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Posted by: ljk4-1 Sep 21 2005, 03:25 PM

astro-ph/0509595 [abs, pdf] :

Title: A Gravitational Tractor for Towing Asteroids

Authors: Edward T. Lu, Stanley G. Love

Categories: astro-ph

Comments: 4 pages, 1 figure - to be published in Nature

We present a concept for a spacecraft that can controllably alter the trajectory of an Earth threatening asteroid using gravity as a towline. The spacecraft hovers near the asteroid with thrusters angled outward so the exhaust does not impinge on the surface. This deflection method is insensitive to the structure, surface properties, and rotation state of the asteroid.

http://arxiv.org/abs/astro-ph/0509595

Posted by: helvick Sep 21 2005, 04:40 PM

Neat. I'd like to double check the numbers but the idea neatly resolves a whole host of problems with the other ideas that have been put forward.

There are some other issues - the 20 year mission time would need some work, as would the nuclear ion drive but both are definitely possible now.

Scaling it up for a >500m diameter monster heading directly for us that's discovered only a few years out is a bit of a problem but it's still neat.

Posted by: BruceMoomaw Sep 21 2005, 05:00 PM

This was proposed about a year ago by one of the astronauts -- can't remember which one. It does look as though it might actually work.

Posted by: Bob Shaw Sep 21 2005, 06:48 PM

Sadly, I get blocked from viewing the file - anyone care to repost, or to point me somewhere else?

Thanks!

Bob shaw

Posted by: dilo Sep 22 2005, 05:40 AM

Bob, here the PDF version I downloaded from ArXiv...
The proposed method is simple but seems a little bit inefficient to me... in the example they give, it needs a 10 ton spaceship hoovering 50m above a 200m asteroid for 20 years using a nuclear ion drive!
This is a relatively heavy spacecraft and wide deviation angle of thrust reduce it's efficiency... I have impression that a smaller probe anchored to surface and using in-situ material (heating it or escavating and accelerating material) would be more efficient, even if a little bit more complicated to make...

Posted by: Bob Shaw Sep 22 2005, 09:40 AM

Dilo and Rodolfo:

Thanks for the file (Rodolfo e-mailed it to me, Dilo posted it).

I have to say that it seems like a perfect way to move asteroids, so long as you catch the blighters early. It's *not* a resource-harvesting technology, for which you would need much more push, but is instead a gentle nudge designed to perturb dangerous visitors away from us at low-cost and with few gotchas. As you may gather, I like it!

It'd also be applicable to Martian terraforming via impacts - you could deliver a fair amount of dust onto the poles to start climate change, etc, or even use an asteroid to punch through the surface of Europa prior to some serious oceanic exploration, or a *real* Deep Impact on a comet, or...

In short, anywhere that a decent-sized bang over a timescale of say ~100 years would be a Good Thing. Just don't use squid as pilots!

Bob Shaw

Posted by: tty Sep 22 2005, 05:29 PM

On the other hand a landed probe could only thrust intermittently unless it was sited at or near a rotation pole and the asteroid is to be moved more or less along its axis of rotation. Also many asteroids are probably zero-strength rubble piles. Trying to move such by a landed probe might only turn one big crater into a crater chain, which may not be an improvement. This is a very clever technique and the only drawback I can see is that it is slow.
When warning time is short I think the old idea of using multiple nuclear charges to push the impactor aside may still be the best idea since the thrust would be fairly evenly spread and using directed-energy charges it would also be almost all in one direction.

tty

Posted by: RNeuhaus Sep 22 2005, 08:11 PM

Is there any real Earth's survival against asteroides/meteors proposal that is to implemented at the present time? I haven't heard any of this from NASA, JAXA, ESA. It is time to prepare and later would to late and will cost us a much higher price than a longer term investment.

I think it is of first priority for the preservation of Earth's life. Let us experiment with a safe asteroide different than ones of Apophis 2004 MN4 to see the results so that we can feel more confident for next similar mission.

