Planetary Resources has us thinking about mining the asteroids to extract useful materials, but learning more about these objects will benefit us in all kinds of ways. Not only do asteroids offer up clues about the early Solar System, but getting to understand their composition and structure will be a key element in any future plans to change an asteroid trajectory. The topic comes to mind periodically as various asteroids make close approaches, and right now I’m looking at asteroid 2012 DA14, which will close to within 22,000 kilometers this coming February.
2012 DA14 is a small asteroid, discovered in early 2012 at the Observatorio Astronómico de La Sagra in Spain, and it is not an impact threat for us next year, although prudence dictates keeping an eye on it for future orbits — the object is recently enough discovered that we’ll need to study it longer to get a better read on future encounters. I see that the University of Central Florida is organizing a viewing party in Orlando on February 15 to track the progress of the asteroid as it zips past us, with Michael A’Hearn, who led the Deep Impact mission, and Harold Reitsema (B612 Foundation) on hand to discuss asteroid research and tracking projects.
Meanwhile, an interesting story comes out of MIT involving a graduate student in the Department of Aeronautics and Astronautics there named Sung Wook Paek, author of a new paper on asteroid deflection. Paek’s notion is that pellets of paint powder launched from a spacecraft close to a problematic asteroid could be used to greatly increase its albedo. The now more reflective asteroid would be nudged off-course slowly but surely by solar photons. All of this would depend on getting to the asteroid long enough in advance to let the method work.
Paek’s work grew out of a call for papers from the United Nations’ Space Generation Advisory Council, whose technical paper competition Paek was able to win, a feat that took him to Naples to present the paper at the International Astronautical Congress in October. The competition was all about new ways of deflecting an asteroid, many of which involved launching a projectile to collide with the object, or setting off a nuclear device near enough to it to disrupt its orbit. We’ve also discussed methods like ‘gravity tractors’ in these pages, where the tiny effects of a spacecraft’s gravitational field work, over time, to draw the asteroid into a new orbit.
Image: The more methods for asteroid deflection we examine, the larger our toolkit in case we ever do find one on a dangerous course. Credit: GETTY.
In Paek’s method, the paint pellets would contribute their own impact to help bump the asteroid slightly off course, while the paint itself would eventually take advantage of solar photon pressure. Using the asteroid Apophis as his model, Paek calculated that five tons of paint would cover the surface (Apophis is about 450 meters in diameter) in a five-micrometer thick layer. Total time to move the asteroid out of an Earth-bound trajectory: 20 years, highlighting the need to get to such objects as soon as possible. Lindley Johnson, program manager for NASA’s Near Earth Objects Observation Program, calls Paek’s proposal an innovative variation on various methods to use solar radiation pressure. In any case, having a wide range of deflection options is only prudent in the event we ever do discover an asteroid on a truly threatening trajectory.
Ao you’ve got an asteroid painted, with the idea that over time solar radiation will cause a deflection. (What a really splendid idea!)
Now … assume you have a large laser in solar orbit for propelling spacecraft with light sails. Which no one can economically justify at present ,,,,
I see a convergence of interests.
You triggered my curiosity re: the Space Generation Advisory Council, which led to my finding their website.
All we need now is to find a few asteroids full of gold that might get things kickstarted for another space race? ;-)
Cheers, Paul.
There is no substitute for a hydrogen bomb.
Adapt it: use a convenient asteroid as a basis for a large planetary probe. Put instruments all over the surface, paint one side (or add a sail — good idea — or add a small NTR using asteroid material as reactive mass), and let it go wherever it needs to be sent.
I thought I’d read about the paint idea back in the 90s.
This method has the disadvantage that it works only once on any given asteroid. If the same one ever poses a threat again in the future (a higher solar orbit does exclude does not exclude it from intersecting with that of Earth later again).
Paul, just FYI:
A Permanently-Acting NEA Mitigation Technique via the Yarkovsky Effect
http://aeweb.tamu.edu/aemp/resources/albedo.pdf
Wrapping a superconducting coil around the waist of the rock and powering it with a nuclear or photo cell power supply would create a large magsail effect which could be used to deflect the rock a little to miss the earth. On creation of the field we could then use a standoff nuclear weapon whose ionised fallout would impact the field giving an added push if needed.
