ST-080 LUG, SSTO 36 Ton Space Truck(wip)

[Jakalth]

UPDATE: The LUG is now Orbit, but only just. A few little adjustments made it capable of lifting cargo to orbit now. I've only been able to get it to orbit once though. It's quite the challenge to get it up there without burning through all the fuel. More info and Craft file available in third post.

I've been trying my hand at making a SSTO heavy lifter. The goal is to simply lift a 36 ton orange fuel tank to orbit using a Space Plane, without having any discarded boosters. I've done all the work using no mods at all, making all the adjustments in my head using only the center of mass and center of lift baubles as a guide. So far I've only been having mixed results. It is a lot harder then it sounds. What follows is a set of pictures showing the changes I made to the design all in an attempt to reach orbit. It's not the prettiest craft, but it'll do, eventually, hopefully...

I present the ST-080 "LUG"

My first attempt was to make a shuttle type craft that can at least get it's self into high altitude, and possibly sub-orbit, without carrying any payload. I had some success at this on my first try. This is the initial design...

The craft has a MK3 central fuselage with a nearly full length section of MK2 fuselage on each side of it. The wings are unbraced other then 2 vertical sections of wing panels that link the top and bottom wings together, adding some rigidness to the design. The wings are fully doubled with a large open space between them. It uses a single Kerbodyne KR-2L liquid fuel engine for high altitude and 10 Turbojet engines for climbing. The craft flew decent enough, but it became immediately apparent that it majorly lacked power. So I began a series of modifications that eventually led too this...

The craft now has a pair of orange fuel tanks on each side, along with 3 liquid fuel tanks capped with ram air intakes and a cluster of extra engines. I also had to add a pair of RATO pods(RT-10s) to the front to help lift the nose up. The craft at this point was quite heavy, topping 400 tons in weight, not including the 36 ton orange fuel tank in the cargo bay. The engine arrangement was getting out of control as well. It is still using a single KR-2L engine, but the number of turbojet engines has gone up to 18 engines. The whole craft is getting bulky and a bit unstable to fly at this point due to all the extra tanks packed under the wings. It is still suffering from a power shortage so once again, I tackled the lack of power in a different way, clipping the engines together to clean up aerodynamics. The results became this...

The cleaned up aerodynamics, achieved by clipping the engines together into just 4 mounting points made a dramatic improvement. The Lug was a lot quicker to climb and seemed, at first, like it was going to be orbit achieved. But that is when the instability and lack of power creaped in yet again. This time with BOTH the jet engines and the liquid fuel engine. I was also getting a lot of side slip when transitioning from air breathing flight into rocket flight. So once again, I needed to make some changes. I added extra vertical tail fins to the ends of the wings to help a bit with side slip and tucked a few more advanced sas modules inside the belly of the craft. The single KR-2L engine was no longer enough to fill the high altitude roll, so I tested using 2 KR-2L engines, 2 Rockomax Mainsail engines, and even an S3 KS25x4 engine cluster. The Mainsail pair ended up being the best fit. I also added 6 Mark-55 Radials to the back for extra thrust and for orbital maneuvering. For the Turbojet engines, I kept adding more until I finally reached a number that allowed the craft to actually fly to altitude with some kind of speed. 32 Turbojet engines all clipped into 4 mounting points. The final results of all this editing was a craft that could gain altitude fairly quickly, for its size. It even had enough fuel that it could actually reach a fairly extended sub-orbit, without touching the fuel in the carbo bay. I finally gave it 1 last all or nothing, I added 2 more orange fuel tanks to the sides of the craft and clipped them into the existing orange tanks. I then went throughout the craft and tied every loose object together using strut connectors and went for the launch.

Everything was proceeding well. It was gaining altitude well, had loads of fuel, and was stable. Reaching 12,000m, the jet engines ran out of air and I switched to the liquid fuel engines. The craft was still mostly stable and climbing well(for a brick, I guess) with only a tiny shudder in the now turned off jet engines. It looked like I was going to reach orbit after all... BOOM! It all went to pieces... The tiny shudder in the jet engines turned into a big oscillation that transferred into the wings and set them a fluttering, untill the stresses were too much and it all flew to pieces in a very dramatic spray of parts and lag. Re-trying the launch resulted in the same thing. And no matter how I tried modifying it from this point, I always got the same result. Stable flight, if slow, up too 12,000m. Smooth transition to liquid fuel engines. Then complete diss-assembly at just over 15,000m with all hands lost. Only way left to fix this was to pretty much rebuild the whole thing. So I did.

