A presentation by Lt. Col. Lindley Johnson (AFSPC liaison officer to the NRO) stated the joint agency search goal as "To the extent practicable, the National Aeronautics and Space Administration, in coordination with the Department of Defense and the space agencies of other countries, shall identify and catalog within 10 years the orbital characteristics of all comets and asteroids that are greater than 1 km in diameter and are in an orbit around the Sun that crosses the orbit of the Earth."
In November 1998, the joint agency Partnership Council directed the NEO Task Team to staff its recommendations through their respective headquarters to include specific costs, schedule, and trade space of options and their ability to meet the stated goal. These studies concluded that the NEO detection goal can be accomplished with current hardware and funding, meeting the goal by the end of 2009.
The near-term actions to implement this goal are the expansion of the Lincoln Lab (MIT) LINEAR program to use a second 1-m telescope in New Mexico, so that LINEAR will operate 2 telescopes each at 18 nights/month. An effort will also be made to extend operations of the NEAT (JPL) detector on the 1-m USAF GEODSS telescope in Hawaii from 6 to 18 nights/month. Farther in the future, the agencies will transition the NEAT search to a 1.2-m telescope at Hawaii, and the possibility will be investigated for expanding the search to use additional AFSPC telescopes. The general plan in all these observing programs is for AFSPC to provide the telescopes and NASA to support the operations associated with NEO searches.
A more detailed statement of the search strategy and requirements is contained in a letter from NASA Administrator Daniel Goldin to General Richard B. Meyers, Commander in Chief of the Space Command, dated April 6, 1999. In part, Mr. Goldin wrote: "Succinctly stated, the requirement is to search 20,000 square degrees of sky each month and to detect all moving objects in that search space to an apparent visual magnitude of 20.5. Analysis, to date, on the characteristics of the small but significant population of NEOs observed, indicate this depth in magnitude and monthly sky coverage will enable us to inventory at least 90 percent of the entire population of large NEOs (>1 km) within 10 years of the start of the survey, a goal established by the congressional direction given us.
"Currently, there are two search projects that are funded by NASA but which rely heavily on Air Force support. We believe these projects together, when they reach their full potential, will provide the primary means for achieving the above goal. The first is the Lincoln Near Earth Asteroid Research (LINEAR) project, funded by NASA, but which uses both state-of-the-art detector systems developed for the Air Force and two Air Force telescopes at the Experimental Test Site (ETS) at Socorro, New Mexico. The second is the Near Earth Asteroid Tracking (NEAT) project which is currently being supported on one of the operational Maui Ground Electro-Optical Deep Space Surveillance telescopes.
"Cooperative discussions with the Air Force Space Command have led to the identification of an Air Force Research Laboratory 1.2 meter telescope at the Maui site for use by NEAT. If the NEAT camera can be accommodated on this telescope, it will enable the NEAT project to continue making an important contribution to the search effort at the dimmer magnitudes, while allowing the heavily used GEODSS telescope (now used part-time to support NEAT) to be returned to full time space surveillance operations.
"We believe that the two LINEAR telescopes (one currently operating and a second scheduled for future operation) at the ETS and the NEAT camera on the 1.2m at Maui, if operated in close coordination, will be able to search 20,000 square degrees of sky per month for all NEOs brighter than magnitude 20.5. This year our funding for all phases of NEO survey work, including discovery, follow-up, ground-based characterization, support of the Minor Planet Center, and our new program office at the Jet Propulsion Laboratory (JPL) in Pasadena, California, is $3.5M. NASA is committed to sustaining a vigorous search effort until the stated goal is reached. We solicit your continued support to these two projects so important to the success of the NEO survey effort. "We briefly note that our ground-based survey work on NEOs is but a small part of NASA's total program of studying the comets and asteroids that comprise the NEO population. Space-based efforts include NASA's Near Earth Asteroid Rendezvous (NEAR) mission, which will spend a year closely studying the near-Earth asteroid Eros. The Deep Space-1 spacecraft, an exciting technology mission, will study the asteroid 1992 KD. The recently launched STARDUST spacecraft will return cometary dust samples to the Earth in early 2006. NASA has selected another mission, the Comet Nucleus Tour (CONTOUR) mission, to investigate three diverse cometary nuclei. In addition, NASA is a partner on two non-US missions, the ROSETTA mission which will perform a landing on a cometary nucleus and the Japanese MUSES-C mission which will return a sample from a near Earth asteroid. The data returned from these missions on the physical and chemical nature of the target bodies will be absolutely vital if we are presented with a future need to modify the orbit of an Earth-threatening NEO."
