Kerbal Space Shuttle and rocket Economics

[Red Iron Crown]

Well basically... the cost of additional fuel to heft the more massive SSTO is less than the cost of the discarded stage(s) and fuel for the upper stage. It's less efficient, but still works out cheaper.

This is the part I'm struggling with. Why is it cheaper for a fully recoverable SSTO, but not for a partially recoverable STS-staged rocket? It seems to me there is a continuum of both efficiency and cost:

Fully recoverable ----- Semi recoverable ----- Fully disposable

SSTO ------------------ STS-style --------- Regular staged rocket

It seems like the economical properties should vary along this continuum, so if an SSTO is cheaper than a disposable then a semi-recoverable should fall somewhere between. What am I missing?

[Vegetal]

Kerikbalm: It makes sense because the shuttle itself only has a nuclear engine. No huge and unnecessary engines.

The only parts they carry which are useless for interplanetary missions are wings and landing gear, which are very light. Just the mk2 cockpit being 2 tons lighter than the 3 kerbal capsule is already a huge advantage. If you have to ditch the entire craft when reentering, and only land the capsule, even more so.

With the tug method, you have to refuel it after each mission, and for it to make economical sense, you have to do it with a SSTO space plane, which is very time consuming. With my shuttle method, I can use a very efficient spacecraft, and then land it directly on ksc. To be fair, it's pretty much like a conventional interplanetary mission, the difference being that I land directly on the runway for full recovery.

[Frozen_Heart]

This is the part I'm struggling with. Why is it cheaper for a fully recoverable SSTO, but not for a partially recoverable STS-staged rocket? It seems to me there is a continuum of both efficiency and cost:

Fully recoverable ----- Semi recoverable ----- Fully disposable

SSTO ------------------ STS-style --------- Regular staged rocket

It seems like the economical properties should vary along this continuum, so if an SSTO is cheaper than a disposable then a semi-recoverable should fall somewhere between. What am I missing?

With my old shuttles I did find they were slightly cheaper than disposables if you recovered the orbiter. However you often end up throwing away more than with a disposable rocket simply due to more tanks and SRBs being needed to get to orbit.

[Norcalplanner]

I find it hard to see how a rocket SSTO can compete economically with a staged rocket for massive payloads. I'm prepared to be proven wrong, but it seems obvious to me that a SSTO is sacrificing lifting power (edit: and needs much more wet mass) to bring useless recoverables to orbit.

Anybody?

I think a lot of it depends on what your definition of "massive" is.

Back in the Heavy Lifter Challenge, I created an SSTO vertical launch rocket that lifted a 40 ton payload (orange tank, 2.5m monoprop tank, and some other bits) for less than 20,000 funds after recovery. And yes, my entry was gamey as heck.

http://forum.kerbalspaceprogram.com/threads/122243-Heavy-Lift-Economy-Challenge

[GoSlash27]

This is the part I'm struggling with. Why is it cheaper for a fully recoverable SSTO, but not for a partially recoverable STS-staged rocket? It seems to me there is a continuum of both efficiency and cost:

Fully recoverable ----- Semi recoverable ----- Fully disposable

SSTO ------------------ STS-style --------- Regular staged rocket

It seems like the economical properties should vary along this continuum, so if an SSTO is cheaper than a disposable then a semi-recoverable should fall somewhere between. What am I missing?

RIC,

That continuum does pretty much hold in my experience. The problem is that an STS style semi-recoverable is so much more massive than a "layer cake" semi- recoverable for the same payload. A traditional semi- recoverable is just an upper stage and parachutes, while an SSTO is an entire spaceplane. The lower stage winds up 2-3x more expensive than it needed to be and that's the lion's share of the launch cost.

Best,

-Slashy

- - - Updated - - -

Not quite true if it leaves the atmosphere, climb fairly steeply so that you have time to circularise before it re-enters switch to it and ride it down to a landing. SRB's can't really be done this way in stock but liquid boosters are fine with it just add a probe core for safety.

Oh, I'm aware of that. There are also cases where both vehicles are atmospheric and you can switch to the boosters and land them before the upper gets out of physics range.

But those alter the launch trajectory from the ideal profile and are a major PITA to execute. And if you do it wrong you run the risk of losing the entire vehicle.

For planning purposes I assume that anything jettisoned during the launch is written off.