This new and improved version has a slightly longer main fuselage, to hold more fuel. A longer section of MK2 fuselage on each side, for more fuel. A pair of orange fuel tanks with X200-16 tanks on each end, for more fuel, and C7 2.5m - 1.25m adapters on each end instead of nose cones, for more fuel. There is a pair of X200-32 tanks nested inside the orange tanks, at the center of mass as well. The tanks are all properly piped too the center fuselage so all possible fuel can be accessed by the liquid fuel engines. It has 7 ram air intakes and 10 structural intakes for air. There is both a KR-2L and a a Mainsail engine nested together on the back with 8 Mark 55 radials, and a total of 36 Turbojet engines split up between 6 mounting points. The craft is now topping 450 tons in weight with the orange fuel tank(jumbo-64) in it's cargo bay. But it has more then enough thrust to lift its massive bulk. After doing some test flights, which are a slow process due to frame rate lag and the sheer bulk of the LUG, I am now able to get this craft into a good long sub-orbital flight. But, so far, I have not been able to extend its flight into full orbit... Adding more fuel does not fix the problem, it only means I have to increase the thrust of the engines, by adding more. The results of doing this are that I now need more fuel to get into sub-orbit once again. So for now, this is it. I have succeeded at making a SSTO that can lift a 36 ton jumbo-64 orange tank. But, I have failed at making it orbital... *errggggg*

Edited February 4, 2015 by Jakalth

[Columbia]

Woah. That is amazingly huge. I can't believe you got it to fly!

[Jakalth]

Download for the ST-080 "LUG" : HERE

The ST-080 "LUG" is now available for download. Be warned, it is not the most pleasant craft to fly. But, if it's flown gently(aka go full throttle and hang on) it can get into orbit, but only just. The challenge of flying it is finding the right angle of ascent so that you do not burn through too much fuel using the Turbojet engines, yet still have enough speed so that the rockets simply have to raise it's altitude. There is about 1200 liters of liquid fuel more then is needed for a direct to orbit flight so you do have some wiggle room. The cargo can be adjusted slightly, like adding a docking port for refueling orbital craft, but adding too much weight might make the LUG unable to reach altitude. It currently has a Jumbo 64 fuel tank in its cargo bay with some RCS tanks, a probe core, and RCS thrusters to move it around.

The challenge here: get the LUG into orbit and deploy the fuel tank for refueling other craft.

Specs on the LUG:

40 turbo jet engines

2 Kerbodyne KR-2L advanced engines

8 Rockomax Mark 55 Radial engines

2 RT-10 SRB(used as RATO pods)

about 25000 liters of liquid fuel and oxidizer.

gross take off weight = 438.1 tons

part count = 531

amount of lag it generates = moderate to high...

cargo capacity = at least 36 tons, probably no more then 38-40

Everything comes back with the LUG other then the 2 RT-10, which are discarded during liftoff. And of course the cargo it left in orbit.

Action groups:

1: jet engines on, rockets off

2: rockets on, jet engines off

3: KR-2L's off, Mark 55's on

4: Deploy/Retract solar panels

0: close/open air intakes.

Liftoff is achieved by dropping the engines to 0% thrust and activating the first stage(all the engines). Then using action group 1 to turn off the rocket engines. Now simply give it a little throttle, by slamming the engines to fully power. Once near the end of the runway, at about the last 25 meters of the runway, activate the second stage to kick in the RATO pods. Hold climb at this point until the nose starts to lift(when it leaves the end of the runway), and keep holding climb until the nose has pitched up to about 20 degrees. Activate the third stage, when the nose reaches 20 degrees up, and send those RATO pods flying off into the wild blue yonder. Be sure to thank them for their help, and for not taking out the nose of the LUG. At this point, you'll want to start nosing down to prevent the LUG from pitching up too far. Keep it below 35 degree angle for now, 30 works the best. Pitching up too quickly here will cause it to tumble out of control. Let it stabilize at this angle and climb up to an altitude of at least 800m. At, or above, 800m, start to slowly bring the nose up again until its nosed up at a 45 degree angle. The LUG does not respond real quickly so you'll need to control the lift until it has stabilized at this new angle. Now just let the LUG sit at this angle until you reach about 12000m. There are two options here, the safe route and the risky route. The risky route gives you a better chance of going orbital.

Safe route: at 12000m, use action group 2 to switch from jets to rockets and use the rockets to get you into an extended sub-orbit before deploying the tank.

Risky route: at 12000m, start watching the air intake levels very closely. The intake levels can drop to 0 and the engines will keep running at full throttle for several seconds. This will happen between 12300m and 12600m. Don't panic just yet. keep holding onto full jet throttle until you get the first engine flame out. At this point, immediatly use action group 2 to switch to rockets before the LUG can deviate off course, which will not happen quickly, but it is not easy to correct course once it does. Now use the rockets to get you Orbital. If you can judge acceleration and burn rate correctly, you'll be able to just reach orbit.

If you can get it orbital, there may be a little issue. The LUG does not currently have any other means of DE-orbiting its self. You might end up needing a rescue tug to nudge it out of orbit. But, you should still have some liquid fuel left for attempting a landing.

Edited February 4, 2015 by Jakalth