LM's Proposed ISS Cargo Spacecraft: Jupiter & Exoliner

[Budgie]

How much dV does it take to deorbit anyway? Since the container needs electronics anyway, could you mount SRBs on it? That way, the tug would need to only orient the container retrograde and move out the way

[Nibb31]

you put one down for a second, then grab it once you're done.

There's no putting down a football in orbit and expecting it to stay exactly where you left it. If the Exoliner is left without attitude control or power, it will just float around, drift, tumble, and you're going to have a hell of a time getting it back.

There's an extra end effector at the back of Jupiter.

Aha! I didn't spot that in the pictures! Thanks for pointing it out.

Well, I guess I'm sold then.

[Kryten]

One of the competitors has been dropped from CRS-5; while there's no official word of which one, the rumours are very much centering on Jupiter.

[Rakaydos]

It's the old (very old) concept of a space tug. The idea makes sense on paper: keep the propulsion module on orbit and only launch dumb canisters.

In practice, it's a different story though (like always). In order for the tug to dock with the canister, the canister is going to need some sort of attitude control, which means that it needs avionics, power, and RCS. It needs to carry the propellant to refill the tug for the next mission. After the rendez-vous with the station, the tug needs to deorbit the canister and reboost itself into orbit, which is going to waste a lot of dV, meaning that the canister has to bring along more propellant than if it just had to rendez-vous and deorbit itself. The canister also needs two docking systems instead of one, one to dock with the tug and the other to dock with the target.

So in the end, if your cargo canister has a docking system, avionics, RCS and propellant, then it might as well just fly itself to the destination. The tug idea doesn't save a lot in terms of mass, but adds a lot of complexity to the mission because you have an additional docking event and two vehicles to control instead of one.

If the RCS, Avionics and Docking system (at least on the dumb pod side) are lighter/cheaper than an engine of the efficency of the tug, the tug can make economic sence. Somethign as simple as a ferrus plate on a probe can handle docking, and avionics are getting smaller and lighter all the time.

[B787_300]

It is Semi-Official Official that Exoliner/Juipter is out of CRS2. If you think about it it is WAY over engineered for a ISS supply run. The only way that it gets built is if LockMart funds it itself and does something like launch to GEO and use it to either deorbit the old geosats or put them in a Graveyard orbit. (and have people pay them to reopen the slots in the geobelt.

[Rakaydos]

(and have people pay them to reopen the slots in the geobelt.

It's only a matter of time before we rename it the Kessler Ring.