*edit* OTOH I have built cheap lifters before where a jettisoned stage is dumped just short of full circularization. There's plenty of time to circularize the payload and then switch to the dumped stage without any risk. It doesn't recover for much, but hey... free money

Best,

-Slashy

Edited September 16, 2015 by GoSlash27

[Red Iron Crown]

That continuum does pretty much hold in my experience. The problem is that an STS style semi-recoverable is so much more massive than a "layer cake" semi- recoverable for the same payload. A traditional semi- recoverable is just an upper stage and parachutes, while an SSTO is an entire spaceplane. The lower stage winds up 2-3x more expensive than it needed to be and that's the lion's share of the launch cost.

Ah OK, I see what you are saying. So if a rocket used STS-style staging (i.e. disposable SRBs, disposable fuel tank, recoverable main LFO engine(s)) but used lighter recovery equipment and omitted the heavy crew pod and cargo bay, it would likely be more cost effective than a staged rocket, if I understand correctly.

[GoSlash27]

Ah OK, I see what you are saying. So if a rocket used STS-style staging (i.e. disposable SRBs, disposable fuel tank, recoverable main LFO engine(s)) but used lighter recovery equipment and omitted the heavy crew pod and cargo bay, it would likely be more cost effective than a staged rocket, if I understand correctly.

RIC,

I would think so. Especially if you lose the wings/ gear/control surfaces etc and take the 10% hit. In fact, no reason why you can't recover the tank for at least half it's value. This is KSP, so the tank won't necessarily overheat and disintegrate. IME sometimes the tank blows up and sometimes it doesn't.

Best,

-Slashy

[KerikBalm]

Ah OK, I see what you are saying. So if a rocket used STS-style staging (i.e. disposable SRBs, disposable fuel tank, recoverable main LFO engine(s)) but used lighter recovery equipment and omitted the heavy crew pod and cargo bay, it would likely be more cost effective than a staged rocket, if I understand correctly.

as I said here:

http://forum.kerbalspaceprogram.com/threads/134243-Kerbal-Space-Shuttle-and-rocket-Economics?p=2198929&viewfull=1#post2198929

and here:

http://forum.kerbalspaceprogram.com/threads/134243-Kerbal-Space-Shuttle-and-rocket-Economics?p=2199068&viewfull=1#post2199068

Bigger disposable lower stage to launch a biger recoverable upper stage, results in disposale of the same amount of stuff... and now you have a higher fuel bill.

Kerikbalm: It makes sense because the shuttle itself only has a nuclear engine. No huge and unnecessary engines.

The only parts they carry which are useless for interplanetary missions are wings and landing gear, which are very light. Just the mk2 cockpit being 2 tons lighter than the 3 kerbal capsule is already a huge advantage. If you have to ditch the entire craft when reentering, and only land the capsule, even more so.

With the tug method, you have to refuel it after each mission, and for it to make economical sense, you have to do it with a SSTO space plane, which is very time consuming. With my shuttle method, I can use a very efficient spacecraft, and then land it directly on ksc. To be fair, it's pretty much like a conventional interplanetary mission, the difference being that I land directly on the runway for full recovery.

Sorry, but that doesn't sound much like a shuttle.

That LV-N is basically contributing nothing to the launch at sea level, its thrust contribution is insignificant for most of the launch.

What you have is a recoverable LV-N upper stage.

Slapping some parachutes on your upper stage, and not decoupling the capsule at the end - so you recover the entire upper stage, has always been more economical than throwing away absolutely everything.

Does your design even have a cargo bay? or is your LV-N "shuttle" the payload itself?

[Warzouz]

This is the part I'm struggling with. Why is it cheaper for a fully recoverable SSTO, but not for a partially recoverable STS-staged rocket? It seems to me there is a continuum of both efficiency and cost:

Fully recoverable ----- Semi recoverable ----- Fully disposable

SSTO ------------------ STS-style --------- Regular staged rocket

It seems like the economical properties should vary along this continuum, so if an SSTO is cheaper than a disposable then a semi-recoverable should fall somewhere between. What am I missing?

The most expensive part of a launch (not counting LKO payload) is usually the stage you take-off with : the first one. It's true that SRB are quite cheap, but their inefficiency requires you use a lot of them.

IMO, If you use a STS, you'll recover it, sure. But you have to put it to LKO. What is the size increase of your first stage to do that instead of a cheap second stage ou won't recover ? The answer is not that obvious. The cost inefficiency many have noticed may be related to the first stage increased cost for the real payload.

