Tiny Minmus Sample Return

sevenperforce · August 23, 2017

Can you get a surface sample from Minmus, with a command pod, with a launch vehicle less than 10 tons, shorter than 6 meters, with less than 13 parts, and cheaper than 10,000 credits?

I daresay I can.

Done for this challenge:

I present: the Magnificent Micro Minmus Munchmobile! Weighing in at only...wait for it...5.815 tonnes!

No part clipping (although the ROUND-8 tanks place very closely, which helped). As you'll see, I didn't use any decouplers; this saved me weight, part count, cost, and height. I plan to use explosive decoupling to get rid of the booster, and hopefully I can blow off the tanks on a re-entry just steep enough to overheat them but not so steep that the pod can't survive.

All the ROUND-8 tanks, as well as the Mk0 LF tank, are full. I drained the command pod of monoprop, and I only filled the lower FL-T100 about half full of oxidizer to give myself a bit more LF right before the RAPIER loses its airbreathing thrust. Speaking of which, I disabled manual mode switching and programmed an action group to close the intake when I switch modes, to cut drag.

I toyed with drop tanks, but the part count, cost, and drag losses were prohibitive.

Lifting off! I'm monitoring a lot throughout the flight so I locked a bunch of the windows open. This takes a very specific pitch curve. It'll make orbit without trouble, thanks to plenty of thrust on the Spark, but making orbit with enough dV is the tricky bit.

I'm keeping an eye on the RAPIER's thrust as well as the lower fuel tank. It's set to drain after the Mk0 tank so I'll know when I'm almost out of LF.

This ascent was tough, because if I did the gravity turn early, I burned through all my LF waaaay too low in the atmosphere; if I did the gravity turn late, I would be going too fast to turn efficiently. I didn't want to throttle down, though. So I tipped my nose over early and then pitched up hard, so that once I needed to turn I could just drop from SAS-hold to prograde and take off.

Supersonic and rolling over. This places the differential drag from the intake on the top of the craft, helping me to keep my nose up during the early acceleration phase.

Starting to drain LF from the FL-T100, so I don't have much airbreathing time left.

As planned, excess LF is bingo just as the RAPIER thrust starts to drop precipitously.

Now, things start happening FAST.

I can tell I'm almost out of fuel on my booster. Explosive decoupling is always hairy...

And I'm starting to lose fuel in my top tank (see top left), so it's time to blow the fairing and ignite the Spark to decouple!

Bam. There goes the booster. Jenton looks appropriately horrified.

Thankfully, I've already got a good ascent. I tried doing this with the Ant, but the thrust just isn't enough, and the isp losses make it barely worthwhile anyway.

Not at full thrust...I don't want to push my Ap too high.

The numbers on that resource tab are awfully low!

It'll take about half a minute to circularize.

Almost there....

And I made orbit! With quite a bit of dV. Is it enough to go as far as I need to go? Well, we'll see.

To save propellant on the Minmus injection burn, I'm going to take a loop around the Mun. Gotta wait for it to line up, though. Ignore all the tracked objects on the left; this is my challenges save that I'm also using for the Orion Style challenge.

Setting up the slingshot.

And here's my slingshot into Minmus's SOI!

This burn is going to use almost all of my fuel.

And there you have it! Looks like I'll need to make a correction burn during the Mun swingby.

Set up the swingby.

Burning gingerly.

I'll take that!

Coming up on Minmus...

Uh oh. Did I really send an engineer on this mission? Crumbs. Oh well, gotta wing it.

Capture burn.

That'll do it!

So...it looks like I have enough fuel to get home, but not enough to make the landing on Minmus. What to do?

Well, I'll just lower my apoapsis to around 240 km...

...and hop out!

Just a tiny, miniscule RCS puff to lower my periapse below the Minmusian mountaintops.

Warping down. This will be touch-and-go.

Starting the RCS braking burn.

Still braking hard.

Timing has to be perfect. If I'm right, I think I can hit the surface with quite a bit of residual velocity and let friction bleed it off.

Not this much velocity, though.

Steady as she goes...

I think 20 m/s is just about the cutoff.

Ouch! But hey, I made it!

Nommmmmmmmmmmmmmm!

No time to waste. Without the ability to set nodes (or even thrust prograde, really), I have to use the ship's velocity vector as my guide. Can't afford to wait for another orbit, either, because I'll be out of the path.

Set up the target.

Liftoff!

Burning up and forward.

I just wanna barely clear these mountains.

Aiming to have my Ap just reach the ship's Pe.

Really disorienting when I reach "orbit" and it switches targeting modes.

Closing as carefully as I can.

And there's my orbit! I didn't expect to get a rendezvous on my first go-round, but at least I got a nice coelliptic orbit.

Figuring out exactly how much of a burn I'll need to line up for an intercept. Fuel is going to be very, very close.

Made the burn...I have less than 1 unit of monoprop remaining for the rendezvous.

Matched speed!

Looks like a good intercept.

And here we go!

Of course, I managed to come in on the wrong side and had to swing around.

Aaaaaand I got the ladder! With 0.04 units of monoprop remaining.

You better believe I've got that surface sample added.

Burning at Pe would send me out of Kerbin's SOI, so I'm swinging around to Ap.

Escape reached! Will I have enough prop to lower my Pe into Kerbin's atmosphere?

Once-more-around and finding out.

If I have to, I can use a Mun assist to get back home.

Nah!

Here we go! No turning back now.

Here's where things get REALLY dicey. If I come in too hot, I'll burn up the engine, the tanks, AND the capsule. Too cool, and the tanks and engine will survive. Which will throw off my CoL/CoM balance and turn me into a lawn dart, making my chute useless.