NC State Study Shows How To Deflect Asteroids and Save The Earth (attach a long tether and ballast)

[OKIsItJustMe]

http://news.ncsu.edu/news/2009/04/wmsfrenchasteroid.php

News Release

NC State Study Shows How To Deflect Asteroids and Save The Earth

Media Contact(s)

David French, [phone]

Matt Shipman, News Services, [phone]

April 16, 2009
FOR IMMEDIATE RELEASE

You may want to thank David French in advance. Because, in the event that a comet or asteroid comes hurtling toward Earth, he may be the guy responsible for saving the entire planet.

French, a doctoral candidate in aerospace engineering at North Carolina State University, has determined a way to effectively divert asteroids and other threatening objects from impacting Earth by attaching a long tether and ballast to the incoming object. By attaching the ballast, French explains, "you change the object's center of mass, effectively changing the object's orbit and allowing it to pass by the Earth, rather than impacting it."

Sound far-fetched? NASA's Near Earth Object Program has identified more than 1,000 "potentially hazardous asteroids" and they are finding more all the time. "While none of these objects is currently projected to hit Earth in the near future, slight changes in the orbits of these bodies, which could be caused by the gravitational pull of other objects, push from the solar wind, or some other effect could cause an intersection," French explains.

So French, and NC State Associate Professor of Mechanical and Aerospace Engineering Andre Mazzoleni, studied whether an asteroid-tether-ballast system could effectively alter the motion of an asteroid to ensure it missed hitting Earth. The answer? Yes.

"It's hard to imagine the scale of both the problem and the potential solutions," French says. "The Earth has been hit by objects from space many times before, so we know how bad the effects could be. For example, about 65 million years ago, a very large asteroid is thought to have hit the Earth in the southern Gulf of Mexico, wiping out the dinosaurs, and, in 1907, a very small airburst of a comet over Siberia flattened a forest over an area equal in size to New York City. The scale of our solution is similarly hard to imagine.

"Using a tether somewhere between 1,000 kilometers (roughly the distance from Raleigh to Miami) to 100,000 kilometers (you could wrap this around the Earth two and a half times) to divert an asteroid sounds extreme. But compare it to other schemes," French says, "They are all pretty far out. Other schemes include: a call for painting the asteroids in order to alter how light may influence their orbit; a plan that would guide a second asteroid into the threatening one; and of course, there are nukes. Nuclear weapons are an intriguing possibility, but have considerable political and technical obstacles. Would the rest of the world trust us to nuke an asteroid? Would we trust anyone else? And would the asteroid break into multiple asteroids, giving us more problems to solve?"

The research was first presented last month at the NC State Graduate Student Research Symposium in Raleigh, N.C. The research, "Trajectory Diversion of an Earth-Threatening Asteroid via Elastic, Massive Tether-Ballast System," has also been reviewed and accepted for presentation this September at the American Institute of Aeronautics and Astronautics SPACE 2009 Conference and Exposition in Pasadena, CA.

-shipman-

[w4rma]

1. So what would a 500 mile tether be made out of that would be strong enough to stay intact?

And with what do we attach the tether? Such a long/heavy tether would require some really super glue.

[OKIsItJustMe]

3. Carbon nanotubes perhaps?

This is the idea for how to build a "space elevator" (which amounts to the same thing.)
http://en.wikipedia.org/wiki/Space_elevator#Cable

[phantom power]

4. Except that this would be a microgravity environment.

I'm not sure the forces would be very large, unless the tethered system passed close to a planet, in which case tidal forces might build up.

[OKIsItJustMe]

5. I noticed he called for an "elastic" tether

I don't know if that would be for an initial "switching yard" shock, or if (perhaps) he is planning on an ongoing force. (It occurred to me that you might have some sort of dynamic system here.)

[tinrobot]

7. ..and how big of a spool would they need to transport it?

...and would it tangle when unrolling the spool?

[OKIsItJustMe]

10. Not a very big spool, if you're talking about Carbon Nanotubes

http://en.wikipedia.org/wiki/Carbon_nanotube#Structural

However, don't kink it.

[phantom power]

2. The best weapon we could have against an impact is...

long lead time. The farther in advance we can be aware of any threat, the less we need to nudge the orbit.

I like this guy's approach. Appealingly low-tech.

[pscot]

6. "All we have to do" said the mouse

"is tie a bell arounds the cat's neck. That way we'll hear her coming." As usual, the devil is in the details.

[muriel_volestrangler]

8. How much ballast? How do you get it there?

And how do you match its velocity with the asteroid, so that you can attach it?

[OKIsItJustMe]

9. How big is the asteroid? Where is it?

We've demonstrated the ability to send probes to rendezvous with asteroids.

We've hit them with heavy masses, orbited and even landed on them.
http://discovery.nasa.gov/near.html
http://near.jhuapl.edu/

So, why is it so far-fetched to imagine attaching a tether to one?

[muriel_volestrangler]

11. I wasn't asking questions about the tether

Some kind of mass is put at the other end; it has to be significant to have an effect (that's why they call it 'massive'). I'm asking how big. Although the article didn't say so, people have also proposed putting a solar-powered ion rocket on (or near - either using a tether, or just gravitational attraction between the asteroid and the spacecraft) the asteroid. That allows you to use a longer period of time to run your rocket, compared with trucking a large mass to somewhere near the asteroid.

See http://www.newscientist.com/article/dn14414

[phantom power]

12. The mass could be the spacecraft itself...

attach one end of the line to the asteroid (piton gun?) and then just unwind.

One thing I noticed is that he's using the length of the line to compensate for actual mass. To shift the center mass by a given amount, you can either add more mass, or keep the mass the same and use a longer line.

Almost all of these schemes are based on very small delta-v over long periods of time, preferably with long lead times. Even better when there is > one orbit between "now" and "impact." since gravity maneuvers can be used to magnify a small delta v input.

[OKIsItJustMe]

13. That was my thought (i.e. spacecraft as mass)

As for attaching the cable, a few thoughts occurred to me:

1. If you can orbit an asteroid, you may be able to lasso one. (Space cowboys needed.)
2. A probe having landed on an asteroid might attach itself to the asteroid and play out cable (perhaps to another probe?)