As for SSTO rockets, it doesn't really matter. All you pay for is fuel and recovery error margin on the dry cost (which is 3% for me). How many engine I put in a launcher will only cost me 3% of their cost. If I couldn't recover the whole ship, I would focus on retreiving the take-off stage and throw away the orbit insertion stage which is usually MUCH cheaper (for a regular rocket anyway).

SSTO space planes have the same problem : they have much added mass to LKO, BUT, their "take-off stage" (which isn't jettison) is very highly efficient. This largely compensate for the overweight.

[Captain H@dock]

Just the mk2 cockpit being 2 tons lighter than the 3 kerbal capsule is already a huge advantage.

4 seats mk2 crew compartement is lighter than said cockpit...

AS for SSTO refueling being time consuming: Well, that's the reason why it's cheaper... Time is money.

[The_Rocketeer]

OTOH I have built cheap lifters before where a jettisoned stage is dumped just short of full circularization. There's plenty of time to circularize the payload and then switch to the dumped stage without any risk. It doesn't recover for much, but hey... free money

[Vegetal]

Kerik: Some of them have, to transport a micro lander. If shuttle-like for you is using the shuttle's cargo bay to deliver payloads to LKO, then it's really inefficient, I agree. And slapping a bunch of parachutes on the last stage is probably the same weight, or more, than a couple of wings and landing gear. I prefer doing controlled landings, but then again I'm a pilot...

Captain Hadock: I know, I usually use the cockpit because I like it, but making the craft drone controlled and using just the crew compartment would make it even more efficient.

Indeed, the exact STS approach in ksp is not cheap. As some said before, the increased size of the launcher in order to lift the orbiter together with the payload obviously offsets the recovery benefit. Speaking about stock of course, you could use recovery mods.

[KerikBalm]

Kerik: Some of them have, to transport a micro lander. If shuttle-like for you is using the shuttle's cargo bay to deliver payloads to LKO, then it's really inefficient, I agree.

[GoSlash27]

The should work for the STS ET then shouldn't it, assuming a fairly low orbit? Then the only parts really 'lost' are your SRBs, which if you stick to one pair is... about 2200 roots (discounting fuel).

Suddenly the STS is feeling more affordable.

Well... the tank is technically recoverable whether or not you're lifting a shuttle orbiter. In fact, it's easier to recover the tank intact while still attached to an engine than it is to recover a tank by itself. The engine makes an excellent heat shield.

In other news, yeh I guess my intuition was just off on the staging/SSTO rocket debate. I didn't really believe it until I started comparing cost in an optimisation calculator, but seems there's no doubt now.

Which begs the question, is it ever worthwhile to build a staged ascent rocket (edit: I mean for Kerbin, obvious dV requirements on Eve make SSTOs kinda impractical)? Once you're up there it's another matter...

Well... from a purely economic standpoint I would say no... But a lot of times you have other priorities than cost per tonne or limitations in the tech tree/ facilities that preclude SSTO lifters.

Best,

-Slashy

[Warzouz]

...

Which begs the question, is it ever worthwhile to build a staged ascent rocket (edit: I mean for Kerbin, obvious dV requirements on Eve make SSTOs kinda impractical)? Once you're up there it's another matter...

True, this is a real question. Further more, SSTo rockets have another advantage : they keep the same aero profile up to LKO, no need to bother about flipping second stage and adding fins in the middle that may screw your first stage balance (Eve experince...)

I use SSTO a lot because they are easy to fly. After dozens or hundreds hours playing KSP (ask my wife ), the real challenge is not ascending to LKO anymore.

On the other hand, the purely cost efficent argument fades when you get a lot of cash. Past a certain point, you don't need to recover those SSTO recoverable stages. For example, in my career game, I could send to LKO 40 of my ludicrous "600T to LKO" stage, even I converted 100% science and cash to reputation.

I remember in beta 0.9, I designed a lot of first stages (preciserly calibrated for the payload). As it was in science game mode, I went to asparagus to ahev some mass efficiency. Tweaking multiple boosters took me quite some time. In the end, I visited Duna and all Jool's moon. But much less than in my current game in which I went everywhere. All the time I didn't designed ascent stages to LKO, I used it to land on Dres, Moho, Eve, Eeloo and built space tations everwhere...