About tugging or pushing, the first is simpler and elegant but slower since the spacecraft cannot push harder than the gravitational atraction force. The second is more complex but it has greater throughput and more dangerous of losing the trajectory control. These terms are elaborated according to the intuition and not by the math calculations.

I think that every nations must contribute resources and money to concrete this project since it is a Earth's survival project.

Rodolfo

Posted by: garybeau Sep 22 2005, 11:20 PM

A lot of intermixing of English and Metric units in that report. Didn't that get us
in trouble once already?
If we are going to try and move an asteroid around, let's make sure we get it right.

Posted by: RNeuhaus Sep 26 2005, 11:15 PM

At least there is a project for deflection of an asteroide from ESA:

September 26

Two Asteroid Targets Chosen for Deflection Test

The European Space Agency (ESA) has selected two asteroids as potential targets for a mission aimed at deflecting a nearby space rock.

After a comprehensive review, the space agency selected the near-Earth objects 2002 AT4 and 1989 ML as primary targets for its upcoming Don Quijote mission. The mission will send two spacecraft, dubbed Hidalgo and Sancho, to an asteroid in hopes of slightly deflecting the space rock’s path.

The Don Quijote mission will visit only one of the two asteroid targets – a final decision will be made in 2007 – and calls for the Hidalgo craft to slam into the space rock at a high speed while Sancho records the event, ESA officials said. The Sancho probe is slated to arrive at the asteroid earlier than Hidalgo to observe the object before and after the impact, they added.

Don Quijote’s mission is designed to demonstrate the feasibility of changing an asteroid’s orbit – however slightly – using conventional spacecraft technology. Two teams are expected to flesh out plans for the mission’s spacecraft pair, with a final design selection to made in 2007 along with the target space rock, ESA officials said.

-- SPACE.com Staff.

More information, http://www.esa.int/gsp/completed/neo/donquijote.html

Rodolfo

Posted by: ljk4-1 Nov 10 2005, 02:40 PM

'Gravity tractor' to deflect Earth-bound asteroids

NewScientist.com News Service Nov. 9, 2005

NASA scientists have come up with a surprisingly simple yet effective
way to deflect an Earth-bound asteroid: park a large spacecraft
close by and let gravity do the work, creating an invisible towline
to tug the rock off its deadly course.

The strategy crucially relies on our ability to detect an
asteroid threat about 20 years in advance. For...

http://www.kurzweilai.net/email/newsRedirect.html?newsID=5014&m=7610

Posted by: ljk4-1 Nov 17 2005, 02:17 PM

DEFLECTING INCOMING ASTEROIDS (Science Show: 12/11/2005)

There is a long tradition in film and literature of an asteroid being
diverted at the last moment from its collision course with Earth by the
miracles of space technology. Back in the real world, a study by Britian's
Engineering and Physical Sciences Research Council will look at some
realistic ways to avoid catastrophic collisions. Dr Ed Lew from the Johnson
Space Centre says that, with a couple of decades notice gravity could be
used to deflect an incoming asteroid.

http://www.abc.net.au/rn/science/ss/stories/s1502451.htm

Posted by: Toma B Nov 17 2005, 03:29 PM

I think that this is one of those "NEVER TO BE" projects...
Besides there is much better way to deflect incoming asteroid...
The right way is this:




You don't have to destroy it JUST MOVE IT...

Posted by: ljk4-1 Nov 17 2005, 04:37 PM

I thought among the big arguments *against* nuclear weapons use on a threatening NEO was that if the NEO was too big, a nuclear explosion would not budge it. Also, if the NEO is essentially a big rubble pile barely held together by gravity (which is what Itokawa sure looks like), then a detonation might only shatter the space rock and just spread the debris over more places on Earth.

My favored scenario is attaching a rocket or two or more on the NEO and having the continual thrust from their engines eventually push the rock into a non-threatening orbit. Not destroying the NEO also saves it for future study and space resource use.

Posted by: dvandorn Nov 17 2005, 05:15 PM

Don't dismiss the value of breaking up a large impactor.

