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Retrospections Lecture Presidential Commission on the "Moon, Mars and Beyond" initiative Edward Lu: Why Move an Asteroid?
 
Edward Lu: Why Move an Asteroid?
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Meteorites, Comets and Asteroids
Posted:   05/16/04

Summary: The global defense against asteroids includes proposals to change the orbit of a hazardous, incoming rock. Doing this engineering in space by 2015 has much to do with how to control another world's orbit--with nothing but empty space to push off of.

Why Move an Asteroid?

Testimony of Edward Lu, B612 Foundation, before the Subcommittee on Science, Technology and Space of the Senate Commerce Committee, 7 April 2004, before the U.S. Senate Subcommittee on Science, Technology and Space dealing with defense against asteroid impacts.


Thank you for the opportunity today to discuss a bold new proposal to demonstrate altering the orbit of an asteroid. I represent the B612 foundation, a group of astronomers, engineers, and astronauts, concerned about the issue of asteroid impacts. Recent developments have now give n us the potential to defend the Earth against these natural disasters. To develop this capability we have proposed a spacecraft mission to significantly alter the orbit of an asteroid in a controlled manner by 2015.

KT_hit
The painting titled "K/T Hit" by artist Donald E. Davis. This impact occured 65 million years ago, ending the reign of the dinosaurs.
Image Credit: Don Davis


Why move an asteroid? There is a 10 percent chance that during our lifetimes there will be a 70 meter asteroid that impacts Earth with energy 10 megatons (roughly equivalent to 700 simultaneous Hiroshima sized bombs). There is even a very remote one in 50,000 chance that you and I and everyone we know, along with most of humanity and human civilization, will perish together with the impact of a much larger kilometer or more sized asteroid. We now have the potential to change these odds.

There are many unknowns surrounding how to go about deflecting an asteroid, but the surest way to learn about both asteroids themselves as well as the mechanics of moving them is to actually try a demonstration mission. The first attempt to deflect an asteroid should not be when it counts for real, because there are no doubt many surprises in store as we learn how to manipulate asteroids.

Why by 2015? The time to test, learn, and experiment is now. A number of recent developments in space nuclear power and high efficiency propulsion have made this goal feasible. The goal of 2015 is challenging, but doable, and will serve to focus the development efforts.

comet_jupiter
Fragments of Comet P/Shoemaker-Levy 9 colliding with Jupiter (July 16-24, 1994).
Credit: NASA


How big of an asteroid are we proposing to move? The demonstration asteroid should be large enough to represent a real risk, and the technology used should be scaleable in the future to larger asteroids. We are suggesting picking an asteroid of about 200 meters. A 200 meter asteroid is capable of penetrating the atmosphere and striking the ground with an energy of 600 megatons. Should it land in the ocean (as is likely), it will create an enormous tsunami that could destroy coastal cities. Asteroids of about 150 meters and larger are thought to be comprised of loose conglomerations of pieces, or rubble piles, while smaller asteroids are often single large rocks. The techniques we test on a 200 meter asteroid should therefore also be applicable to larger asteroids.

What does "significantly alter the orbit" mean? If proposed asteroid searches are enacted, we expect to have decades or more of warning before an impact. Given this amount of warning, to prevent an impact only requires that the orbital velocity of an asteroid be altered by a small amount, less than of order 1 cm/sec, or about .02 MPH. This is a tiny velocity increment, considering that the orbital speeds of asteroids are of order 70,000 MPH. However, this is still a very difficult task since the mass of a 200 meter asteroid is of order 10 million tons.

Why does the asteroid need to be moved in a "controlled manner"? If the asteroid is not deflected in a controlled manner, we risk simply making the problem worse. Nuclear explosives for example risk breaking up the asteroid into pieces, thus turning a speeding bullet into a shotgun blast of smaller but still possibly deadly fragments. Explosions also have the drawback that we cannot accurately predict the resultant velocity of the asteroid -- not a good situation when trying to avert a catastrophe. Conversely, moving an asteroid in a controlled fashion also opens up the possibility of using the same technology to manipulate other asteroids for the purposes of resource utilization.

tunguska_event
"I was sitting in the porch of the house at the trading station of Vanovara at breakfast time and looking towards the north... suddenly the sky was split in two, and high above the forest the whole northern part of the sky appeared to be covered with fire." --Farmer Sergei Semenov of the Tunguska event, 1908
Credit: www.s-d-g.freeserve.co.uk


How can this be accomplished? This mission is well beyond the capability of conventional chemically powered spacecraft. We are proposing a nuclear powered spacecraft using high efficiency propulsion (ion or plasma engines). Such propulsion packages are currently already under development at NASA as part of the Prometheus Project. In fact, the power and thrust requirements are very similar to the Jupiter Icy Moons Orbiter spacecraft, currently planned for launch around 2012. The B612 spacecraft would fly to, rendezvous with, and attach to a suitably chosen target asteroid (there are many candidate asteroids which are known to be nowhere near a collision course with Earth). By continuously thrusting, the spacecraft would slowly alter the velocity of the asteroid by a fraction of a cm/sec --enough to be clearly measurable from Earth.

What will we learn from this? It is important to remember that this mission is merely a first attempt to learn more about the mechanics of asteroid deflection. There are a number of technical complications, as well as many unknowns about the structure and composition of asteroids. However, the way to make progress is to build, fly, and test. Much of what we will learn is generic to many proposed asteroid deflection schemes, with the added benefit of being able to answer important scientific questions about asteroids themselves. The best way to learn about asteroids is to go there.

How does this fit into the new Exploration Initiative at NASA? In the near term, this mission would be an ideal way to flight test the nuclear propulsion systems under development as part of the Prometheus Project. It could also serve as a precursor to a crewed mission to visit an asteroid. Such missions have been proposed as intermediate steps to test spacecraft systems for eventual longer term crewed missions to Mars.

In the longer term, the ability to land on and manipulate asteroids is an enabling technology for extending human and robotic presence throughout the solar system. If we are to truly open up the solar system, this mission is a good way to start. It is likely that someday we will utilize asteroids for fuel, building materials, or simply as space habitats. The B612 mission would mark a fundamental change in spacecraft in that it would actually alter in a measurable way an astronomical object, rather than simply observing it. Human beings must eventually take charge of their own destiny in this way, or we will someday go the way of the dinosaurs when the next great asteroid impact occurs.


Related Web Pages

Great Impact: Part I
Great Impact: Part II
Great Impact: Part III
Impact Hazards Website
NASA/JPL Near Earth Object Program


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