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Valid Candidate ARM Observation Campaign Paul Chodas, NEO Program Office, JPL/Caltech KISS Workshop on Applications of Asteroid Redirection Technology April 7-9, 2014 1 Numbers of Near-Earth Asteroids (NEAs) • 99% of Near-Earth Objects are asteroids (NEAs). • Current number of known NEAs: ~10,777, discovered at a rate of ~1000 per year. • Since 1998, NASA’s NEO Observation Program has led the international NEO discovery and characterization effort; this responsibility should continue in the search for smaller asteroids. • 95% of 1-km and larger NEAs have been found; the completion percentage drops for smaller asteroids because the population increases exponentially as size decreases. ~60% • Numbers for 10-m-class NEAs: ~20% Estimated population: ~30,000,000 <1% Number currently known: ~380 Estimated number that meet <<1% Ref. Concept orbital criteria: ~10,000 ~95% Number currently known: ~17 2 NEA Population vs. Absolute Magnitude & Size Diameter (km), assuming Albedo = 0.14 7 m ) H (powers of 10) (powers of 140 m Numbers Ref Alt Size Size Number (< Range Range Diagram courtesy of Al Harris 3 NASA’s NEO Search Programs: Current Systems Catalina Sky Pan-STARRS Spacewatch Survey U of AZ U of HI U of AZ Arizona & Australia Haleakala, Maui Arizona • Currently, most Near-Earth Asteroid discoveries are made by: Catalina Sky Survey (60%), Pan-STARRS-1 (30%), and Spacewatch (2%). • Enhancements to current surveys and entirely new surveys are coming online now and over the next 2 years. • These enhancements will increase capabilities to find hazardous asteroids in general, as well as ARM candidate targets. 4 Sky Coverage, Feb.-Mar. 2014 Courtesy of Tim Spahr, Minor Planet Center The Asteroid Search Process & An Interesting Find • Each region of sky is imaged 3-4 times over ~80 minutes. • The images are compared to look for moving objects. • On October 7, 2008, the Catalina Sky Survey found a very interesting object: 2008 TC3, headed for impact. • Discovered at 1.3 lunar distances, 19 hr before impact. • Impact location was predicted 11 hours before impact. • The object was clearly very small and would likely break up on entry. Discovery images of 2008 TC3 from Catalina Sky Survey Primary Enhancements for ARRM Candidate Discovery • NEO Time on DARPA Space Surveillance Telescope • Large 3.6m telescope, first light: Feb 2011, now in testing. • Developed for DoD Space Situational Awareness. • Testing of NEO detection capability: Winter 2013-14 • Routine NEO observing is planned to start in April 2014. • Enhancing Pan-STARRS 1, Completing Pan-STARRS 2 • Increase NEO search time to 50% on PS1: March 2014. • Complete PS2 (improved copy of PS1): Late 2014. • Accelerated Completion of ATLAS • Set of small telescopes with extremely wide fields of view covering the entire night sky every night, but not as deeply. • Final design completed. 1st system completion: Late 2015. • Prototype being set up at Mauna Loa NOAA site. 7 Observation Campaign Enhancements for Discovery In Work or Potential Ops Facility V FOV lim (deg2) Improvements Date Catalina Sky Retune observation cadence Late 2014 Survey: Mt. Bigelow 19.5 8 Increase FOV to 19.4 deg2 Late 2014 Mt. Lemmon 21.5 1.2 Increase FOV to 5.0 deg2 Mid 2014 Increase NEO time to 50% Mar 2014 Pan-STARRS 1 21.5 7 Current Surveys Increase NEO time to 100% Apr. 2014 DARPA SST 22+ 6 Begin bulk data delivery - MPC Apr. 2014 Palomar Transient Improve software to detect 21 7 Mid 2014 Facility (PTF) streaked objects Pan-STARRS 2 22 7 Complete telescope system Late 2014 ATLAS 20 40 Entire night sky every night x2 Late 2015 Future Surveys Vlim = limiting magnitude , FOV = Field of View 8 Radar Observations of ARRM Candidates Bennu (OSIRIS-ReX Target) Goldstone 70 m Arecibo 305 m 2012 XB112, size ~ 2 m Rot period: 2.6 min • For the Reference Concept, a candidate must ! pass < ~6 lunar distances to be detected; ~75% of current candidates could have been detected. • For the Alternate Concept, a candidate must Range pass < ~8 lunar distances to have a high enough ß SNR to detect boulders. • Radar observations can provide: • Size and shape to within ~2 meters. • High precision range/Doppler orbit data. Doppler frequency à • Spin rate, surface density and roughness. 9 9 Infrared Characterization of NEOs NASA InfraRed Telescope Facility (IRTF) • Dedicated Planetary Science Observatory • Spectroscopy and Thermal Signatures • On-call for Rapid Response on Discoveries Spitzer Infrared Space Telescope • Orbit about Sun, ~180 million km from Earth • In extended Warm-phase mission • Thermal Signatures, Albedo/Sizes of NEOs • Longer time needed for scheduling NEOWISE Reactivated NEOWISE • ~3 year warm phase dedicated to JPL NEO Search/Characterization data Sun-synch LEO collection. 