GaryChurch’s point is spot on :)
Systems that work gradually, like using orbiting masses, lasers, and this technique using solar photon pressure are only useful if you have a great deal of time to act before hand. Good to have, efficient, and, when appropriate, the first and best choice in your toolbox, but you need a serious heavyweight system behind it.
It would be rather tragic if political difficulties prevent Earth from having an H-bomb asteroid defense system when a large mass is detected on a sure collision course with only months to react.
Something to keep in mind with these Earth orbit-crossing asteroids is that all such subtle collision-avoidance schemes are not permanent. All they really do is alter the orbital parameters. While this means that a collision from a near-future crossing may be avoided, the same cannot be true for all future crossings. It can take a billion years but in time there likely will be a collision.
That may be sufficient for our purposes but it is not a permanent solution. Neither is shattering the asteroid since it just creates multiple smaller asteroids, most of which will have similar but different Earth-crossing orbits.
“Neither is shattering the asteroid”
That is just in the movies. An H-bomb would be detonated near the surface to push it.
The same specially designed directional bombs, AKA pulse units, are the ony practical method of propelling a spaceship through interplanetary space. They can also be used to push things besides spaceships.
But the one thing you cannot do is light them off in the Earth’s magnetosphere without the fallout eventually coming to Earth,
Fortunately we have the perfect place to assemble, test, and launch a nuclear mission, and also fill up a cosmic radiation shield with water; The Moon.
New and Improved Antimatter Spaceship for Mars Missions
http://www.nasa.gov/exploration/home/antimatter_spaceship.html
JoeP said on October 30, 2012 at 14:40:
“It would be rather tragic if political difficulties prevent Earth from having an H-bomb asteroid defense system when a large mass is detected on a sure collision course with only months to react.”
Or a group of fanatics who think that the PHA is part of “God’s Will” and want it to hit Earth.
Yet another reason why we need to start colonzing space NOW.
Mephane:
Not quite. The next time around we could use black paint….
Does anyone know how the paint would behave in micro gravity on the dusty surface of a tumbling asteroid? Since the obvious answer is no, how can we know just how much affect the paint might have on any particular asteroid? If we don’t know the exact amount of push that would be generated, how can we be sure that we are not going to increase the chance of collision rather than avert one? I prefer GaryChurch’s technique.
Great idea ! Now beware, it would work only non rotating objects. I assume most of the asteroids do rotate, do they? thus cancelling the effect of solar photons over one rotation period
I agree with GaryChurch and JoeP–asteroid deflection should be thought of in the same way as a ballistic missile defense system which offers boost, post-boost, re-entry, and terminal descent options to destroy incoming missile warheads. Thus:
The long lead-time paintball, Yarkovsky effect, and gravity tractor methods would be analogous to the boost and post-boost anti-ballistic missile options. The thermonuclear bomb method that would be used to nudge an asteroid (or fragment it, depending on the device yield, its detonation distance from the asteroid, and the asteroid’s size and physical strength) would be analogous to the short-range, nuclear-armed ABMs (Anti-Ballistic Missiles) that the U.S. Safeguard ABM system used (the Soviet/Russian ABM system is still deployed around Moscow). Also:
Both long lead-time and short-warning time asteroid deflection options are needed because we cannot count on having the luxury of years or decades to deal with a threatening asteroid. Also, any long-period comet that was found to be on an Earth impact trajectory would almost certainly afford little warning time, and a thermonuclear bomb would have a greater effect on an icy comet nucleus than on a rocky or metallic asteroid.
@Ron S:
Shattering is a fine idea, so long as the pieces of debris all are small enough that they just burn up in Earth’s atmosphere. The problem is how to achieve that, just setting off a nuke on the asteroid’s surface would most likely not suffice.
