Thursday, November 8, 2007
10:00 a.m. - 12:00 p.m.
2318 Rayburn House Office Building
On Thursday, November 8, 2007 at 10:00 a.m., the House Committee on Science and Technology's Subcommittee on Space and Aeronautics will hold a hearing to examine the status of NASA's Near-Earth Object survey program, review the findings and recommendations of NASA's report to Congress, Near-Earth Object Survey and Deflection Analysis of Alternatives, and to assess NASA's plans for complying with the requirements of Section 321 of the NASA Authorization Act of 2005.
Astronomers estimate that millions of asteroids, comets, meteoroids, and other cosmic debris orbit within the vicinity of Earth and the Sun. The Earth is continually bombarded by these remnants from the formation of the solar system. Small objects ranging from the size of a dust particle up to a size of about 50 meters in diameter do not pose impact threats to Earth, because they burn up and disintegrate upon entry to the Earth's atmosphere. However, larger objects pose potentially catastrophic threats because they would not disintegrate before impacting the Earth. Near-Earth Objects (NEOs) are defined as asteroids and comets whose trajectories bring them within 45 million kilometers (km) of the Earth. NEOs larger than about 140 meters, whose orbits about the Sun bring them within 7.5 million km of the Earth's orbit, are classified as potentially hazardous objects (PHOs). Most of these objects are asteroids. According to NASA, there are currently 900 known Potentially Hazardous Asteroids (PHAs). NASA scientists estimate that the population of PHOs is about 20,000 objects.
The literature on NEOs is not entirely consistent on the threats posed by various sizes of objects. Information from NASA's Near Earth Object Program webpage [http://neo.jpl.nasa.gov] and other sources indicates the following:
Past NEO Impacts and Events
Evidence from past major NEO impacts or aerial explosions illustrates the catastrophic consequences that these objects can have:
Within the last two decades, instances of objects that passed near Earth brought increasing interest in identifying NEOs and exploring options to protect Earth from a potential NEO impact. For example:
Determining the population of NEOs, including those in the PHO category, can only be achieved by conducting a search campaign using ground-based or space-based telescopes, or a combination of the two.
Previous Congressional Actions Related to NEOs
Congress has taken a number of steps since 1990 to promote increased understanding of NEOs and the potential threat they pose, as well as potential options for protecting Earth from hazardous NEOs. In 1990 the National Aeronautics and Space Administration Multiyear Authorization Act of 1990 directed NASA to conduct two workshop studies on NEO detection and interception. In 1993 the House Science and Technology Committee held a hearing to review the results of the two reports, and in 1994 [by means of House Report 103-654, which accompanied the National Aeronautics and Space Administration Authorization and Space Policy Act for Fiscal Year 1995] gave further direction to NASA to coordinate with the Department of Defense and international space partners on identifying and cataloging NEOs greater than 1 kilometer in diameter that are in an orbit around the Sun that crosses Earth's orbit within the next decade. In 1998, NASA established a Near-Earth Object Program Office at the Jet Propulsion Laboratory and established its Spaceguard Survey. The Survey had the goal of detecting and cataloging 90 percent of NEOs 1 km or larger by the end of 2008.
NASA's Current NEO Survey Program and Budget
The Spaceguard Survey was housed in NASA's Exploration Systems Mission Directorate in recent years, but earlier this year it was moved to the Science Mission Directorate. NASA's report to Congress states that the current budget for the program is $4.1 million per year for Fiscal Years 2006 - 2012. NASA officials report that the annual budget is allocated as follows: $3 million are used to support the search teams and ground-based telescope facilities, $500,000 is allocated to JPL for studies on near-Earth objects, $400,000 is provided to the Minor Planets Center at the Smithsonian Center for Astrophysics to refine the orbital coordinates of NEOs that have been detected, and the remainder is allocated to additional NASA-funded studies.
NASA's report to Congress states that as of December 2006 the Spaceguard Survey had identified 701 of the estimated 1100 NEOs larger than 1 km that are believed to exist.
Recent Congressional Action on NEOs
Section 321 of the 2005 NASA Authorization Act directed NASA "to plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near-Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects 5 to the Earth. It shall be the goal of the Survey program to achieve 90 percent completion...within 15 years after the date of enactment of this Act." Section 321 also directed NASA to report to Congress on an analysis of ground-based and space- based alternatives to conduct the Survey; a recommendation on which Survey option to pursue and a proposed budget; and an analysis of options to divert an object that threatens impact with Earth.
