ASTEROID APOPHIS: DEALING WITH EARTH'S FUTURE TROUBLEMAKER Leonard David, Space.com
3 November 2005 BOULDER, Colorado – The potential for a newly discovered asteroid smacking into the Earth in 2036 cannot be discounted. NASA has sketched out a response strategy in the outside possibility that the space rock becomes a true threat. NASA’s action plan was the result of prodding by a group of astronauts, scientists and other technical specialists uneasy about the current lack of action to protect the Earth from the impact of near Earth objects (NEOs). The object was found last year through the efforts of NASA’s Spaceguard Survey. In 1998 NASA formally initiated the Spaceguard Survey by adopting the objective of finding 90 percent of the near Earth asteroids larger than 3,280 feet (one kilometer) diameter within the next decade - before the end of 2008. Asteroid 99942 Apophis – first labeled as 2004 MN4 -- is estimated to be roughly 1,000 feet (320 meters) in diameter. Were it to strike Earth, it would not set off global havoc but would generate significant local or regional damage, experts say. Worrisome to asteroid watchers is the exceptionally close flyby of Earth by Apophis on April 13, 2029. So close in fact, the space rock will be naked-eye visible as it darts by. And what can’t be ruled out at this time is that Apophis may pass through a gravitational “keyhole” – a spot that alters the asteroid’s trajectory as it zips by our planet and might put it on the bee-line lane for banging into Earth seven years later. Concern over asteroid Apophis and the ability to precisely chart its trajectory -- and take steps if needed to deflect the object -- were fervently voiced by the B612 Foundation, chaired by Russell Schweickart, a former Apollo astronaut. The group requested that NASA carry out an analysis that included the possibility of placing an active radio transponder on the object. Doing so at a fairly early date would yield the requisite orbital accuracy of the asteroid as it sped through space. In a June 6 letter to NASA Administrator, Michael Griffin, Schweickart on behalf of the B612 Foundation called for support in “resolving an issue of critical importance” - namely whether a scientific mission should be launched to asteroid Apophis in the near term. Such a probe, if dispatched, Schweickart stated, would provide knowledge of the asteroid’s orbit in time to initiate a deflection mission in the unlikely event one should be required. The position of the B612 Foundation was that the mission should be staged, pointing out that NASA’s NEO program personnel apparently did not concur with that view. A spacecraft mission to Apophis would augment tracking of the object from the ground, the letter to Griffin explained, and also carry out a number of scientific duties too. NASA provided a formal response to the B612 Foundation’s June communiqué via an October 12 letter from Mary Cleave, Associate Administrator for Science Mission Directorate. That NASA reply came with an appended detailed analysis by Steven Chesley of NASA’S NEO Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The study by Chesley dug into Apophis’ orbit, under varying conditions, and contained other items pertaining to the space agency’s findings about the Apophis matter. “The key conclusion to be taken from this analysis,” Cleave explained in the letter, “is that aggressive (i.e., more expensive) action can reasonably be delayed until after the 2013 observing opportunity. For Apophis, the 16 years available after 2013 are sufficient to recognize and respond to any hazard that still exists after that time.” Cleave noted in the letter that while Apophis “is an object whose motion we will continue to monitor closely in the coming years, we conclude a space mission to this object based solely on any perceived collision hazard is not warranted at this time.” Not ruled out by Cleave, however, is the prospect of Discovery-class, low-cost missions sent to Apophis, “based on purely scientific arguments,” she said. “Indeed, the asteroid’s orbit is particularly attractive for spacecraft rendezvous, and the extraordinary close encounter in April 2029 provides a unique opportunity to investigate a number of scientific NEO issues,” Cleave explained in the letter. While Schweickart said that the NASA response to the B612 Foundation’s concern is a step forward, there are other issues still to be resolved. One matter involves radar tracking of Apophis. On one hand, radar plays a crucial role in being able to rationally determine the future likelihood of a NEO impact and potentially in planning for a deflection mission when required. Yet the availability of NEO radar tracking, and the budgets to support this work in the future is highly uncertain, even precarious, Schweickart and the B612 Foundation emphasize. Radar hits of Apophis at each opportunity through 2021 are important to keep watch of the object’s whereabouts. “Tracking these asteroids once you know they exist and pinning down their orbits is really not science,” Schweickart told SPACE.com. “This is public safety. It’s disaster preparedness.” When Apophis swings by Earth, Schweickart said the asteroid will likely change its orbit. Also, its spin characteristics may be altered. Due to Earth’s gravity tugging on the object, “asteroid quakes” could reshape Apophis, he said. Moreover, still far from resolution is a “whose in charge” proclamation about troublemaking NEOs, Schweickart said. “It would be great if we had NASA doing this as a regular process. Unfortunately, the mindset that’s essentially required by their budget is to think about discovery, not to think about the potential need for deflection,” Schweickart added. “Until your mindset is oriented that way, you’re going to miss things.” Until an agency is identified that is responsible for all of this, Schweickart cautioned, everybody is “begging time and bumming bucks” from some other program. “This whole thing is sort of in a precarious position until somebody gets around to assigning agency responsibility,” he said. Regarding the skill required to deposit a transponder on Apophis, Schweickart saluted Japan’s Hayabusa asteroid sample-return mission, now in progress. That craft is scheduled to make two landings on its target asteroid – Itokawa -- later this month. The mission is geared to haul back samples of the object to Earth. Scientists at Japan’s Institute of Space and Astronautical Science (ISAS) are working day-by-day issues in readying the probe for contact with the asteroid, including release of a mini-robot onto Itokawa that will move about and survey its rocky surroundings. ISAS is a research arm of the Japan Aerospace Exploration Agency (JAXA). “It’s an impressive mission,” Schweickart said, sure to yield operational experience and lessons learned on how best to execute duties on asteroid Apophis. The ruin stemming from asteroid Apophis colliding with Earth would potentially be very great. Indeed, the consequences, Schweickart suggested, would dwarf those seen as a result of the Indian Ocean tsunami in December 2004, hurricanes Katrina and Rita in September of this year, and the Pakistan earthquake last month. In regards to global preparedness in handling these unusually devastating events of late, “it’s basically out of sight…out of mind,” Schweickart said. “That’s the real challenge for society. The things that you