End game (which ever "science" or "career" game mode) looks like sandbox. The cost efficiency only matters in mid game, when you leave Kerbin SOI. But again, as for the MPL debate in another topic : it depends on what you want. If you like grinding satelites fees, you don't need recoverable SSTO.

Maybe something could be done to change the game balance makin SSTO rocket less appealing but I don't know what to do (avoiding wrecking all the gamplay)

[KerikBalm]

Which begs the question, is it ever worthwhile to build a staged ascent rocket (edit: I mean for Kerbin, obvious dV requirements on Eve make SSTOs kinda impractical)? Once you're up there it's another matter..

When your own time is worth more than the hassle of recovering your SSTO... when you could just go to the contracts building and look for a plant flag or transmit science contract instead.

[The_Rocketeer]

When your own time is worth more than the hassle of recovering your SSTO... when you could just go to the contracts building and look for a plant flag or transmit science contract instead.

I don't know about this, it feels like your questioning the validity of a causal (not casual) game experience. I mean, sure, if you don't want to worry about funding your missions or cleaning up your space trash, play sandbox.

[GoSlash27]

I don't know about this, it feels like your questioning the validity of a causal (not casual) game experience. I mean, sure, if you don't want to worry about funding your missions or cleaning up your space trash, play sandbox.

[The_Rocketeer]

Well... I wouldn't go *that* far. There's a lot to be said for the gameplay of disposable staged lifters. Technically you shouldn't use anything but SSTO spaceplanes to get to orbit if cost effectiveness is that important.

Best,

-Slashy

Yeh, I don't disagree here, I just find KSP more satisfying when I struggle through the higher-effort parts to reach my goal. If my goal is to beat the economics of KSP, de-orbiting things safely is basically paydirt.

[KerikBalm]

Well, thats actually what I've been doing in my career... all spaceplane's to LKO since unlocking the Turboramjets....

But in sandbox... throw a payload on top of some kerbodyne tanks with mammoths/KR-2Ls

I've even started looking into more expensive, but faster launching systems - at this point, all I care about now is avoiding space debris - I've got a lot of money saved up.

Yesterday I experimented with an Aerospike/turboramjet rocket that just launches into a gravity turn.... I wanted to launch a probe to moho

It didn't have the dV in orbit that I wanted, and in the end, I just took out a 3 engine Mk2 spaceplane I hadn't used in a while, stuck a probe in there.

The 3 engine mk2 design is much faster (in real time) to get to orbit than my 38 engine monstrosities that mass nearly 400 tons on the pad, and deliver ~125 tons to orbit.... which I had recently been using, and left me a little "burned out" with SSTOs.

Going back to smaller payload helped make it more fun... launching a standardized pre-built station for LDO, LIO, LEO, LGO (Duna/Ike/Eve/Gilly), and then ISRU tankers with minor variations, and surface habs+landers/Nuclear tugs for use in the target orbit... and so on, got a little tedious with the low frame rates.

Then I looked at what I'd want to send to Jool... and shuddered...

I think for RP reasons, I'll wait until my probes actually reach there and return data before I launch surface habs and orbital research bases+ fuel depots... etc to the Jool system.

With the funds from selling mobile lab science, I may even go back to disposables for large payloads too

100 tons to LKO is going to be about 100,000 funds...

Thats paid off from less than 200 data into a science lab with full commitment to patents licensing....

[Frozen_Heart]

Oh god shuttle economics are ugly in 1.0. I can manage a cost of 3330 per ton if I take 18 tons to orbit which is the max.

Its more likely that the payload will be less than half that amount which is coming out at around 7000 per ton.

Then again my fully disposable staged rocket is getting 3562 per ton which is even worse. It can manage 13 tons to orbit.

Edited September 18, 2015 by Frozen_Heart

[Vegetal]

I think I misunderstood the point then Kerik, my interplanetary craft resemble a shuttle quite a lot on the launch pad. You are right on the maths, the wings and landing gear make it a little bit less efficient, but as I said, controlled landings...

I don't find STS style to LKO useful in any way, as you said, we can easily single stage to anywhere in the kerbin system, and the difficulty imposed by the game to part recovery accentuates this.

