Skylon-esque SSTO, >4.6 ton payload to LKO, no clipping

[Horn Brain]

I was trying to make a mock Skylon, but the RAPIER engines are not powerful enough with just two of them for a vehicle that lifts the size payload I wanted to bring (my test payload was a 4.5 ton fuel tank), so I had to use four engines. It turned out ok, though, and I've designed a small lander that fits in the payload area which is capable of easily travelling to the Mun and back, maybe even Ike if you're careful. Part clipping was not used and it's all stock! I even managed to use the Mk1-2 and Mk2-3 adapters in a way that isn't hideous.

Craft file: Google Drive

Photos:

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Flight instructions:

1.) On load, switch control to the probe core at the back end. Turn on SAS and hit '3' to close non-essential intakes. Throttle to full and space to start engines.

2.) Once you hit about 80 m/s, pull up gently until the nose moves. Watch the tail because it will drag. Just nose up a little bit and wait for the craft to slowly lift off the runway, or else just wait for the end of the runway and pull back a little more. It takes off ok but you have to be patient if the payload is full.

3.) Once clear of the ground, nose up to 45 degrees and hold until the intake air drops below about 0.20. Hit '3' again to engage the remaining intakes. This moves the center of drag far forward and the vehicle becomes slightly unstable, so now is a good time to turn on RCS. If your payload's center of mass is high, you will definitely have to be careful from here on out to prevent from flipping backwards. Don't trust SAS, but leave it on.

NOTE: To be very clear, you pretty much have to hold 'W' all the time while all the intakes are open to keep it from flipping over. SAS sometimes gets overpowered and switches to "damping mode" which doesn't do a damn thing. If you build your payload to have a low CoM, this is not such a big issue.

4.) Lower the nose to prevent flameout. You should now start to rapidly accelerate up to over 1000 m/s surface speed. Just keep climbing and keep the nose down so you don't flip. When the intake air drops to about 0.15, it's time to switch to rockets.

5.) Hit '2' to disable all the air intakes, the engines should switch to rocket mode automatically. Since the intakes are closed, the vehicle is more aerodynamically stable again, and you can raise the nose to about 45 degrees to pick up the apoapsis and get out of the atmosphere. IF YOUR PAYLOAD IS TOP HEAVY (like the included payload) THROTTLE BACK TO 75% OR SO OR YOU WILL DO BACKFLIPS.

6.) Once the apoapsis is above 45 km, follow the prograde vector until the apoapsis is above about 80-85km and kill the engines. You can use RCS or more fuel to counteract drag if it becomes a problem.

7.) Circularize at the apoapsis. If you did it right, you should have extra oxidizer and liquid fuel for return. Staging will detach the payload. Using RCS, just give 'I' a tap or two and you should drift free of the payload.

8.) Deorbit and land. I recommend hitting 2, then 3 to turn on the rear air intakes to aid in stability if you are using the jets to fly once you slow down. The vehicle doesn't glide well until it reaches the lower atmosphere, but you can turn slowly if you're patient. Keep about a 30 degree dive and only pull up to land. Be careful of the tail dragging again when you flare.

That's it. I hope you enjoy. What's the heaviest thing you can launch with it? I've only tried 4.6 tons, but I know it can do more because I delivered that payload after doing two backflips.

Edited December 27, 2013 by Horn Brain