Both paint and solar sails work with reflected sunlight. The question becomes which approach has the lowest mass per unit perpendicular area. I suspect that extremely thin solar sails can achieve a lower mass per area. The sail starts with a factor of approximately three since it is a relatively flat surface instead of a 3-D potato shape. Sails would also address Mephane’s point about the one time use. The only advantage of paint would be simplicity, particularly with rotating asteroids.
My only concern with a nuclear strike is the possibility of fragmenting the incoming planetoid so that instead of one big space rock to worry about, we will then have many space rocks striking mulitple places on Earth.
Remember the Tunguska event of 1908 was caused by a chunk of celestial matter smaller than the original estimate of a ten-story building in size. Had it hit a city instead of the Siberian wilderness, we would have seen a Hiroshima level event forty years before the real one.
Since planetoids and comets will be zipping past and at us for ages to come, colonizing space is our real best bet against species degeneration or extinction.
Mephane, there is no way to achieve uniformly small-sized shrapnel. If we could, I would only partly agree with your conclusion since many of the pieces would miss Earth and survive to fractionally increase the space navigation hazard.
This is not unlike “space wars” where one blows up a satellite. The pieces become a long-term hazard until they (due to their smaller size, and more eccentric orbits) reenter the atmosphere.
Jim Early == the notion was that solar sails riding on laser beams look like a beautiful idea on the back of an envelope, but might be dificult in reality because of the high cost of a solar-orbiting laser, especially if there just isn’t much demand for any form of spacecraft, Which is the present situation. OTOH, if the cost of developing a big solar orbiting laser can be partially ascribed to an asteroid avoidance system, the economics might change….
“Shattering is a fine idea”
Hmmm. I don’t think so. Not if it is a planet killer. There are city killers, civilization destroyers, and planet killers. Cracking a planet killer just makes a bunch of civilization destoyers that might render us extinct anyway. A city killer could get away with cracking it but why? You have to hit it exactly when just getting close to it and detonating will deflect it.
The H-Bomb would be very effective against Comets, they are mostly water ice and other volitiles ices, heating would cause massive out gassing driving it to vapourise and fall apart, hopefully not hiding great chunks of Iron.
A nuclear explosion above the surface of an asteroid would be ineffective, most of its energy would be lost into space.
In my opinion, the best way to deflect an asteroid is to bury a nuclear charge at just the right depth and detonate it. The result would be an almost intact asteroid, but with a huge crater in it. The ejecta would be thrown into space with nearly the full energy of the explosion, and serve as reaction mass. The asteroid would be deflected much more than a surface explosion could ever achieve.
“Does anyone know how the paint would behave in micro gravity on the dusty surface of a tumbling asteroid?”
Exactly my thought. There’s something of a difference between, “A five micrometer thick layer of paint on a 450m sphere would weigh five tons.” and “Five tons of paint (Applied by any feasible process) would leave a five micrometer thick layer on a 450m asteroid.” Putting a thin layer of paint on top of dust isn’t a trivial task. Think surface tension…
Evaporating aluminum onto the asteroid might be a feasible approach; You could probably build a fairly robust radio-isotope powered system for evaporating aluminum, and deposition would hardly disturb the surface at all, while providing a very reflective surface. Further, as the effective thickness is only a fiftieth as thick is needed compared to the paint; The aluminum and deposition system could probable be lighter than the paint alone.
Dawn Sees “Young” Surface on Giant Asteroid
10.31.12
Like a Hollywood starlet constantly retouching her makeup, the giant asteroid Vesta is constantly stirring its outermost layer to present a young face.
Data from NASA’s Dawn mission show that a form of weathering that occurs on the moon and other airless bodies we’ve visited in the inner solar system does not alter Vesta’s outermost layer in the same way. Carbon-rich asteroids have also been splattering dark material on Vesta’s surface over a long span of the body’s history. The results are described in two papers released today in the journal Nature.
“Dawn’s data allow us to decipher how Vesta records fundamental processes that have also affected Earth and other solar system bodies,” said Carol Raymond, Dawn deputy principal investigator at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
“No object in our solar system is an island. Throughout solar system history, materials have exchanged and interacted.”