don’t know about are one thing. But the things that you do know about, and don’t do something about…those are the ones that are really tough.” Fully concurring with NASA’s response is Alan Harris, a senior research scientist and asteroid expert for the Space Science Institute headquartered here. Harris noted, as has been underscored by the B612 Foundation, that if Apophis is indeed on an impact trajectory, then ground-based radar observations will not be able to refine the impact probability to greater than 20 percent. “That is, we would still not know better than one-chance-in-five whether the impact would really occur or not,” he told SPACE.com. “We really would need a transponder to improve tracking enough to firmly establish that an impact would occur,” Harris said. What has been overlooked, or at best under-emphasized, Harris added, is a point raised in the NASA response. Ground-only tracking has a 99.8 percent chance of eliminating any chance at all of an impact. Thus, there is only one-chance-in-500 that ground-based tracking will fail to resolve the issue in favor of no impact. “For this reason I think the NASA conclusion is entirely sensible,” he said. Harris said that there are Apophis observing opportunities every 6-8 years, with each one having about a 90 percent chance of eliminating any possible impact. At each of these “shoulder” times, he said, one can re-evaluate the “wait and see” strategy if the impact possibility does not go away. “Certainly it seems appropriate to play the ‘wait and see’ game until after the 2013 observing opportunity,” Harris stated. None of this diminishes the opening that Apophis presents for purely scientific investigations, which could incidentally contribute to the NEO hazard issue, he said. Harris said that he would not recommend a “deep impact” type of scientific mission, “lest we have the misfortune to deflect it into a keyhole, but other than that, Apophis is a very attractive mission target.” Asteroid Apophis, and the discussions it has sparked are welcomed, observed David Morrison, a space scientist and asteroid specialist at NASA’s Ames Research Center, situated in Silicon Valley, California. “I am pleased that this dialog is taking place,” Morrison said. “This is the first time that serious possibilities for dealing with a real but low-probability future impact have been discussed in a technically professional way, rather than receiving the ‘Hollywood treatment’”. Morrison said that he considers it remarkable that the Spaceguard Survey has reached the
level of maturity where such an asteroid could not only be found, but its orbit understood well enough to deal with “keyholes” and other subtleties. “Apophis represents for me a symbol of the coming of age of Spaceguard and of asteroid impact studies in general,” he said. The possibility of Apophis hitting Earth on April 13, 2036 is real, Morrison said, even if the probabilities now seem to be very small. “These probabilities represent uncertainties in our knowledge of the orbit, not a failure of the science.” But whether the asteroid will strike Earth or not, Morrison concluded, the challenge is to resolve which case is correct. “With more observations over a longer time span, we will be able to tie this down.” =================================== ASTEROID APOPHIS AND PLANETARY PROTECTION: ALAN BOYLE TALKS TO DON YEOMANS MSNBC, 1 November 2005
Alan Boyle, Science editor
Planetary scientist Don Yeomans laughs at the title of "asteroid czar," but as the manager of NASA's Near-Earth Object Program, he's arguably the go-to guy for asteroids and other celestial objects that could blast us back into the Stone Age. Over the past decade, Yeomans and his colleagues at NASA's Jet Propulsion Laboratory in Pasadena, Calif., have had to cope with a series of asteroid alerts - arising in part because astronomers are getting so much better at spotting space rocks that have a chance of crossing Earth's orbit sometime in the next century or two. The biggest concern right now has to do with an asteroid called Apophis, which will have a close encounter with Earth in 2029 and might even hit us in 2036, depending on how its orbit changes between now and then. NASA says Apophis will almost certainly miss Earth - but just in case, Yeomans and other at the space agency have sketched out plans for space missions to divert the asteroid if necessary. NASA issued its plan as a response to concerns expressed by former astronaut Rusty Schweickart, who is calling attention to potential threats from near-Earth objects as the chairman of a California-based group called the B612 Foundation. Yeoman discussed Schweickart's concerns, NASA's response and the bigger picture behind near-Earth objects on Tuesday in an interview with MSNBC.com. During the discussion, he made clear that he doesn't let his status as NASA's chief asteroid-watcher go to his head. For someone who watches out for cosmic doomsdays, Yeomans seems remarkably grounded. "Several months ago, the Pasadena newspaper did an article on strange jobs, and I was there with a belly dancer, a tattoo artist and a dog groomer," he said with a laugh. "So that's the kind of company I keep here." He also keeps company with a growing array of skywatchers, including researchers at JPL's own Near Earth Asteroid Tracking project in Hawaii, professionals at other facilities such as the Lincoln Near Earth Asteroid Research project in New Mexico - and hundreds of amateur astronomers around the world. "Back in the early '90s and before that, this near-Earth object issue was looked upon, even among our scientific colleagues, as sort of a crazy topic," he recalled. Some even thought NASA was using near-Earth objects as a ploy to get more money, he said. But since then, asteroid-watching has gotten a lot more respectable. "We shouldn't be going hard over and devoting a lot more resources than what we have now, perhaps," he said. "But the modest level of spending that NASA is doing now - about $4 million a year - is probably appropriate, at least for the time being, for the insurance that we get as a result of tracking these objects into the future. We don't get the giggle factor nearly as much as we once did." Although the study of near-Earth asteroids has come a long way in the past decade, one big question still hangs in the air: Who takes over if Yeomans and his colleagues actually spot an asteroid or comet heading our way? At least officially, it's not NASA. True, NASA identifies and tracks potentially threatening near-Earth objects, and NASA does have plans to respond to Apophis if necessary. However, dealing with an actual threat is not part of the space agency's job description, Yeomans said. "NASA does not have the charter to look at that, nor does anyone else," he said. "That's the point - no one does at the moment." * * * * * * Here's the edited Q&A from Tuesday's interview, beginning with a discussion of NASA's plans to divert Apophis if necessary: MSNBC.com: It's interesting that there is a timetable for dealing with this particular asteroid. Could you talk about the thinking that goes into how you approach something like this, which is a very low-probability but high-impact event? Yeomans: The first point to be made is that the whole point of NASA's near-Earth object search is to find these objects well in advance of any threatening encounter. Once you have a couple of