Plan to operate the Arecibo Planetary Radar for Near-Earth Object Characterization and Spacecraft Mission Support

Plan to operate the Arecibo Planetary Radar for Near-Earth Object Characterization and Spacecraft Mission Support: 2009-2013 Introduction The Arecibo Observatory’s planetary radar system is a major contributor to our knowledge of the inner solar system It plays a critical role in the tracking and characterization of near-Earth objects (NEOs), and its observations of the planets and their satellites complement and support spacecraft missions With the increasing discovery rate for NEOs and the advent of new, more powerful, search instruments such as Pan-STARRS, NEO observations will dominate Arecibo’s planetary radar program over the coming years However, continuing studies of the surfaces of the Moon, Mars and Mercury are providing significant support for spacecraft missions and new observations of Venus will provide unique information about that planet’s surface and interior Until the newly initiated Pan-STARRS NEO search program begins discovering new objects in a routine fashion, we will not know what the demand for follow-up observations with Arecibo will be but we are anticipating that between 500 and 1,000 hours of observation will be required per year Other planetary observations will require roughly an additional 100 hours The NEO observational program will be a significant ramping up of the current program requiring increased support for operations, maintenance, data acquisition, data reduction and analysis, and submittal of the results to NASA’s Planetary Data System (PDS) for archiving While no funds are being requested for education and outreach programs, NAIC has a vigorous program in this area centered on the Angel Ramos Visitor Center at the Arecibo Observatory Funding for the Center’s building was raised locally in Puerto Rico from the Angel Ramos Foundation and other institutions, and the NSF contributed funding for the exhibits related to astronomy and atmospheric sciences and the Observatory’s role in these disciplines Over 100,000 people visit the facility each year, including approximately 30,000 school children on guided tours A teacher-training program has been conducted during the summers of the past several years, and a new, expanded program of school student visits is being initiated in conjunction with the Puerto Rico Department of Education The Arecibo NEO Observing Program • 2.1 Background and Past Results The radar system on the NSF’s Arecibo Telescope in Puerto Rico is one of only two very high powered radars in the world that are used for studying solar system bodies including NEOs: nearEarth Asteroids (NEAs) and Comets The other one is on NASA’s Deep Space Network 70 m antenna at Goldstone in California’s Mojave Desert With its 300 m (1,000 ft) diameter telescope and radiated power of one megawatt, the Arecibo radar is over 20 times more sensitive than the one on the Goldstone antenna However, because of its limited steerability, Arecibo can only -1- observe about half the sky observable with the Goldstone antenna making the two systems very complementary Because of its greater sensitivity and scheduling flexibility, the Arecibo radar system has carried out 65% of all radar observations characterizing NEOs, 47% of the known binary NEOs were discovered with Arecibo (most of the rest were discovered with optical telescopes), and data from Arecibo was used for 85% of the NEOs for which precision radar distance and velocity astrometric measurements have been made for orbit determination Radar has been used to study 220 near-Earth asteroids with the great majority of the observations being made by Arecibo The NSF and NASA funded 1990’s upgrading of the Arecibo telescope and radar system combined with the increasing discovery rate of NEOs have resulted in a series of breakthrough results based on both astrometric and imaging observations Highlights of the imaging (characterization) observations include; 1) Observations by both Arecibo and Goldstone of 4179 Toutatis provided the first of many high quality radar models of NEAs (Hudson et al., 2003; Fig 1); 2) The first of many contact binary NEAs, 4769 Castalia, was discovered (Hudson and Ostro, 1994); 3) the existence of true binary NEAs was confirmed in 2000 (Margot et al, 2002), allowing asteroid densities to be directly measured for the first time; 4) Subsequent observations have shown that 16% of NEAs are in binary configurations (Fig 2), an important input to planning for the mitigation of a NEA which may threaten Earth; 5) The first triple NEA was discovered in February, 2008 (Fig 3) further complicating mitigation planning -2- Figure Model of the near-Earth asteroid 4179 Toutatis derived from Arecibo and Goldstone radar observations Image courtesy of R S Hudson (Washington State University) and S J Ostro (JPL) Figure Left: Model of the main body of the binary asteroid 1999 KW4 based on radar observations Right: Model of the binary system for 1999 KW4 from radar observations showing the smaller “moon” in orbit about the main body Images courtesy of S.J Ostro (JPL) and D Scheeres (University of Michigan) Figure Five images of the triple asteroid SN 263 made with the Arecibo Observatory radar system in February, 2008 The main body is about km in diameter, the larger moon about km -3- and the smallest body is about 400 