Hybrid Rocket Addiction

[Warmblood]

I built some jet/rocket hybrid launchers recently, and I'm finding that I'm using them for almost all my launches now. The combination of detachable jet engines and rocket power really seems to work wonders in reducing the overall weight of the craft and improving the efficiency of its lower stage engines. Here's the sort of thing I've been using:

The highest stage in this variant is a tiny lander for a Gilly landing. This one is approaching the maximum pad liftoff weight for 12 jet engines, so it has some liquid boosters for liftoff assistance. I usually kick on the main engine at around 13-14k, not amazingly high, but more than enough to get the rest of the platform into orbit without any trouble. The payload section can achieve orbits of 150-200k using only fuel from the orange tanks.

The main downside is high part count due to the engines. Your payload shouldn't be too complicated or it will cause serious lag. Wobble is manageable with struts, and detaching the jet engines usually goes smoothly... usually. Ideally, they fly above the rest of the rocket and start spiraling away. Sometimes Murphy's Law intervenes. But, the failure rate is reasonably low for me.

So, thoughts on hybrid rockets? Suggestions?

[magnemoe]

Tips, use an jet only first stage. for an payload as this 6 engines, central fuel stage, pipes to engines on struts. use the 2-1 adapter on top of each engine and two ram intakes. Now you need an action group to both shut down the jet engines, decouple the first stage and you can just as well start second as well fire up second stage as well.

For second stage use two lv30 on tanks as side boosters for the nuclear stage to get enough trust to get you in orbit.

[ComradeGoat]

Bind jet separation to a custom function and have it shut down the engines and close the intakes at the same time. Stage separation will be less ... exciting.

[ComradeGoat]

Oh, and do a gravity turn early, to get the most out of your air breathers.

[HoY]

I've started using a 12jet 4lvn lifter for bringing fuel to orbit and come back empty for refueling. Part of the laythe mining project. Jets are extremely good for reusability

Payload fraction is just under 40% with them. (105t on pad 40t delivered in orbit, don't remember landed dry mass tho)

[SecondGuessing]

I use TurboJets as the first stage for pretty much all my light craft. Using them means your design can be so much smaller and simpler, as is clear from my MiLO (listed in the link below).

[Zephram Kerman]

This is one of my favorite things. Those jets are very helpful.

Possibly, you could reduce the wobble by locking the jets' gimbals. Since they are in the middle of the ship, they can't help you steer anyway. Use another control group to disable them all at once, easily.

[Warmblood]

"action group to both shut down the jet engines"

--That may be good idea. I use that practice on all spaceplanes but hadn't carried it over yet.

It was just this particular rocket that needed an additional rocket bottom stage. For smaller payloads it's jet only. I have experimented with a central fuel tank, arrayed engine bottom stage, but it had some stability issues. I may take a look at that design again, since you're right, this design carries more jet fuel than it needs.

[Unistrut]

Put your launch clamps in the stage after the jets, so you can ignite them, get them up to speed, and then let go of your rocket. If you're also going to fire up rockets, put them on the second stage with the launch clamps.

My medium cargo lifter rides jets only to about 15km and then an action group shuts them off and the next stage dumps 'em and fires up the rockets.