decades to work with, this problem becomes tractable. So the object was discovered as part of the program here, and we ran the orbit calculations forward and found this close approach in 2029. Then we discovered that depending on the circumstances of that close approach in 2029, there could be what we call "resonant returns." In 2036, seven years after the 2029 return, the earth has gone around the sun seven times, of course, and the asteroid would have gone around six times. And they arrive at the same place at the same time, if the object passes through a 600-meter [2,000-foot] "keyhole" in 2029. Now the chances of that happening are pretty minuscule, but it hasn't been ruled out yet. The plan is to continue observations of this object, both optically and with radar, and according to our statistical analysis, there's an opportunity next May for radar observations, and at that time there's a 50-50 chance that this remaining 2036 possibility will disappear, because the orbit gets that much better. And then in 2013, there's yet another opportunity. If the risk doesn't go away next year, there's a 96 percent chance that it will go away in 2013. Q: And that's based on the fact that as you make more observations, you know the orbit more precisely? A: That's right. Q: Isn't there also something called the Yarkovsky effect that you would be looking for in 2013? A: Sure. The Yarkovsky effect is one of the largest contributors to our uncertainty about this object. As an asteroid is heated by the sun - at asteroid noon, for example - you can imagine that if the asteroid were not rotating, the heat of the sun would simply heat it up and it would reradiate some of that heat back toward the sun. But the asteroid is rotating, of course. Just as the earth does not get hottest at noon but gets hottest at 3 o'clock in the afternoon, there's a thermal lag. The asteroid actually reradiates much of its energy not directly back toward the sun, but there's a component that's in the direction of the asteroid's motion or counter to it, depending on which way it's rotating. That introduces a rocketlike thrust on the asteroid itself ... and that affects the orbit and the position of the asteroid as a function of time. It's a very small effect, but over a few decades, it's quite important. Typically, in order to completely understand the Yarkovsky effect, you have to understand the surface. Is it solid rock? Is it jumbled rock? ... If you understood the surface completely, as well as the rotation pole and the direction, you'd be able to model this rather well. But even without that, we can simply look at the difference between our predictions of where the object should be, not including the Yarkovsky effect, and the actual position in a few years, and say, "All right, the difference is due to the Yarkovsky effect.". We're confident that we can model that Yarkovsky effect, given additional observations. Q: And that explains why you would be so much surer in 2013 than you would be in 2006? A: That's right. And in 2021, there's yet another radar opportunity. By then we will know the Yarkovsky effect rather well. Even without a mission, we would know with a precision of a few hundred meters. So we could almost certainly tell whether the asteroid will pass through this keyhole in 2029. Again, it's far more likely that it will not than that it will. [B612 Foundation Chairman Rusty Schweickart's] point was that you won't know whether it will definitely miss this keyhole until later on, after the 2013 encounter, so you'd better mount a mission now. He's thinking in terms of a rendezvous, so you'd have to have a lot of time. Our point is that there's no hurry - yet. If this thing doesn't go away in 2013, there's still time to mount a precursor mission that might drop off a transponder to track this thing to an accuracy of a few meters. In the unlikely event that that still doesn't remove the threat in 2036, there's time for a subsequent deflection mission along the lines of the Deep Impact comet mission. That's a much faster mission, if you run into it rather than making a rendezvous and nudging it. That was the point: He maintained initially that we needed a lot of time and we had to start now. ... What we're saying is that there are faster and less expensive ways to attack this problem, should it still be a problem in 2013 - which is frankly quite unlikely. Q: In this case, would hitting the object make enough of a difference to alter the asteroid's course? A: Any change in velocity that you give the asteroid before the 2029 encounter is dramatically magnified as a result of that encounter. For example, the analysis that we did showed that if you give the asteroid a modest tenth of a millimeter per second change in velocity, over three years that amounts to a 25-kilometer [15-mile] change of position - which would move it out of the 600-meter keyhole. It takes very little to get it out of this keyhole. We're not trying to move it kilometers, or hundreds of kilometers, or thousands of kilometers. We just need to move it a few hundred meters and get it out of that keyhole. And if we do that, it misses completely in 2036. Q: In terms of the dynamic analysis, would a projectile on the scale of Deep Impact's impactor make that much of a difference for a 400-meter-wide object, or would you have to scale up the projectile? A: Actually, scale it down. A 1,000-kilogram [2,200-pound] spacecraft would do that. Deep Impact's mothership and impactor together were more than that. A tenth of a millimeter per second is next to nothing, and the keyhole is next to nothing. That's what allows us to get away with this. Normally, if you had an Earth-threatening encounter, you would want to move the asteroid at least an Earth diameter. Now you'd be talking about thousands of kilometers. But because of this keyhole, we only have to do a few hundred meters. Q: Rusty had said that this is an unusual case, because you do have this scenario where the movement of the course doesn't have to be all that much. He said that in the case of a larger asteroid, you would have a bigger problem - and we don't really have a good idea how to deal with that. Is that something you would subscribe to, that more needs to be done to deal with larger asteroids? Or if you had enough notice, could you make that small amount of motion and move the larger asteroids away? If you have to move something a centimeter a second to move it an Earth diameter away in 10 years, it's proportionately less if you have 20 years or 30 years, so it gets down to a few millimeters per second. The key is to discover these things early, and that's exactly the goal of NASA's search programs. I've been warned, and warned, and warned again by NASA Headquarters not to sign NASA up for any mitigation responsibilities - because NASA does not have that responsibility at the moment. So I'm not to say anything on that. Q: What would have to happen to make those sorts of studies? Rusty has said that there should be an agency designated to protect Earth from near-Earth objects and address some of these mitigation measures - whether it's a national or international agency, or set up under an international treaty. Is there a range of political scenarios for that? A: What would have to happen, of course, is that the policy makers and Congress would have to direct NASA or the Department of Defense or someone