Full article here:
http://www.nasa.gov/mission_pages/dawn/news/dawn20121031.html
To give us a somewhat terrestrial scale idea of how much paint weighs in bulk, when they removed the white paint from the external fuel tank on the Space Shuttles after the first two missions in 1982 and for the rest of the flights, they saved over 600 pounds in liftoff weight.
After hearing about all these high-tech schemes to avoid a collision, I am beginning to think that it would be cheaper and less disruptive to just let the rock hit us. The impactor (per completeness of NEA surveys) will most likely be well under 1 km in diameter. The impact will be precisely predicted, and so will its effects. So move any population out of the way (tsunami zones, impact zone) and then rebuild. I bet it would be more economical and loss of life would be kept low since the predictions would be accurate.
I know, this is nowhere near as exciting as setting off bombs, holding interplanetary paintball tournaments, or the making of follow-up heroic movies.
Ron S: I think there was a movie like that.
I was irritated that they didn’t nuke it :-)
Ron S said “The impact will be precisely predicted”, and though I can imagine that for a meteorite whose trajectory intersects us like a bullseye, I would find that hard to believe that for a grazing approach which would be much more sensitive to the initial conditions. Since the Earth has a significant gravitation focusing effect there should be more of that second type.
“A nuclear explosion above the surface of an asteroid would be ineffective, most of its energy would be lost into space.”
No…..directional bombs, as a I wrote earlier in the thread; “The same specially designed directional bombs, AKA pulse units, are the ony practical method of propelling a spaceship through interplanetary space. They can also be used to push things besides spaceships.’
A trillion or so dollars (we do not know exactly how much) spent on directed energy star wars weapons makes your statement “most of the energy wasted” not very credible.
GaryChurch:
Conservation of momentum dictates that even the most “directed” weapon will be directed in two opposite directions, one of them missing the asteroid entirely. For the other half, there is the issue of reaction mass: If only the mass of the bomb itself is available, use of energy to impart momentum will be very inefficient.
Energy/momentum efficiency will be highly dependent on how large of a fraction of the asteroid itself is used for reaction mass, and this fraction is certainly a lot larger for a subsurface explosion than an above surface one.
For these reasons, I do stand by my assessment, regardless of the amount of money that was spent on directed energy star wars weapons. A lot of money was spent on bunker busters as well, and while neither of the two was developed for our present purpose, I would submit that the latter are likely more useful here than the former.
Well, I guess you are right. Explode the device after it penetrates with the directed energy end pointed “up” and it will blast a huge amount of material away from the planet and this is going to shove it harder than a space ship pulse unit. But this is unnecessary for a city buster, which is only a small rock and not a desirable counter for a civilization destroyer, which might just shatter into a bunch of city busters. Absolutely for a planet killer- taking care not to shatter it into multiple civilizations destroyers. Whether you hit it with a plasma pulse just above the surface or penetrate and use ejecta depends on the size of the threat.
” it will blast a huge amount of material away from the planet ”
Sorry, from a asteroid or comet of course, not planet.
GaryChurch, I am a little confused with your following comment “for a planet killer- taking care not to shatter it into multiple civilizations destroyers”. And here is my problem.
It is my understanding that for a planet killer (unlike for your other classes), it is not the effect primarily derived from the blast, but the total heat dumped onto the Earth’s crust that is the agent of destruction. This would seem to remain exactly the same if it is broken up, especially if you consider that the gravitational field of an asteroid this size would be sufficient to prevent these fragments separating very far (unless we employ truly colossal, and highly directed energies to do so). Am I missing anything?
Yes, it would be important to keep the explosion shallow enough to avoid shattering the asteroid into fragments that go forward or backwards instead of sideways. This will be highly dependent of the material and texture of the rock. A solid blob of iron will work a lot better than a heap of rubble…
“Am I missing anything?”
Just assuming I am. Yes, it would still be a planet killer.