m in size Image courtesy of M Nolan, NAIC/Arecibo Observatory One category of interest is the “Potentially Hazardous Asteroids” (PHAs), those that can potentially come within 0.05 AU of the Earth given their orbital uncertainties Over the past few years, the accuracy of the Earth impact prediction based on precision radar astrometry for a few PHAs has been limited not by the accuracy of the radar measurements but by the inability to accurately model all of the very small forces on these objects in addition to that due to the Sun’s gravity One of these forces, the Yarkovsky effect, is related to sunlight absorbed by the body and its re-emission as heat Precision radar astrometry over several years of a small asteroid, Golevka, demonstrated in 2003 (Chesley et al, 2003) that this effect can modify the orbits of small asteroids significantly even over decades This has revolutionized our understanding of how small asteroids in the main asteroid belt between Mars and Jupiter are transported into the inner solar system to become NEAs and, some, PHAs In an analogous manner to the Yarkovsky effect, solar radiation can also modify asteroid rotation states via the YORP effect This effect was recently confirmed by a combination of Arecibo radar and optical observations (Taylor et al, 2007) The rotation state of an NEA is an important input to modeling the influence of the Yarkovsky effect on asteroid orbits The power of radar astrometric observations to contribute to determining whether a particular NEA poses a hazard to Earth was demonstrated by the recent observations of Apophis This small, several hundred meters, NEA was detected optically in June, 2004 and an orbit determination made that showed it approaching very close to the Earth on April 13, 2029 Arecibo radar astrometric observations in 2005 and 2006 resulted in a much more precise orbit prediction indicating that Apophis would pass significantly closer to the Earth on April 13, 2029 than the prediction based on optical observations, so close that, while it will definitely miss Earth, it will pass inside the orbits of our geosynchronous satellites (Giorgini et al, 2008) Apophis will again approach Earth in 2036 and with the probability of an impact depending on it passing through a “keyhole” approximately 600m in size, on its passage by Earth in 2029 making the probability of an impact in 2036 very low However, the NEA needs to be monitored and the next opportunity for radar astrometric measurements is not until 2013 If an impact cannot be ruled out using measurements obtained in 2013, then additional radar data are ten times as likely to rule out an impact as optical observations alone (Chesley, 2005) The Apophis experience clearly demonstrates the power of radar astrometric measurements to allow precise orbit predictions far into the future Apophis may end up as just a near miss but this may not be true for other NEA/PHAs discovered in future searches 2.2 Proposed NEO Program Near-Earth Asteroids: As discussed above, radar observations play an important role in predicting the future orbits of NEAs and measuring many of their physical characteristics such as size, shape, rotation state and, in the case of binary objects, their mass and density Radar can measure distances to NEOs to an accuracy of about 10 m (30 ft) and their line-of-sight velocity to an accuracy of about mm per second (12 ft per hour), orders of magnitude better than the -4- equivalent optical measurements For potentially hazardous asteroids (PHAs), optical observations based on measuring their changing position on the sky over days or weeks in many instances cannot rule out a possible future impact with the Earth To so can require optical positional measurements spanning years or decades and would still not have the positional accuracy obtained by combining optical and radar distance and velocity measurements over a very short time span For future searches, radar astrometry, the measurement of distance and line-of-sight velocity, can be used to help cull the number of PHAs – not all the newly detected NEOs will be observable with radar - so that we can concentrate on the few that really are potentially hazardous For these objects, additional precision radar measurements are extremely important to assess the impact probability and the need to take action to mitigate the threat Over 70% of PHAs will be observable with the Arecibo radar within 20 years of their discovery and 60% within 10 years (Fig 4) Figure Fraction of NEAs that can be observed by radar for astrometry (red) or characterization (black) The more we know about NEOs in general, and about specific ones that pose a threat to Earth, the easier it will be to design effective mitigation strategies “Know your enemy” would seem to be good advice in this instance Since spacecraft can visit only a few Near Earth Objects, Earthbased radar, by providing measurements of their sizes, shapes and rotation states, is the best method for understanding their diversity The single clearest result of the Arecibo and Goldstone radar observations of NEOs is the discovery of the great variation in their properties; they are not just a collection of collisional shards This suggests a similar variety in their production and in the mechanisms that deliver them into near-Earth orbit Any activity that depends on the physical properties of near-Earth