[X] My Assistant

[ljk4-1]

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

[dvandorn]

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

[Bob Shaw]

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

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

[ljk4-1]

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