Romain Edison

I've read of this proposal a few years ago - it's predicated on the idea that asteroids might be poorly cohered and that any attempt to fix a reaction engine will be sub-optimal (rocket slowly digs itself into rubble pile).

There's nothing wrong with the idea, but the engineering problems for a reasonably large asteroid are not trivial.

Davide Vatteroni

My understanding is that the 'gravity tractor' is quite well suited to manoeuvring rubble-piles as the force is not applied through a discrete number of 'hard-points' such as anchors/tethers and the like.

Of course, the inverse-square law still applies, so although one would ideally move rubble-piles around with relatively distant massive objects, engineering and costs dictates that one might be quite close - a few km perhaps and so there will be a 'tide' within the rubble-pile.

Davide Vatteroni

:D

Yes, moving a rubble pile with a nearby microscopic black hole would be problematic.

Pebbles at the surface are removed readily and ejected, and the rest of the rubble pile is unmoved.

Thus, it is is an engineering problem to have a sufficiently large and massive object *far* from the pile so that it isn't Roche-limit disrupted.

The idea is bright, the technical implementation is rather difficult. To provide sufficient gravitational pull over sufficiently long time we need to place very heavy object (spacecraft ?) to suitable controlled position or we need less heavy spacecraft and to apply its pull over very long time... Of course, each case is very specific (asteroid mass, orbit, available time to collision with Earth....)

as i recall soon, "they" are hitting a object with a large slug to see if it moves ... i will try to find the link to the mission.. from what i hear, as long as we "hit it" far enough away, we can control the trajectory. so only three main variables, distance from earth, size of object, and size of our impactor ie., slug . Please note that this assumes the object is solid enough to take the impactor without breaking apart.

https://www.livescience.com/how-to-stop-asteroid-from-hitting-earth.html

from people at MIT, on various ways to deal with it.........

Dear Douglas:

It helps me a lot,thanks for your attention!

Hi,

The Answer to your question: Yes but expensive.

Why is this idea prevails? Because the unit can be reused many times and nukes don't really solve the problem.

How can it be done? Practically if you consider the present rocket's maximum capacity (falcon heavy, starship, saturn5, etc), around 64,000 Kg to 150,000 Kg payload; it will take several voyages into space to dump enough usable mass to generate enough gravity which could steer away incoming asteroid. Then These units need to be deployed as far as Jupiter or Saturn so that it has enough time to tug along the asteroid and slowly pull them off trajectory.

Looking at the re-usability of these units over many times (Assuming the units will survive all sorts of radiations and controllable from the earth like voyager), gravity tractors are feasible solutions, at least as a backup plan!

good points, will have to look at this later. much eaiser to send a huge bomb to break it up, or the shock wave could deflect the object...

Yes it can be done. It is not trivial , but it's an Engineering problem. With reasonably sized spacecraft it works only for Asteroids with long warning times (at least several years), i.e. small required deflections to miss Earth. It is a good method for Asteroids that are so called rubble piles, that is only loosely connected objects. This is because it does not risk unpredictable break ups of the Asteroid. Here’s a brief description: https://www.neoshield.eu/mitigation-measures-kinetic-impactor-gravity/gravity-tractor-spacecraft-asteroid/