objects, such as hazard mitigation, resource utilization, and the study of meteorite delivery, must take into account the heterogeneity of the NEO population The great variety of sizes, shapes, rotation states and configurations (binaries), means that reasonable statistics for the population requires observations of a large number of objects NEOs form a very diverse population encompassing a large range of sizes, shapes, rotation states, densities, internal structure and binary nature While spacecraft have visited a very small number of NEOs, radar provides by far the best and cheapest, means to survey these characteristics for a large number of -5- objects Knowing the range of characteristics facilitates the design of effective mitigation techniques that can be applied to an object with any of these characteristics For an object that we know poses a direct threat to Earth, radar can provide vital input to mitigation planning including planning for any precursor space mission In addition, scientific missions to asteroids use radar reconnaissance for target selection and mission planning The large number of asteroids to be discovered by the new asteroid search programs coming on line as part of the Pan-STARRS and, eventually, the Large Synoptic Survey Telescope (LSST) projects will require a significant increase in the frequency of radar observations to keep up with characterization and precision astrometry of the discoveries The Arecibo Observatory and the Pan-STARRS project are negotiating a Memorandum of Understanding that will facilitate the rapid transfer of information on new NEO detections to the Observatory Once the initial Pan-STARRS telescope is in routine operation – thought to be in about one year – we will have a much better idea of its discovery rate for NEOs, how many of these are in orbits making them potentially hazardous to Earth, and how many of these Arecibo can observe and refine the orbits Many of them will approach close enough the Earth to allow imaging observations with Arecibo, further increasing the database of NEO types and characteristics Until this experience is obtained it is not possible to give a reasonable estimate for the amount of Arecibo radar observing time that will be required We are predicting that it will be in the range of 500 to 1,000 hours per year Comets: Besides asteroids, the other class of NEOs observable with the Arecibo radar is comets A total of 13 comets have been detected with radar (12 of these at Arecibo) This is much smaller than the number of near-Earth asteroid detections, simply because close-approaching comets are rarer than NEAs Nevertheless, the potential scientific payoff from a comet radar detection is high, especially if the comet comes close enough to be imaged by the radar Radar imaging is the only Earth-based method capable of unambiguously determining the size and shape of a comet nucleus, since it is immune to the coma confusion that affects optical imaging Three comet nuclei have been imaged with radar so far, all within the past three years The most recent of these imaging observations was that of Comet 8P/Tuttle in January 2008 Some of the nucleus images from those observations are shown in Fig These images provide strong evidence that Tuttle is a contact binary, the first binary comet (orbiting or contact) that has been observed In addition to nucleus detection and imaging, radar observations can also detect echoes from a surrounding cloud of large grains in the inner coma Since radar echoes are only sensitive to grains larger than a few centimeters, the detection of a "coma echo" can provide unique information on the large-size end of a comet's ejected particulate distribution Large cometary grains are important not only because they comprise a large fraction of the total nucleus mass loss, but also because they contribute to meteor streams, infrared dust trails, and the overall interplanetary dust budget Nine of the 13 radar-detected comets, including 8P/Tuttle, have shown echoes from large-grain comae, illustrating the important role of large-grain production in cometary activity Finally, it is important to stress the role that Earth-based radar can play in supporting or complementing comet spacecraft missions Radar can help to identify comets that would make potentially interesting spacecraft targets (such as Tuttle) Comparisons between radar and spacecraft observations of the same comet enhance the science return of a comet mission In fact, an excellent opportunity for this comes in October 2010, when the Deep Impact -6- spacecraft is scheduled to make a flyby of Comet 103P/Hartley At that time Hartley will only be 0.120 AU from Earth, making it an excellent radar opportunity for Arecibo Figure Sequence of radar images of the nucleus of Comet 8P/Tuttle from Arecibo observations on January 4, 2008 The time lapse between images is 26 minutes This image shows Tuttle to be a contact binary with a total length of 10 km and a rotation period of 11.4 hours Image courtesy of J Harmon, NAIC/Arecibo Observatory Planets and Satellites The Moon: The Arecibo radar systems provide a unique capability to probe far below the visible surface of the Moon in support of resource and hazard studies for human exploration In particular, the radar data reveal variations in the abundance of titanium-bearing minerals, the thickness of resource-bearing volcanic