NASA's Near-Earth Object Survey and Deflection Analysis of Alternatives Report to Congress
NASA's report, Near-Earth Object Survey and Deflection Analysis of Alternatives, Report to Congress, prepared in response to Sec. 321 of the NASA Authorization Act of 2005, was submitted to Congress in March 2007. The study was led and managed by NASA's Office of Program Analysis and Evaluation. The report is a condensed version of a longer, un-circulated version that included the analysis on which findings of the report to Congress were based. The 2007 report to Congress provides options for meeting the Survey goals by 2020, as required in the Act, and options for meeting the goals on a longer timeframe. However, the report does not provide Congress with NASA's recommended option for conducting the Survey or provide a cost estimate for that Survey.
The report's basic conclusion is that "NASA recommends that the program continue as currently planned, and we will also take advantage of opportunities using potential dual-use telescopes and spacecraft--and partner with other agencies as feasible--to attempt to achieve the legislated goal within 15 years. However, due to current budget constraints, NASA cannot initiate a new program at this time."
In addition, the report contained a number of additional findings, including:
The NASA report also describes the general advantages and disadvantages of using ground versus space-based search systems and analyzes an approach that includes a combination of ground-based and space-based NEO search capabilities:
The NASA report suggests that the goals of the Congressionally-mandated survey could be met by acquiring shared access to a proposed ground-based NSF/DOE, telescope system, the Large Synoptic Survey Telescope (LSST) and a potential Air Force telescope system, the Panoramic Survey Telescope and Rapid Response System (PanSTARRS). In addition, this exemplar search program would require an additional LSST-type telescope dedicated to the NEO survey effort.
LSST is proposed as a large-aperture, wide-field telescope. According to literature from the LSST project, the telescope will "Conduct a survey over an enormous 7 volume of sky; do it with a frequency that enables repeat exposures of every part of the sky every few nights in multiple colors; and continue this mode for ten years to achieve astronomical catalogs thousands of times larger than have ever previously been compiled." LSST was recommended as a high priority initiative in the 2001 National Academies Astronomy and Astrophysics Decadal Survey. In addition, the 2003 National Academies Solar System Exploration Survey included the following recommendation: "The SSE [Solar System Exploration] Survey recommends that NASA partner equally with the National Science Foundation to design, build, and operate a survey facility, such as the Large Synoptic Survey Telescope (LSST)... to ensure that LSST's prime solar system objectives are accomplished..." LSST has not yet been approved as new project start by the National Science Foundation.
The director of the LSST project is expected to testify that LSST could complete the mandated survey within 12 years from the start of the telescope operations. This goal would involve modifications to the observing strategy and to the data processing procedures. The LSST project estimates that the cost of an LSST NEO survey over 12 years would be about $125M.
PanSTARRS is being developed by the University of Hawaii with funding from the U.S. Air Force. A main goal of PanSTARRS is to detect potentially hazardous objects. PanSTARRS is planned to be a system of four individual telescopes that will survey large areas of the sky at a high degree of sensitivity. The prototype one-mirror PanSTARRS telescope is complete; a full 4-telescope system has not yet been approved.
The NASA report to Congress also indicates that by using a space-based infrared telescope [along with the LSST and PanSTARRS systems], NASA could exceed the mandated requirement and detect an estimated 90 percent of the PHO population by 2017.
An additional capability that could be brought to bear on the NEO survey task is NASA's Wide-field Infrared Survey Explorer (WISE), which is scheduled for launch in 2009. The WISE spacecraft will survey the sky in the infrared band at high sensitivity. Asteroids, which absorb solar radiation, can be observed through the infrared band. NASA officials told Committee staff that NASA plans to use WISE to detect NEOs, in addition to performing its science goals. NASA expects that WISE could detect 400 NEOs [or roughly 2 percent of the estimated NEO population of interest] within the spacecraft's 6 month - 1 year mission.
It should be noted that the National Academies' 2001 report New Frontiers in the Solar System report [the solar system exploration decadal survey] commented on the potential value of ground-based observatories for detecting near-Earth objects: "The SSE Survey's Primitive Bodies Panel endorses the concept of a large telescope capable of an all-sky search strategy that would reveal large numbers of near-Earth objects...also endorses a telescope that would enable the physical study of such objects by spectroscopic and photometric techniques. The panel heard 8 recommendations for the Large Synoptic Survey Telescope (LSST) and the Next Generation Lowell Telescope (NGLT)...Other options, including the Panoramic Optical Imager concept, should be explored and a choice made that NASA can support in the next decade.
According to the NASA report to Congress, once a NEO is identified, further characterization of its mass and orbit are required to "assess the threat" as required in the Act. Characterization involves observations that provide details on an object's structure, whether it is a single or binary NEO, its porosity, rotation rate, composition, and surface features. NASA's report to Congress discusses the need to characterize an object to inform decisions on mitigation.
According to NASA officials, characterization is usually focused on those objects that are identified as posing a potential threat. Both optical and radar ground-based systems can be used, however radar provides precise orbital determinations more quickly than optical systems. A dedicated in-situ mission to observe the object would provide the greatest detail on the character of the object and, according to the NASA report to Congress, help to "confirm the probability of impact and characterize the potential threat if deflection is necessary."