to take responsibility for this, and then they would begin the studies necessary to come up with those options. As I mentioned, NASA does not have the charter to look at that, nor does anyone else. That's the point - no one does at the moment. Q: The charter that NASA has is to identify those objects. A: Identify and track. But not mitigate, and not deflect. They're really sensitive about that. Q: But in the case of Apophis, there is some talk about a deflection scenario ... A: Right. Well, we did that analysis to directly respond to Rusty's letter to [NASA Administrator] Mike Griffin. It was a pretty quick and dirty analysis, just using the fact that Deep Impact was so successful. We showed that this could be done more quickly than Rusty thought, so we don't have to do anything now. We can wait until after 2013, when this is almost certainly going to go away. But even if it doesn't, we still have options to deal with it. ... Q: In terms of the technical options, hitting an asteroid with something is one alternative. And the other alternative would be to put something that has a thruster on the asteroid, and nudge it into a different course over a long time frame. Does that pretty much cover it? A: Oh, no. Those are just two of many options. You could put up a sun-focusing mirror nearby, and focus sunlight on one side of the asteroid, and the ablation of material on the front side would introduce some thrust on the asteroid. You could mount a shuttle engine on one of these things, but then you'd have to worry about the rotation. You'd have to pulse every time it came back to the same location. Or you could have mass drivers. That has been suggested. The weapons lab folks suggested buried nuclear devices for standoff nuclear blasts that would ablate the front side and introduce a thrust. Or blow it up soon enough so that the shrapnel would miss the earth. You don't want to blow this thing up just before impact, because then you've got a shotgun effect that would be worse. Not too many people are comfortable with this nuclear option, but the Lawrence Livermore folks were sort of keen on that one, as was [nuclear-energy pioneer] Edward Teller in his day. ... There are a lot of techniques that could be used, assuming you have the time. The key is, you have to find them early, and then things are tractable. If you find it too late, within a year of impact, there's not a whole lot you can do. You just evacuate, if it's small enough to cause only local damage. And if it's not, then ... Well, the big ones, the ones that cause global problems, are the easiest ones to find. And that is NASA's goal now, to find the ones that are larger than a kilometer. We're doing well, actually: We're up to 807 out of a total population of about 1,100 asteroids of that scale. Once we find them, they're no longer a problem, because we can track them for 100 or 200 years in the future, and keep an eye on them. None of them are a problem, but it's the smaller ones - and there are hundreds of thousands of them that we haven't been able to deal with yet, because we don't have the telescope apertures yet. Q: And I suppose there's also an issue with long-period comets, as well as asteroids that spend almost all their time inside Earth's orbit. Those are some of the things that are mentioned as "out-of-the-blue" threats. A: That's true. There are the Atens, the objects that spend most of the time interior to Earth's orbit. They are difficult to find, because they don't appear in darkness very often. There is at least one NASA program that is looking as close to the sun as possible to find those, and they've found a few. You mentioned the comets. Now, they're the wild cards. The bad news is, if they come in from the outer solar system, they don't start outgassing until they get well inside the orbit of Jupiter, and thus don't show themselves. It only takes 9 months to get from Jupiter's orbit to Earth's orbit. So that's the bad news. The good news is, in terms of numbers, there are 100 times more asteroids than comets in the near-Earth space. So asteroids are really the major problem, and we can deal with them. Comets are 100 times less of a problem, in terms of numbers, and we can't really deal with them anyway at the moment. So we're concentrating on the asteroids at the moment. It would take a lot more highly developed technologies to discover comets early enough to do something about them. We'd have to have sensors out beyond the asteroid belt, near Jupiter's orbit, looking for these things. And even if we found them, the orbit determination at that distance would be so poor, we couldn't predict precisely whether they would be a threat until they got in a lot closer anyway. So at the moment there's no clear path for dealing with long-period comets. But they're a 1 percent problem, compared to the 99 percent problem of the asteroids. Q: Could you refresh my memory on missions to near-Earth objects that are in the works? I know that Japan's Hayabusa mission to bring a sample back from an asteroid is nearing its climax, and then there's the European Rosetta mission. A: Hayabusa is an interesting mission. Their target body, Itokawa, is a near-Earth asteroid that's representative of the type of asteroid that would most likely be a problem. The structure of the object looks like a rubble pile, but the bulk density is not unlike Eros, which means it's not completely all rubble held together by its own self-gravity. You mentioned Rosetta, which will set down on the surface of a comet in another few years. I think that's about it, unless Deep Impact gets a follow-on to another comet. And of course there are several Discovery proposals in the works for comets and asteroids, but they haven't been selected as yet. Q: It sounds as if Apophis itself might be a candidate for a Discovery mission someday. Well, that's the thing with near-Earth objects: Many of the ones that represent the largest potential threats are also the easiest ones to get to, because they're in very Earthlike orbits. So the rule of thumb is that the more Earthlike an object's orbit is, the easier it is to get to. So it's one of the easiest objects to reach in terms of a rendezvous mission. It does make sense, to me anyway, that somebody would suggest this as a Discovery mission. We could put sensors on board the asteroid, and watch the asteroid perhaps readjust itself as it flies by in 2029. It's going to be a naked-eye object. It's going to go underneath geosynchronous satellites. I mean, it's going to be quite a show. You could engage the guy on the street rather well with this mission. ... That object, to my mind, is less of a threat and much more of interest for scientific purposes and engaging the public in this issue. So I think this is an opportunity that we shouldn't pass up. =============================== THREATENING ASTEROID JUST NEEDS A NUDGE - FROM A GRAVITY TRACTOR Mark Peplow
