APOD: Gravitational Tractor (2013 Feb 21)

[Chris Peterson]

Wuh-oh. Both the earth and moon show visible discs in that image. Just a gut feel, but I'm betting by that point it would be too late to inflict a significant course change on the asteroid. So... DUCK!

Two other possibilities: the asteroid could be in an orbit similar to Earth's, in which case the tug could be used to prevent a future collision, many orbits in the future. Or, if the body was in a highly elliptical orbit, we could be seeing the end of the mission, perhaps 20 years after the orbit tweaking got underway, and the orbit is already a safe one.

[Chris Peterson]

Moving all that mass around to intercept an asteroid would be very inefficient. Also unnecessary. If the object is a puffball, like the one that just arrived over Russia, then interception is not really necessary. It will break up in the atmosphere just like that one did. Only the solid ones are really dangerous. So a contact propulsion system would work fine and be much faster an more efficient.

It depends on size. A several hundred meter comet or "puffball" could be devastating to the Earth.

I don't think there's an inherent difference in efficiency between a contact and non-contact system.

[Ron-Astro Pharmacist]

As long as we are talking science fiction (which time has shown to actually become reality in some cases) why not be open to all suggestions. We may have plenty of time to come up with a viable option with that day’s technology. The only way we will be able to cope with the situation is keep thinking. If we throw our hands up and say, “We can’t do that!” and have no plan, we surely will fail.

And of course I want to throw in the reverse idea. Change our position slightly. Capture a small object and put it in a stable orbit. Not big enough to greatly affect the Earth gravitationally but big enough, over a great period of time, to affect where we would have been without its additional mass.

Or here’s another potentially viable idea. Build something in a stable orbit slowly over time that we can occupy, move from point to point if necessary to change Earth’s position, and have a permanent outpost in a stable Earth orbit.

As Alex Filippenko said in his course on Astronomy, a potentially catastrophic event may be the one thing that finally will bring the nations of Earth together on a mutually beneficial project to make us forget our petty differences.

[Guest]

Seriously, do we all not think this idea is hard enough to realize as it stands? Imagine how much money, resources, and potential for error would be involved in this project.

This is much, much cheaper and easier to manage than manned expeditions around the Solar System. Sure its [sic] expensive, and sure there are technical challenges. But they are well within our financial and engineering means given a bit of incentive... like a massive collision a few years in the future.

we all do not think this idea is hard to realize as it stands. we all also do a bit of simple cost/benefit analysis:

cost manned mars space flight: $10^10 benefit: photos, rocks, publicity, a bit of arcane astrogeology.
cost james webb telescope: $10^9 benefit: photos, astrometry, spectroscopy, a bit of arcane cosmology.
cost asteroid deflecting tractor: $10^8 benefit: salvation of earth, humanity, downton abbey.

the single greatest difficulty here is not scientific, technical or budgetary, but political. and public opinion wags politics.

[neufer]

cost asteroid deflecting tractor: $10^8
benefit: salvation of earth, humanity, downton abbey.

• In that order

(Two word answer: "Milady's Soap")

[StarCuriousAero]

It's important to note here that this tractor idea is by no means a solution to every asteroid. This COULD be the preferred solution to a larger asteroid (that would cause enough damage such that we should be worried), with a well known orbit, that we know is on a future collision path with earth, with an orbit such that we have enough time to influence its course AND one with an orbit that we are capable of inserting this tractor into. An asteroid that may fit this description Apophis, although extremely unlikely. Currently, to the best of my knowledge, there are no other asteroids that remotely fit this description, but that doesn't mean they won't be discovered. If so, hopefully enough of the wealthier scientifically active countries could pool funds and implement a solution, potentially this one (although expensive, not necessarily cost prohibitive and certainly not technologically prohibitive).

Last month, a close encounter with Apophis allowed a revision of its orbit, such that impact has now been ruled out as a possibility.
" Goldstone single-pixel observations of Apophis have ruled out the potential 2036 Earth impact.[21][36][9] Apophis will then come no closer than about 14 million miles — and more likely miss us by something closer to 35 million miles.[21] The radar astrometry is more precise than was expected."
http://en.wikipedia.org/wiki/99942_Apophis

Although now outdated, this still made me laugh: poor Russia.
http://en.wikipedia.org/wiki/File:2036_ ... f_Risk.jpg

[neufer]

Wuh-oh. Both the earth and moon show visible discs in that image. Just a gut feel, but I'm betting by that point it would be too late to inflict a significant course change on the asteroid. So... DUCK!

Two other possibilities: the asteroid could be in an orbit similar to Earth's, in which case the tug could be used to prevent a future collision, many orbits in the future. Or, if the body was in a highly elliptical orbit, we could be seeing the end of the mission, perhaps 20 years after the orbit tweaking got underway, and the orbit is already a safe one.

