# Talk:Gravity tractor

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## Acceleration from body radius and tractor mass

It might be considered useful to present the relationship, for the optimal orbit around a spherical asteroid, between the acceleration achieved, the radius of the asteroid, and the mass of the tractor. I believe that I can provide this (assuming the asteroid to greatly outweigh the tractor), but it would need checking. 82.163.24.100 (talk) 19:14, 31 March 2009 (UTC)

See http://www.merlyn.demon.co.uk/gravity2.htm#GT. 82.163.24.100 (talk) 12:12, 1 April 2009 (UTC)
The obvious placing of the orbiting tractor is at a radius such that, firing aft, the exhaust just misses the asteroid surface. However, that cannot be optimum, unless it is necessary to mimimise fuel use : if the exhaust is directed slightly outwards, there is a second-order effect on the towing efficiency, but the tractor can be moved inwards by a first-order amount which has a first-order effect on the towing force. 82.163.24.100 (talk) 16:38, 3 April 2009 (UTC)

The tidal forces are indeed small; but at the maximum they are larger than the average propulsive force. The tractor is a heavy object near to the asteroid's surface. One should consider whether surface material can be lifted; at least for likely masses, it seems not. 82.163.24.100 (talk) 11:55, 6 April 2009 (UTC)

## Merge from Gravitational tractor

As far as I can see, a gravitational tractor is just another name for the gravity tractor. Therefore, I suggest it to merge into one article. Any (other) opinions? EmilTyf (talk) 23:55, 19 May 2009 (UTC)

Agreed. Anything in Gravitational tractor not here needs to be put here, and Gravitational tractor removed. 82.163.24.100 (talk) 17:00, 31 August 2009 (UTC)
I've gone ahead and done the merge. I didn't bring the text over from the old Gravitational tractor, because I didn't spend the time to crunch through all the numbers and compare them with the ones in this article. It seemed fairly duplicative, but if someone wants to take a closer look, go ahead. Kingdon (talk) 01:36, 31 December 2009 (UTC)

## Reaction Mass Counterreaction

I completely agree with Kingdon's edit summary for edit 345033626 - the clause added in the previous edit was awkwardly worded and not very helpful. However, Patrick is correct that the fate of the reaction mass is a big issue for a hovering tractor. Wouldn't the exhaust slamming into the target (towed) object impart a force in the opposite direction of the (already minuscule) pull of the tractor? I don't know the numbers, but that's got to be a significant hurdle if not an outright negation of the intended delta-v.

I am therefore adding a paragraph under the Limitations section describing this problem. If my reasoning is wrong, please discuss here. Z.S. 17:16, 17 March 2010 (UTC)

I don't see any obvious problems with that text, but really it should be based on what the sources say rather than original research. I would imagine things like the distance between the craft and target and whether the reaction mass is in a tight beam or a wider one might matter, for example. Kingdon (talk) 14:06, 29 March 2010 (UTC)
Found and added one reference pretty quickly; I'm sure other, more in-depth ones exist. I'll hunt more diligently for them when I've got a bit more time for it. Thanks for responding! Z.S. ......(talk) 14:12, 30 March 2010 (UTC)
Thanks. Having that one is a big improvement over not having it cited. Kingdon (talk) 01:14, 4 April 2010 (UTC)
Found really cool, detailed JPL study done for B612 Foundation. The study specifically ponders a tractor vehicle with main thrusters angled 45° away from the object. If I happen across more references later, I'll put them in, but I think this is adequate for now. Z.S. ......(talk) 17:39, 8 April 2010 (UTC)
Guys, I attended Caltech, but I still don't understand the details of how a gravity tractor works. This article needs a clearly written explanation. WilliamSommerwerck (talk) 19:04, 8 December 2013 (UTC)

## rusty thinking

"According to Rusty Schweickart, the gravitational tractor method is also controversial because during the process of changing an asteroid's trajectory the point on Earth where it could most likely hit would be slowly shifted across different countries. It means that the threat for the entire planet would be minimized at the cost of some specific states' security. In Schweickart's opinion, choosing the way the asteroid should be "dragged" would be a tough diplomatic decision."

There was a Superman comic-book story in which a Metropolis scientist had discovered an asteroid headed for the Earth, that would hit (note that I did not say impact) Metropolis in a week's time (or so). How could he have possibly have known what path the asteroid would take once it entered the atmosphere? He might be able to predict within a thousand miles or so, but I bet he'd have trouble coming even that close.

Furthermore, it's assumed that whatever method is used to deflect the object will be sufficient to guarantee its missing the Earth altogether, and by a wide margin -- or why bother? WilliamSommerwerck (talk) 19:04, 8 December 2013 (UTC)

I'm confused about why the asteroid is going to be on impact trajectory at one point... That sounds like a terribly inefficient orbit adjustment. Then again, I'm no rocket scientist. 7yl4r (talk) 03:03, 16 April 2014 (UTC)