Dueling over asteroids
Posted: Wednesday, March 21, 2007 5:50 PM by Alan Boyle
Former astronaut Rusty Schweickart is to asteroids what Al Gore is to global warming, and Schweickart is none too pleased with NASA’s latest strategy for coping with potential threats from the sky.
Those plans came out this month in the form of a report to Congress, laying out an analysis of the various methods for detecting and dealing with potentially hazardous asteroids and comets. It's all part of NASA's legislative mandate to find 90 percent of such near-Earth objects, or NEOs, wider than 460 feet (140 meters) by the year 2020. An asteroid that big could devastate a city-sized region if it were to hit Earth.
Schweickart, who flew on Apollo 9 in 1969, set up the B612 Foundation to raise awareness about NEO threats - and he's organizing a series of workshops under the aegis of the Association of Space Explorers to develop an international plan for dealing with them.
"Not to make it sound overly dramatic, but you're not dealing with just science, you're dealing with public safety issues," he told me today. "You're dealing with the survival of life."
That's why he's taking the new report so seriously. NASA's official view is that the most efficient way to divert a potentially threatening NEO is by setting off a nuclear bomb nearby, to nudge it into a safe orbit. "The implication is that it is the preferred way to go to deflect essentially any near-Earth object," Schweickart complained.
In contrast, Schweickart argues that the so-called "nuclear standoff" option should be used only as a last resort. He contends that 98 percent of the potential threats can be mitigated by using less extreme measures. For example, he favors the development of a "gravity tractor" - a spacecraft that would hover near an asteroid for years at a time, using subtle gravitational attraction to draw the space rock out of a worrisome path.
To kick it up a notch, Schweickart said a threatening NEO could first be hit with a kinetic impactor - say, a scaled-up version of the Deep Impact bullet that hit Comet Tempel 1 back in 2005 - and then the orbital track could be fine-tuned using the tractor. Navigational sensors aboard the tractor would check to make sure the NEO was on a completely safe path.
"This combination is obviously the way to go," he said.
NASA sees it a different way, however. The report said the gravity tractor concept and similar techniques would be the "most expensive" ways to divert an asteroid: "In general, the slow push systems were found to be at a very low technology readiness level and would require significant development methods," it said.
Schweickart said NASA must have "misunderstood or mischaracterized" the gravity tractor concept. And he worried that the report may make things tougher for researchers working on kinder, gentler ways to head off killer asteroids.
"It may be harder to continue with that research," he said. "The irony is that NASA ought to be doing that research.
"But beyond that, there is also the issue that people are beginning to wrestle with this question on a much larger basis internationally," he said. "The idea that the only way you can protect Earth from these things is to compromise all your principles about nonproliferation would be shocking to anybody else. Almost anytime the United States is going to say anything about this, eyebrows are going to go up."
Schweickart already has written a 13-page retort to the report, as well as a letter to NASA Administrator Michael Griffin asking him to reconsider the agency's policy. Both are available from the B612 Foundation press page as Word documents. Schweickart is also calling on NASA to release more of the background analysis that went into the final report.
"I just felt that it was inappropriate that this stand unchallenged - not only unchallenged, but unsupported," he said.
He feared that his anti-nuclear stand might make him "persona non grata" in NASA circles - but astronomer Donald Yeomans, the head of NASA's Near Earth Object Program Office at the Jet Propulsion Laboratory, said Schweickart's idea of combining kinetic impactors with gravity tractors had merit.
"That's an interesting concept if you wanted to do non-nuclear," Yeomans told me.
He pointed out that the NASA report was merely aimed at outlining the viable options for dealing with potentially threatening NEOs, and that the nuclear standoff explosion would be a "viable option for almost anything." (NASA isn't crazy about planting a nuke right on a NEO, a la "Armageddon," because of the risk of breaking the object into hazardous pieces.)
The kinetic impactor, perhaps combined with a gravity tractor or monitoring device, would be the most straightforward way to head off a NEO threat - and would probably be preferred for the smaller-scale threats.
"You really don't have one technique that fits all - except for this standoff blast, perhaps - but I don't think anyone is comfortable with this nuclear option," Yeomans said. "I think nuclear is there and available, but it's sort of a last resort. That's my own opinion. ... It's politically a tough sell, and it gives most people the willies."
One thing that nearly everyone agrees on is the need to devote more resources to hunting NEOs in the 460-foot-and-up range. The NASA report suggested two options for complying with Congress' requirements: either building a new ground-based telescope facility dedicated to the asteroid search, or putting a new infrared telescope into a Venus-like orbit. Unfortunately, NASA says it can't afford either option for the time being.
"The decision of the agency is we just can't do anything about it right now," Lindley Johnson, program scientist for near-Earth object observations at NASA Headquarters, told The Associated Press.
The Venus-orbit telescope may sound expensive (with a price tag in the range of $1 billion to $1.2 billion, compared with $800 million to $1 billion for the ground-based facility), but Schweickart said he'd put a "very big plus sign" on that option. Yeomans noted that a similar mission called NEOCam had been proposed in the past, with the L1 gravitational balance point between Earth and the sun serving as the telescope's vantage point.
"If what you're interested in is just the letter of the law, then there are a number of options," Schweickart said. "But if what you're really interested in is being prepared to deal with the threat, then that infrared telescope in Venus orbit is much more valuable - because without it, you're relegated to looking at things from the surface of the Earth. And it's very difficult to pick up things that are largely inside Earth's orbit."
For example, the asteroid Apophis spends nearly all its time inside Earth's orbit, and that location is what's making it hard for astronomers to figure out whether or not it will hit Earth in 2036. Yeomans said that, for now, the odds of collision are still set at 1 in 45,000 - but that may change once additional analysis from the University of Hawaii's Institute for Astronomy is added to the mix.
Astronomer Dave Tholen is reportedly still working on the analysis, which should become available soon. "He's so good that it's well worth waiting for," Yeomans said.
Will Apophis be crossed off the list of threatening asteroids? Or will we have to wait until 2013 to get the final answer? Stay tuned, and keep an eye on NASA's list of cosmic threats.