The report presents two broad strategies for diverting asteroids from a collision path with Earth. "Impulsive" options would involve the use of conventional or nuclear explosives and have immediate results. "Slow push" options would achieve deflection results over a period of time.
The report includes the following findings on deflection alternatives:
Critics of NASA's analysis of deflection options argue that NASA's report focuses on atypical asteroid threats rather than the objects of size ranges that have a much higher probability of actually impacting the Earth. They argue that NASA's focus on the less likely scenarios results in a set of deflection requirements that are skewed towards nuclear explosives. If the focus would be placed on addressing the deflection requirements of the smaller, more common PHOs, the critics of NASA's analysis would assert that "over 99 percent of them can be deflected using non-nuclear means." One of the witnesses at the hearing, Mr. Russell "Rusty" Schweickart, will discuss issues related to NASA's analysis of deflection options, as well as identify what he believes are serious technical flaws in NASA's report to Congress.
Planetary Radar Facilities
The Arecibo Observatory in Puerto Rico, which has been described as "the largest and most sensitive" ground-based radar telescope on Earth, has been used to reduce the uncertainty of NEO collision estimates and refine the time period of when a NEO may pass near Earth. In addition, radar observations are more precise than data from optical telescopes in identifying details on the mass, shapes, trajectories, sizes, and on whether the NEO is a single object or part of a binary system. In 2005, Arecibo observations improved the estimates of the trajectory for the object, Apophis, which is on a path that will take it close to Earth in 2029. Research using the Arecibo Observatory also helps improve our understanding of how solar radiation influences near-Earth objects. 10
Arecibo is operated by Cornell University under a cooperative agreement with the National Science Foundation. A 2006 independent review of all NSF ground-based astronomy facilities recommended that "The National Astronomy and Ionosphere Center [Arecibo Observatory] ...should seek partners who will contribute personnel or financial support to the operation of Arecibo... by 2011 or else these facilities should be closed." At present, the planetary radar facility at Arecibo is funded through FY2008. Funding beyond that date is uncertain.
NASA's Goldstone Deep Space Tracking Station
The only planetary radar facility other than Arecibo is NASA's Goldstone Deep Space Tracking Station in Goldstone, California. Goldstone is less sensitive than Arecibo, however its steerable antenna allows it to see a larger portion of the sky. NASA is planning to replace the current Deep Space Network antennas and is looking at a number of options, including phased array antennas. The current replacement options do not appear to provide a planetary radar capability comparable to that of the existing Goldstone facility.
The 2003 National Academies Solar System Exploration Survey report contained the following recommendation: "In addition, NASA should continue to support ground- based observatories for planetary science, including the planetary radar capabilities at the Arecibo Observatory in Puerto Rico and the Deep Space Network's Goldstone facility in California...as long as they continue to be critical to missions and/or scientifically productive..."
NEO Contributions to Science, Human Exploration, and Resource Utilization
The NASA report notes that an increased search for and characterization of NEOs will benefit scientific discovery and study of Kuiper Belt Objects, as well as in determining whether certain comets originated in the Kuiper Belt. Further data on NEOs could also provide information that could be used to consider extracting and using asteroid resources and for considering a potential human mission to an asteroid. A 1998 National Academies Report on The Exploration of Near-Earth Objects notes that:
"Although it would be difficult to justify human exploration of NEOs on the basis of cost-benefit analysis of scientific results alone, a strong case can be made for starting with NEOs if the decision to carry out human exploration beyond low Earth orbit is made for other reasons. Some NEOs are especially attractive targets for astronaut missions because of their orbital accessibility and short flight duration. Because they represent deepspace exploration at an intermediate level of technical challenge, these missions would also serve as stepping stones for human missions to Mars. Human exploration of NEOs would provide significant advances in observational and sampling capabilities."
NEO-Related Activities at the United Nations
The United Nation's Committee on the Peaceful Uses of Outer Space (COPUOS), Scientific and Technical Subcommittee has discussed and considered the issue of NEOs. In 2006, the subcommittee established a Working Group on Near-Earth Objects to focus on the issue over the 2006-2007 timeframe and also formed an Action Team. Over the next 1-2 years, the subcommittee plans to continue to obtain reports on NEO activities and to address the need for more international coordination on observations and follow-up studies. The subcommittee also plans to work on international procedures for handling NEO threats.
Space Science Missions to Comets and Asteroids
In addition to its ground-based Spaceguard Survey program, NASA and non-U.S space agencies have launched, or are planning to undertake a number of space science missions to study asteroids and comets. NASA's report to Congress notes that information gained from these missions benefits the agency's current NEO program. A number of past, current, and future missions of note include:
Wednesday, November 7, 2007
Source: House Committee on Science, Space, and Technology