It has been said, and said more often these days, that humanity is good at dealing with trouble in the here-and-now; and terrible at dealing with disaster in the future. Consider the response to the Haiti earthquake on one hand, and the just released report from the National Research Council (USA), Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies. The report was commissioned by NASA, which was charged by the U.S. Congress with developing a program that would locate and track 90% of Near-Earth Objects (NEOs – asteroids, comets, other debris) 140 meters in diameter or larger by 2020. 140 meters (or about 460 feet) is the size of asteroid that could cause enormous damage to any region of Earth it struck. Ironically, the NRC report probably cost nearly the amount of money NASA has available yearly to carry out the mission ($4 million), which may explain why the report was wanted in the first place.
One of the most obvious points of the report: NASA is grossly underfunded to achieve the results desired by Congress for the end-date of 2020. This was not news; an interim report had said the same thing a couple of years ago. The current report is direct and realistic: Serious funding is required, if 2020 (or anything near then) is a serious target. Congress could (and should) fund a two-pronged approach: A satellite NEO detector, and a ground-based detector. If it couldn’t fund both, then go with the ground detector. The report pointed specifically to the ground-based facility at Arecibo (Puerto Rico, USA), which has been budget cut almost to closing, as invaluable for detecting NEOs.
People might (and do) say, “What’s the rush?” Right. The odds of being struck by a seriously damaging object – an impact event – are measured in one-in-so-and-so many thousand years. The problem is, in this kind of lottery, the odds are terrible but sooner or later somebody “wins”…that is, impact events don’t happen very often, but they do happen and the consequences range from extinguishing most life on Earth, to an aerial blast that levels a city the size of New York. That’s why they make Hollywood disaster movies about being hit by an asteroid. It’s also why the U.S. Congress and governments in other parts of the world are committed to spending (some) money to detect any NEOs that might hit Earth.
The NRC report takes this commitment into account, but points out some important weaknesses above and beyond lack of funding: First and foremost, we know that there are different types of objects (24 types of asteroids by one classification method, for example), but we know next to nothing about how to realistically deal with these different types if we needed to prevent one from hitting Earth. The report points out that recent studies indicate NEOs as small as 50 meters can also cause severe damage, and while not the thrust of any detection program, these smaller objects should also be cataloged. The logistics and methods of preventing a hit were cited as other major areas of weakness:
The report also examines what is known about methods to defend against NEOs. These methods are new and still immature. No single approach is effective for the full range of near-Earth objects, the committee concluded. But with sufficient warning, a suite of four types of mitigation is adequate to meet the threat from all NEOs, except the most energetic ones.
Civil defense (evacuation, sheltering in place, providing emergency infrastructure) is a cost-effective mitigation measure for saving lives from the smallest NEO impact events and is a necessary part of mitigation for larger events.
“Slow push” or “slow pull” methods use a spacecraft to exert force on the target object to gradually change its orbit to avoid collision with the Earth. This technique is practical only for small NEOs (tens of meters to roughly 100 meters in diameter) or possibly for medium-sized objects (hundreds of meters), but would likely require decades of warning. Of the slow push/pull techniques, the gravity tractor appears to be by far the closest to technological readiness.
Kinetic methods, which fly a spacecraft into the NEO to change its orbit, could defend against moderately sized objects (many hundreds of meters to 1 kilometer in diameter), but also may require decades of warning time.
Nuclear explosions are the only current, practical means for dealing with large NEOs (diameters greater than 1 kilometer) or as a backup for smaller ones if other methods were to fail.
Although all of these methods are conceptually valid, none is now ready to implement on short notice, the report says. Civil defense and kinetic impactors are probably the closest to readiness, but even these require additional study prior to reliance on them.
The bottom line of the report was in one sense, money; but in another sense it was ignorance. There is so much we don’t know about NEOs; not just how many, and where they are, but also what kinds are there, and how do we deal with them? Perhaps the NRC report can be put together with the Augustine Commission report (USA), which called for considering the exploration of NEOs as a fitting target for manned space flight. The combined reports might illuminate a path to both the bottom lines.