The Hermes-Demeter Mission

Behold Hermes.

 I actually have no idea how mission numbering would work in a NASA-style nomenclature system for the following series of missions. I do consider the whole operation to be individual missions, but at the same time, the operation itself is basically a (functionally) infinite iteration of such missions.

After the catastrophe with Barbara, it became evident we needed a new system to get the Kethane we're mining from the Munar surface to a 100 km equatorial orbit around Kerbin. True to Kerbal engineering, anyone using ten parts where fifty would do the job just isn't trying hard enough, so I changed the entire mode of operation to a two-vessel system - remote tug Hermes and remote miner Demeter.

Amazingly precise MechJeb landing autopilot is why I use it.

 So, I'll skip the tedium of some very routine launches and go straight to explaining how the system works.

Demeter swoops in for a landing.

Hermes is basically a Kethane tank with two (stock) nuclear rockets strapped to the front of it - it's better to pull than to push - that sits parked in 15 km "equatorial" orbit around the Mun. Demeter, which is a largish remote mining probe that was put in munar orbit separately, descends to the surface, fills up on Kethane (part of which she bleeds off to restock her own fuel reserves), and then blasts back up to Munar orbit to rendevous with Hermes. The whole thing should take five trips to the surface to refuel, at which point Hermes breaks orbit and heads for our fancy 100km Kerbin orbit.

That's the theory, anyway.

Didn't even have to manually park it.

Do you remember the problem I had with Barbara, the system that failed so badly I explosively de-orbited it out of spite? That's right, delta-v calculations in the Vehicle Assembly Building don't account for the weight of the Kethane. Without that function, I have to calculate it manually using the rocket equation, which is part of what I'll be covering Friday.

Kerbinrise at the Mines.

So, my calculations support that, for the Demeter vehicle, with a full tank of Kethane, I have just a little under the 810 m/s of delta-V required to reach a 14 km orbit around the Mun. No problem - burn up to a 10 km orbit, then convert a little bit of the Kethane, then rendezvous.

Off we go to see Hermes!

 I suck at Rendezvous. Now, watching Mech Jeb having done it a couple times, I at least understand the maths involved a bit better, but I can't do it remotely as fuel-efficiently as Mech Jeb, who often does it with as little as an extra 100 m/s of delta-v, at least around the Mun. So, we set up Mech-Jeb, and watch the system burn up to a high orbit to get better phasing, Hohmann transfer down to the station itself, and then park.

Then, we get to the fun of docking. I actually enjoy docking, when I'm not docking the same two ships a hundred and fifty times, but today I was trying to multi-task my gaming (how sad is that?) so I let the computer handle it.

Hey Buddy!

 As it turns out, the same efficiency I like in the Rendevous Autopilot is the opposite of what you get in the Docking Autopilot, with MJ using about five or six times the mono-propellant I would normally use to do the job manually. This isn't too big of a deal, until you get into the truly fancy math and realize that adds an extra trip or two to completely fill Hermes (now that I'm burning even more Kethane replenishing monoprop stocks).

Basically as close as you ever REALLY want to be in space.

Now Kiss!

That's another one of those "not a huge problem" deals, since apart from the final few feet of landing, the whole system pretty much runs itself with only periodic inputs from me, if I'm using mech-jeb (and for something this tedious, that's the plan). But it was an annoyance I didn't really consider and I might make some adjustments to the Demeter design in the future if I feel it isn't up to snuff (or if I happen to lose one.)

Once you're docked, it's as simple as transferring the fuel over, then using the on-board conversion units to top up Demeter's tanks to about 900 m/s delta-v (to leave a little emergency room in there), landing it again, and starting the cycle over.

Basically, I won't be covering any more Demeter missions until it's time to take Hermes home, barring any accidents, and I'll probably only show that once.

Docked, Hermes-Demeter is treated as one spacecraft.

Back to the Grind!