New idea on asteroid defense Options

[dvandorn]

OK -- before y'all get all het up over the topic title, let me emphasize that this is *my* new idea for asteroid defense. I want to know what people think.

My idea deals with the subset of NEOs that are rubble piles. I'm assuming that a rubble pile is made up of numerous small bodies ranging from sub-micron size up to pieces of solid rock as large as 20 or 30 meters across.

My idea is based on the concept that the Earth's atmosphere can handle the impact, over a period of days and weeks, of thousands of tons of meteorites without generating catastrophic atmospheric heating. The reason the entire mass of an asteroid will cook you whether it comes in intact or in millions of pieces is based on the concept that the entire mass enters the atmosphere within a very short time frame.

So -- if you can bust a rubble pile apart such that the rubble enters the atmosphere over a period of days, or weeks, and if you can push the larger frags away from impacting trajectories, you'd be reducing the overall impact of even a large-ish rubble pile. Depending on how much mass is in the entire pile, you could reduce the overall impact of the event to eliminate any serious threat to life on Earth.

So -- the idea is to choose a point in the asteroid's orbit where you can maximize the spread of the rubble into the largest ellipse possible prior to its impacting the Earth. You use whatever means is most efficient to effect a *relatively slow* disassembly of the rubble pile into this disperse ellipse. And here's the point that I don't think I've read or heard anyone come up with before -- you attach propulsion and attitude control systems to the largest remaining chunks and steer them into trajectories that are designed to 1) disperse the remaining rubble even further, and 2) push them onto trajectories that don't impact Earth.

This is why you want the *relatively* slow initial breakup speed. You use the gravity interactions between the large chunks in their planned traverses of the rubble to spread it all out to your specifications.

If you have a good decade to plan and implement such a defense to a given body, I think it might be one of the few strategies that could be done within our current technologies. It would be expensive -- you'd have to jet around within the initial debris field, attaching propulsion modules to the biggest chunks, and you wouldn't be able to design your large-chunk trajectories until after the breakup was effected. It would take a lot of energy for the maneuvering, and you'd have to have rather massive armor to jet around within the rubble field. But it's do-able with current technologies, if not easily.

-the other Doug

[lyford]

let me emphasize that this is *my* new idea for asteroid defense.

Are you sure you thought this up on your own?

[nprev]

97310 with six guys left? Haven't seen a 'Stroids score like that since high school...

oDoug, it sounds possible but I wonder about practical. Seems like this would require a very large & labor-intensive manned mission to accomplish the fracturing & attach the deorbit packages to the major chunks. I also wonder about the risks to the crew (or even to an armada of extremely sophisticated unmanned vehicles) during the breakup phase.

Shooting from the hip, here, I'd estimate the price tag at about $20 billion with at least five years of development time (and also assuming that a lot of readily adaptable off-the-shelf hardware like the mature Constellation fleet is available). Worth it, of course, if it works & we face a significant impact threat

[JRehling]

It seems to me that given enough lead-time, the best approach is to nudge the thing off course so that it just misses the Earth. If you only have to nudge it by 4,000 km and you have lead-time of a year, then naively you only have to impart a delta-v of 0.13 m/s.

Naturally, for larger bodies, small delta-vs still translate into a lot of kinetic energy, but then, so does blasting an object apart. I'm sure that less kinetic energy is involved in a nudge than an explosion (which would naturally accelerate the individual pieces by much more than 0.13 m/s). A nuclear weapon might end up doing more nudging than blowing-apart regardless of our intentions.

For really long lead time (multiple orbits), I think the desirable situation is to determine on which upcoming pass the object would come nearest the Moon and then just steer it right into Luna, eliminating that particular threat permanently.

[nprev]

For really long lead time (multiple orbits), I think the desirable situation is to determine on which upcoming pass the object would come nearest the Moon and then just steer it right into Luna, eliminating that particular threat permanently.

Wouldn't that be a bit more difficult to accomplish in terms of guidance requirements given that the Moon's orbit is geo- rather than heliocentric? Seems as if the delta-V would have to be extremely precise, and I don't know of a way to make large changes in velocity with great accuracy. (Not so bad with mass drivers or ion thrusters, but of course these take considerable time).

My take on the whole thing is that, generally, any delta-V that takes a threatening asteroid out of an uncomfortably close encounter ellipse (guess "prolate spheroid with semimajor axis roughly aligned along the object's net orbital motion vector" would be more accurate ) is all that's needed. We can get fancy later when it's time to start mining the things.

BTW, that brings up a poser: What do we do if we find a threatening object that turns out to be very rich in metals or volatiles (long-period comets excluded because, uh, they'd exclude us in any case)? I'm thinking that we'd want to do more than just deflect it or destroy it, we should think about putting it in an accessible orbit for later use.

[tty]

If you have time enough I think the "gravity tow" concept is best. It will work on a rubble pile too. And if you don't have time enough, then I would suggest that the least bad alternative would be to use one or more penetrating nuclear charges, and hope to bust it up into pieces small enough to air-burst. That would be nasty, but probably not as nasty as a direct hit.