News@Nature, 9 November 2005 The next time an asteroid threatens to crash into the Earth, forget about calling Bruce Willis; send for a tractor driver instead. A pair of NASA astronauts has unveiled a design for an innovative space tug that could one day save the world. Even a relatively small asteroid some 200 metres wide could be nasty if it hit the Earth, potentially taking out a small country. Researchers have taken this threat very seriously, and are looking at ways to predict future collisions and prevent them. Just as in the film Armageddon, in which Bruce Willis helps to destroy an incoming asteroid, scientists have considered detonating a large nuclear device to split a rock into less threatening chunks. Although that may be a spectacular solution, Edward Lu of NASA's Johnson Space Centre in Houston, Texas, dismisses that as "the blast and hope method". "The reason it's not a good idea is that you don't know the outcome," he explains. The internal structure of asteroids is poorly understood, and blasting the spinning rock at the wrong instant could even make the situation worse, he says. "What you really need is something controllable," Lu argues. And that means a space tug. The difficulty with this is that an asteroid could be little more than a pile of rubble, making it difficult for the tug to hitch up. And as most asteroids rotate, an engine anchored to the surface would have to be fired intermittently to push the rock in the right direction, wasting precious time. So Lu and his fellow astronaut Stanley Love propose a spacecraft that simply hovers over the surface of the asteroid, using gravity as a towline. In this week's Nature1, they calculate that a 20-tonne craft could safely deflect a typical 200-metre-wide asteroid in about a year, assuming there is 20 years of warning to launch and get into position. "I think it's a fascinating idea," says David Morrison, a researcher at NASA's Ames Research Center in Moffett Field, California. Morrison chairs the working group on near-Earth objects for the International Astronomical Union. Morrison agrees that the threat of near-Earth asteroids should be taken seriously. Observation programmes such as the Spaceguard Survey are now scanning the skies for rogue rocks. "But no one has spent significant money on the issue of how to deflect it if we found one," says Morrison. "Those asteroids we have discovered already are not an immediate threat," says Morrison. But given their rate of discovery, Morrison estimates that there may still be a handful lurking in space that have Earth in their sights. Lu, who is part of the B612 Foundation, a group of space scientists who want to see asteroid-deflecting technology in place by 2015, has high hopes that the gravity tractor will be built. To get it up and running, Lu recommends that the US government invests in nuclear-powered ion-propulsion engines, which are more manoeuvrable than chemical ones and are less vulnerable to running out of fuel. NASA recently cut the programme dedicated to developing this kind of propulsion system in favour of more immediately applicable projects. The B612 Foundation recently lobbied NASA to put a radio transmitter on the 320-metre-wide asteroid 99942 Apophis. The rock is expected to pass just 30,000 kilometres from the Earth in 2029. This will alter its orbit such that it has a slim chance, about 1 in 15,000, of hitting the Earth in 2036. NASA responded with a 'wait and see' strategy, promising to track Apophis to see whether it passes through the tiny 'keyhole' of space that would put it on a collision course. This would still leave enough time to mount a mission to avert disaster, the agency said. But Lu argues that a tiny deflection a few years before the close approach of 2029 would definitely prevent a later impact, and could be achieved with a one-tonne gravity tractor. "It's always easier to do advanced planning than clean up after a disaster," he cautions. Reference: GRAVITATIONAL TRACTOR FOR TOWING ASTEROIDS Nature 438, 177-178 (10 November 2005)
Edward T. Lu and Stanley G. Love Abstract: We present a design concept for a spacecraft that can controllably alter the trajectory of an Earth-threatening asteroid by using gravity as a towline. The spacecraft hovers near the asteroid, with its thrusters angled outwards so that the exhaust does not impinge on the surface. This proposed deflection method is insensitive to the structure, surface properties and rotation state of the asteroid. ============================= ASTEROID POSES TINY DANGER, BUT IT MAY BE LURED AWAY
Henry Fountain
The New York Times, 22 November 2005 From a human perspective, Earth-crossing asteroids can have good timing or bad timing. Good timing is when the asteroid and the Earth don't meet. Bad timing is when they do.
Astronomers say that an asteroid with a 1,000-foot diameter discovered last year may have bad timing. There is a slight possibility that the rock, 99942 Apophis, will hit Earth in 2036 after coming within about 20,000 miles in 2029. A collision could cause regional devastation on a scale far worse than last year's tsunami.
"The most likely thing is that it is not going to be a threat," said Rusty Schweickart, a former Apollo astronaut and chairman of the B612 Foundation, which is concerned about protecting Earth from asteroids. "There's 5,499 chances out of 5,500 that it's going to miss us."
The trouble with Apophis, Schweickart said, is that the one chance cannot be ruled out yet. Better optical and radar observations are needed to determine the asteroid's orbit, but the best measurements cannot be made until 2013. That creates a different timing problem. If the threat from Apophis cannot be ruled out by then, will there be time to deflect it?
Schweickart's group is not sure and has urged NASA to plan a robotic mission to put a radio transponder on the asteroid so that its orbit can be precisely determined. If such a mission takes 10 years to design and execute, it will still give plenty of time to plan and carry out a deflection mission. NASA has said that planning for a transponder mission can wait until after the more precise measurements are made in 2013.
"I have a very high confidence that we can pinpoint exactly the track it's going to follow," said Andy Dantzler, director of NASA's solar system division. In the unlikely event that in 2013 a transponder mission would still be necessary, there would be enough time for that and a deflection mission, if needed, he said.
Schweickart said NASA's response was "probably fine." But he added that it made "aggressive assumptions about how good things are going to be and how much we're going to know."
Edward Lu, an astronaut and a board member of B612, said a transponder mission makes sense, given the time line and the potential risks. "We buy insurance for stuff that's a lot less likely than 1 in 5,500," he said.
Should deflection prove necessary, Lu said, it will have to happen before 2029 so that Apophis will miss a "keyhole" - a region in space only 2,000 feet wide where Earth's gravitational pull will put the asteroid on a collision course. Deflecting it after that, when it would have to miss a much bigger target, Earth, is not technologically possible in so short a time.
Lu and another astronaut, Stanley Love, have a proposal for how to go about deflecting the asteroid: use a spacecraft to tow it, but without a tow line. In a brief paper in Nature, the two describe how such a gravitational tractor, hovering near an asteroid with its engines canted to avoid the exhaust's hitting the surface, can slowly pull it into a different orbit.
The pulling force would be only about one newton, or roughly the amount of force used to hold a full cup of coffee. "But the point is, if you hang out long enough, it can add up to a substantial oomph," Lu said.
========================= ARE WE READY FOR DOOMSDAY?
