Jet Booster Testbed

[DJRWolf]

I decided to try out using jet engines in place of SRB's for my craft and it turns out they are not half bad. Granted you have to fire them up and let them get to full power before you let go of the clamps but it works. Next I need to try it out as more normal side strap on boosters to large (and then on the huge when they come out) size rockets.

My first design, after finding that the engines take fuel out of the middle rocket fuel tanks I reverted to VAB and added fuel transfer lines. But then I ran into big problems with stage separation since they would last all the way up to it could not get any more air to burn.

The Mk II design I put the jet boosters in a quad under the normal rocket to make staging safer and it work well...then I noticed just how little jet fuel the design used and decided to tweak it.

The Mk IIB design is in general the same except it has 2 Mk 1 Fuselage's per jet engine instead of the Mk II's 3 per engine saving a little weight.

After getting to the "Coast to circularize burn" point this is how much fuel was left in the first rocket stage on 2 different launches.

Download Mk IIB here:

https://dl.dropboxusercontent.com/u/5052189/Jet%20Test%20Alpha%20IIB.craft

[Dispatcher]

I occasionally use jets as boosters. As for the fuel use, when flying rockets (as opposed to planes or SSTO planes), so little fuel is used that I either just tie the jets into the rocket fuel tank(s) or I stack a small rocket fuel tank onto each jet. The mass of leftover oxidizer is less than the mass of unused jet fuel in the tanks you were using, and of course now the oxidizer can be set to empty anyways.

Yes, with jet boosters, I always stage them first, prior to igniting the rocket engines and releasing the clamps. Very little fuel is wasted doing so. As for jet efficiency, check out the graphs in my sig line.

[SofusRud]

I agree that jets can be useful as boosters, but you are kinda shooting yourself in the foot by giving them that much jet fuel. There is no way they can use it up before running out of air. I would think that one can per engine would be plenty

[ndiver]

I was using a relatively similar system for small probes. The main difference being that i eject the jet engines and air intakes once they shut down :

Here is the screen http://image.noelshack.com/fichiers/2014/08/1393077441-screenshot22.png

[barrenwaste]

I use Jets as boosters, too. I don't use rocket fuel cans with them, though, I use the jet fuel can. I burn straight up to about 15k then nose over and burn off the rest of the fuel in the jets to gather speed. I always dump them just before burn out, yeah, you have to use seperatrons, but no biggie.

[Jouni]

I use jet-boosted rockets routinely for small payloads. If you fly them like spaceplanes, the payload can be quite big compared to the lifter.

In principle, you can use the same idea with bigger payloads. In practice, while the jet engines in KSP are ridiculously powerful, they are still very weak compared to rockets, especially at sea level. To get large payloads off the launchpad, you need a huge number of engines, leading to really ridiculous designs.

[barrenwaste]

Jouni, mix in sets of both kinds of jets for more power. Use asparagus staging to burn off the fuel in the jets that you want to dump first due to thier weaker thrust at higher altitudes.

[Jouni]

Jouni, mix in sets of both kinds of jets for more power. Use asparagus staging to burn off the fuel in the jets that you want to dump first due to thier weaker thrust at higher altitudes.

Basic jets would just make the ship more complex without any real benefits. If we assume that we need 1 turbojet per 10 tonnes during the final acceleration, the ship in my example would still need at least 10 turbojets. By replacing the remaining 6 engines with basic jets, we could perhaps reduce the total number of engines by 1 or 2. The ship would still have way too many engines, and the overall design would look even more silly.

2.5-meter turbojets would solve the problem. With them, you could have a kerbal version of the experience of boarding a B777 and realizing that the engines are almost as wide as the hull of a midrange passenger jet.

[DJRWolf]

I did try the new RAPIER engine and it did not have the thrust needed to get the job done alone. Been doing some more tweeking by adding more air intakes and it has been extending the life of the jets to a higher altitude. Now to work on getting it more refined. The pointers have been nice and thank you for them.