ash deposits, and the subsurface properties of areas in permanent shadow that may harbor water ice Ongoing radar work will map the entire visible hemisphere to aid in landing site planning, and in the geologic interpretation of other types of data from missions like the Lunar Reconnaissance Orbiter -7- Figure An Arecibo 12.6-cm wavelength radar image of the Aristarchus Plateau, a 200-km uplifted region covered by fine-grained, radardark volcanic ash deposits that may contain important resources for lunar explorers The curved feature at center is the largest volcanic channel on the Moon Aristarchus crater, 40 km in diameter, is the bright circular feature at lower right Image courtesy of B A Campbell, Smithsonian Institution Venus: One of the major unanswered questions about Venus is whether the planet is still geologically active and, if so, how active? The Arecibo radar has the capability to image the surface of Venus at km resolution (Fig 7) Current images suffer from ambiguity problems but the installation of 13 cm wavelength receiver systems on the EVLA, the National Radio Astronomy Observatory’s interferometric array of antennas in New Mexico, expected to be completed by 2012, will allow unambiguous radar imaging of Venus at km resolution with transmission from Arecibo and reception of the echoes with the EVLA Comparison of new imagery with Magellan images would potentially allow recent large volcanic outflows to be detected Figure 7: Arecibo/Green Bank Telescope radar image of Venus at km resolution The Theia Mons volcano is visible at lower left and Sappho Mons at middle right This image was obtained in les than 30 minutes Image courtesy of D B Campbell, Cornell University -8- Precise radar speckle interferometric measurements of the spin vector of Mercury using the Goldstone, Arecibo and Green Bank Telescopes have shown that Mercury still has a molten outer core (Margot et al, 2007) Similar precise (one part in 10 for the spin rate) measurements of the spin vector of Venus will allow its precession rate to be measured providing information about the internal structure of that planet Mars: Despite the great successes of Mars orbiters and landers in recent years, Earth-based radar continues to make unique and complementary contributions to Mars studies Arecibo remains at the forefront of this work, thanks to the enhanced sensitivity afforded by the last telescope upgrade The first Mars observations with the upgraded S-band radar were made during the planet opposition in late 2005 These observations produced high-quality radar images covering much of the planet surface at 3-km resolution Similar observations were also made during the 2007/8 opposition and additional observations are planned for the 2010 and 2012 oppositions (after which Mars passes south of the telescope pointing window for several cycles) Probably the most important utility of this type of radar imaging is for mapping spatial variations in small-scale surface and near-surface roughness (rough lava flows, rocks, etc.) An example of an Arecibo radar image from the 2005 observations is shown in Fig Although the HiRISE imager on the MRO spacecraft can achieve resolutions approaching the decimeter scales to which the Arecibo roughness measurements are sensitive, it cannot see below surface dust mantles and also does not give the sort of large-scale coverage that radar can provide with just a single observation The radar reflectivity images are not only of intrinsic scientific interest for what they tell about Mars surface texture, but also provide a resource for lander site evaluation and for planning future Mars orbiting synthetic aperture radar (SAR) missions Figure Arecibo radar image of the Elysium region of Mars Bright shades correspond to strong radar echoes, mostly from rough-surfaced lava flows The surface resolution averages km and the lines demarcate 10 degrees of latitude or longitude 3 Technical IssuesIssues Technical -9- The Arecibo planetary radar system has two major and several small maintenance and upgrading requirements to bring it to, and maintain, full performance The most immediate concern is the primary electrical power, about 2.5 MW, needed for the transmitter This is currently provided by a Solar turbine generator as the commercial power line does not have adequate capacity The generator needs a major refurbishing and also does not meet current environmental requirements The cost of correcting these problems or, alternatively, upgrading the commercial line, could be as high as $1.5M This issue is under active study by Cornell University In the slightly longer term, new klystrons will be needed for the transmitter The transmitter requires two klystrons and we have one spare However, the klystrons are now 14 years old, two of them have been rebuilt and their reliability is in question The lead-time for procuring new klystrons is over one year Three new klystrons would cost over $1M A number of small improvements are needed in the radar system’s data acquisition hardware, data analysis systems and data archiving capability Education and Outreach As mentioned in the Introduction, the Angel Ramos Foundation Visitor and Educational Facility at the Arecibo Observatory opened to the public in early 1997 Since then, over 1,000,000 visitors have enjoyed its educational exhibits program This represents an annual average above 