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.
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.