In their never ending quest to find something to do in space that does not involve going to the Moon, the wizards of space policy in the administration have seized on one of the nuttier ideas floating around space circles these days. Based on a study last year by the Keck Institute for Space Studies, it is rumored that the new budget will propose to spend $100 million next year on a mission to “retrieve” an asteroid and bring it back to Earth-Moon (cislunar) space for detailed examination by humans. Some see this as fulfilling the prophecy of President Obama in his 2010 appearance at NASA’s Kennedy Space Center – that since we wouldn’t be sending people back to the Moon (because “We’ve been there”) we would instead send them to a near-Earth asteroid (NEA) in preparation for an eventual human trip to Mars sometime in the 2030s. Maybe.
How far out is this idea anyway? Not totally, but quite a bit. In part, its degree of rationality is dependent on exactly how this mission fits into a general spaceflight strategy. Since we do not have the latter, it’s hard to evaluate this proposal in programmatic terms. So we must look at it as one possible “strategic” direction for human spaceflight for the next decade.
What’s the argument for moving an asteroid from its normal orbit to cislunar space? Basically, the Orion spacecraft is a cislunar vehicle, capable of transporting people on missions of a few weeks duration within that zone of space and returning them to Earth (but not capable of much beyond that region). If you exclude the lunar surface as a destination, there’s no place to go in cislunar space, except space itself. A current scenario of a mission to “L-2” (the quasi-stable libration point 60,000 km above the center of the lunar far side) has to make up work for the astronauts to do there; one idea suggests that the astronauts “control” a robot collecting samples on the far side of the Moon, but that concept has not been fleshed out in detail nor is any planned surface sample rover and return vehicle in the development budget.
The principal programmatic virtue of the L-2 point is that Orion can reach it, so it is a prime “not-the-lunar-surface” place to go. But it looks bad to go somewhere where nothing exists and then to do nothing once you get there – a “close but no cigar” scenario. Hence, the ostensible plan about controlling robots on the surface of the Moon was developed (incidentally, such a robot could just as easily be controlled from the Earth using a communications relay satellite orbiting the Moon). But the President said we were going to an asteroid. So what’s the hold up?
Leaving aside the issue that few (or no) near-Earth asteroids are suitable targets for human missions, at least with current space systems (launch vehicle, life-support, total delta-v), the basic problem with human missions to NEAs is time – the length of travel time to get to a NEA, added to the amount of loiter time around it when you get there, followed by the time needed to get you safely home again. During all this time, the crew is exposed to the full fury of solar particle events (the “coronal mass ejections” that can fry you in a few minutes time) and the steady stream of galactic cosmic rays – radiation unfiltered or stopped by the Earth’s Van Allen radiation belts which protect crews aboard the ISS in low Earth orbit. Add to this issue the fundamental problem of abort scenarios. If things go wrong with your spacecraft soon after departure what do you do? Can you get back home? Usually, the answer is “not quickly or easily.” The concatenation of these events usually ends in the sinisterly bureaucratic phrase, “loss of crew.”
The Keck Institute study of last year was hailed as a masterstroke to solve the asteroid mission dilemma (i.e., supposedly so many interesting targets but not the ability to get people to them): Bring an asteroid to cislunar space, park it at an L-point and examine it at our leisure. Such an effort would be beneficial to a long-term scientific examination of the object, knowledge that we will need to understand tasks like resource extraction and processing. So let the mountain (well, okay, maybe a knoll) come to Mohammed.
The problem with re-arranging the Solar System for our personal convenience is that it’s difficult in time, energy and effort. Only the smallest asteroid could possibly be brought back to cislunar space; the object described in the Keck report is only a few meters across – a dried mud ball. An asteroid that small will have virtually no geological diversity, thus giving us limited information about asteroid evolution (NEAs almost that large already exist in meteorite collections on the Earth.) A body that size could be significant for resource utilization, except that we don’t yet know what we would process, how we would extract materials from it, and what we would do with the products once we have them. Water is an extremely valuable resource in space, but the current fly-and-discard template of the Orion-SLS architecture does not feature an easy way to incorporate water into creating new capabilities. The idea that platinum group metals (PGM) mined from an asteroid could pay commercially might be tested in such a scenario, but it’s not clear that a NEA suitable for capture and transport to cislunar enables that, given that we don’t know at this point even the nature of the feedstock we’ll get for processing.
There is one more issue to consider with asteroid hauling: Safety. An asteroid brought to one of the L-points has little chance of an accidental encounter with the Earth, but this may be a case where perception counts for more than fact (regrettably, an increasingly frequent event in science these days). The recent Russian meteorite fall created an enormous publicity stir and many in the space community have sought to use that event to their advantage, with visions of fat federal contracts granted to ward off evil spirits raining down from the sky. It’s one thing to ask for massive amounts of government money to protect the Earth from impact devastation; it’s quite another to ask for same to go and retrieve one of the dread objects. Of course, this will be portrayed as an effort to learn how to “mitigate” asteroid collisions with Earth, but there’s nothing we can learn from a hauled rock at L-2 that we could not learn from a small robotic mission to a NEA safely situated in its own orbit around the Sun. The idea that we can actually deflect an asteroid is still controversial, even in scientific circles where some will believe anything.
In the current wilderness of unattainable space policy ideas, this one certainly stakes out new territory. Since we can’t get to an NEA, let’s bring one to a place to which we can get, thus successfully avoiding the place that we should be exploiting in order to attain true space faring capability – the lunar poles. What to do and learn at this rock parked above the Moon is left as an exercise for the student.
Previous posts on human asteroid missions: