NAUTILUS-X: Getting Past the Moon, In Style

The Nautilus-X, having shaken out in cislunar space, heads out for its first mission to an NEO, 2001 CQ36, in late May of 2021. Composite of two images sourced from NASA.

The Nautilus-X, having shaken out in cislunar space, heads out for its first mission, a 354-day round trip to Near-Earth Object 2001 CQ36, in late May of 2021. Composite of two images sourced from NASA.

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.


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

Plymouth Rock: 405 Years and Counting


The Plymouth Rock mission would have taken two Orion MPCV spacecraft, one modified for extended life support, and turn them into a single spacecraft that could undertake a six-month long mission to a small Near-Earth Asteroid. Promotional image courtesy of and ©Lockheed Martin. Click for a larger view.

What it was: A 2009 proposal by Lockheed Martin to use its Orion manned space capsule as the core of a deep space mission to the Near-Earth Asteroid 2008 EA9.

Details: Until the turn of the 21st century there were three commonly assumed steps to manned space exploration: Earth orbital, then the Moon, then the planets. While the physical gap between the first and second of these is considerable, it’s nothing compared to the step that follows. The average distance to the Moon is 384,400 kilometers; Mars never approaches the Earth to less than 54.5 million kilometers and the nature of orbital mechanics means that the path taken by any reasonable spacecraft going there must be much longer. There are several reasons why there were just eight years between the first man in space and the first Moon landing while it’s been more than four decades since with no sign of a Mars mission, but that gap is one of the biggest.

Meanwhile in recent years Lockheed Martin has been building the Orion Multi-Purpose Crew Vehicle (MPCV), an Apollo-like spacecraft built around a Crew Module and a Service Module that is currently due to make its first unmanned flight in 2014. True to its name, the Orion is supposed to be adaptable enough that it can be used for all of the missions that NASA might reasonably fly in the future, and in search of more business Lockheed has been keen to suggest ones of its own.

Plymouth Rock was one of their suggestions for the Constellation Program that began in 2004. It looked to bridge the gap between the Moon and Mars by focusing on something we’ve learned about the solar system in the last few decades. In 1980 there were fewer than twenty known asteroids that approached the Earth significantly more closely than Mars (“Near-Earth Objects” or NEOs), but as of November 24, 2012 advancing astronomical technology and fear of a reprise of the impact that killed the dinosaurs had inflated that number to 9946. Why not visit one of them somewhere out past the Moon? Not only would it increase general scientific knowledge, it would let NASA test out the technology that’s going to be needed to support astronauts on a trip to Mars without having to commit to a year or more’s travel like a full-fledged Mars mission would need.

Lockheed Martin selected 2008 EA9 as the mission’s destination, with the caveat that this selection was highly dependent on the launch date and any of a couple of dozen small asteroids might serve as a substitute. The sole criterion was that the target had to have an orbit particularly similar to Earth’s, which meant that none of them was at all notable: none even had a formal name, just a serial number, and none was larger than 75 meters in diameter. 2008 EA9 itself is approximately ten meters across.

A plain Orion wasn’t going to do the job, as it was designed for two weeks of support to the Moon and back. So a modified second Orion—the Deep Space Vehicle—would also go along for the ride. It would have been put on top of an Ares V rocket, which would have lifted it and an attached injection stage (the Earth Departure Stage, or EDS) with propellant into Low Earth Orbit. A smaller Ares I would have launched the regular Orion shortly thereafter; only two astronauts would be aboard rather than the up-to-seven that the Orion could house in Earth orbit, simply because more than that would eat through the mission’s supplies in less time than it would take for the trip there and back.

The two Orions would dock nose-to-nose in orbit and the EDS would be fired to push them on their way. Once it was out of propellant the stage would jettisoned and the Plymouth Rock spacecraft—one imagines it inevitably would have been named Mayflower—would deploy four large solar panels and begin a 92-day outbound journey. This was the other reason for only having two astronauts: each would have only 9 cubic meters to live in during the trip.


A geocentric view of the Plymouth Rock mission’s trip to and from 2008 EA9 as it approaches Earth in late 2019. Promotional image courtesy of and ©Lockheed Martin. Click for a larger view.

Roughly 12 million kilometers later the ship would arrive at 2008 EA9 and take up station about 100 meters away. The asteroid’s mass would be so small that there would be no need to worry about its gravity, to the point that the astronauts could spacewalk over to it at will, depressurizing one of the Orions whenever they needed to enter or exit their craft.

Only something resembling the MMU “jetpacks” from the early days of the Space Shuttle would be needed to explore the asteroid as it’s likely that the tiny world’s rotation would produce centrifugal forces stronger than its gravity. Altogether this would produce a negative net force pushing anything that touched 2008 EA9 back off the surface again. This is actually a point in 2008 EA9’s favour as many asteroids are believed to be rubble piles held together by nothing more than their mutual gravitation, an arrangement that would be dangerous to explore. If 2008 EA9 spins like it’s believed to, though, it must be a solid object and so relatively stable.

After five days of exploration the astronauts would fire the engines on the modified Orion and begin their return home. This would take them another 95 days and, upon arrival at Earth, they would abandon all of their craft except for the conventional Orion’s crew capsule, which would take them down to Earth.

What happened to make it fail: As originally conceived Plymouth Rock would have been part of the Constellation program, and relied on the program’s Ares I and V rockets. With the cancellation of Constellation budget in October 2010, the mission could not go ahead as planned.

What was necessary for it to succeed: A mission to a NEO was considered one of the “big three” possible missions for Constellation (along with a return to the Moon, and a mission to Mars). While NASA tended to show it as one based on an Orion mated with an Altair lander—Constellation’s equivalent of an Apollo LM—Lockheed Martin was probably in the right in contending that two Orions were the way to go. Very few asteroids that approach Earth have noticeable gravity, so a lander would be an expensive way to do something that could be done with an astronaut on EVA instead.

As a result, Plymouth Rock likely would have gone ahead sometime around 2020 to 2025 if Constellation had continued. That said, it may be not entirely dead yet. Constellation has been replaced by the Space Launch System, which is different in detail from the earlier program but similar in broad strokes. The Orion itself is still going ahead as the manned spacecraft for SLS, and so it would be easy enough to launch a close facsimile of Plymouth Rock—though probably all in one shot aboard one of the Block IA SLS rockets being developed, as they have the throw weight to do so rather than taking two launches as per the original mission design.

Interestingly it appears that NASA may actually be interested in doing so. As of this writing a Moon landing has been taken off the list of first exploratory missions, with a lunar orbiter likely to be the first and rumours of a small station at the Earth-Moon L2 point to follow. NASA is studying a similar mission they call “Asteroid Next”, but as late as last week Lockheed Martin was still proposing a “Plymouth Rock” with a new date (2024-2025 or 2029) and a different target (either 1999 AO10 or 2000 SG344, depending on the mission date).

The latter target is an interesting choice as there’s some chance that 2000 SG344 isn’t an asteroid at all, but instead the upper stage of Apollo mission rocket abandoned in orbit and lost until its rediscovery a decade ago. If NASA does pick up on the modified Plymouth Rock then that’s something that will have to be determined before any launch in 2029.

A simple animation of a Plymouth Rock mission showing the joint Orion craft travelling to 2000 SG344 (one assuming that it’s a natural asteroid) can be seen here on YouTube.