Lifter/fuel tank reuse.

[Skorpychan]

I've noticed an unhealthy trend lately, of parts of my rockets ending up in stable orbits. So, I had a thought. Why not just fit docking ports to them, so I can corral them in a parking orbit together, and use them for fuel storage?

They already have high TWR due to powerful lifting engines, so they can get anywhere in the system pretty quickly. They're already up in stable orbits. All they'd need is batteries, probe core, and a docking port.

Has anyone tried this?

How would you go about towing a large tank around by a side-mounted docking port?

It would have to be a side mount; engine at one end, decoupler at the other, don't want to create more junk with stack separators floating about.

How does being drained of fuel effect CoM of the tanks, if they have an engine on the back?

Should I even bother towing them, and just add fuel to them so they can get there themselves?

And would a tug be able to properly leave behind something to provide RCS fuel to the tank, if I put control blocks on them beforehand?

[Taki117]

if you use Sr. docking ports those can be your decoupler, and then all you would have to do is attach probe cores beneath that (And an RTG or some solar panels for power) and you are all set. As far as side mounted towing, I would disable the engine on the thing being towed (Especally if it is more powerful than the one doing the towing) and be sure you have lots of reaction wheels to counter the uneven thrust. If a tank is drained of fuel then the CoM would naturally shift towards the engine. Unless they already have juel in them you are better off towing them. (Save file editing for that purpose, imho is cheating) If done right a tug would be able to leave behind an RCS fuel tank, you would just have to put Sr. docking ports on both ends (One to connect to the tank, the other to connect to your tug) however, be mindful that this is going to shift your COM, so it would be best to plan this ahead.

[Skorpychan]

Sr docking ports as decouplers are a non-starter. They just don't handle the Gs of my lifter designs.

[Murph]

Sr docking ports as decouplers are a non-starter. They just don't handle the Gs of my lifter designs.

They do if you carefully strut around them.

[Geschosskopf]

Sr docking ports as decouplers are a non-starter. They just don't handle the Gs of my lifter designs.

Just put the port on the payload and put a decoupler under it. That always works for me. Once the decoupler fires, the docking port is exposed for use.

But seriously, fuel stations anywhere within the Kerbin system are usually more trouble than they're worth; it's quicker and easier just to send a tanker to where it's needed. The only real exception to this is if you're in the habit of sending spaceplanes to other planets because these usually need to be refueled as soon as they get in orbit. If you're not doing that, then the easiest way to deal with spent boosters is to just deorbit them.

There are a couple of options for that. The easiest is to put a probe core (and probably RCS) on the booster. Once in orbit, separate it from the payload, switch to controlling the booster, use the RCS to point it retrograde, and burn off the remaining fuel to deorbit. Usually, the probe core has just enough electricity for this without needing a battery or RTG on the booster, especially if running the booster engine makes electricity.

[Smidge204]

Depending on your target altitude and mass of the stage, you could use Sepratron motors to try to deorbit stages on separation. Seems like a viable low mass, automatic method with no probe bodies etc to worry about.

Unless you INTEND to re-purpose them, instead of just wanting to clear junk...

=Smidge=

[Skorpychan]

I figure that if they're up there, I may as well reuse them, and save launching other things up there.

[Kasuha]

Regarding the original problem, if you're starting to have too much debris in orbit, it might be a good idea to redesign your lifters so they drop the last droppable stage a bit earlier while you're still suborbital.

Then you may consider employing Tracking Station's Heavy Duty Lasers and get rid of that debris. It's not that much about the danger that it will hit something, rather about the lag it generates just by its presence (even if it's nowhere near, each piece of debris takes a bit of CPU power).

Regarding usage of docking port Sr, my whole space program is based on them. I don't even need to strut them to anything in most cases as long as I make sure they don't get too much load. Below you can see my lifter lifting one fuel module. Notice struts which are taking load off the docking port's connection. The bottom docking port is not strutted. The top one is, because the connection between the port and the SAS module is exceptionally weak. These struts go from the fuel tank right to the port. There are usually no problems with these connections in space where you don't need as much thrust as during liftoff.

Below it is my interplanetary ship made of such modules.

Edited December 12, 2013 by Kasuha

[maltesh]

This is a Cantanker.

It's a Clampotron Sr Docking Port, a Probe brain, a 2m battery, a Rockomax Jumbo-64 tank, a 2m reaction wheel and a Sr Docking Port from end to end. Arrayed around the middle are a pair of RTGs, a pair of the cylindrical monoprop tanks, a pair of Clampotron Docking Ports and a pair of Clampotron Jr docking ports. It also has 8 RCS ports.

When I build a rockomax-based asparagus-stage lifter, a Cantanker is almost always the fuel supply for the central booster. On the bottom end is a Rockomax Skipper, attached directly onto the Clamp-o-Tron Sr. Like any other docking ports, a clamp-o-tron sr can be used to disconnect anything attached to its business end, docking port or not, so I use that to disconnect the skipper and let it fall into the atmosphere before circularizing.

On the other end is a Tugbot.

Tugbots are my typical all-purpose smace movers, using two LV-Ns, and a pair of stack-mounted docking ports for both pulling and pushing payloads.

Pretty much anything I send anywhere that doesn't have its own LV-Ns for propulsion is going to wind up being pushed to its destination by a Tugbot, with an attached Cantanker.

I started doing this for pretty much the same reason the OP mentions: I started winding up with partially-empty tanks scattered around without brains or docking ports, so the Tugbot-Cantanker combination was developed so that the part of the spacecraft most likely to wind up in a stable orbit could be used as fuel, raided for fuel, built into something else, or deorbited at whim. I don't actually refuel from loose Cantankers aall that often (as I typically have much larger fuel depots in-situ for those), but it's nice to have them just in case, and the probe brain means I can rename them after how much fuel they have left in them.

[EtherDragon]

Once you get good at rendezvous and docking, modular orbital builds is the next logical step, for sure.

The problem for refueling a half-full can of propellant is that you need to bring another can up to do the job - then you have two cans, one newly filled, one that's half full and needs to de-orbit, or be shot with OJUICE (Orbital Junk Universal Incendiary Cremation Equipment).

If you have a partially full can of prop, and it has a docking port - build a TUG and see if you can get them consolidated into a fuel stop.

[Skorpychan]

If you have a partially full can of prop, and it has a docking port - build a TUG and see if you can get them consolidated into a fuel stop.

That's what I was figuring to do. They normally end up empty, because screw wasting precious DeltaV. But I thought adding a little fuel would get them to a decent parking orbit.