Duran Duran - Stock space shuttle

[Zwolff]

Every now and then I see someone post their space shuttles, so I thought I would break my forum lurking by sharing my own, now that it might stop working when the space plane parts are redone, and stock cargo bays are introduced in the next update. I have also included some of the design commentary on how I solved the asymmetric design, for those that want to try building their own design.

The shuttle with empty cargo bay have a total vacuum ∆v of 5041 m/s, where 633 m/s is shared by the orbiters orbital manoeuvreing system and reaction control system. The orbiter can reach around 85 km carrying a small satellite and 5 kerbals and still have enough ∆v for orbital manoeuvres and reentry. At main engine cut-off, the shuttles desired appoapsis can be reached, requiring around 2-300 ms ∆v for circulisation. Just like the real thing, if glides like a brick during reentry requiring a rather steep aproage and level out close to the runway.

The cargo bay has a small docking port in the front and a medium docking port in the back for satellite attachment, and a medium port angled outward for docking to stations. The bay doors consist of a separate craft that is undocked from the closed position and redocked in the nose cone port exposing the cargo. The cargo bay craft has a probe, batteries and lamps making cargo bay openings and closings possible at night.

During the flight to orbit, there are 5 critical points that causes problems when designing the shuttle because of the asymmetric thrust; take-off, just before solid booster separation, just after booster separation, just before external tank separation and in orbit. Solving one might throw off another, so a lot of back and forth testing is required.

The in orbit point is the easiest and the first one I solved. After building the orbiter, with the desired cargo space and fuel, the only thing required was to attach the orbital engines to a small cubic strut and angle them slightly downward, through the orbiters centre of mass.

When the orbiter attached to the external tank is flying only using the space shuttle main engines, there are two parameters that can be fine-tuned. One is the angle the engines are attached to the orbiter, and another is how the external tank is emptied affecting its centre of mass. I first tried out an angle of the engines that had the thrust vector approximately through the upper part of the external tank. Now I wanted to make sure that during the phase of the flight between solid booster separation and main engine cut-off and tank separation, the tanks centre of mass stayed as close to this point as possible. This was done by creating the external tank out of smaller tanks, and trying out different tanks to attach the fuel line to, varying how the tank is drained. The fuel line attachment, and the main engine angle, can be seen in the image Ascent in the Imgur album below.

Before booster separation the fact that the shuttle main engines thrust vector is far of the tanks centre of mass is overshadowed by the fact that the solid boosters are of the shuttles centre of mass in the other direction. This was the hardest part of the problem to solve, as it is not possible to throttle the solid boosters and the problem worsen as fuel is burned. Replaceing the solid rockets with liquid ones was not a good option, as I only wanted to reduce thrust in the booster, not the main engines. The solution came when I realised that I needed 4 solid boosters anyway (2 on each side clipped into eachother) making it possible to do a different thrust limiting factor on them. One pair of sold boosters are thrust limited to 65% and one pair to 50%. This way, one pair burns out before the other, and the torque caused by of-centre thrust is never more than the SAS modules on the external tank can handle.

For take-off, the most important factor is that the shuttle has enough thrust to weight ratio to take of, and to be reasonably balanced between main engines and solid boosters. This was reasonably easy to correct by varying the thrust limit on the solid boosters. The only problem I found left unsolved is the fact that just after launch the angle of the main engines pushes the shuttle horizontally, so one has to throttle down the main engines a bit and turn the craft so it flies upwards again. As the shuttle picks up speed, one can throttle up again.

Images from a typical shuttle mission can be seen in the Imgur album below. I hope you enjoy the album and text, and that some of you will be inspired to try to create your own space shuttles. This is by far my most fun ship, both doing the design and to fly into space and land again.

Javascript is disabled. View full album

Edited September 14, 2014 by Zwolff

[Giggleplex777]

Very nice! Can we get a download?

[montyben101]

What happens to the cargobay? Do you re rendezvous with it?

[Zwolff]

Here is a download: https://www.dropbox.com/s/iz9io0t2xwk1n4z/Duran%20Duran.craft?dl=0 Note that it has mechjeb on at the moment so I could figure out the ∆v and stuff.

Some flight tips:

Just after launch throttle back a bit so it is easier to straighten up the craft going up. Begin gravity turn around 8-9000 m. As soon as the solid boosters burn out, jettison them and be prepared for a shift in thrust vector from one side of the centre of mass to the other. Reach the desired appoapsis using the shuttle main engines, as you dont have much monopropellent for orbital manoeuvreing if you use it to also raise the appopsis. Especially for satellite retrieval missions, which use up a lot of monopropellent for rendezvous and docking.

When opening the cargo door, I undock it from the closed position, wait for it to drift away a bit and time warp so it stops rotating, pitch up so I face the door with the orbiter and docks with it using the docking node in the nose. In the image above where the orbiter is docked at the asteroid outpost, you can see the open cargo bay door docked to the orbiters nose behind the orange fuel tank. Closing is same thing but in reverse. The tail fin goes between the 2 I-beams ensuring it goes on straight when closing.

[Jett_Quasar]

Nice design - and good idea for the cargo bay. If you add a small controller and RCS to the bay door it may be easier to dock (just a suggestion).

JR

[Nik_601]

Cargo bay is really nice)

And thanks for a download link!

[Zwolff]

Nice design - and good idea for the cargo bay. If you add a small controller and RCS to the bay door it may be easier to dock (just a suggestion).

JR

Yeah, I did this in my earlier designs, but I found that the orbiter was easier to control than the bay door. So I ended up always flying the orbiter docking to the bay door, in staid of flying the bay door docking to the orbiter. Therefore I removed the RCS systems on the door to save weight.

[Aetvo141]

Looks good.

[gmpd2000]

Nice craft, but in the album, you misspelled "Approage", It's "Approach"