The above statements by Lt. Col. Johnson and NASA Administrator Goldin provide a clear and highly specific statement of the NASA and USAF goals and their strategy for meeting these goals. Probably the most difficult task is to achieve NEA detection at V = 20.5 with the 1-m USAF telescopes, which have previously been used for more rapid surveys that do not extend this deep. To achieve the Spaceguard goals, the three NASA-AFSPC telescopes, as well as others supported by NASA (such as Spacewatch, LONEOS, and the Catalina Survey) will need to be coordinated to work together as a team. LONEOS and Catalina are both still in their test phases, and improvements are expected in each over the coming months. In addition, if the anticipated discovery rate is achieved, it will be necessary to enhance the follow-up capability on other telescopes, primarily through international agreements. In this coordinated search, it will not be possible for the discovery telescopes to do their own follow-up, a topic discussed extensively by NASA's Shoemaker Committee in its 1995 report on the Spaceguard Survey.
Meanwhile, following is a snapshot of current discovery performance prepared by Al Harris of JPL. The values in the table are the numbers of NEOs brighter than absolute magnitude 18.0 (e.g., D > 1 km) discovered in successive 6-month periods.
NEA DISCOVERY SUMMARY (D>1km) JULY 97 THRU JUN* 99
*Scaled from actual discoveries Jan-Apr 1999.
We have so far discovered about 18% of the NEAs larger than 1 km. The current discovery rate is approximately 70/yr, dominated by the LINEAR program (using one telescope). The current performance of the survey is roughly a factor of 5 below that required to meet the Spaceguard goals using the criteria that Harris has applied in the past. In a recent re-evaluation of these criteria, Harris now suggests that at this point in the survey, we should be discovering about 500/year, or a factor of 7 more than at present. However, Harris also notes that there is considerable uncertainly in this figure, and additional modeling would be useful. He will be speaking on this subject at the IMPACT workshop in Torino in June 1999.
The expansion of LINEAR to two telescopes and the increased performance anticipated from NEAT could bring this system performance to within a factor of 2-3 of that required if the 1-m telescopes can achieve detections at magnitude 20.5. Additional modeling of the total performance of these instruments used in a coordinated manner will have to be done, as well as actual experience to determine if performance at V = 20.5 is realized. Clearly, however, we have made tremendous strides in the past year, and NASA with its USAF partners has a goal to complete the survey (to 90%) by 2009.
For your information, following is the membership of NASA's NEO Program Office Steering Group (where IAU = International Astronomical Union):
Michael A'Hearn, President of the Solar System Division of the IAU
Andrea Carusi, President of the Spaceguard Foundation
Paula Cleggett, Deputy Associate Administrator, NASA Public Affairs Office
Timothy Ferris, University of California, author
Lindley Johnson, Lt. Col., US Air Force Space Command
David Morrison, President of the IAU Working Group on NEOs
Hans Rickman, Assistant General Secretary of the IAU
Irwin Shapiro, Director of the Harvard-Smithsonian Observatories
Donald Yeomans, NASA NEO Program Manager, JPL
Carl Pilcher, NASA Solar System Exploration Theme Director
Tom Morgan, NASA Planetary Astronomy Discipline Scientist
In a separate news item, the Authorization Committee of the US House of Representatives has passed a 3-year bill for NASA that authorizes expenditure of up to $10.5M for NEO searches for each of the next three fiscal years. This represents an increase of $7M per year over the current and anticipated NASA rate of expenditure for this purpose. This authorization is a clear statement of interest from Congress in pursuing the Spaceguard survey. However, to actually be translated into additional funds for NASA, this House authorization would have to be supported by similar action in the Senate Authorization Committee, plus be voted by the full House and Senate, plus be supported by the respective House and Senate appropriation committees, plus be passed as an appropriation by both House and Senate, plus be approved by the President.