By Marcia Dunn, The Associated Press
28 November 2005 CAPE CANAVERAL, Fla. -- Imagine last year's tsunami, last month's earthquake in Pakistan, and Hurricanes Katrina, Rita and Wilma all rolled into one -- and then some. If nations can't handle those calamities, what's going to happen when an asteroid collides with Earth? In 30 years, there is a 1-in-5,500 chance that a smallish asteroid will land a bull's eye on our planet. At 360 yards wide, it could take out New York City and much of the surrounding area. Fortunately, experts believe further observations of the asteroid, 99942 Apophis, will almost certainly rule out an impact in 2036. Nevertheless, it's precisely that kind of predictable and preventable threat -- and the thought of being ill-prepared for it -- that alarms the world's normally intrepid spacefarers who are calling for action. They issued an open letter at the Association of Space Explorers' annual congress last month in Salt Lake City, making a rare, united push for strategies and spacecraft to prevent a cosmic pileup. Two of the astronauts -- Apollo 9's Rusty Schweickart and shuttle and space station veteran Ed Lu -- have even helped establish a foundation to spotlight the issue. "There are always natural disasters and it always seems as though the preparation is somewhat less than adequate. But we have had a series of quite substantial ones here in the last year," Mr. Schweickart said in an interview with The Associated Press. Hollywood's depiction of cosmic collisions -- think "Armageddon" and "Deep Impact" -- has heightened public awareness, "but regrettably with the wrong solutions and overdramatization," Mr. Schweickart said. "You don't want to send up Bruce Willis and others to save us. That's Hollywood silliness," he said, chuckling. Instead, technology is far enough along that an asteroid could be deflected before hitting Earth, he said. For now, the astronauts are being cautious -- some say too cautious -- in their approach. "A lot of the folks working in this area are really attuned to not being Chicken Little, saying, 'Hey, this is going to kill us, it's going to kill us,' " Mr. Lu said. "That's not what we're saying. We're saying that you need to start thinking about it ahead of time because afterward is way too late. "The possible consequences are way worse than your run-of-the-mill natural disasters like earthquakes and tsunamis and hurricanes. As bad as they may be, this can dwarf them." Astronauts know better than most just how small and fragile and vulnerable the planet is. "When you go around it in an hour and a half, again and again and again and again, day after day, in some cases now, month after month after month, the Earth becomes a pretty small place," Mr. Schweickart said. "And then, of course . . . most astronauts tend to be aware of things like asteroids and their impacts. I mean, we romped around the moon after spending years in preparation by looking at every impact crater and volcano here on the Earth." It's time, the space explorers say, for NASA to step up to the plate. The association wants NASA to expand its Spaceguard Survey, a program that discovers and tracks near-Earth objects -- asteroids and comets -- that are at least two-thirds of a mile across. So far, 807 of an estimated 1,100 of these big, rocky asteroids have been discovered in the inner solar system along with 57 comets; California's Jet Propulsion Laboratory is plotting their future tracks. An asteroid two-thirds of a mile wide, at impact, would be enough to easily take out a good-sized European country. By comparison, an asteroid or comet believed to be six to seven miles across wiped out the dinosaurs 65 million years ago. The space explorers want the many smaller, but still dangerous asteroids tracked as well. Altogether, 3,611 near-Earth asteroids of all sizes have been discovered, with an estimated 100,000 more capable of setting off a tsunami the size of the one that shook the Indian Ocean last December. Scientists are carefully watching Apophis, which will whiz by Earth in 2029, passing within an unnerving 18,640 miles. That's a few thousand miles closer than many communications satellites and 220,000 miles closer than the moon. In 2036, the concern is that it will move in even closer, leading to the 1-in-5,500 chance it will strike. For a few hundred million dollars, the astronauts say, NASA could launch a scouting mission to Apophis in the next decade or two to place a radio transponder on the surface and thereby plot its course. But Donald Yeomans, manager of NASA's near-Earth object program, contends that mostly likely, radar and telescope observations will ultimately rule out any risk of impact. Mr. Schweickart agrees that based on the current odds, a deflection mission for Apophis would be a waste of money. "But the question is, do I agree with it when it's 1-in-100, when it's 1-in-50, if it's 1-in-20. That is a policy question. At what probability do you begin to spend hundreds of millions or billions of dollars in order to do something?" That's not the only sticky policy question. Are some places on the planet more dispensable than others? The point of impact, for instance, could be inadvertently shifted from one part of the world to another by an intervening spacecraft, jeopardizing one country instead of another. Who's liable if an asteroid-deflecting mission goes awry? Indeed, who decides if such a mission is needed and how far in advance should that decision be made? Nuclear electric propulsion would be ideal for quickly getting spacecraft to potential killer asteroids and nudging them out of Earth's way, the astronauts say. But the technology for such an "asteroid tugboat" is on hold, a recent casualty of budget cuts. Rep. John Culberson, R-Texas, is sympathetic to the astronauts' concerns and has asked NASA to see what might be needed to protect Earth from asteroid impacts. Nuclear-powered spacecraft could either land on the asteroid and apply a small but continuous force over months in order to alter its Earth-smashing course, or hover above the asteroid and use its gravity to push it aside. Forget about any sensational last-minute asteroid crackups, "Armageddon" style; the pieces could wind up on a collision course with Earth. Mr. Schweickart and Mr. Lu's B612 Foundation -- named after the home asteroid of the Earth-visiting prince in Antoine de Saint-Exupery's "Le Petit Prince" -- is pushing for an orbit-altering demonstration by 2015 on a harmless, way-out-of-the-way asteroid. The European Space Agency also is proposing a practice mission called Don Quixote to alter an asteroid's course, but it's yet to be formally approved. NASA's Deep Impact spacecraft smashed into a comet for scientific reasons in July; by design, it barely altered the comet's path. "We're sitting in a shooting gallery, with hundreds of thousands of these things whizzing around in the inner solar system. So it's just a matter of time," said Mr. Schweickart, board chairman of the B612 Foundation. Fortunately, the technology to protect us is ready for the task, he said, and that's "the beauty of it." ============================= ASTEROID PROBE YIELDS INSIGHT FOR PLANETARY DEFENSE Leonard David, Space.com Senior Space Writer