1) The asteroid will indeed return to that same spatial location in the future but not necessarily in one sidereal year or any multiple of one sidereal year when the Earth & Moon would be there at the same time.

<<The sidereal year is the time taken for the Earth to complete one revolution of its orbit, as measured against a fixed frame of reference (such as the fixed stars, Latin sidera, singular sidus). Its average duration is 365.256363004 mean solar days (365 d 6 h 9 min 9.76 s).>>

2) A gravitational tractor works most efficiently (i.e., maximal {F ⋅ v} power) when the asteroid's velocity is, itself, maximal (e.g., at perihelion and/or during a planetary encounter).

• Note that a change in the asteroid's (sun) radial velocity by 1 cm/s will permanently change the orbit by only ~50km.
  
  However, a change in the asteroid's orbital velocity by 1 cm/s will not only permanently change the orbit, itself, by ~100km but (more importantly) it will permanently modify its sidereal period by ~30 seconds. This permanent ~30 second change in sidereal period will cause the asteroid to drift ~900km per year in its orbital location and thus prevent any predicted future collision with Earth more than a decade or so out.

3) The APOD is primarily intended to symbolically represent a gravitational tractor pulling an asteroid away from Earth.

[Anthony Barreiro]

Sure its expensive, and sure there are technical challenges. But they are well within our financial and engineering means given a bit of incentive... like a massive collision a few years in the future.

Yeah, if that doesn't motivate humankind enough, I don't think anything could.

As Alex Filippenko said in his course on Astronomy, a potentially catastrophic event may be the one thing that finally will bring the nations of Earth together on a mutually beneficial project to make us forget our petty differences.

Umm, accelerating global warming? Acidification of the oceans? Melting polar sea ice and glaciers? Massive species loss comparable to when the dinosaurs died off? These things are already happening due to our daily human activity right here on Earth. The solutions are technically feasible: burn less carbon, stop cutting down the forests and extracting fossil fuels, eliminate frivolous waste, return to regionally sustainable economies and agricultures, ramp up the use of solar and wind energy. If global warming won't motivate humankind to change our ways, I'm not terribly hopeful that a predicted asteroid impact decades in the future is going to get us all singing kumbaya.

[Chris Peterson]

Umm, accelerating global warming? Acidification of the oceans? Melting polar sea ice and glaciers? Massive species loss comparable to when the dinosaurs died off? These things are already happening due to our daily human activity right here on Earth.

Yes, but those things are slow. People are quite adept at ignoring uncertain futures, like frogs being slowly stewed. An asteroid comes with a bona fide expiration date for the biosphere. I do think that most people view the idea that a billion people will die on March 19, 2028 a little differently than they view the idea that coastal flooding could impact hundreds of millions of people in 50 years.

[FloridaMike]

How would you feel about this or similar technology being used to insert a non-threatening object into lunar orbit for commercial purposes? Too big of a risk or no-brainer?

[neufer]

How would you feel about this or similar technology being used to insert a non-threatening object into lunar orbit for commercial purposes?

Too big of a risk or no-brainer?

What sort of non-threatening object did you have in mind

[Anthony Barreiro]

Umm, accelerating global warming? Acidification of the oceans? Melting polar sea ice and glaciers? Massive species loss comparable to when the dinosaurs died off? These things are already happening due to our daily human activity right here on Earth.

Yes, but those things are slow. People are quite adept at ignoring uncertain futures, like frogs being slowly stewed. An asteroid comes with a bona fide expiration date for the biosphere. I do think that most people view the idea that a billion people will die on March 19, 2028 a little differently than they view the idea that coastal flooding could impact hundreds of millions of people in 50 years.

Last summer's drought in the US midwest was not slow. Superstorm Sandy was not slow.

Until there is a confident prediction of a large asteroid impact some years or decades in the future we won't know how humanity would respond to such a prediction. You may be right that everybody will quickly and efficiently give the engineers the necessary resources to figure out how to avert the impact, and that the engineers will agree on and implement a workable plan. I'm not so sure.

In the mean time ...

NASA scientists say 2012 was the ninth warmest of any year since 1880, continuing a long-term trend of rising global temperatures. With the exception of 1998, the nine warmest years in the 132-year record all have occurred since 2000, with 2010 and 2005 ranking as the hottest years on record.

http://www.nasa.gov/topics/earth/featur ... temps.html

[FloridaMike]

How would you feel about this or similar technology being used to insert a non-threatening object into lunar orbit for commercial purposes?

Too big of a risk or no-brainer?

What sort of non-threatening object did you have in mind

Sorry, badly worded.

I was speaking of an object that poses no risk to us in its current orbit being moved for commercial purposes. I think the Company Planetary Resources is currently looking into the possibility. I wonder what the environmental impact study will look like. Possibly another photo-copy of an Alaskan oil drilling platforms EIS like was used for the Deepwater Horizon drill?

