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Highlad

Funds per metric ton - How efficient are your lifters/spaceplanes?

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I have been on an extended break from KSP and although I haven't played in months, I have been keeping up to date on reddit, the forums and of course the dev blog. Anyway, I've been getting back into the swing of things and have decided to build a fleet of reusable lifters and SSTOs.

So far my SSTO, the Raven, can put a ton into a 200km orbit for about 1700 funds. I thought that it was a bit expensive so I went about adapting a lifter I had designed 'back in the day'. The original lifter, the Socrates was semi reusable; the lower stage was completely normal but the upper stage could deorbit and land at KSC. I updated it and now both stages are recoverable. It can lift around 20t to LKO (100km) and return to KSC for about 690 funds per ton. Surprisingly it was cheaper, faster and more fun to fly than the Raven. Yey!

But bigger is always better and more boosterz is always a good thing, so I decided to build a heavy version of the Socrates. It ended up being able to lift about 60t to LKO and return both it's stages to KSC for around 660 funds per ton!

I'm amazed that building bigger can actually be cheaper!

Anyway, I was curious what kind of per ton cost you guys are getting out of your SSTOs what with the new update causing all sorts of havoc for spaceplanes.

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My best SSTO can do about 15t to Minimus for about 400 kredits/t. Maximizing for LKO I suspect 250 kredits/t is possible but the problem with Spaceplane SSTOs is for me they max out around 50-60t. I have seen a 136t lifter but it would be maxing my part count limit.

http://forum.kerbalspaceprogram.com/threads/116729-Stock-Payload-Fraction-Challenge-1-0-4-Edition?p=2124872&viewfull=1#post2124872

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Anyway, I was curious what kind of per ton cost you guys are getting out of your SSTOs what with the new update causing all sorts of havoc for spaceplanes.

The question does not compute. I only use SSTO spaceplanes as crew shuttles for interplanetary ships that have returned but can't land. This is mostly because nearly everything I put in space is too wide for spaceplane cargobays anyway, and spaceplanes take so long to reach orbit that if I assembled my ships out of stuff that would fit in them, that's all I'd ever have time to do.

But it's also becuase I don't care about money spent on lifters. I design my ships to fit in my budget and consider everything that leaves the ground as money I'll never see again. While I do use SRBs as much as possible on my rockets, I don't bother recovering any stages, and in fact pay $400 extra per stage to blow them up with TAC Self-Destruct (it's cool and it eliminates debris). And despite this extravagance, I have no trouble whatsoever in become rich enough to buy entire planets :). Therefore, I have no incentive to strive for efficiency.

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My little personnel transports work at under $150 per kerbal, which is under $300 per tonne.

My large tankers are about $80 per tonne.

Best,

-Slashy

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I also cannot say how much my lifters cost ...

I usually design the whole system for its mission from the ground off.

(well, even if I could, the costs would not be comparable as I play with Realism Overhaul, meaning that the stock fuel and engines are replaced by more realistic engines and real life fuels).

I only track the total costs and dV per mission as well as science and money earned (and how much money I got from recovered spaceship parts)

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80 per ton? thats pretty cheap... what sort of capacity do you have with them?

I just got exact stats for the cost of my last heavy SSTO spaceplane flight.

The payload was a 91.21 ton Eve lander, encased in a 12.9 ton fairing (those fairings are heavy still!)

It was very wide, and thus not very aerodynamic... I'm wondering if I should have even used the fairing... I think it may not actually have helped in the long run... anyway...

Total LF used was: 16,239 units for a cost of 12,991.2 credits

Total Ox used was: 13125 units -> 2362.5 credits

Fuel costs were thus: 15,353.7

I had never considered it before... but that fairing is killing my efficiency. (granted, this was an unusually big payload, even for my lifter)

Its 14% the weight of my payload... and the cost... I thought recovering the fairing base would recover all the funds (even though IRL, it wouldn't work like that) for the fairing... it doesn't (you get back 900 for the base).

That darn fairing cost 7,500 after recovery of the base.

The flight thus cost ~22,850 to get 91.21 tons to orbit, or 250 credits per ton.

It wasn't the most efficient flight in terms of ascent, or fueling amounts (considerable excess LF, not so much excess oxidizer - but I hauled 26.37 tons of fuel to orbit, just to take it all back down).

If I took a payload with no fairing (just on a stack behind the cockpit), and put that 26 tons of unused fuel in the payload, and the fairing mass to the payload, then in theory I'd have 91.2+12.9+26.4 = 130.4 tons to orbit for the cost of 15353.7 in fuel... or 117.67 per ton.

Probably better due to aerodynamics (like suppose I just had a line of ore tanks, no bits hanging out, or a wide draggy fairing)

I could probably make a design that does better in terms of credits per ton, but I like the one I have now with its very versatile payload capabilities...

This was the payload that I just got those numbers from, and got it to a 110x90 km orbit:

11907224_10103814781863393_6333836243015857510_n.jpg?oh=4b71a2e0593fcfbfb15632c40ef75530&oe=567BDC84

The only modification was the radial mounts on the heatshield+airbrake sections were rotated inward, as were 1 set of fins.

...

Oh, and a radial mount pylon, plus I-beams to come in front of the nose where a probe core and docking port were put, and then strutted to the rest, because the eve lander had no nodes left to attach things too (luckily strut mass is only added to one part, not both, and that part will be discarded as it goes down to eve

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For KSP, I think time is a more important unit of currency.

A rough guestimate of my best lifter puts it at 4.8 seconds per ton. (50 tons to orbit in ~ 4 minutes)

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80 per ton? thats pretty cheap... what sort of capacity do you have with them?

KerikBalm,

My "BigHoss" is rated for 28t LF&O per flight. I don't build spaceplanes to carry anything that doesn't pass through a docking port and I don't build them to go any farther than a station in LKO and back.

You've got a radically different mission for your spaceplanes and I don't envy that challenge :D

I used to focus on payload fraction, but I realized that fuel fraction was really key to economical SSTOs, so now I design for that. Aerodynamically clean, balanced to an economical profile, and designed to use the minimum fuel mass in the launch process.

My spaceplanes are about as glamorous as a Maytag washer.

Best,

-Slashy

Edited by GoSlash27

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