Also you might want to be a wee bit careful about moon impacts, a lot of the secondaries would probably end up on Eart. Now a Mars impact on the other hand....

[Del Palmer]

BTW, that brings up a poser: What do we do if we find a threatening object that turns out to be very rich in metals or volatiles (long-period comets excluded because, uh, they'd exclude us in any case)? I'm thinking that we'd want to do more than just deflect it or destroy it, we should think about putting it in an accessible orbit for later use.

Good thinking, although it would be nice to study it up-close before we mine the heck out of it...

Regarding disposal a la luna, I don't think that would be compatible with expected future uses of the Moon.

[Guest_PhilCo126_*]

By the Way... This year SpaceGuard will celebrate its 10th anniversary:

http://spaceguard.esa.int/SSystem/SSystem.html

http://impact.arc.nasa.gov/presentations_main.cfm
Philip

[peter59]

Tonight, binary asteroid 2008 BT18 passed 1.4 million miles from Earth.

http://www.universetoday.com/2008/07/14/bi...des-past-earth/

[Greg Hullender]

Also worth mentioning is that NASA's offical word on the subject is that "nuclear stand-off explosions were found to be 10-100 times more effective than the non-nuclear alternatives".

http://neo.jpl.nasa.gov/neo/report2007.html

This is the full report:

http://www.nasa.gov/pdf/171331main_NEO_report_march07.pdf

Rusty Schweickart makes a counter argument that although the other methods aren't as powerful, they're only needed for really big rocks, and by 2020, NASA will already know where all of those are.

http://www.sciam.com/article.cfm?id=nasas-...nuclear-weapons

Oh and everyone seems to agree that fragmenting the asteroid makes things worse, not better. I can guess why, but I haven't seen that clearly spelled out anywhere.

--Greg

[Thucydides]

Most asteroid defense schemes fail because they are too slow or too limited in effect. Many Earth crossing asteroids have been spotted literally "at the last minute" rather than 5 or 10 years in advance, and that leaves very little time to send a mission, much less decide which of the various alternatives will work out best.

The answer has to be very high performance vehicles; high thrust and high ISP; which only leaves the Orion nuclear drive. "Next Big Future" outlines a conceptual high performance interceptor here: http://nextbigfuture.com/2009/02/unmanned-...lear-orion.html, but this paragraph sums it all up:

Get to high velocities with only a few explosives and small shock absorbers or no shocks at all. Launch against a 100 meter chondritic asteroid coming at 25 km/sec. 1000 megatons if it hits. Launch when it is 15 million kilometers away and try to cause 10000km deflection. A minimal Orion weighing 3.3 tons with no warhead would do the job. 115 charges with a total of 288 kiloton yield. Launch to intercept in 5 hours. Ample time to launch a second if the first failed.

A Gigaton of kinetic energy will ring anyone's bells, and even a rubble pile asteroid will have a significant fraction of its mass converted to vapor or plasma, and the rest diverted into many non Earth crossing orbits. The nose of the spacecraft can open up like an umbrella once clear of the atmosphere to ensure the energy is transferred to the asteroid and not lost by punching through the mass of the target.

A more versatile and capable Orion vehicle would include shock absorbers that are unlocked after clearing the atmosphere and the ability to go at a much more leisurely pace. If the asteroid was a rich source of metals and volatiles, a soft "landing" could be arranged and the Orion used to gently nudge the asteroid into a safe orbit for exploitation.

The physics is easy, managing the political considerations and deflecting the "junk science" objections would make the project very hard......

[Vultur]

Yeah, I don't think the public opinion would ever let NASA build an Orion...

Unfortunate, because the fallout would be insignificant compared to the effects of being hit with an asteroid. (Some things I've seen make it sound like it would be insignificant, period, with modern technology; apparently the right kind of launch plate would help a lot.)

[SpaceListener]

I think that the most feasible solution would put a pair surveillance satellites at two Lagrangian points: L1 (near to Sun) and L2 (shadow from Moon). On the other hand, I think that the selection of these points L1 and L2 is due to the fact the most asteroids travel to and away from Sun. I might be wrong.

[nprev]

Re NEO detection, the existing ground-based programs (Spaceguard, LINEAR, etc.) are doing an outstanding job. I don't think that a space-based asteroid survey system of any sort would provide any significant gain in the discovery rate at this point, and certainly not enough to justify its cost.

[SpaceListener]

Re NEO detection, the existing ground-based programs (Spaceguard, LINEAR, etc.) are doing an outstanding job. I don't think that a space-based asteroid survey system of any sort would provide any significant gain in the discovery rate at this point, and certainly not enough to justify its cost.

Why not significant gain?

There, the view has much better vision so the time of anticipation is sooner.

About the cost, don't mind it since any hit of asteroid on Earth might out-weight to the mission cost.