It is 14 November 2019 and the 50th anniversary of the Apollo 11 mission, when humans first walked on another world, has been and gone but today a new and exciting voyage begins. A massive booster stage pushes a spacecraft out of Earth orbit. This vehicle comprises two Orion capsules docked nose to nose; on board are two NASA astronauts, the first people to venture into interplanetary space. For the next three months this fragile bubble of life from Earth coasts across the void until 20 February 2020 when it rendezvous with another world. This is a tiny asteroid designated 2008 EA9.
The pair of spacesuited explorers leave their vessel to fly across to their destination and make history as they become the first humans to touch another world since the Apollo 17 crew left the Moon in December 1972. Earth is a distant 12 million km away, appearing as a brilliant bluish star accompanied by the smaller dot of the Moon against the darkness. In five days of in situ research the crew extensively photograph the asteroid, take samples of it and deploy a package of instruments across its surface. On 23 February 2020, one of the Orions is discarded and the remaining spacecraft sets off for the voyage home. Three months later the crew descend to their homeworld under their capsule’s vast parachutes on the last day of May. At last humanity’s reach has been extended across the Solar System.
At the moment this is all science fiction, but there is a possibility that it could happen. The mission profile described above come from a fascinating report entitled Plymouth Rock: An early human mission to Near Earth Asteroids using Orion Spacecraft published by aerospace giant Lockheed Martin (developers of the Orion vehicle). This detailed yet surprisingly readable (kudos to the authors!) document, begins by outlining how in the past couple of decades astronomers have discovered some very small asteroids whose orbits around the Sun are similar to Earth’s, travelling in the same direction and at the same speed. These discoveries are a spin-off from projects to locate potentially threatening Near Earth Objects. A round trip mission to one of these asteroids is roughly as difficult as landing on the Moon. This means that they represent a new potential destination for human space exploration in the near future with favourable mission opportunities occurring a few times each decade. Missions are feasible in 2019-2020, 2028 and 2029 (other candidate asteroids, perhaps easier to reach or more scientifically interesting are sure to be found) . All of the possible target asteroids identified in the study are tiny, between 5m and 50m in diameter.
The authors believe that a pair of slightly modified Orion spacecraft would be capable of providing the necessary
propulsion, living space and life support capability for a couple of astronauts for the months needed to reach and return from a NEO. One of the two Orion spacecraft would have to be be modified into a new configuration called the Orion Deep Space Vehicle. This would replace the conical Crew Module (with its heavy heat shield) with a larger habitat module designed for deep space operations rather than atmospheric re-entry. To conserve propellent, the Orion Deep Space Vehicle is left behind at the asteroid, perhaps acting as a permanent platform for scientific instruments. The crew must endure the next 98 days squeezed together in the smaller Crew Module.
One vital piece of hardware for the proposed mission is the Heavy Lift Launch vehicle needed to break the combined Orions free from Earth’s gravity. This would have been the now-cancelled Ares 5 rocket, hopefully the new space launch system that NASA has been mandated to prepare by 31 December 2016 will be an alternative.
The Plymouth Rock report is a private venture by Lockheed Martin and was not requested by NASA. It is clearly meant to provide an expanded role for their Orion design. This craft was originally meant to be the post-Shuttle workhorse of NASA’s crewed spaceflight programme, and would have carried four astronauts at a time to and from both the International Space Station and lunar orbit as part of Project Constellation. Early this year, President Obama set in motion the cancellation of this underfunded initiative. In fact the president wished to end the development of the Orion vehicle but political machinations by its supporters have preserved it in the reduced role of an emergency escape vehicle for the ISS. As of the present, Plymouth Rock has no official government support and needs new hardware to be developed. However there is a crumb of comfort: the Obama Administration’s approved “flexible path” for NASA’s future calls for a human mission to a Near Earth Object by 2025 (as a rehearsal for a Mars orbital mission in the mid-2030s).
Let us be optimistic and say that the US government (perhaps anxious to show that a nation some perceive as being in decline is still an optimistic and dynamic world leader) approves this project in the near future and that over the next decade all goes well. All the new hardware is developed relatively smoothly, after all the Apollo spacecraft and Saturn 5 rocket were flying less than a decade after being funded (and indeed so was the Space Shuttle). What have the astronauts chosen for this historic voyage in store for them? Six months in freefall for a start, with all the deleterious consequences for their health, such as atrophicaton of their muscles and embrittlement of their bones. Hopefully decades of practical research on board space stations will have lead to suitable treatments for this hazard.
The six month round trip will be cramped: outwards each astronaut will have about 10 cubic metres of space to live in (reduced by about 10% to allow room for food and other personal consumables), on the return trip, after one Orion is jettisoned, the crew are limited to about 4 cubic metres per person in the Orion Crew Module. Note that architects of jails in Victorian times expected prisoners to tolerate 23 hour a day confinement in cells equivalent to about 35 cubic metres per felon, conditions regarded as appalling today. The crew will be further from the rest of humanity than anyone has ever been before so they will have to cope with any technical or medical emergency that arises by themselves. Radio signals will take up to 40 seconds to span the abyss between their craft and homeworld. Their conditions may resemble some highly unethical psychological experiment, hopefully the two explorers will endure their forced confinement cheerfully and remain on speaking terms!
What will they find at their destination and what will they learn there? Very little is known about the accessible asteroids. As the potential target asteroids are small, faint and visible for only a few weeks or months at a time, astronomers know very little about them. Their dimensions and even rotation rates remain largely mysterious. Probably the accessible asteroids are a varied selection of stony, iron and carbonaceous objects like other observed asteroids. Some may be essentially solid lumps, others loose piles of rubble. Surprisingly occasionally very small asteroids have been found which rotate very rapidly, with rotation periods ranging from a few minutes to a couple of hours. These examples are probably monolithic rather than rubble piles since centrifugal force would throw off loose materials. If observations of the target asteroids eventually shows that they are similar fast rotators, that will make EVAs near them rather tricky (the astronauts are assumed to be equipped with modernised versions of the Shuttle’s Manned Maneuvering Unit, the “jetpack” used for untethered spacewalks in the 1980s). In fact the explorers are unlikely to walk on the asteroid as its feeble gravity will make this too difficult and the instruments they will deploy on its surface will need secured there with pegs, adhesives or even magnets (should the asteroid be composed of iron).
I am enthusiastic about this scheme, seeing it as a Good Thing. If it were to go ahead the mission would teach us so much about the smaller bodies of the Solar System and indeed the origin of the planets. The practical experience gained of travelling to an asteroid and working on it could be vital should be we ever be confronted with an oncoming Earth impacting asteroid. It would nice too to see astronauts as explorers once again rather than technicians or repairmen. I am not optimistic about ever seeing this exact mission go ahead but I hope something like it will happen soon.