Least fuel to Kerbin orbit challenge

[Ocirne94]

Objective: get to Kerbin orbit (Pe > 70 km) starting with the least fuel (liquid+oxidizer+solid).

• Stock parts only (sandbox mode), no mods, manual piloting (SAS/RCS/reaction wheels allowed), no cheating, no refuelling.
• Multi stages allowed but be nice and don't use decouplers for propulsion.
• All stock engines allowed excepted electric.
• Payload/reentry not required, just get a pod to Pe > 70 km.
• Scoring: least fuel at takeoff (liquid+oxidizer+solid) wins. Unused fuel doesn't matter.
• Tip: you don't need to take off with completely filled tanks.

 

My record (pictures to come): 30.6 liquid fuel + 22 oxidizer = 52.6 units.

Edited February 16, 2016 by Ocirne94
Missing details

[Nich]

20.8 LF + 13.2 ox = 34 units

I left 1 LF in the tank when I separated from the panthar

 

Edited February 16, 2016 by Nich

[numerobis]

I have a theoretical solution with 16.2 LF and 8.8 OX.

The important bit: switch to a smaller probe. Both engines are vectoring, so we don't need the reaction wheels: we can use the okto2. That saves 60kg. Doesn't sound like much, but it's a bit over 38% of the upper-stage dry mass. Given Nich needed 10.47 LF and 12.8 OX, my smaller stage will require just 6.42 LF and 7.85 OX.

And then, there's another trick: according to Nich we need 9 units of LF for the jet. There's plenty of room for that in the Oscar. Just put it there, make the decoupler cross-feed, and ditch the Mk0 tank.

So we're trying to pack 15.42 LF and 7.85 OX into an Oscar. The closest we can tweak this to is 16.2 and 8.8.

Given the mass reductions, there might be a reduction in LF needed by the Panther, but I'm not sure it's really significant. My concept on reduced the dry mass of the panther stage by 10%.

 

Now, to fly this... it is so insanely twitchy.

[Nich]

Ha ha I had forgotten I had taken that much fuel out of the Oscar.

Oh and for flight path if pe doesn't make it over 40km before 1400 m/s there is too much drag to accelerate to orbital velocity.

[numerobis]

@Nich: you didn't take that much fuel out; you need to switch to a lighter probe body to be able to fit all the fuel in the oscar.

I flew a handful of times last night, had trouble with control because when I'd hit a button, I'd suddenly be upside down. Turn on SAS, it oscillates like mad. I remembered at the end of my session that I could reduce the gimbal, and that will probably do it.

The panther's CoM seems to be quite far ahead of the visuals of the part; I get a center of mass ahead moving of the probe body when I add the engine, whereas normally it's barely ahead of the ant.

Edited February 17, 2016 by numerobis

[Nefrums]

14,4 LF, 8,8 OX

One Panter and one Spider engine.

Had some problems with running out of electric charge for the probe core

 

 

 

[dunebugmi]

Can I use an ion drive?  

[ihtoit]

4 minutes ago, dunebugmi said:

Can I use an ion drive?  

ion=electric, so I'd guess the answer to that one would be "no".

(edit: I have sent up clusters of very simple comsats consisting of a flat OKTO core, one antenna and an RTG, for a payload weight of next to nothing. Pretty sure I can get it lighter.

Edited February 29, 2016 by ihtoit