Trying Make a more Efficient SSTO

[cheeseit]

So I just recently finished my round trip to Laythe with an SSTO. It wasn't very efficient and the ship was ugly as all hell though. It took my 3 dockings above kerbal then 3 more above Laythe do the whole trip. It also ended up as a rescue mission with the first failed attempt.

My main goal now for myself in KSP is to make much more efficient designs mainly for SSTO's. I can get my ship into orbit very easily but then I end up with very little oxidizer and I need to refuel once in Orbit to do anything worthwhile. The goal I have set for myself is to reach the Mun in one shot without a refuel on the way.

I downloaded the B9 aerodynamics pack and it makes the ships look 1000000x times better but I still can't make an efficient design it feels like. I usually take my ship right after take off at a very steep angle of ascent up to around 20,000 feet and then get to about 1000 m/s at this point I'm usually running out of air so I swap to rocket mode and angle up and get my apoapsis to around 80,000 then circularize.

Is my launch really bad or do my designs just suck?

This is what my new ship looks like atm. I tried this engine set up and then just decided to use 4 rapiers.

Any advice would be greatly appreciated.

Edited February 13, 2014 by cheeseit
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[Bean]

I don't see any pictures, but try to bleed more speed out of the air stage, keep altitude and try to get past 1500m/s, sounds like you have more than enough liquid fuel to do this before using the rocket stage

[cheeseit]

Yeah I usually end up with about 400 excess liquid fuel after my oxidizer runs out. I'll try to stay in the atmosphere longer.

[Jouni]

Three things:

1) Replacing RAPIERs with a mix of turbojets and rocket engines can improve efficiency, especially when you plan to go beyond LKO. It makes building and flying the SSTO harder, but it's something to consider.

2) Having more air intakes than engines allows you to reach higher speeds and higher altitudes before switching to rockets. I personally don't do that, but most people do.

3) Ram air intakes work better at higher speeds. This means that if you climb too fast, you run out of air at lower speeds and lower altitudes.

[arq]

You can 'airhog' SSTOs by adding intakes to making getting to orbit almost arbitrarily easy and efficient. But I personally don't like to do this.

The biggest thing is to reduce your oxidizer until you finish with basically no extra (so that you burn out of oxidizer and liquid fuel at the same time, after switching to rockets).

Lose the second LV-N. Having more than 1 on a ship this small is a waste because they're so heavy. You only need 1 to get you from LKO to Mun and back, possibly with some 48-7S engines for extra thrust for getting into LKO and for takeoff/landing on Mun.

[Mobjack]

Is my launch really bad or do my designs just suck?

The reasons your designs are inefficient is because they don't suck. The secret to making an efficient SSTO is intakes, intakes and more intakes.

Air intakes are extremely overpowered for SSTO's. With enough intake, you can run your jet engines at 35,000 meters going 2300 m/s. All it takes is a little more dV to actually get into orbit.

If you want to make something efficient, don't build something that looks good and could work in real life. You just need to find a way to attach as many intakes as possible.

[ComradeGoat]

You're carrying two LV-Ns. Those things are *heavy*.

Build light. Two turbojets and an LV-N. Once you're at a decent speed and a decent height (say 1700 m/s and 25,000m), run them at the same time to push you to orbit if your plane is too heavy for the jets to do it.

Check out this guy: stock, except for Engineer Redux and a Protractor. I got Engineer Redux to show the delta V in space by thrust limiting the jets in the VAB to 0 (handy trick). That's the heaviest single pilot SSTO I have, and it has an embarrassment of delta V in space.

(there are some radial intakes under the engines that you can't see in this view too)

Another way to do it is to build light and then dock your plane to a carrier rocket in space, which has enough delta V to get to Laythe and back.

[John Crichton]

Good advice here

As other have said:

1) 1 Nuke is enough for all but large SSTOs.

2) Use more air intakes.

3) Don't go straight up to 20k, you will be too slow at 20k to take full advantage of the air intakes. I tend to go straight up to 10k and then gradually move to 60 degrees by the time I'm at around 20-25k. I'm at 45 degrees by the time I hit 30k. Obviously all depends a bit on your ship and number of intakes.

4) Don't activate your Nuke before the very last moment. Coast to your apoapsis the second it hits your desired height and fix your periapsis.

5) Consider a 2-stage approach. You might not need the lift of the entire SSTO, make it so that a separate lander detaches from the wings and other necessary stuff. The Hondo is a great example of that...can make it from Kerbin's surface to the moon and back, twice.

6) Turbojets & 1 Nuke seems to be a good combo for efficiency.

7) If you're willing to use mods, look into Kethane...I'm working on a Kethane SSTO at the moment. Would solve all your range issues I recon.

8) Use a carrier rocket in Kerbin orbit. SSTOs are light, so you don't need one with huge DeltaV. Alternatively, use an interplanetary ring...a few examples are on the forums.