What it was: A large spacecraft concept intended for long-term missions developed in response to two goals in the NASA Authorization Act of 2010: developing a crewed exploration vehicle capable of operating beyond Low Earth Orbit, and incorporating new technologies into NASA programs.

Details: Long-term readers may have noticed that, even for a blog devoted to space projects that didn’t happen, few of the ships discussed here are very big. Contrast this with the regular images of spacecraft in science fiction, even the ones with pretensions to realism like 2001: A Space Odyssey and Mission to Mars. Gravity is a harsh mistress and real spacecraft like Soyuz and Apollo are miracles of miniaturization because the cost of launching anything larger is prohibitive.

The notable exceptions are vehicles that were proposed for missions beyond the Moon, such as the Manned Venus Flyby or Mars Expedition 1969. You can get away with stuffing three astronauts into a space the size of a walk-in closet for a week or two, but it becomes a problem if you want to do it long enough to go to Venus, or Mars, or even a Near-Earth Object. This is one of the main reasons why, as of this writing, the leading candidate for NASA’s “next step” mission involves an unmanned craft grabbing a large boulder off a NEO and taking to lunar orbit, then sending a crewed mission in the relatively small Orion capsule to this “moon of the Moon”.

One of the most recent concepts to go build a big ship for further out came in January 2011. The NAUTILUS-X (supposedly a tortured acronym for Non-Atmospheric Universal Transport Intended for Lengthy United States eXploration, but almost certainly instead a shout out to the Nautiluses of Rickover and Verne as well as the X-planes of the past) was floated as a concept by NASA’s Technology Applications Assessment Team as part of a general program to build infrastructure and spacecraft that either developed or integrated new technology.

Prior to the building of the craft two main projects would be undertaken: the development of cryogenic propellant depots for placement in LEO and at the Earth-Moon L1 point, and the building and testing of an inflatable centrifuge ring for attachment to the ISS. Once these were in place, the NAUTILUS-X would refuel at one and incorporate a finished version of the other.

The centrifuge ring is perhaps the most interesting part of the concept, as it would have represented the first time anyone had tried to generate artificial gravity in space (barring an experiment with Gemini 11 that produced an imperceptible 0.00015 g) despite the fact that dodging the problems of free-fall this way has been a dream since the earliest days of spaceflight. The intention was to aim for a ring 30 feet (9 meters) in diameter spinning at a rate of 10 RPM and producing a third of a g—much less than Earth, but more than the Moon and comparable to Mars.

Furthermore the centrifuge was to be the keystone of another aspect of NAUTILUS-X: it and a number of other cylindrical, non-rotating modules were to be inflatable, a coming technology that’s actually due for its first test starting in a few weeks when the Bigelow Expandable Activity Module (BEAM) is to be launched by SpaceX and then attached to the ISS. On the LEO and NEO versions of the craft there would be three of these, and a extended-duration mission (up to 24 months) version would have ten. In both cases two would be used for logistics and one for environmental control, a plant-growing facility, and an exercise area. The remainder on the extended-duration craft would be used for stores and a gradually increasing amount of living space as the stores were used.

The NAUTILUS-X would be built in pieces over a proposed 2-3 launches, at least one of which would be by a heavy launcher (the SLS, though that was still seven months away from being proposed publicly) putting the “spine” of the space vehicle into LEO. This was to have consisted of a solid operations module 14.5 meters long and 6.5 meters wide. Attached to the end of this would be a truss for supporting the inflatable units and a propulsion unit docking collar—the innovative idea behind this being that the NAUTILUS-X could swap out propulsion units depending on the mission. A solar electric ion engine was assumed for the basic setup, with more a nebulously defined unit for a Mars mission. In the same area of the ship was a radiation shelter using the LH2 and LOX fuel tanks around it for shielding.

At the front of the core module would be an Orion MPCV docking port and a small command/control and observation deck would stick out of the core’s side; a similarly sized “industrial” airlock stuck out the other. Once built the NAUTILUS-X could use its ion engine to slowly spiral out from Earth to the Earth-Moon L1 point, where it could be used as a passive space station-like fuel depot and headquarters for up to six astronauts launched later (it being impractical for them to be aboard during the spiral because of the Van Allen radiation belts) en route to the Moon. The craft would also be well-positioned to be take astronauts to NEO objects.

After a mission, NAUTILUS-X would return to a pre-arranged propellant depot in geosynchronous orbit for refuelling, while the astronauts on-board would return on the Orion that had brought them to it in the first place. They would re-enter, of course, but NAUTILUS-X was designed to stay in space permanently. Ultimately, a bespoke propellant depot would take its place at L1, letting the craft be used solely for missions and making it possible to refuel without returning to GEO repeatedly.

The design and build of the NAUTILUS-X was projected to cost a total of US$3.7 billion over 64 months beginning in 2015, with the shakedown mission (one sticking close to the Earth) taking place around 2020-21.

What happened to make it fail: It was too much, too soon. While NASA’s budget has gone up a bit since 2010, the Obama administration and various Congresses have been relatively cool to money for manned space exploration, many statements to the contrary, and so NASA has been hard-pressed to meet all the goals set out for them in 2010. Accordingly they’ve been focusing on the Orion MPCV and the Space Launch System as the two parts necessary to reach all the other goals. As NAUTILUS-X would be fulfilling the goal all the way down at the other end, it or anything else like it (for example, 2012’s Deep Space Habitat) have made no progress at all.

What was necessary for it to succeed: More money is the main one. Despite the addition of new technology to the NAUTILUS-X there’s nothing inherently absurd or difficult about the concept. Depending on how the tests of the inflatable centrifuge ring went on the ISS it would have undergone a redesign to a greater or lesser extent, but it’s a fairly conservative extrapolation of current space technology and almost certainly could be built in one form or another.

A more subtle problem is its reliance on a propellant depot. There’s reason to believe that there’s considerable internal debate at NASA over the wisdom of storing propellants in orbit, and without an orbital “gas station” a reusable ship with no re-entry capability is pointless.

Links

The original public presentation of Nautilus-X (PDF Format)

A very nice rendered video of the construction and then flight of the Extended Duration Explorer