Oh yes I just read Sherwin Williams is teaming up with Air-Soft to make a paint ball that will work between
-675 K and 9000K and be applied via a 25 mile long rail gun powered by a tesla coil the size of New Jersey
Lots and LOTS of work has been done on using nuclear weapons to deflect asteroids and the nominal height of detonation above the surface is somewhat surprising, as it’s measured in meters. We’ve got lots and lots of nuclear weapons, so this is the method of choice for ANY size asteroid. Especially since deployment and operational times are short compared to any of the other methods. Even a rubble pile civilization buster could be handled when it was quite close to the earth, since any deltav imparted would cause most of the mass of the fragments to miss the earth. In any case, it’s much better to have kiloton sized explosions at 15-30 miles altitude than thousand megoton sized ones at the surface! (the flux of kiloton sized objects is roughly 5 a year, to within a factor of a few). The earth’s atmosphere has quite a high heat capacity and roughly half the energy will be radiated back into space…..(one Very Bad Astronomer I know has never grasped this, even when explained to him using small words).
Review: Near-Earth Objects
The occasional close flyby of the Earth by a small asteroid provides regular reminders of threats—and benefits—such objects pose to us. Jeff Foust reviews a book by a leading expert on near-Earth objects about the peril and promise of these bodies.
Monday, November 26, 2012
http://www.thespacereview.com/article/2192/1
http://www.technologyreview.com/view/508906/mars-astronauts-likely-to-witness-1-megaton-asteroid-impacts/
The Physics arXiv Blog
December 17, 2012
Mars Astronauts Likely to Witness 1 Megaton Asteroid Impacts
The latest estimate of asteroid impact probabilities on Mars suggests a three year mission would experience a 1 megaton event
Asteroid impacts are among the most feared of natural catastrophes. So estimating the risk they pose to humanity is an important task.
One method is to look at the number of impacts in the past and use this as a guide to the future. This isn’t entirely straightforward since the distribution of crater sizes we see today depends not only on the rate of impact in the past but also on the rate of disappearance via processes such as erosion, tectonic changes, obliteration by other craters and so on.
Nevertheless, various groups have measured the distribution of crater sizes and come up with estimates of future impact probabilities.
Today. William Bruckman and pals at the University of Puerto Rico at Humacao do exactly this kind of analysis but with a twist. They derive impact probabilities for Earth but also for Mars. Their conclusion is that astronauts visiting Mars for just a few years are likely to witness a significant asteroid impact.
Bruckman and co’s work is one of mathematical modelling and testing. These guys have created a model that describes the rate of impact on Earth and tested it against the existing data.
Their model suggests that Tunguska-type events of around 10 megatons should occur roughly once a century and smaller 1 megaton events once every 15 years. They say that both these predictions are compatible with crater counts and most other estimates.
Emboldened by this success, they apply the same model to Mars, where impact rates are likely to be higher because of its proximity to the asteroid belt. Here’s the interesting part: these guys calcaulte that Mars experiences a 1 megaton event every three years.
That’s significant because future missions to Mars may well last several years. “We expect that Mars visitors spending a few years there will have a high probability of witnessing a megaton-type meteorite impact.” they say.
That’s could have an important impact on any mission. “These impacts are likely to cause more damage on the surface than on our planet, due to the much lower atmospheric Martian density,” they conclude.
The one problem of course is how this squares with the actual experience of exploring Mars using robotic landers and rovers. These missions have together clocked up several decades on the surface. It’s not at all clear that any of them have been hampered by, or even noticed, a 1-megaton asteroid impact.
Nevertheless, these kind of predictions require further study.
Any visitors to Mars will be no strangers to danger, of course. A mission would involve the significant risk of launch, a landing on a foreign planet and a launch home again, plus the intense radiation throughout both legs of journey and the time on the Red Planet. As if that weren’t enough, they’ll now have to worry about the possibility of a megaton asteriod impact.
All the more reason, if any were needed, to rely on the cheaper, safer, more capable efforts of robots for the foreseeable future of Martian exploration.
Ref: http://arxiv.org/abs/1212.3273: Earth and Mars Crater-Size Frequency Distribution and Impact Rates: Theoretical and Observational Analysis