14 December 2005 BOULDER, Colorado – Following roughly two months of notable operations at asteroid Itokawa, Japan’s Hayabusa probe is damaged goods. Hindered by thruster and gyroscope breakdowns, the spacecraft is under makeshift attitude control with engineers hoping to finesse the craft onto a homeward-bound trajectory back to Earth. On Wednesday, the Japan Aerospace Exploration Agency (JAXA), announced that the troubled spacecraft would not begin its return flight back to Earth for at least another three years, owing to critical system failures including a fuel leak. Hayabusa was to begin its trek home in mid-December, when Earth and the asteroid it now orbits are at a relatively close distance. The probe was to drop a capsule in the Australian outback in June 2007. Whatever its destiny, Hayabusa, has generated priceless data for future treks to similar objects—by robots and humans. The intrepid robot is a heads up, not only for how best to utilize asteroid resources, but also to spoil a space rock’s aim if found to be on a direct-hit heading for Earth. Now some 180 million miles (290 million kilometers) distant from Earth, Hayabusa is over 340 miles (550 kilometers) away from Itokowa, chugging through space at a modest three miles (5 kilometers) per hour. A turning on of the craft’s propulsive ion engine this week is planned. Hayabusa is a project of Japan’s Institute of Space and Astronautical Science (ISAS), a research arm of JAXA. The multi-tasked robot not only deployed hardware atop the space rock. It made repeat touchdowns on the asteroid too. But whether it succeeded in bagging specimens of Itokawa—a goal of the complex mission—remain unclear. During operations at Itokawa, the probe released an ultra-small MIcro/Nano Experimental Robot Vehicle for Asteroid—MINERVA for short. But it was released too high above the asteroid with the camera-carrying device never reaching Itokawa’s rock-strewn surface. When it arrived at its target in September, Hayabusa began a close-up imagery sweep of the potato-shaped Itokawa, roughly measuring 1,800 feet (549 meters) long by 590 feet (180 meters) wide. "The rocky and rough surface of the asteroid was surprising," explained Donald Yeomans, Supervisor of the Solar System Dynamics Group at the Jet Propulsion Laboratory in Pasadena, California. "The 16-minute light travel time [between Earth and the spacecraft] makes real-time communications very difficult." The Hayabusa team did manage a near perfect touch-and-go operation on November 15, Yeomans pointed out, but the subsequent communications with the spacecraft was well below the nominal rate of data stream. Yeomans said that touching down on the surface of asteroid Itokawa was a tough assignment. "The Hayabusa Operations Team changed strategies and plans as they learned more about the navigation of a spacecraft near a nearly mass-less body," he said. Hayabusa operations spotlighted that rehearsals were very important for touchdown on the small asteroid, Yeomans said. "My personal opinion is that results from the Hayabusa mission can be used to engineer more robust strategies for future asteroid rendezvous missions," said Daniel Scheeres, Associate Professor of Aerospace Engineering at the University of Michigan in Ann Arbor. Scheeres said that the Japanese probe is a true "pathfinder" and an important technical demonstration mission. "The results from the current mission will be essential for developing a better understanding of the actual asteroid environment, and for making large advances in asteroid science," Scheeres told SPACE.com. "Clearly, the lessons learned from this mission will fundamentally influence all future asteroid rendezvous missions," Scheeres said. Over the years, various schemes have been proposed to deflect an asteroid found to be scary to Earth. Blasting an asteroid with focused sunlight, strapping rocket motors to one, detonation with with a nuclear bomb or just smacking it via a kinetic impactor similar to that used during NASA’s Deep Impact mission in July—all these and other techniques have advocates and detractors. What’s needed, however, is better understanding of asteroid structures before a deflection is undertaken. The Hayabusa mission has been closely monitored by officials within the B612 Foundation, an organization with the goal of significantly altering the orbit of an asteroid, in a controlled manner, by 2015. The group’s name stems from the asteroid home of the Little Prince in Antoine de Saint-Exupery's child’s story: The Little Prince. The foundation advocates honing the capability and technological wherewithal to anticipate and impede Earth-impacting asteroids. Of late, the group has been on the campaign trail to call attention to asteroid Apophis. The object makes an exceptionally close flyby of Earth on April 13, 2029. More importantly, this passer-by might have its trajectory altered during the swing-by, possibly putting it on a devastating direction toward Earth seven years later. The B612 group has advocated placing an active radio transponder on the object. Doing so at a fairly early date would yield the requisite orbital accuracy of the asteroid as it careens through space. It is no wonder that B612 Foundation chairman, Russell Schweickart, a former Apollo astronaut, has been keenly observing Japan’s Hayabusa mission, the loss of the MINERVA, as well as the touch-and-go cosmic choreography done by the probe. "Things don’t ‘fall’ normally around small cosmic bodies," Schweickart told SPACE.com from his office in Tiburon, California. "The local gravity is so low that any lateral velocity has an exaggerated effect. The behavior of objects around asteroids is counter-intuitive, if not absolutely chaotic," he explained. "Because of this low gravity, we B612’ers talk about ‘docking with’ a near Earth object and not ‘landing on’ one," Schweickart added. In fact, NASA astronaut Edward Lu. on the B612 Foundation’s board of directors, recently co-authored a plan with fellow astronaut Stanley Love for a "no touch" asteroid tractor. The idea is to use gravitational forces of a spacecraft to ever-so-slightly pull an asteroid into a non-threatening orbit if the object was indeed found to be on a collision course with Earth. Schweickart said that he’s eager to learn more about what Hayabusa was able to glean about its asteroid target, from finding out the mass of the space rock and its spin rate, as well as the orientation of the spin axis of Itokawa. "These are the sorts of parameters that we would have to determine prior to docking in preparation for an ‘asteroid tugboat’ type operation." Schweickart added. "Of course, for the stand-off gravity tractor, these things are not necessary bits of knowledge...only interesting." In some ways, deciphering genuine difficulties encountered by the Hayabusa mission itself from glitches in spacecraft hardware has been tough to do. Still, it is apparent that Hayabusa has offered both important science data regarding asteroids, as well as information on how to operate spacecraft around and on the mini-worlds, said Clark Chapman, a planetary scientist here at the Southwest Research Institute’s Department of Space Studies. He is also on the B612 Foundation’s Board of Directors. As an asteroid specialist, Chapman noted that he was thrilled by the images produced by Hayabusa, but very disappointed about the loss of MINERVA. "Remember this is a proof-of-concept engineering mission, not a science mission," Chapman explained. "We really do have to learn how to operate in the vicinity of an asteroid if we are ever going to use them for space resources or if we are going to have a reliable capability to deflect a dangerous one," he told SPACE.com. ============================= HOUSE NASA AUTHORIZATION BILL (DECEMBER 17, 2005) Following is NEO language from the House NASA Authorization Bill, which is presumably consistent with the final NASA Authorization Bill passed by both Houses of Congress on December 21: House Report 109-173 - NATIONAL AERONAUTICS AND SPACE ADMINISTRATION AUTHORIZATION ACT OF 2005
