Munstak Industries is proud to present - Kethane Orbital Tanker 01 (the Mary Jane)

[tntristan12]

So I designed and built a spacecraft in Kerbal Space Program that I am particularly proud of. Why is this so special? Well, the reason I'm proud of this one is because I designed it on pen and paper before I even touched the game. In theory, my design would meet all of the same delta-v requirements and mission parameters if it were built in real life. Rather than just attach a bunch of engines and boosters together and fiddle with it until it worked, I took a systematic approach to quantifying exactly what I needed it to do, and ended up designing the spacecraft to match up with that. One of the things I enjoy the most about KSP is how real-world math can be applied to it, and the results usually come out to be very much what you would expect in reality!

So this spacecraft is called a fuel tanker because it brings back Kethane from the Mun in a pre-measured quantity. I have a resource mining outpost on the Mun that is capable of processing a certain amount of fuel (16,000 units / 32 tonnes of Kethane, which works out to be an approximately equivalent mass of fuel and oxidizer per generation cycle). I have a shuttle that brings those 32 tonnes into Munar orbit, and once it gets there it offloads a little over 37% of that (or 6,000 units / 12 tonnes). The tanker itself holds 30,000 units / 60 tonnes of cargo, but does not require much fuel because I use ultra-efficient LV-NB engines that come with the KSPX mod pack. The result is it ends up offloading 80% of its fuel (or 24,000 units / 48 tonnes) to my orbital space station, which I worked out exactly because 24,000 units is the Kethane storage capacity of my space station in orbit around Kerbin. I intentionally weighted the rest of my spacecraft so that it would need to convert the remaining 20% back to fuel and oxidizer for the next mission cycle, because I wanted to be able to empty my surface miner exactly 4 times to fill up the tanker exactly once.

So how much does it weigh? Well based on the delta-v and mission requirements I determined that it needed an initial mass of 48.837 tonnes, with a structural mass (mass of everything that isn't fuel+oxy, Kethane, or tanks to hold either of those) of 28.46 tonnes. The cargo mass is 60 tonnes, and it carries 12 tonnes of fuel and oxy (the equivalent of three FLT-360 fuel tanks, which I like to use as a unit of measure for how much fuel a spacecraft contains) to complete each mission cycle. It isn't very often that you have to add mass to a spacecraft to get it to perform as intended, so I had some fun with it and used the opportunity to make it as aesthetically pleasing as possible while still adding all the required functions (comms, power generation, docking capability, RCS, etc). I basically started with a structural mass budget of 28.46 tonnes and subtracted from that total as I added parts to it, starting with the largest and most necessary items (the thing isn't going anywhere without engines after all), and then getting down to frivolities like aesthetics afterwards.

One thing it needed was a replaceable heat shield, because it is designed to aerobrake in Kerbin's atmosphere upon returning from the Mun (I'm using deadly re-entry now). It comes with a 6.25 meter heat shield that needs to be jettisoned to free up the Sr. docking port at the front after each mission cycle (there are radial docking ports it could use, but my reasoning was that after each use the heat should would essentially be used up, and mission planners would want a fresh heat shield for each mission cycle as one of the safety requirements). Another thing I added to the craft in order to bulk it up to the necessary initial mass was a hitchhiker storage unit - although the ship is unmanned, it is able to comfortably seat 4 crew immediately aft of the heat shield for the purposes of changing out the outpost crew on each mission cycle. Finally, it carries its own Kethane conversion unit so that it can refuel the Keth-o-Hopper Tanker Shuttle (the one that brings the Kethane to Munar orbit) on site.

So what did it end up weighing when all was said and done? Exactly 48.837 tonnes - no more, no less! I used the Tsiolkovsky Rocket Equation to calculate the delta-v for each stage in the mission and it came out to exactly what I had intended for it to be: 1,200m/s going there (900m/s to get there + 280m/s to get into orbit + 20m/s safety margin), and 400m/s going back (280m/s to break orbit + 100m/s for orbital maneuvers after aerobraking + 20m/s safety margin). The target burn mass for getting there was 6.931 tonnes of fuel. I ended up burning about 6.51 tonnes - the margin on the trip there is less than half a ton of fuel (I'm glad I built in that 20m/s safety net)! As of yet I haven't tested the trip back, but if the margins work out similarly I should be cutting it just close enough that I don't waste a lot of fuel needlessly pushing around dead weight.

But enough about the design. Let's see some pictures of it in action!

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If anybody wants to play around with it in their own game, I've made the .craft file available for all to enjoy! The mods you'll need are KSPX, Kethane, Deadly Re-Entry, RemoteTech (I use a couple of antennas from that pack), and MechJeb (if there's enough demand I can load a version of the craft without it). Have fun with it, and happy minings!

Oh, and one last thing. If anybody is interested in building their own fuel tanker craft, I've uploaded a mathematical guide to tanker construction here. It's fascinating stuff, for the mathematically inclined!

[Rune]

Good to see someone spending the time to work out things the old fashioned way! Good old Tsiolkovsky, right? Me, I long since decided I wouldn't use a calculator for playing a computer game, so I allow myself kerbal engineer redux. But I love it when my rough mental calculation probes right when I slap on the part

Rune. I already have to break my brain enough in RL. ^^'