0.24's Cost-Effective Lifters Challenge

[buzz66boy]

√4880/ton, 492 tons, √2.4 million

http://forum.kerbalspaceprogram.com/threads/87798-492-ton-Payload-Capable-SSTO

[Camaron]

Make it cost after recovery if you want the spaceplane crew in. My heavy lifter costs √176,000 for a payload capacity of around 50 ton, but the only expense is a few thousand in fuel.

With this request, and buzzboy's interesting submission, I've made two parts. One scoreboard with recovery counted, one without.

I welcome you to the contest, flyboys!

[LostOblivion]

Is it not generally true for space launches that launch costs typically increase exponentially with rising payload mass? This means that small payloads would generally be cheaper.

[Tweety]

2) 2,801.5564: Tweety's 1285kg Probe Lifter v2.1

As much as I would love to be THAT efficient, I have calculated and recalculated my costs being 3502 per ton. Don't take this out of context as its not malicious but how did you calculate it? Payload is 1.285t and the lifter is 4500 funds.

I'm just confused

Edit: Tonight I may also try for the 'bigger is better' option...

Edited July 24, 2014 by Tweety

[Jouni]

Is it not generally true for space launches that launch costs typically increase exponentially with rising payload mass? This means that small payloads would generally be cheaper.

No. Launch costs increase exponentially with delta-v requirements, but linearly with payload capacity. If you have a rocket that can lift 10 tonnes, you can strap a million of them together to lift 10 million tonnes. (In practice, things would obviously not be that simple.)

[LostOblivion]

Makes sense!

[NikkyD]

KSP has a huge problem for some while now with its assortment of engines.

The most efficient plane is the one that has the most efficient engines.

You could say the winner is the one with the best delta-v for money ratio. And if you think about what gives you delta-v, its (roughly) engine TWR and ISP.

Now look at the handful of engines that we have and what they cost... its a no-brainer.

best one is the KR-2L, TWR of 39.2 and ISP 320 to 380. Try to replace this engine with multiple others, you will come up with more expensive solutions. Its the same old story all over again, try to replace a Mainsail with ... with what ?! You can't.

Well... you MIGHT, atm because of the super cheap boosters. But you cant make a successful rocket with boosters only. So you need at least one engine and voila, you're in the middle of it.

Using a 909 hardly makes sense, it once had an astonishing ISP with 390 but now most big starter engines go up to 370 or even 380. You can makes sense to build rockets in a way that you drop empty fuel tanks but keep the engine, use a KR-2L with 380 in space. No need to switch to a 909 with 390, because the amount of 909s you would need is crazy. For longer trips however there is no way around LVNs with 800 ISP.

The only other thing to consider when talking scale is that, for spaceplanes, once you have a certain setup, you only need to add x more engines and y more fuel and wings. The more you add, the less influence the cockpit mass has. If its a rocket however more a lifter, then you dont need a cockpit, its usually part of the payload. So once you find the best ratio with ONE engine, just multiply it and it will be the same...

There is no real point in building a 1000t thing, i did a quick test and with a KR-2L u can get about 10t into orbit (with 1 biggest tank). Multiply that by a number and it will still be the same ratio.

[Pecan]

...i did a quick test and with a KR-2L u can get about 10t into orbit (with 1 biggest tank). Multiply that by a number and it will still be the same ratio.

Exactly what I have done, as well. KR-2L for 10t and 4 of them strutted together for 40t, just as you and Jouni say:

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The central orange tube there, and its accessories, is the payload. There's a bit more fuel than you specify because of the parachutes, landing-legs, batteries, etc. 100% recovery if you fly it right, and a lot simpler than a comparable stock spaceplane.

Edited July 24, 2014 by Pecan

[Wanderfound]

With this request, and buzzboy's interesting submission, I've made two parts. One scoreboard with recovery counted, one without.

I welcome you to the contest, flyboys!

Thanks for the invite.

You may need to open it up to FAR, though; I doubt that there are any serious flyers using stock physics.

[Camaron]

You may need to open it up to FAR, though; I doubt that there are any serious flyers using stock physics.

Solid point. FAR allowed now, but only in the section which counts recovery.

[Dave Kerbin]

6) No part of the Payload can be used to help in achieving orbit.

I'm pretty sure it's ok but just to clarify: Can the payload include a control element (probe core or command pod), or must that be included with the launcher.

[NikkyD]

good point dave, for fairness it should be with the lifter so that the payload can be a pure container

[Camaron]

Good Question. That rule is really only intended to say that if your Payload includes RCS or Engines, that they cannot be used to assist in achieving orbit. RCS used sparingly as a stability agent, or SAS and control modules are allowed. (and really, necessary if the Payload is going to be useful.) I may re-write the rule to be clearer.

[Slugy]

KSP has a huge problem for some while now with its assortment of engines.

The most efficient plane is the one that has the most efficient engines.

You could say the winner is the one with the best delta-v for money ratio. And if you think about what gives you delta-v, its (roughly) engine TWR and ISP.

Now look at the handful of engines that we have and what they cost... its a no-brainer.

best one is the KR-2L, TWR of 39.2 and ISP 320 to 380. Try to replace this engine with multiple others, you will come up with more expensive solutions. Its the same old story all over again, try to replace a Mainsail with ... with what ?! You can't.

Well... you MIGHT, atm because of the super cheap boosters. But you cant make a successful rocket with boosters only. So you need at least one engine and voila, you're in the middle of it.

