The CRS contract that buys Dragon and Cygnus capsules to deliver cargo to the ISS will run out before we know it, so NASA is soliciting proposals for the CRS-2 contract. And while there isn’t development money in CRS-2, it’s open to anybody with a viable plan. SpaceX and Orbital Sciences are both competing, of course, proposing another round of their existing vehicles, and Boeing has also submitted a proposal to use a cargo variant of CST-100 for the same job (which would have the same major advantage as Dragon, in that it would allow recoverable downmass). And Sierra Nevada is expected to propose Dream Chaser.
But now a new contender has come up with a rather innovative idea. Lockheed Martin is proposing a tug-cargo-container combination that would for the first time manage something that has been one of the major spaceflight holy grails for a long time: a ship that loiters on orbit to shuttle dumb payloads back and forth.
This vehicle would, like Cygnus and HTV, rely on a cargo container from Thales Alenia, based on the MPLM modules, called the ExoLiner. Unlike Cygnus or HTV, ExoLiner would have no propulsion or guidance; it would be more like the MPLMs, subject to the whims of the spacecraft transporting it. The other part of the system would be Jupiter, an on-orbit tug based off the bus used for the MAVEN Mars orbiter and equipped with a small remote manipulator system provided by MDA Corp, the same Canadian company that built the RMS and SSRMS.
Here’s where it gets really cool. The Jupiter-ExoLiner system would launch in a single unit. Jupiter would deliver ExoLiner to the ISS. At the end of its mission, it would depart, then loiter on orbit until a new ExoLiner is launched. It would rendezvous with the ExoLiner, still attached to its Centaur booster, and then swap its old, trash-filled ExoLiner for the new one. The Centaur would relight to dispose of itself and the old ExoLiner, while Jupiter would carry the new one to the ISS. Unclear to me is whether an orbital refueling system is needed for Jupiter, but in any case, it’s a pretty bold idea. It might not go far; Lockheed’s late entry to the CCiCap competition (an Orion-derived capsule boosted by the monstrous Liberty rocket proposed by ATK and Arianespace) didn’t get off paper. But it sure would be cool to see the tug concept realized in this manner.