Ok; CNN does it again.
Yes; we've discussed the odds of an asteroid before. Well this article doesn't seem to be as bad as usual (although there's alot to pick on), but; the reason I'm here is the following:
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.
Hover? Gravity? of the spacecraft? Does anyone know what they are talking about?

Finally, an answer: asteroid tractor
But; another question.
"method won’t disturb the asteroid’s rotation or composition."
I understand not disturbing the composition, and not disturbing a lot of other factors. But what are the effects of disturbing the rotation? Does it have something to do with the stability of it's trajectory?

APOD has an illustration.

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Everything I need to know I learned through Googling.

How NOT to Deflect an Asteroid

Impactors are the greatest threat this planet faces, posing a greater threat than any hurricane or tornado. And yet we have fewer numbers of researchers examining the sky for comets and asteroids than we do meteorologists, who derive their professions name specifically from the impacts of space rocks upon our atmosphere, often with catastrophic results, as in the Tunguska event.

We have yet another killer space rock inbound, whose strike potential has proved to be more likely than once thought:
http://www.space.com/news/051103_asteroid_apophis.html

As bad as this news is, we have even greater cause for concern in that the organization that has championed the cause of Asteroid Defense has described a deflection method that is highly questionable to say the least:
http://www.space.com/businesstechnol...d_tractor.html

I am not an anti-nuclear activist, though many in academia seem to be (Jay Melosh, Michio Kaku, etc. )

But neither am I the only one who has concerns with the nuclear electric approach:
http://www.newscientistspace.com/art...astronomy.html
http://www.spacedaily.com/news/nuclearspace-04d.html


Yet this concern repeatedly falls upon deaf ears thanks to the infatuation many have with this technology on the part of individuals who have no experience in space propulsion and absolutely no interest in the launch vehicles needed to orbit them safely. One only needs to consider the repeated failures of The Planetary Society and its schizophrenic penchant to place overthought payloads atop underperforming launch vehicles like Volna.

The safety of the Earth is simply too important to be left in the hands of such amateurs.

The problem stems from indifference on two levels:

A.) Indifference to the absolute necessity of a robust space program on the part of the general public, and worse;
B.) The even greater level of indifference and outright hostility shown to the launch vehicle development community on the part of scientists and payload designers who fail to appreciate big rockets because they aren't sexy enough.

The B612 Foundations scheme for diverting asteroids consists of having a spindly, undersized version of an NEP/JIMO contraption "draw off" an asteroid by perturbing its orbit--using only the mere presence (no contact!) of the spacecraft... rather like how a mouse is supposed to intimidate an elephant I suppose.

"Maybe if we stared at it hard enough it'd..."

But if the actual collision of the Deep Impact craft upon its target was likened to "a gnat getting hit by a tractor-trailer rig," how are we supposed to take B612's concept seriously?

I have many questions about this technology:

What if a small meteoroid strikes the asteroid to be deflected, negating the already negligible influence the undersized JIMO type craft could ever have?

Is there any "surge" capability in such low thrust craft? (Hardly)

What if a fragment of a meteoroid punches a hole in the craft's radiators --which are a must in order to shed heat?

Can such a first generation nuclear craft start with the same reliability of the latest generation of nuclear submarines?

Can such a low thrust craft even be built?

And most importantly...

Shouldn't you at least have a big chemical upper stage to push the craft out of Earth/Moon so you can responsibly pull the rods?

If the answer to the question above is yes (to save wear and tear during the slow spiral out), why not save a step--and a lot of development money--and just have a big chemical interceptor to start with?


A simple, rugged fuel tank loaded with propellants will also have the mass needed to draw an asteroid away from its threatning orbit. Plus, such a rocket stage could also make contact and use its own thrust in an emergency. A nuclear thermal craft combines higher Isp and thrust. The JIMO type craft described by B612 is too small and weak to have much influence, gravitational or otherwise.

So why not use the same HLLV architecture that Griffin and others have called for as part of VSE, and leave NEP at home for now seeing that Apophis is closing quickly and Congress moves slowly? http://www.spacedaily.com/news/oped-04zc.html
http://www.xprizenews.org/News/index.php?p=1059

Could it be the hostility on the part of the scientists to the real concerns of engineers and 'launch vehicle boosters' that I described?

Probably.

Isn't Earth's safety more important than such childishness?

Certainly.

Let me leave you with this:

What many NEP-apologists fail to admit is that JIMO was getting to be such a mass pig that it would have taken an HLLV to get it in space to start with--at least to do it right. Otherwise, with Titan extinct, you must use the same troubled ISS piece-at-a-time assembly process, with each load atop lousy no-engine-out EELVs like this one:

http://spaceflightnow.com/delta/d310...launch/03.html
http://www.spacedaily.com/news/oped-05zi.html
http://www.spacedaily.com/news/oped-05za.html


Now imagine a nuclear pile atop that.

Any Questions?

Good.

So write your congressman. Support HLLV and Mike Griffin.

And tell B612 to begone.

Okay, time for a little refresher in nuclear chemistry...

