Can't cram in enough dV to SSTO

[NFunky]

Hey guys, been a while since I've had a chance to read these forums or even play KSP, but I'm finally diving back in.

Been playing around with trying to make an SSTO in Kerbol 3.7, and tweaked reentry heat to make it closer to an Earth reentry. It's turning out to be a lot harder than I expected. I have a couple different issues, but the biggest one is simply getting enough dV.

It takes around 5500 to reach a 70x70 orbit, and I've heard you can get between 1200-1500 m/s with airbreathing engines, but that still leaves more than 4300 m/s that has to be done anaerobically.

Even with the Aerospike, I am having a really hard time cramming that much fuel into a rocket body with reasonable dimensions. I can get around 4200 in a decently controllable design, but as soon as I add wings and extra jet fuel (let alone if I'm using seperate air-breathing engines), it drops to under 4000.

Could you guys point me in the direction of some example designs that contain this much dV? Or give me any tips or ideas as to how to go about this? I'm thinking about moving up to RSS, but if I can't do an SSTO in 3.7x, there's no way I'll be able to with a 6.4x scale.

Thanks

[KerikBalm]

I didn't think people SSTO'd in RSS.

If you use RSS, you'll want to use realistic parts too, which have better mass ratios and TWRs, and in some cases, better Isp.... so....

As to your question... I don't know... the right mixture of LV-Ns?

[Scarecrow88]

Orbital velocity at 70x70 is around 2300-2400 m/s. In the current aerodynamic model, I can get my craft up to about 1300 m/s at 22k altitude in air breathing mode, which means that not a lot more is required to actually reach orbit on rocket engines. Also, a lot less dV is required to get to orbit in the current aerodynamic model, arounf 3200 m/s and not the 5500 you think you need.

Re-reading your post, I am thinking you are not playing KSP on a PC platform, as the version number does not correspond, so what I said above may not hold true on the platform you are playing.

[Captain H@dock]

Re-reading your post, I am thinking you are not playing KSP on a PC platform, as the version number does not correspond, so what I said above may not hold true on the platform you are playing.

I'm fairly sure the 3.7x he's mentionning is a scale factor, not a version number. kerbol A.Bx refers to the Kerbol System where all distances are multiplied by the A.B decimal number. I'm assuming other physical properties are scaled appropriatly, hence the higher dV requirement to orbit.

edit: Also, considering how much I've struggled to make a Tylo chemical re-usable lander with an aerospike (which is similar to your dV requirement => 5,000 ish dV), I suspect OP won't be able to get any decent payload fraction with KSP default parts.

Edited October 5, 2015 by Captain H@dock

[NFunky]

Sorry, I should have clarified that better. I am indeed talking about a scaled up Kerbol system (in KSP 1.0.4). And yeah, it's just the planet radii and distances that are scaled up, although I've also scaled up reentry heating myself.

With a bit more experimentation, I believe I can get about 4300 anaerobic dV into a single stage vehicle, but only with a fairly low TWR. I'm doing all this in sandbox BTW, so no cost, size or part constraints. I just want to build an SSTO of some kind (rocket or plane).

[Clipperride]

Have you tried stripping things right back and designing a small Mk2 SSTO? I've not played with in larger scale environments, so I may be completely wrong, but in regular KSP its easy to get trapped in the engines/fuel/drag vicious circle. I imagine it's even more of a problem as the scale increases. My other "work around" is SS(and a bit)TO where you get your engines up to speed quickly using detachable SRB's on the runway or soon after take off.