol.  Just for fun and variety, I'm playing a modded solar system for this career.  Duna has Bop and Pol orbiting it close in, like Phobos and Deimos.)

Even better, the heat shield didn't even explode when it came back down-- it has a pretty low terminal velocity when inflated, even on Duna. So now I've got my lander standing there, with the discarded heat shield a few hundred meters away. The tableau looks just like one of those NASA Mars rover landing sites.

Incidentally... the landing was a lot more fun than the usual routine, too.  I'm playing 1.4.2, meaning that landing legs are bugged and I wanted to set down super gently so they wouldn't explode.  But I'm also playing with Scatterer and SVE, meaning that Duna has all these dense dust clouds blowing around... and I was landed pretty close to sunset, so that I didn't have a shadow to go by.  So I was flying almost blind and trying to keep the descent speed low, and the tense last bit before touchdown felt like the suspense in a NASA control room, in a way that most of my landings don't, these days.

So... this was one of those rare missions that turned out to be a whole lot cooler than I expected.  (And gave me an opportunity to use sepratrons, which normally I never have any use for.)  And it was just because I happened to build a somewhat unusually-designed ship, in order to satisfy a silly contract.

The best example of KSP serendipity I've played in a while.  Gosh, that was satisfying.  :)

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3 minutes ago, Snark said:

I'm playing a modded solar system for this career

what mod?

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I love that picture of the shield ascending towards Ike. 

I'm still surprised how beautiful this game is (and Scatterer always helps too)

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On 4/23/2018 at 5:13 PM, DAL59 said:

what mod?

Just vanilla Kopernicus, and a set of custom configs I've put together to arrange the solar system for challenge and novelty.  Kopernicus makes this super easy to do.

I figured I'd do a career play-through to see how fun it is, then if I like it enough, post it as a mod (super lightweight, since there are no new planets-- it's just a few little config files).

For the curious, details of the modded solar system in spoiler.


Design goal:

  • Make routine stuff more interesting.  In stock, I get bored with Moho and never do anything interesting there; and I never visit Dres or Eeloo at all.  And I've been to Mun and Minmus so many times I'm sick of them, so do something to jazz them up and add challenge.
  • Make some interesting tableaux.  Have interesting skies to look at while I'm flying around.

So, here's what I've done:

  • I've moved Moho to a highly eccentric orbit, considerably closer in to the sun.  Needs more dV to get there, and ships had better have radiators on them.  So it's a bit more of a challenge now.
  • To compensate for that, and make Moho more interesting, Gilly becomes a moon of Moho, in a very low equatorial orbit.  Moho looks huge.  Gilly makes a convenient place to mine fuel.
  • With Gilly gone, Eve needs a moon.  Give it Ike, and make it orbit fairly close in, not unlike the Duna/Ike pair in stock KSP.  I've got other plans for Duna.
  • The Mun moves into a funky orbit, inclined over 60 degrees, highly eccentric, and perfectly semi-synchronous (i.e. takes exactly two Kerbin days).  I've arranged it so that it slides spectacularly huge across the eastern sky near KSC every couple of days at periapsis.  Makes for some neat views when launching.  :)  Putting the Mun in an orbit like this not only makes for great screenshots, but also adds quite a bit of challenge to going there.  And its SoI at periapsis comes close enough to Kerbin to make it an interesting challenge to build comsat networks.
  • Dres moves to be a "pseudo-satellite" of Kerbin.  What I mean by that is, it's still orbiting the Sun... but in an orbit with exactly the same semimajor axis as Kerbin, and just a touch of eccentricity.  The result is that it's forever about 150,000 km from Kerbin, and from Kerbin's point of view seems to "orbit" once a year.  (Unabashedly stole the idea from the moon Aptur in the New Horizons mod.)  This makes it an interesting destination that can be reached any time (no waiting for launch windows), but still needs a bit of navigational thought.  Also, it's a distance that gives the 2G antennas more of a reason to exist (they don't really seem to have any use in stock KSP, other than the Jool system).
  • Minmus moves to be a satellite of Dres.  So, where Kerbin used to have two convenient moons, it now has one inconvenient moon, and two reasonably-accessible "pseudo-moons" that are a bit harder to get to than Minmus used to be.
  • Duna keeps the same orbit, but now has Pol and Bop orbiting close in, like Phobos and Deimos.  Both are in somewhat elliptical orbits, in a 3:1 resonance so they never collide even though Bop's Pe is lower than Pol's Ap.  I've set it up so that Duna basically has no "safe zone" near it at all:  at Pe, Pol's SoI comes within 1 km of the top of Duna's atmosphere.  So there's basically nowhere safe to put a satellite in Duna orbit unless you go way out past Bop's apoapsis.
  • Snagging Dres left a gap in the solar system, so Jool moves inwards to where Dres' old orbit used to be.
  • I stole two of Jool's moons, so to compensate, move Eeloo to be a moon of Jool.  It's on an oddball inclined, eccentric orbit that goes closer in than Val but way farther out than Tylo.  It's carefully arranged so that it collides with neither moon (it has the exact same orbital period as Tylo, and I've nudged Vall to be in a perfect 2:1 resonance.)  Result is that it's interesting to navigate around, and comes close enough to Vall on each periapsis that it generates some pretty sky images.
  • I've also added a compatibility patch for Outer Planets, so that if it's installed, all of them are moved inwards to compensate (with Sarnus moving to Jool's old orbit, and the other planets' orbits scaled down accordingly).  Also, in this case, Eeloo stays in Sarnus orbit, as OPM normally does.

Overall, I've been pretty happy with it so far.  I'm about midway through a career.  I've explored Mun / Minmus / Dres, which was way more fun for me than just doing Mun / Minmus in a stock play-through, and now I'm starting to get probes in places like Moho and Duna.  Pretty soon I'll be sending kerbonauts out, and probes to various other places.

The Duna / Pol / Bop system looks like this:



[UPDATE]  Okay, I've published the rejiggered solar system as a mod, here:


On 4/23/2018 at 5:16 PM, Noobton said:

I love that picture of the shield ascending towards Ike.

(Pol) :wink:

Edited by Snark
Add link to the Snarkiverse mod, now that I've published it
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OK, have to admit, that was fun!  :cool:

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FYI, for anyone who was curious about the modded solar system in which I was playing this game, and who may want to try it out, I've now published it as a mod:


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I always imagine the Interstellar docking theme playing when something intense is happening.

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