0.24's Cost-Effective Lifters Challenge

[gchristopher]

I tested an all stock (plus Mechjeb) recoverable spaceplane lifter that uses intake spam (without debug clipping) to lift a 22.9t payload for 27.8 √/ton cost. Note that this is NOT using FAR, which should probably have its own category.

Stats:

Launch Weight: 47.572t

Payload Weight: 22.9t (Only a 48% payload fraction, airhog planes max out around 70%)

Launch Cost minus payload: √204,734

Recovery Value: √204,097

Fuel: LiquidFuel: 920 starting / 139 landed Oxidizer: 440 starting / 376 landed.

The flight profile was to climb steeply to ~20km altitude, level off and use jets to accelerate to an orbital speed of about 2,340km/s at ~35km altitude, then maintain that speed using intake spam until about 63km, altitude, so apoapsis was 63.5km and periapsis was 35.4km when switching to the LV1-N engines for the rest of the ascent. Getting into orbit only burned 30 oxidizer.

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The craft file is here. 27.8 √/ton is pretty cheap and this isn't even a particularly good airhog spaceplane. I didn't put any effort into tuning it for efficiency, such as the relatively low payload fraction.

I hope that we'll see better cost performance from less cheesy approaches, but it looks like intake spam might also lead to better cost in addition to the biggest payload fractions.

[Damaske]

Its a bunch of station parts nothing that can help lift something up, Although some do store power, monopropellant, as with fuel and oxidizer but I can avoid using them Or in the case of the fuel and rcs fuel Lock the unit so the fuel can not be used. The thread for it is here that also shows the parts in there pre-texture glory.

[Camaron]

I've expanded the rules to allow the Payloads to contain Mod parts, but they must not add thrust during the launch.

[Damaske]

I've expanded the rules to allow the Payloads to contain Mod parts, but they must not add thrust during the launch.

Thank you very much, and now off to make my design.

[Wanderfound]

Best I got so far is 296 Kr/t with a reusable spaceplane, so I suspect that should be the cheapest approach. Think of it this way. If the craft is 100% reusable, then only cost is the fuel. Cheapest dV by burning fuel can only achieved by air-breathing engine (1200 Isp!) and beathing for as long as possible during the ascent. Rather low TWR is the issue however, so I failed to produce reliable heavy lifters that takeoff using jets. I suppose someone must have succeeded, so would like to see it.

http://forum.kerbalspaceprogram.com/threads/88628-Kerbodyne-D7-Heavy-X5-a-heavy-lift-SSTO-spaceplane

Two turbojets, six RAPIERs, no need to burn oxidiser until about 30,000m.

[gchristopher]

I'm surprised we haven't seen more reusable testing. I can think of four launch profiles that might be compared: (stock only)

1. Ballistic rocket ascent
   
2. Ballistic jet ascent, switching to rockets (without much lift from wings)
   
3. "Reasonable" spaceplane ascent, switching to rockets in atmosphere
   
4. "Airhog" ascent, switching to rockets exoatmospheric with a high semimajor orbital axis
   

There's room for interpretation between some of those categories. You can fly a wingless jet-rocket (profile 2) quite a long ways, picking up orbital speed at the 20-30km altitude and raising your semimajor axis before switching to rockets. The only difference between a reasonable spaceplane and an airhog is the number of intakes, and there's no way to firmly set a limit there. To me, the difference is that a normal spaceplane doesn't achieve BOTH a high apoapsis and high semimajor axis, where an airhog with 1 intake/ton can easily leave the atmosphere with a 40-50km semimajor axis, and be less than 50dv from orbit just using jets.

Maybe also compare a vertical landing profile vs. a runway landing. (Or with and without parachutes?)

I don't think the weight categories will end up mattering too much, since a 100 ton lifter can be made just by doubling all the parts in a 50 ton lifter, etc.

Has anyone tried recovering a pure rocket in .24 yet?

With only two results in this thread, there's not a ton to report yet:

[table=width: 500, class: grid]

[tr]

[td][/td]

[td]Runway[/td]

[td]Rocket Landing[/td]

[td]Parachute[/td]

[/tr]

[tr]

[td]Ballistic rocket[/td]

[td][/td]

[td][/td]

[td][/td]

[/tr]

[tr]

[td]Ballistic jet[/td]

[td]~300 √/t (Tsynique)[/td]

[td][/td]

[td][/td]

[/tr]

[tr]

[td]Spaceplane[/td]

[td][/td]

[td][/td]

[td][/td]

[/tr]

[tr]

[td]Airhog Plane[/td]

[td]~30 √/t (me)[/td]

[td][/td]

[td][/td]

[/tr]

[/table]

[Radam]

Did physics change in .24.2? I think it didnt much, so let me get my craft from a year ago:

http://forum.kerbalspaceprogram.com/threads/41094-The-100-recoverable-lifter-Megathread?p=615850#post615850

Basically delivering 27t to low orbit with about 2500 in fuel costs, basically a ratio of about 92/t.

I did recently mess with rapiers and so far Ive got them to down to about 125/t. With FAR, my experience was that its actually easier. And the craft also doesnt disintegrate on descent.

EDIT:

My entry into this is a Rapier Pineapple Lifter. Starts very slow, but delivers 41t to 71km orbit, then landing, in all using 2690LF/2660LOX. Calculated cost is 61√/t.

http://imgur.com/a/dEY3o

In this instance I have only FAR and MechJeb installed. With FAR, what ends up helping so much is lower drag and lifting body effect.

Only problem with this approach is that it takes a third of the tech tree to unlock all needed parts. But I guess if you shoestring your scientific research around kerbin then there might be enough. And then go into interplanetary space.

Edited August 7, 2014 by Radam