What in the world is an unpowered ultralight anyway? I thought they called those "gliders"

[KerikBalm]

I came back to Space shuttles today... I took my previous design that was costing ~1,500 funds per ton to orbit... and that design I hadn't even fully fleshed out the orbiter (no airbrakes, no landing gear, hadn't tested stability).

As it was pointed out in this thread, we can't recover the SRBs without a mod, but the external tank is doable... so I made a design with a larger ET that has parachutes.

Larger so that the ET is carried further, and I can reach orbit and switch back to the ET

Next, I got rid of the "for the fun" monoprop OMS, and expanded my orbiter's internal fuel capacity. This combined with the slightly larger ET + some ascent profile optimization + using launch clamps to hold the vehicle much higher on the launchpad (seems kind of cheap, and Im not sure how much it actually matters), enabled me to loft a larger payload.

Thus the % of what I get to orbit that is simply my orbiter and not payload is reduced.

I got a 36.2 ton payload to a 107.4km x 81.3 km orbit with >120 m/s left in the tanks for a deorbit burn.

I recovered the ET in the sea to the east of KSC, but as it was sandbox, I'm not sure what the % was... it wasn't even halfway to the otherside of kerbin.... so I'm going to guess it was 75% recovery.

The economics thus come out as follows:

Cost to Launch:

98.426

ET (empty) cost:

10,842

Orbiter Recovery @ 100% and no fuel:

63,532

Launch Clamp Recovery:

1,200

Assuming 75% ET recovery:

8131.5 + 63532 + 1200 = 72,863.5 Recovered funds

98,426-72,863.5 = 25562.5 Net cost of getting the payload to orbit

25562.5/36.2 = 706.14 funds per ton to LKO

This is less than half my earlier cost per ton!!!

It now also beats the best fully disposable system I've seen so far.

With zero recovery, I could remove the 6 raidal parachutes (400 each), and arrive at a net cost of 897.6 /ton... which also beats fully disposable designs.

I didn't take pictures of the 4th variant I made, this was the 3rd variant that I made, and the first one I attempted to land:

From the outside, its nearly identical to the mk4... the mk4 only has 2 monoprop engines (to make use of the monoprop in the mk3 cockpit, and 2 spherical radial monoprop tanks inside.. the monoprop is there to deorbit it). Also, the mk4's wings have been moved slightly back (for stability) and lower (mostly for looks, to have a flatter bottom like the real shuttle, but it also slightly helped with CoM and CoT issues)

Some vernor thrusters were also removed on the mk4

That large monoprop tank, the large battery, and a large reaction wheel have been removed, the toroidal tank at the bottom (which was reserved for the fuel cells) and the fuel cells have been removed.

In place of that is a Rockomax X200-16 Fuel Tank in the mk4.

~700 per ton isn't bad... still worse than an SSTO rocket, and its still harder to recover than an SSTO rocket... and by the time you have size 3 parts (like the KR-2L engine), you should be able to build some pretty good SSTO rockets...

Maybe I'll try making a mk2 shuttle

Edited October 10, 2015 by KerikBalm

[Fiddlestyx]

Question to KerikBalm, do you have a .craft file for that shuttle? I made one almost exactly like that and it will not fly. Even if it gets in the air, it just rips itself apart when turning. I don't want to use your shuttle, just see what's different in mine, so I can learn.

Also, what is that white box in the top right corner?

[KerikBalm]

Well, I think I posted a craft file earlier in the thread, its a very similar shuttle, that was coming out to 1,500 funds/ton.

I don't think I had it loaded fully up to capacity though. The test payload was ~18 tons

Here is the new one... half an orange tank's worth of stuff, total, added to the shuttle.

The test payload here is just over 36 tons, and its coming in under 800/ton with recovery.

https://www.dropbox.com/s/x6nwnfjitruxmjn/Space%20Shuttle%20mk4.craft?dl=0

As for the white box... Thats the only mod I use (occasionally I add HE)... its KER... but I don't know what is wrong with the icon...

Also (realizing I sort of Necro'd my own thread), to respond to Vegetal... quite a while ago:

"What in the world is an unpowered ultralight anyway? I thought they called those "gliders""

Not all ultralights are unpowered, and not all gliders are ultralights.

If I said ultralight glider, you'd probably think something like this:

When what I really fly is something like this:

http://cdn.c.photoshelter.com/img-get/I00008vGusG1Zh1Y/s/750/san-francisco-fort-funston-hang-glider-california108411.jpg