10 NEA Characterization Process Rotation, Light curves Shape Initial detection, astrometry, Rough Additional Precise Radar photometry orbit astrometry orbit Precise Rough Approximation of Apparent Absolute Size magnitude magnitude Thermal infrared Approximate Phase curves Albedo Colors, Spectral Spectroscopy type Density Mass Observations Astrometry over Area/Mass Intermediate parameters months or years Ratio Objectives NEA Albedo Distribution Albedo distribution of NEAs at a constant Diameter Albedo distribution of NEAs at a constant H magnitude 0.3 0.4 Median Albedo 0.14 0.3 D H t 0.2 t n Median n a a t t Albedo s s n n 0.24 o o c c t t 0.2 a a n n o i o i t t c c a 0.1 a r r F F 0.1 0 0 0.01 0.1 1 0.01 0.1 1 Albedo Albedo Albedo distribution at a given diameter vs. Albedo distribution at a given H mag. Data from NEOWISE (Mainzer et al.), diagram courtesy of Al Harris ARM Candidate Nomenclature Guide • “Potential Candidate”: – An NEA whose orbit parameters satisfy rough constraints on launch date, return date and total mission ΔV. – Absolute magnitude indicates size lies roughly in the right range: < 10 m for the Reference Concept and ~50-500 m for the Alternate Concept. • “Characterizable”: – Approaches the Earth (or Spitzer) close enough, and with suitable enough observing geometry, that its physical properties can be adequately characterized; or a robotic precursor mission is available. • “Valid Candidate”: – For the Reference Concept, a Potential Candidate whose physical properties have been adequately characterized (size, mass, rotation rate) and lie within acceptable ranges to achieve mission goals. – For the Alternate Concept, a Potential Candidate whose surface has been characterized so that the existence of boulders of the size which can be returned can at least be inferred. – Detailed mission design has been performed using feasible launch and return dates, and the upper bound on the mass (entire NEA or boulder) is less than the maximum return mass from the mission design. • “Selectable Target”: – Meets programmatic constraints (e.g., achievable schedule and acceptable return size), and has identified but manageable risks. 13 Characteristics of Reference Concept Candidates Characteristic Reference Value < 2 km/s desired; upper bound ~2.6 km/s Vinfinity relative to Earth (roughly, 0.85 < a < 1.25, e < ~0.17, i < ~6 deg, à synodic period > ~3.75 years) Natural return to Earth in 2020-2026 timeframe Natural return to Earth (“Return” means close approach within ~0.3 au) <1,000 metric tons Mass (Upper bound varies according to Vinfinity) Spin rate < 2 rpm, < 0.5 rpm desired Rotation State Non-Principal-Axis rotation: OK 7 m < mean diameter < 10 m (roughly, 27 < H < 31) Size and Aspect Ratio Maximum dimension <~13 m, aspect ratio < 2:1 Known Type preferred, but not required Spectral Class (C-type with hydrated minerals desired) 14 Candidates for the Reference Concept • Simulations suggest there are thousands of potential candidate targets suitable for the Reference Concept; the challenge is to find and characterize them. • Current discovery rate of potential candidates: 2-3 per year. • When the discovery enhancements come online, this rate is expected to increase to ~5 per year. • Rapid response after discovery is critical for physical characterization of potential candidates. The process has already been successfully exercised for a difficult- to-characterize candidate (2013 EC20). – Large aperture optical telescopes: Rotation rate, colors, photometry, area-to-mass. – Goldstone and/or Arecibo radar: Size, albedo and rotation state. – Ground-based or space-based IR: Size, albedo and spectral type. – Candidates must approach within ~6 lunar distances to be adequately characterized. • Number of Valid Candidates expected to increase at a rate of 1-2 per year. 15 Physical Characterization of Small ARM Candidates • Radar is essential for obtaining an accurate estimate of size and shape to within ~2 m, as well as rotation state. • Ground-based and space-based IR measurements are important for estimating albedo and spectral class, and from these an approximate density can be inferred. • Light curves are important to estimate shape and rotation state. • Long-arc high-precision astrometry is important for determining the area-to-mass ratio. Assumed albedo p = 0.04 • Mass is estimated from size and shape using an inferred or v assumed density, and it can be constrained by the estimate of the area-to-mass ratio. Even so, mass may only be known to within a factor of 3 or 4. • Final ARM target selection may depend largely on how the Assumed albedo estimated upper bound on the mass of each candidate pv = 0.34 compares with the return mass capability for that candidate. 16 Reference Concept Candidate 2009 BD [1] • Reference Concept candidate 2009 BD, discovered in January 2009, is one of the most well observed small asteroids in the catalog. • Its orbit and optical brightness are extremely accurately known, from hundreds of observations made at 2 dozen observatories. • 2009 BD’s area-to-mass ratio (AMR) and Yarkovsky effect are well measured.
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