Mundane Missions: Kethane Mining on Minmus, Fuel for Yondalla

So, after some debate about "whether or not to bother", it occurred to me that the whole point of setting up the Demeter-Hermes mission was that it was realistically more economical to take fuel from a moon, fly it into planetary orbit, and refuel there than do a half-dozen or so launches with surface-based craft to fuel up a similar-sized ship.

I was off doing some math on the efficiency of the process and I realized that I could fuel the Yondalla Duna Tug much more economically if I was bringing fuel in from Minmus rather than the Mun, which is pretty counter-intuitive given that Minmus is over twice as far away.

Twice as wide an orbit, however, is not the same thing as twice as much delta-v. In fact, round trip from LKO to Minmus is about half the delta-V (that is, half the fuel cost) as the same to the Mun, and so I decided to change my mining operations by moving them to Minmus - as soon as possible, since a design flaw in the Yondalla mission meant that it had to be fully fueled before we could load up the actual cargo.

Now, fortunately, when ZAXA was designing the Hermes Lunar Kethane Tug, it was designed to survive accelerating with the Barbara mining drone attached to it - a design that was carried over for the Demeter Lunar Mining Probe, which was about the same mass. That actually meant that switching moons could be done relatively cheaply.

Demeter picking up one last load.

Now, Demeter-Hermes as a system only communicates with Kerbin via Hermes, and only then when Hermes has line of site to the Asartes satellite constellation. Most of the time, the ship and the probe function autonomously, within a limited set of parameters set by the ground station. Fortunately, on a low orbit of about 25 km, this happens several times a (standard) day, so it's relatively easy for Demeter-Hermes mission control at KSC to send up new instructions.

The game plan was for Demeter to fill her tanks with Kethane, launch, and dock to Hermes as normal. The reprocessed Kethane would then serve as sufficient fuel for a return to Kerbin orbit and then a subsequent Hohmann Transfer to Minmus - at the time this was viewed as the most efficient route (by which I of course mean it was the route I was certain I could make work).

Radiators and Solar Panels Retract as we come in to dock.

However, once Demeter was docked to Hermes, the fuel was converted, and the new delta-v budget of the craft was worked out, it became obvious to me that there was no earthly reason I shouldn't be able to fly directly to Minmus from the Mun.

Snug as a Bug. Goodbye, Mun!

Unfortunately, MechJeb, which I admit I often rely on a bit too heavily, didn't quite know what to make of that, so I had to work out the mechanics of the transfer manually, which were pretty simple math. I used MechJeb to set and execute my manually-calculated maneuver nodes, sat back, and watched. At this point, I should point out that n-body physics isn't the most well understood math in academia at the moment, and that KSP doesn't actually model n-body physics at all - it models the interaction between your active craft and the planet/moon whose sphere of influence you're in, and puts every other object on rails.

I'm pretty sure that's how I somehow ended up on Kerbin Escape Velocity, flying parallel to the planet rather than actually orbiting it. With no good understanding of the recovery for that situation, I used up this mission's "simulation token" (reloaded the quicksave). After that, I flew Mun-Kerbal-Minmus like a good boy, and on the way past dropped off a goodly amount of spare kethane at Theseus, the orbital fuel dump I haven't been using.

That flight, naturally, went without incident, and while we were waiting for the transfer orbits to complete themselves, the industrious little green men of Kerbin built themselves another model of the Luna Kethane Probe. Launching that was relatively easy, but waiting for the most fuel-efficient transfer window meant that Menthe (the probe) and Demeter-Hermes were going to arrive at Minmus at around the same time - and each one had capture windows of about an hour.

To this day I'm not sure why their windows were quite so tight, since I've had more time than that on Munar missions in the past, but having never actually been to Minmus I figured this might be the norm. Either way, it was a bit of a juggling match trying to get both of the ships into roughly-captured orbits.

Home on the Mintball

Unfortunately the mechanics of the game itself and the limitations of the Kethane mod meant that what followed next was going to be several hours of doing other things while I waited for Menthe to completely map the surface. In the end, I didn't, waiting until I'd spotted a rather-rich, rather-large equatorial deposit, before switching back to Demeter and landing her.

Mining on Minmus turned out to be so easy and fuel-cheap that I actually did much of the landing manually, though I continued to rely on mech-jeb for rendevous and docking just for the sake of reliability. After a few trips to the surface, I had a fully-fuelled Hermes with full tanks of Kethane ready to head back to Kerbin. Parking Demeter in orbit, I switched control to Hermes and flew it back to Kerbin, aerobraking to save fuel before settling into a phasing orbit of about 260 km to catch up with Yondalla for docking.

There's probably a rule against using nuclear engines
this close to civilized worlds, but that rule is wrong.

 Docking with Yondalla turned out to be relatively easy - both because Yondalla has a more powerful computer on board (which in game terms means absolutely nothing), and because the relatively large 3.5 m docking port can accept the Clampotron Senior 2.5 m docking port on Hermes, which the Theseus station actually can't.

Because of that, it was pretty easy to hook up, disable fuel feed into Hermes's own tanks, and then use Hermes' own refinery to produce fuel for Yondalla - filling her tanks about three-quarters full. Pleased that I'd only need to make two more trips, I turned Hermes around and sent him back.

Close approach. Similar designs for similar functions!

Returning to Minmus was an easy flight, particularly since I could use a rendevous with Demeter to perform the orbit capture burn, as well as offload a bit of spare fuel into the lander just to be on the safe side.

Disaster struck shortly after we got Hermes fully refueled, when I got distracted during a manual landing I thought was automatic, and crashed Demeter into the surface of Minmus. Hard.

Yeah, about that hard.

Now, on the positive side, I still have Hermes, and it should be trivial to put a new Demeter together and send it to Minmus. On the negative side, I'm coming up on my first transfer window to Duna and losing time. In order to save as much as I could time-wise, I elected to send up a 3.5 m fuel tank with its own RCS and guidance, drop off the fuel, and de-orbit it.

Next time, adventures in staffing!