Everybody knows how Uranium-235, the nuclear fuel of choice, has an extremely long half-life, right? Some thousands of years... anyway, the thing to know is that the half life and the radioactivity are inversely proportional, so...

Uranium-235 is basically non-radioactive

In fact, as far as the radioactivity goes, its barely measureable. Its far too low to hurt anybody, and you can handle large quantities of it in your hands with nothing more than latex gloves. Its chemical toxticity is far, far, far worse than its radioactivity.

What makes a nuclear reactor so deadly then? The radiation is produced by the nuclear fission reaction and by the decay of the fission products ("nuclear waste"). The thing to note though, is that nuclear fission doesn't occur and no signifigant radiation nor waste is produced until the reactor is actually brought to criticality and activated.

Hence, a "fresh" reactor sitting in a rocket on the pad produces essentially no nasty radiation, and won't until it is safely in orbit and activated. If there is an accident and the reactor crashes? Big deal, its not radioactive yet! A fresh reactor produces much less radiation then RTG generators used on space probes.

The Uranium will also be in the form of a ceramic oxide, which if it were to be smashed on rocks if the reactor crashed, would break into big chunks and not be reduced to a powder that would pose a breathing risk. It is also completly insoluble in water (even salt water), and wouldn't disolve and be dispersed in the environment. Uranium oxide is probobly less reactive and toxic than plain old Uranium metal too.

Launching a reactor cold is just not a big risk, its about like launching a big cylinder full of lead oxide.

And say if the reactor had a problem after being activated but is still in Earth orbit? Well thats not a big problem, since the damaged reactor would be safely over a hundred mile away from anybody on Earth and would stay there for years until the fuel was exhausted (after melt down) and the short-lived highly radioactive waste would have dropped to low levels before it might reenter.

Remember, radioactive waste is only highly radioactive because it "burns" so rapidly, and so is all gone after some years...

...Anyway, the thing of it is is that a nuclear-powerd ion engine offers a higher Isp then any known form of propulsion that is readily available, and since it doesn't rely on sunlight, that makes it a definate contender for an asteroid tug.

In the future, NEP will have a place. But conventional methods and NTR need to come first.

This piece was in the September/October issue of American Scientist. It is by Russell Schweickart and Clark Chapman and mostly talks about detecting near-Earth asteroids, particularly about the challenges of detecting ones less than 100 meters.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

Is it my imagination, or is this thread bouncing around a bit? (not bad... just unexpected)
I was hoping to hear an answer to this...

As I understand it (and I might be getting this wrong), the problem isn't so much disturbing the asteroid's rotation, but moving a rotating asteroid.

Let's say you have a rotating asteroid and you land a big rocket on it, nose down, and fire your engine so you can push the asteroid. Unless you are exactly lined up along the spin-axis, the vector of your thrust will be constantly changing direction. The worst case would be if you landed on the equator, so your thrust is now rotating around - you'd have no net push. This is further complicated I suspect by the fact that most asteroids are very irregularly shaped.

The advantage of this method is even if you hovered above the equator, you could still "tug" the asteroid in a single direction.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

That makes sense, but if that's what was meant, then they worded it terribly . (Not acceptible IMO for someoone whose job is writing)
Maybe what they meant was "method won't depend on the asteroid’s rotation or composition".

oh, by the way . Did the thread move and did it change titles? If so, It makes more sense the way it is (I originally started it as a News Media Rant, but it looks like it went the way of meaningful discussions)
If not, I must be getting forgetful.

I guess if you messed up enough you could actually disturb the asteroid's rotation. Lets say you land at the equator and instead of inserting the rocket straight down, you did it at a 45 degree angle to the surface of the asteroid and in the plane of the equator (a drawing would probably help, but I'm no artist). Now when you fired up your rocket, you would actually end up just spinning it faster! If you landed at other places, other than the poles, you would also influence the spin.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

You just time the pulses of thrust when Earth is 'behind' the nozzle of the rocket. Several bursts may be enough. Use a big chemical stage as the 'tractor' and if that doesn't work--just time the thrust with some help from the math whiz kids.

Exactly. If you have the basic delta-v capability it becomes a control issue - and, folks, we are getting very good at control issues once they are recognised as such. Direct thrust would be the right way to go.

I don't disagree, I was just trying to explain this concept. Most of the concepts I've seen have talked about very long periods of time to move the asteroid (months, years?). If you are going to time it and use direct thrust, would this mean cycling the engine on and off hundreds or thousands of times? Might that be a problem?

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

Yes, that occured to me after my post. You would have to carry thrust capability in such a way that either it could be cycled or in sutable increments (multiple/reloadable boosters).

This rock has as many threads on the first page as the planet Saturn. Is this really nessecary?

(Anyway, I'm still sticking with my strategy of aerobraking the thing into a low orbit. A species should live fast and die young imho )

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

What if we could to slow it down,remember,the Earth moves through space one Earth diameter every six minutes.

So all we have to do is to slow it down for six minutes for the Earth to get out of the way.

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I still await the compelling Exhibit A.