Neufer, the graphic you posted kind-of says it all, unintended consequences ....

[emc]

I appreciate that there's a potential solution to specific oblivion.

[Beyond]

I appreciate that there's a potential solution to oblivion.

Oh... i don't know... oblivion has it's advantages.

[alamid419@yahoo.com]

I think that the military will use this "Gravitational Tractor" first before it could be launched in the outer space. These GT is an effective equipment of the military for defensive purposes like: diverting the missile fired as well as the aircraft of hostile forces.

[neufer]

I think that the military will use this "Gravitational Tractor" first before it could be launched in the outer space. These GT is an effective equipment of the military for defensive purposes like: diverting the missile fired as well as the aircraft of hostile forces.

Well...lotsa luck to them with THAT

[Chris Peterson]

I think that the military will use this "Gravitational Tractor" first before it could be launched in the outer space. These GT is an effective equipment of the military for defensive purposes like: diverting the missile fired as well as the aircraft of hostile forces.

Yeah... if the test mass it's carrying is a moon-mass black hole!

[raschumacher]

I think that the military will use this "Gravitational Tractor" first before it could be launched in the outer space. These GT is an effective equipment of the military for defensive purposes like: diverting the missile fired as well as the aircraft of hostile forces.

Well...lotsa luck to them with THAT

At least two Senators and a dozen Representatives would fund the idea with no questions asked other than, "How many will it employ in my state or district"?

[raschumacher]

Umm, accelerating global warming? Acidification of the oceans? Melting polar sea ice and glaciers? Massive species loss comparable to when the dinosaurs died off? These things are already happening due to our daily human activity right here on Earth.

Yes, but those things are slow. People are quite adept at ignoring uncertain futures, like frogs being slowly stewed. An asteroid comes with a bona fide expiration date for the biosphere. I do think that most people view the idea that a billion people will die on March 19, 2028 a little differently than they view the idea that coastal flooding could impact hundreds of millions of people in 50 years.

And as others have pointed out elsewhere, there are multi-billion-dollar industries which want nothing done to stop global warming. There is no such constituency for asteroid impacts.

[ecebe]

Why don't we start collecting all the space junk and hold it as a gravitational mass, in a net or something similar, that we could push where we might need it. If we wait for a threat, we won't have enough time to act.

[TNT]

Why don't we start collecting all the space junk and hold it as a gravitational mass, in a net or something similar, that we could push where we might need it. If we wait for a threat, we won't have enough time to act.

Space junk probably won't have enough gravitational pull to divert the threatening object enough. If the object's mass were larger than the mass of the space junk, it wouldn't work well anyway. Also, we would need a heck of a big net in order to move enough space junk around to even pull the object away from its collision course.

[metamorphmuses]

The whole point is that it isn't manned, and isn't serviceable- both of which make for a prohibitively difficult and expensive mission. Manned would be absurd, since we're talking about a mission likely to be in deep space for a decade or more. Serviceable with robots might be considered, depending on the orbit, but probably isn't necessary. If the HST has taught us anything, it is that making serviceable probes is probably a waste of money.

Hmm, yes, you're right it could not be manned. But surely its trajectory would need to be very precise, and its alignment to the asteroid would have to be precise as well. So, it would need to be adaptive and "intelligent" in its navigation, or it would have to be monitored and remotely piloted by a crew? I admit my ignorance here. I ask myself, what would be the feedback response time necessary to make course adjustments? Because if it were not an artificially "intelligent" craft, and the course adjustments were needed on a minute-by-minute basis, then a remote crew on Earth is not feasible, due to the fact that the asteroid would probably be several light-minutes away from Earth. I'm thinking out loud here.

[Chris Peterson]

Last summer's drought in the US midwest was not slow. Superstorm Sandy was not slow.

They weren't predicted. Not with a date and time. And that makes all the difference. And, of course, for 99% of people they happened to somebody else, which also makes a big difference.

Until there is a confident prediction of a large asteroid impact some years or decades in the future we won't know how humanity would respond to such a prediction. You may be right that everybody will quickly and efficiently give the engineers the necessary resources to figure out how to avert the impact, and that the engineers will agree on and implement a workable plan. I'm not so sure.

It depends on the sort of resources involved, too. Launching something like we see in today's APOD would be dirt cheap- noise in the national budget (let alone the combined national budgets of all developed countries). This thing could be built right now with NASA's existing budget, simply by taking money from other projects.

[Chris Peterson]

Why don't we start collecting all the space junk and hold it as a gravitational mass, in a net or something similar, that we could push where we might need it. If we wait for a threat, we won't have enough time to act.

Collecting space junk is very difficult, and very expensive. It would be much cheaper just to launch the mass.