100,000 visitors, with children (mostly in the form of school groups and summer camps) accounting for 25% of the visitor flow About 500 school groups are scheduled every year, providing island-wide representation Other education and outreach aspects at the Arecibo Observatory, either made possible or enhanced by the Angel Ramos Foundation Visitor Center, include the Teacher in Residence Program, summer teacher workshops, and numerous local media presentations related to space science events A pending grant from the Puerto Rico Department of Education is expected to increase the number of school groups visiting by approximately a factor of two beginning mid-2008 - 10 - S-Band Planetary Radar Program Budget – PY 2009-2013 This budget is based upon the a program budget for NAIC operations of $3,000,000 per year in FY 2009-2013, with the earlier years addressing outstanding maintenance requirements, and ramping up the NEO observations program as the Pan-STARRS and other NEO detection programs come on line The funding proposed provides support for directly affiliated S-Band operating staff and the procurement of supplies and services for operation of the MW S-Band Planetary Radar Transmitter located at the NAIC’s Arecibo Observatory These operating funds are in addition to NSF and other amounts devoted to the base observatory operation The budget estimate assumes a 4% inflation rate and is rounded to the nearest $500 for clarity - 11 - EXPLANATION OF BUDGETED NAIC S-BAND RADAR OPERATIONS FUNDS DIRECT LABOR Salaries and Wages Funds are budgeted for equivalent staff members in Program Year 2009 (increasing to 16 FTE by 2013) engaged in various activities associated with the NAIC S-Band Planetary Radar Program conducted at the Arecibo Observatory These staff positions have been crucial to the successful planning and operation of the S-Band planetary radar system and, in the forthcoming period, will be critically involved in its observational operations The additional employees will include several staff members to perform the additional datataking, processing, and archiving tasks required for the increased observing load In addition, we will add three students, one postdoctoral, one doctoral, and one undergraduate, in order to assure the future health of the program Archival of all data will be a formal part of this program OTHER DIRECT COSTS - SUPPLIES Datataking Equipment The observatory has developed a datataking system for passive radio astronomy that is also optimized for the full performance of the system For radar we require two additional units, one each for Arecibo and the Green Bank Telescope in West Virginia We also require a data archive computer at Arecibo and an off-site backup at the Planetary Data System Small Bodies Node Turbine Fuel Diesel fuel is used for the turbine generator operation that serves as the transmitter's primary power system during test and observing modes In 2009, we expect to need 500 hours of observation ramping up to approximately 1000 hours per year by 2011 These requirements are approximate, but as fuel represents a substantial fraction of the cost of observation, we assume those values for budgetary estimates Fuel is not subject to indirect cost recovery Electronics equipment Funds budgeted for this period are for the acquisition of vital spare parts of system components needed to readily maintain the transmitter and receiver Site Operations As the program is expected to use a substantial fraction of the observing hours at the observatory, funds are included for general site operations Note that the overhead rate of only 11% does not include any site services, which is included as a direct cost here and for all other funding agreements This item includes the turbine power generator and associated equipment, which were formerly included separately as part of the radar program It also includes general computing facilities, telescope operators, etc The 2009-2010 budget includes a one-time cost of overhauling the prime power gas turbine generator and bringing it into compliance with environmental regulations The 2010-2011 budgets include funds for spare Klystron amplifier tubes, which are required for long-term operations and have a very long leadtime (about 18 months) for purchase - 12 - Travel Travel for scientific meeting and also to the Green Bank Telescope for bistatic observations INDIRECT COSTS Cornell Off-site Facilities costs Cornell’s rate for off-campus facilities is 11%, and is not applied to fuel, capital costs, or subcontracts These charges not provide any site services, but include payroll, legal assistance, certifications, and extensive technical consulting services such as environmental health and safety Over the last 10 years, Arecibo has received good value for these costs - 13 - ... Program conducted at the Arecibo Observatory These staff positions have been crucial to the successful planning and operation of the S-Band planetary radar system and, in the forthcoming period,... services for operation of the MW S-Band Planetary Radar Transmitter located at the NAIC’s Arecibo Observatory These operating funds are in addition to NSF and other amounts devoted to the base... NAIC /Arecibo Observatory Planets and Satellites The Moon: The Arecibo radar systems provide a unique capability to probe far below the visible surface of the Moon in support of resource and hazard