This hearing is, indeed, appropriate in recognition of a confluence of factors leading to a renewed interest among the American public in impactors. Within the past few weeks, science fact and now Hollywood fiction have conspired to elevate the issue of impactors beyond the level of "here today, gone tomorrow."

As I prepare this testimony, the movie "Deep Impact" has just opened in theatres across the nation. Hundreds of thousands of Americans have flocked to the film, making it, according to our contacts at Paramount Pictures, the highest grossing three-day weekend opening in the studio's history. All this in spite of "Deep Impact" producer's Steven Spielberg protestations that the March report of a possible 2028 Earth impact by asteroid 1997 XF11 was not generated by the studio's marketing department!

This film is also popular politically. For several weeks, NSS grassroots activists have been using the film's opening to communicate the issues surrounding impacts and impactors to media and opinion leaders in their communities. Through resource packets, theatre displays and in-school presentations, NSS members are providing the American public with much of the basic information they are requesting. Answers to questions as basic as: "What is the difference between an asteroid and a comet?" A good question, considering that "Deep Impact" features a cometary impact, while "Armageddon," due for release on July 1, features impact from asteroids.

The products that come out of Tinseltown are often described as "the stuff of imagination." Certainly, "Deep Impact" and, later this summer, "Armageddon," are primarily derived from the imaginations of their creators. In fairness, however, we should note the considerable commitment made by the producers of "Deep Impact" to work with NASA, its scientists and members of the scientific community who specialize in impact studies to base much of the film's fiction on science fact. But nothing should be left to the imagination when analyzing the peril that can be associated with these objects.

THE PERIL

Scientists believe that dinosaurs became extinct as the result of an asteroid ten miles in diameter impacting the Earth 65 million years ago near what is now the Yucatan, creating a huge crater and mile-high tidal wave that swept what is now the eastern United States, and throwing enough debris into the Earth's atmosphere to cause significant climate change over a considerable period.

In 1908 a comet exploded over Siberia with a force of at least ten megatons leveling a forest 50 miles across. On Nov. 22, 1996, a small asteroid hit Honduras and made a crater 165 feet wide. And there have been many near misses -- lists of which can be found in almost any book about impacts that you read.

The NSS believes that major asteroid impacts are a threat to our planet and to the human race. They are infrequent, but potentially very destructive. We do know that there must be many more Near Earth Objects (NEOs) than scientists have tracked to date. But we do not know how many are in a position to cross Earth's orbit. Completing a systematic process of identification and cataloguing as quickly as within the next 10 - 20 years, and mounting missions to better understand comets and asteroids, should be major priorities.

The United States should have a comprehensive ongoing search capability and a fast-response plan. NASA's announcement in April that it is designating a new field office to "increase financial support for the detection and characterization of NEOs" is encouraging. As other witnesses will no doubt have testified, ensuring adequate funding for such a search is the first step.

What to do next -- and when to do it -- are additional components of a serious NEO detection, survey and mitigation program.

I am certain that the witnesses for this hearing will have presented persuasive arguments on behalf of the critical need to accelerate , and then to mount space missions to provide vital information on NEO composition.

What I would like to address in greater depth is the issue of mitigation. If destroying an NEO was left up to Hollywood, all we would need do is recruit "a few good men," launch them into space in a slightly altered shuttle, loft several nuclear devices at the objects and pray for the best.

But this is not Hollywood.

The primary objective to stopping a threatening asteroid is to nudge it slightly as far as possible before its predicted collision. This "nudge" will change its orbit enough so that it would miss the Earth entirely. A few centimeters per second change in the asteroid's velocity several years before a predicted impact can move the asteroid thousands of kilometers away from the threatened area. Moreover, nudging the asteroid when it is farthest from the sun -- at "aphelion" -- has the highest leverage.

There are two plausible ways to move an asteroid. The first, which would be applicable for smaller asteroids similar in size to the comet that exploded over Tunguska in 1908 (the most likely size of threat that we face in coming decades), would be to hit it with a modest size spacecraft. A one-ton spacecraft would impart over a kiloton of kinetic energy; a ten-ton spacecraft then would provide the kinetic energy equivalent of the Hiroshima atomic bomb. This force would be sufficient to move something up to a half kilometer in size.

However, there are complications. If the asteroid is not a solid rock but more of a "rubble pile" as some appear to be, or if the object was a comet nucleus as we believe the Tunguska object may have been, the spacecraft impactor may fly right through the object or not generate enough kinetic energy to create a meaningful orbit change.

In those cases, the spacecraft may have to be comprised more of an extended mesh rather than a single satellite. Moreover, we must hit the asteroid near its center of mass; a hit on its edge could just add energy to the asteroid's rotation and not change its orbit significantly.

For a larger asteroid, such as the one that led to the extinction of the dinosaurs, the only way to move it enough would be to use a nuclear charge. A direct hit with the nuclear device, however, may do very little, or might even break up the asteroid into a number of smaller but even more dangerous objects. Thus, most experts suggest that the nuclear device be detonated some hundreds of meters from the asteroid's or comet's surface.