SEC. 321. GEORGE E. BROWN, JR. NEAR-EARTH OBJECT SURVEY. (a) Short Title -- This section may be cited as the 'George E. Brown, Jr. Near-Earth Object Survey Act'. (b) Findings -- The Congress makes the following findings: (1) Near-Earth objects pose a serious and credible threat to humankind, as many scientists believe that a major asteroid or comet was responsible for the mass extinction of the majority of the Earth's species, including the dinosaurs, nearly 65,000,000 years ago. (2) Similar objects have struck the Earth or passed through the Earth's atmosphere several times in the Earth's history and pose a similar threat in the future. (3) Several such near-Earth objects have only been discovered within days of the objects' closest approach to Earth, and recent discoveries of such large objects indicate that many large near-Earth objects remain undiscovered. (4) The efforts taken to date by NASA for detecting and characterizing the hazards of near-Earth objects are not sufficient to fully determine the threat posed by such objects to cause widespread destruction and loss of life. (c) Definitions -- For purposes of this section the term 'near-Earth object' means an asteroid or comet with a perihelion distance of less that 1.3 Astronomical Units from the Sun. (d) Near-Earth Object Survey- SURVEY PROGRAM- The Administrator shall plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near-Earth objects equal to or greater than 100 [apparently changed to 140] meters in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the Survey program to achieve 90 percent completion of its near-Earth object catalogue (based on statistically predicted populations of near-Earth objects) within 15 years after the date of enactment of this Act. ANNUAL REPORT- The Administrator shall transmit to the Congress, not later than February 28 of each of the next 5 years beginning after the date of enactment of this Act, a report that provides the following: (A) A summary of all activities taken pursuant to paragraph (1) for the previous fiscal year. (B) A summary of expenditures for all activities pursuant to paragraph (1) for the previous fiscal year. INITIAL REPORT- The Administrator shall transmit to Congress not later than 1 year after the date of enactment of this Act an initial report that provides the following: (A) An analysis of possible alternatives that NASA may employ to carry out the Survey program, including ground-based and space-based alternatives with technical descriptions. (B) A recommended option and proposed budget to carry out the Survey program pursuant to the recommended option. (C) An analysis of possible alternatives that NASA could employ to divert an object on a likely collision course with Earth. =========================== BACKGROUND FROM HOUSE COMMITTEE ON SCIENCE: REPORT ON H.R. 1022, DATED JUNE 27, 2005 PURPOSE OF THE BILL The purpose of the bill is to authorize the Administrator of the National Space and Aeronautics Administration (NASA) to establish a Near-Earth Object Survey Program to detect, track, catalogue, and characterize certain near-Earth asteroids and comets. II. BACKGROUND AND NEED FOR THE LEGISLATION Near-Earth objects pose a serious and credible threat. Recent press accounts of asteroids passing close to the Earth have raised public awareness of the possibility that a near-Earth object could one day hit the Earth with potentially catastrophic consequences. The monitoring and tracking of near-Earth objects will provide advanced warning of potential threats to the Earth, as well as promote advances in the field of astronomy. III. SUMMARY OF HEARINGS On October 3, 2002, the Subcommittee on Space and Aeronautics held a hearing to examine the status of nearby and potentially hazardous asteroids and comets known as near-Earth objects ('NEOs'). Witnesses included: Dr. Edward Weiler, NASA Associate Administrator for Space Science; Dr. David Morrison, Senior Scientist, NASA Ames Research Center; Brigadier General Simon 'Pete' Worden, U.S. Air Force; Dr. Brian Marsden, Director, Minor Planet Center, Smithsonian Astrophysical Observatory; and Dr. Joseph Burns, Irving Porter Church Professor of Engineering and Astronomy, Cornell University. The hearing addressed the risks posed by NEOs, the status of the current U.S. survey effort for NEOs, recommendations for extending current survey goals to include smaller, more numerous objects, and the challenges of data management. The hearing also examined NASA's current goal of identifying and tracking 90 percent of near-Earth asteroids larger than one kilometer in size by 2008. In addition, the hearing explored the question of next steps beyond this survey goal, including the costs, benefits, and technical challenges of extending the survey to include smaller, yet still potentially very hazardous, objects. Agency roles and interagency cooperation in the NEO survey effort were discussed, as well. Finally, the hearing addressed the role of amateur astronomers in this effort. Dr. David Morrison testified on the threat of collisions with asteroids and comets. He stated that the greatest risk today is not from objects large enough to cause global extinctions (such as is believed to have caused the extinction of the dinosaurs), but rather from objects large enough to perturb the Earth's climate on a global scale by injecting large quantities of dust into the stratosphere. Objects of about one kilometer in size pose such a threat and are thus the target of the current survey for NEOs. He stated that the next logical goal is to search for objects that could kill millions of people upon impact. Objects 200-300 meters in diameter, for example, pose the greatest tsunami danger. Dr. Morrison emphasized that the goal of the current survey is not to find objects on their final plunge toward Earth, but rather to identify objects in nearby orbits for future monitoring. Dr. Ed Weiler testified about progress of NASA's current ground-based survey for NEOs, given the current goal of identifying 90 percent of near-Earth asteroids larger than one kilometer in size by 2008. Dr. Weiler stated that there are estimated to be about 1,000 such asteroids, and that the six groups currently funded by NASA for such research have together discovered over 600 objects and are ahead of the predicted schedule. Thus, it is likely that the 2008 goal will be reached. As for extending the survey goal to comprehensively include objects smaller than one kilometer in size, Dr. Weiler felt that to pursue such a goal would be premature. Dr. Weiler stated that if such an extended survey effort were conducted from the ground, then NASA should not play a part in the survey effort because NASA is primarily an agency for space-based missions. He stated that NASA's role is better suited for detailed study of particular asteroids and comets, such as the NEAR-Shoemaker mission and the upcoming DAWN, Deep Impact, and Stardust missions. He also stated that new technology from the Nuclear Systems Initiative and the In-Space Propulsion Initiative should benefit future missions for detailed studies of asteroids and comets. Dr. Joseph Burns testified on the recommendations regarding NEOs from the recent National Research Council report entitled 'New Frontiers in the Solar System.' One of the primary recommendations in the report calls for NASA and the National Science Foundation to contribute equally to the construction and operation of a Large-aperture Synoptic Survey Telescope (LSST), a 6.5-meter-effective-diameter, very wide field telescope that could produce a digital map of the visible sky every week. Dr. Burns stated that the LSST could locate 90 percent of all NEOs down to 300 meters in size, enable computations of their orbits, and permit assessment of their threat to Earth. Dr. Burns testified that NASA should continue to be involved in ground-based NE |