Using a 909 hardly makes sense, it once had an astonishing ISP with 390 but now most big starter engines go up to 370 or even 380. You can makes sense to build rockets in a way that you drop empty fuel tanks but keep the engine, use a KR-2L with 380 in space. No need to switch to a 909 with 390, because the amount of 909s you would need is crazy. For longer trips however there is no way around LVNs with 800 ISP.

The only other thing to consider when talking scale is that, for spaceplanes, once you have a certain setup, you only need to add x more engines and y more fuel and wings. The more you add, the less influence the cockpit mass has. If its a rocket however more a lifter, then you dont need a cockpit, its usually part of the payload. So once you find the best ratio with ONE engine, just multiply it and it will be the same...

There is no real point in building a 1000t thing, i did a quick test and with a KR-2L u can get about 10t into orbit (with 1 biggest tank). Multiply that by a number and it will still be the same ratio.

This is completely wrong, try making an entry to discover why.

Hint 1: A mainsail and orange tank costs less than the KR-2L on it's own.

Hint 2: A KR-2L weighs 6.5t, dumping that and having a 2nd stage with a low weight engine 1.25m engine with fuel gives a better result.

[Slugy]

Here's my entry for the lightweight category.

72.085t lifter, 15222Kr, 9.015 payload : 1688.5 Kr/t and it has a large liquid fuel stage!

The RT-10s are throttled to 80%, and explode just before they run out of fuel. Could lose the strut most of the time ...

Javascript is disabled. View full album

Edited July 25, 2014 by Slugy

[NikkyD]

This is completely wrong, try making an entry to discover why.

Hint 1: A mainsail and orange tank costs less than the KR-2L on it's own.

Hint 2: A KR-2L weighs 6.5t, dumping that and having a 2nd stage with a low weight engine 1.25m engine with fuel gives a better result.

I dont wanna be a hypocrit, you may be right about the cost of KR-2L, but that doesnt change much about the overall imbalance of the engines.

Also i am not sure if my games "cost" values are accurate.

The cost in my game differ from http://wiki.kerbalspaceprogram.com/wiki/Parts

The wiki says boosters (small) are 450, game says 325... which one is correct ?! (just one example)

I use this wiki a lot for planing, if its wrong, im wrong, sadly.

[Camaron]

Several parts costs were tweaked yesterday in the 0.24.1 patch, so the wiki is likely slightly behind. Or, since every single cost was changed for 0.24.0, maybe that's the fault.

In any case, clever staging, weight considerations, etc, can make rockets more or less effective out of the same weight. Simplifying it to how much one engine can lift with a given amount of fuel is not accurate. Please don't continue that argument if you can help it.

[Slugy]

Well having caught the cheapskate bug, and after (too) much fiddling with assorted mostly solid fuel launchers I have a handy one.

A full Mun mission for one for less than 9000Kr, lifter is 4452Kr with a 2.803t payload = 1578.7Kr/t

Includes such luxuries as: a ladder, a light, power, and a linear RCS on the bottom of the capsule ...

It can be flown better than I did in this example (ie sekret emergency RCS not needed), I forgot to take shots of the 1st attempt

All solid boosters are run at 100%.

Javascript is disabled. View full album

[NikkyD]

Question, what about the cost for the mechjeb part ? Imho it shouldnt count as a rocket computer should be able to do all that stuff by itself

[Slugy]

Question, what about the cost for the mechjeb part ? Imho it shouldnt count as a rocket computer should be able to do all that stuff by itself

You can just put it on the payload, which is what I did with this one.

[r_rolo1]

Hum, nice ... while I prefer my rockets without explosive decoupling, thank you it is a impressive feat.

About the launcher, have you tried to use SRB-KD25k for the first stage ? TBH, and at first glance, it would be better to use a SRB-KD25k + a RT-10 in the core of the rocket instead of 2 BACC + 4 RT-10... and , as we are talking of savings by swaps, how about using separatrons to do the circularization ?

[gm537]

Here is my entry for the light weight entries.

First image shows total VAB cost as 58836

The second image shows the payload cost as 14272

Third image shows payload with no rockets attached and with a stable orbit.

And finally the payload mass is shown here: 29.265

My math says:

(58836-14272)/29.265 = 1522.8

(Note: KSP shows a different final mass from KER. Using that mass of 29.67 I get a value of 1502.0 up to you which is used.)

Edited July 26, 2014 by gm537

[gm537]

Exactly what I have done, as well. KR-2L for 10t and 4 of them strutted together for 40t, just as you and Jouni say:

The central orange tube there, and its accessories, is the payload. There's a bit more fuel than you specify because of the parachutes, landing-legs, batteries, etc. 100% recovery if you fly it right, and a lot simpler than a comparable stock spaceplane.

Ummm.... Those are NOT the KR-2L those are the LFB KR 1x2. Haha

[gm537]

Also as a stupid question: How do you do those cool albums that can be flipped through? I just know how to put each image in the post but that takes up a lot of space...

[Slugy]

Hum, nice ... while I prefer my rockets without explosive decoupling, thank you it is a impressive feat.

About the launcher, have you tried to use SRB-KD25k for the first stage ? TBH, and at first glance, it would be better to use a SRB-KD25k + a RT-10 in the core of the rocket instead of 2 BACC + 4 RT-10... and , as we are talking of savings by swaps, how about using separatrons to do the circularization ?

Cheers, I was aiming to have a nice useful rocket in total, and a Mun mission was an obvious choice. That's also the reason for having a little too much fuel in the liquid stage.

I did try a large SRB as a mainstage with some RT10s, but had trouble getting a nice velocity during ascent - you may be right though. Let us know!