Where is a nuclear blast not a blast? In space. A nuclear explosion in space releases a large and sharp radiation pulse, but there is no blast wave because there is no air to support one. When the radiation encounters an object's surface, it deposits heat energy into the surface, much of it to a relatively shallow depth. If the pulse is strong; i.e. if the object is nearby, the heat deposition will be enough to instantly vaporize and ablate some of the surface. As the vapor streams away, it delivers an impulsive thrust to the surface. This phenomenon has been called "x-ray slap." The effect of that slap on the NEO depends on the intensity and distribution of the slap; i.e., the size of the nuclear device and its position relative to the object, as well as the composition of the object.

The result? Deflection, disruption or both. The resulting blast would blow off a portion of the NEO's surface material which, in turn, would push the NEO out of a collision path with Earth. Again, ample warning time and study are essential. Early warning would also allow another mitigation method for smaller objects -- evacuation of the threatened Earth-side area.

Thus, as we have mentioned before, considerable analysis and study of the target object would be necessary prior to any attempt to move it. The ideal preemptive strike for NEOs, really, is knowledge.

In October 1997, the Administration wielded its line-item veto power against the Department of Defense (DoD) Clementine II mission.

Launched in 1999, the mission would have approached an asteroid named Toutatis, sending a rocket equipped with a camera directly to the asteroid. After taking close-up pictures of Toutatis, the camera would have smashed into its surface while the Clementine spacecraft recorded the impact flash and then analyzed any ejected material. The million asteroid intercept mission would have provided vital input to the construction of weapons capable of deflecting asteroids or comets on a collision course with Earth.

Clementine II would have undertaken the first step in direct asteroid mitigation by attempting to strike one or more asteroids to determine their structure and how easy it would have been to move them. At the time, the National Space Society strongly objected to the President's veto and has continued to follow the progress being made by the Department of Defense and other partners to develop alternative solutions. At the time, one of the reasons given by the media for the veto was the "giggle factor" -- the tendency of many in government to scoff at the danger posed by asteroids. The NSS submits that, as evidenced by this hearing, no one is laughing any more about the need to develop a serious program addressing NEOs.

As part of its regroup after Clementine, the DoD is upgrading its network of optical sensors, particularly the GEODDS system, to perform both wide area satellite monitoring and, as a secondary mission, asteroid search. They have been working with the civilian community to make this data available. A preliminary test of the upgraded sensors by MIT's Lincoln Lab has been yielding the largest number of asteroid detections of any sensor system.

In conclusion, I say that the options are there. To choose any one of them in a particular situation requires a comprehensive survey of threatening objects, coupled with in-depth analysis of, and even missions to, both threatening objects and to diverse types of asteroids and comets.

The Society understands that the DoD has offered to co-sponsor scientific community proposals to perform the Clementine II asteroid intercept mission under NASA funding and sponsorship, and that efforts are underway within the scientific community to prepare such a joint proposal. In addition, the DoD continues its microsatellite development efforts. Microsatellites would have been the impactor mechanism for Clementine II and remain the key part of any comprehensive asteroid mitigation effort. One of these microsatellites, XSS-10, is scheduled to fly on the Space Shuttle in 2000 as part of a joint NASA-DoD experiment. Designed as an inspection mission, it has great applicability to future asteroid inspection and impact studies.

The National Space Society urges Congress to continue to support the efforts of the DoD and NASA to create cooperative solutions to the process of gathering knowledge about NEOs.

We also urge this Committee to place on its hearing calendar for 1999 a similar gathering of experts and scientists in order to establish, for the record, progress being made on this very time-sensitive issue.

Finally, we urge this Committee and your fellow Members to communicate with groups such as ours if you ever find yourself doubting the American public's interest in the work you are doing on this issue. As an organization supported completely by individuals from around the world, we stand ready to provide a public litmus test as each new phase is implemented.

Mr. Chairman, thank you for convening the hearing and for providing us with this opportunity for comment.

[For more information, visit <http://www.nss.org/asteroids>.]

Biographical Information
Pat A. Dasch, National Space Society, Executive Director

Ms. Dasch was appointed Executive Director of the National Space Society (NSS) in December 1997. Prior to her appointment, she was Editor-in-Chief of Ad Astra, the Society's magazine, and was formerly Program Director for NSS's popular Dial-A-Shuttle program.

Prior to joining the NSS's Washington, D.C. headquarters staff in 1994, Dasch worked for SAIC (Science Applications International Corporation) as a Planetary Science Analyst in the Solar System Exploration division at NASA Headquarters.

Educated at the University of East Anglia and Oxford University, Dasch worked initially on Earth remote sensing and worked in the Shuttle Earth Observation Program while a Research Associate at the Lunar and Planetary Institute (LPI) in Houston, TX, during the 1980s. From Earth remote sensing she moved into planetary imagery analysis and comparative planetology.

Throughout her space science career, Dasch has published commentary on the space program while also working to convey the fascination of her research to the general public. She has prepared several shuttle Earth observation slide sets released by the LPI. Her most recent educational slide set, "Ancient Life on Mars," produced with Allan Treiman, was released in March 1997.

She has taught university classes in remote sensing and planetary imagery, and undertaken teacher education seminars for the National Air and Space Museum. Her first book, Images of Earth with co-author Peter Francis, won the award for best remote sensing publication of 1984. Dasch is currently working on a second book, Icy World in the Solar System, for Cambridge University Press (CUP) and has a contract, also with CUP, for a third book, Impacts and Asteroids.

Dasch was born in Hampton Court, England. She lives in Washington, D.C., with her husband Julius.