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.

Going to space without fuel.

Launches look like this. Totes Realism.

 So, at long last we make a little bit more progress with our Duna project.

I've decided to call the suite of missions to assemble the spacecraft that's going to Duna Project Yondalla. It's going to be a multiple-flight type of project - so far I've made four launches, and only just assembled the drive system.

Fuel Module and RC Depot in Place.

Many of these launches were made with empty fuel tanks on the "final" stages, just to keep the weight down and make it easier to make the orbits I needed. The construction orbit is just outside that used by Theseus, which will make it easy enough to fuel the ship later, once it is fully constructed.

The struts and Orbital Registration Bus (ORB) arrive on site.

The first launch was the main fuel canister and auxiliary power systems, along with a canister of extra RCS fuel, which will be useful later. This system has its own probe-core controller and short-range communications suite - partly because the former is necessary to keep the object spawned in game, and partly because realism is important and the probe core will help keep the fuel tank stable while we're docking other parts to it.

Maneuvering Alpha Strut into position.

The next launch was three parts launched all as one - a pair of full fuel tanks that double as separation struts for the engine modules, and a nifty little device called an ORB, which I'm using to correctly position the parts in orbit and then dock them to the craft. I've built orb-like designs before, but this is the first one I've built with an actual rocket attached to it, rather than just RCS.

Taking Risks to dock the Beta Strut

This part of assembly was simple, though Mech Jeb made me nervous by taking maneuvers I totally wouldn't. You simply need to dock on the first strut, disconnect the second one from it, dock that to the matching port on the far side, and then go back to Kerbin for the next launch.

It didn't really get complicated until we sent up the engine modules, which had to be docked the right way around. Once that was done, though, it's on to the next phase - designing and testing the first of three landers - A Cargo Hab.

Finished product after two launches.

ORB breaks away to go grab the first Engine Module.

Hauling the first Engine Module into place.

And we're locked.

Stealing some power from the nuclear engine.

Nuclear Engine, parking in orbit beside a station,
moving at about a mile per 5 seconds.

The completed Tug Module. Port side lost a shield.

Green Orbit is our station - this is the space near Kerbin.

Donner and Vasco De Gama: Project Duna, phase 1!

Donner I on the launchpad.

 So in the wee hours of the morning, ZAXA engineers rolled out the Donner Launch Vehicle to the platform. DLV was a purpose-build vehicle on the 3.5 metre platform provided by KW Rocketry, quad-boosted with basically just two stages to orbit - SRB burn and then liquid fuel burn. Donner, a trio of rovers intended to do site selection for a Kerbal colony on Duna, launched shortly afterward.

Donner Launch!

Planning For the Future: Zaxton's Plans for Duna

Duna, the Fourth Planet from Kerbol, is the second-closest of all planets to Kerbin, our home, and far more hospitable to space travel than the closes, Eve. Naturally, this makes it a good prospect for colonization.

Of course, we can't just go off to another planet willy-nilly and set up a new society, any more than you could just go to another continent without a little planning, so we're going to take a conservative approach to colonizing Duna, and her moon, Ike.

Rocketeer's Lexicon: Delta-V

Simplified Rocket Equation

So for pretty much the entire narrative of this blog I've been talking about a quality of my spacecraft called Delta-V. I don't particularly like to type delta-v, but my alt-coding is not the best so I'm not actually sure how to type the actual Greek letter I am referring to. Oh well.

Anyway, delta-V, in simple physics terms, is the amount by which a velocity has been changed. There is one such formula for Delta-V based on a steady rate of acceleration over time that every high school student ostensibly knows and which most of you have forgotten, but that is okay because I'm not referring to it ever again. Delta-V in rocketry (whether real, sci-fi, or kerbal) refers to the amount by which a spacecraft can change its delta-V if you were to expend all of the propellant which it carried. Obviously, in staged rocketry this gets more complicated than single-stage rockets which is a part of the reason I occasionally miscalculate my delta-V budget and wind up doing stupid things like Barbara.

Delta-V is actually pretty easy to calculate manually, with a few known values and a good spreadsheet to keep track of the numbers you need. Alternatively you could use a few separate instances of the calculator app built into your computer, or a mod like Flight Engineer or MechJeb, which is my usual choice.

The formula above gives the formula for Delta-V given the velocity of the exhaust (v-sub-e), and the mass ratio (mass with fuel over mass without fuel) from which you take the natural log (ln). So the natural log of the mass ratio, multiplied by the exhaust velocity, gives you your total delta-v. Nominally.

Now, that only works for a single stage, so remember not to discount the fuel in any of the stages above it when you are calculating the dry mass (m-sub-i). This is part of the reason why it is in my view better to use a program like Flight Engineer or MechJeb for doing these calculations in Kerbal Space Program.

The delta-V calculation, or Tsiolkovsky's rocket equation, is one of the single most important equations in fundamental rocketry. If you play quite a bit of KSP or want to start making model rockets or are going to work for a major space agency (or space corporation) one day, you're going to need it. Advice from the interesting website Project Rho for aspiring hard-sci-fi writers is actually to have it on a poster or t-shirt. I simply memorized it as that was far easier.

Delta-V is so important because it is fundamentally the range of your spacecraft, which is to say a map of real distances in space is actually far less useful than a delta-v map showing the required delta-v to get from point-A to point-B. Making some exceptions for nifty things like the Oberth effect and aerobreaking, your fuel-based Delta-V is going to pretty well limit where you can go and what you can do once you've gotten there. Further, it's a useful measure of range because it already took into account the mass of a craft, so the delta-V of a TDRS satellite tells you exactly as much as the Delta-V of a Star Destroyer.

So, once you've got an idea of delta-v, it's helpful to have a map of delta-V values for the sorts of places you want to go in your world. If you are kerbonaut, there is an excellent one here. Happy Flying.

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.

Theseus, Barbara Return, and a Lesson in Math

Theseus on Station, Pre-Deployment

So, you may recall our last project, in which we landed a kethane workhorse on the Mun. Now that it's got a nice belly full of Kethane and reconstituted Liquid Fuel and Oxidizer reserves, it's time to bring it home.