Each year, the Earth is hit by tons and tons of asteroid and cometary material, enough that, if it were to hit all at once, it would cause an impact big enough to wipe out most life on the planet. But it hits in very tiny fragments that burn up before they reach the ground.

If you could blast a relatively small asteroid, like Itokawa, into billions of grains of sand, its impact would not be noticed. Of course, you couldn't reduce the whole thing to such small particles, larger pieces would remain and would make it through to impact -- but they would be a *lot* smaller than the original impactor, and each would have a lot less effect on the ecosystem.

The whole point is to increase the asteroid's surface area. The more of the mass that's subject to ablation, the more of the mass that will simply burn up in the upper atmosphere and filter slowly down to the surface over the following months. And since we already receive thousands of tons of such material every year, that's not really a threat. The remaining several thousand pieces large enough to make it to the ground might cause a lot of local destruction, but (if they were all kept small enough) would be no worse in overall effect than if a few hundred square km were heavily carpet-bombed.

All in all, I'd rather have a few thousand 100-meter craters and the ensuing, potentially manageable destruction casued by them, than have a single 200-km cratering event whose blast effects would wipe out most life on Earth...

-the other Doug

Posted by: Toma B Nov 17 2005, 05:16 PM

If NEO is to BIG for Hydrogen bomb to nudge it slitely of its Earth-colliding course than nothing that we can make can save us...
If NEO is RUBBLE-PILE bomb will shatter it and there will be a nice meteor storm ( with bright fireballs ) , even if some larger chunk remains it will only cause local damage,nothing on the global scale...
I would more thrust the BOMB because it is several thousand times tried unlike Gravity tractor which never is...

P.S.

AAARRGGHHH!!!!
My English is not so good...
I need 3-5 times more time to write post than most of you guys...

Posted by: Bob Shaw Nov 17 2005, 07:37 PM

Doug:

I think it's a case of 'horses for courses' - but that the gravitational tug remains a striking, and so far as I can see, feasible, new idea which is well worth pursuit. The 'Don Quixote' impact experiment is well and good, but I'd far rather see a tractor experiment sooner rather than later...

Bob Shaw

Posted by: ljk4-1 Feb 14 2006, 05:48 PM

Astrophysics, abstract
astro-ph/0102126

From: Donald Korycansky [view email]

Date: Wed, 7 Feb 2001 22:40:53 GMT (84kb)

Astronomical engineering: a strategy for modifying planetary orbits

Authors: D. G. Korycansky, Gregory Laughlin, Fred C. Adams

Comments: 21 pgs, 7 figs. Paper to appear in Astrophysics and Space Science

Journal-ref: Astrophys.Space Sci. 275 (2001) 349-366

The Sun's gradual brightening will seriously compromise the Earth's biosphere within ~ 1E9 years. If Earth's orbit migrates outward, however, the biosphere could remain intact over the entire main-sequence lifetime of the Sun. In this paper, we explore the feasibility of engineering such a migration over a long time period. The basic mechanism uses gravitational assists to (in effect) transfer orbital energy from Jupiter to the Earth, and thereby enlarges the orbital radius of Earth. This transfer is accomplished by a suitable intermediate body, either a Kuiper Belt object or a main belt asteroid. The object first encounters Earth during an inward pass on its initial highly elliptical orbit of large (~ 300 AU) semimajor axis. The encounter transfers energy from the object to the Earth in standard gravity-assist fashion by passing close to the leading limb of the planet. The resulting outbound trajectory of the object must cross the orbit of Jupiter; with proper timing, the outbound object encounters Jupiter and picks up the energy it lost to Earth. With small corrections to the trajectory, or additional planetary encounters (e.g., with Saturn), the object can repeat this process over many encounters. To maintain its present flux of solar energy, the Earth must experience roughly one encounter every 6000 years (for an object mass of 1E22 g). We develop the details of this scheme and discuss its ramifications.

http://arxiv.org/abs/astro-ph/0102126