This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

30 August 2011

New Papers on low delta-V asteroids, asteroid mission measurement requirements, Human mission NEO targets, and detection of radiation pressure

Several new papers.


Physical characterisation of low delta-V asteroid (175706) 1996 FG3 

Authors: Stephen D. Wolters, Ben Rozitis, Samuel R. Duddy, Stephen C. Lowry, Simon F. Green, Colin Snodgrass, Olivier R. Hainaut, Paul Weissman (Submitted on 08 Aug 2011)

Abstract: Asteroid (175706) 1996 FG3 is a binary asteroid and the baseline target for the proposed MarcoPolo-R sample-return mission. We present thermal IR photometry obtained with the ESO VLT+VISIR together with optical photometry obtained with the ESO NTT+EFOSC2 . An absolute visual magnitude H_V = 17.833 \pm 0.024 and phase parameter G = -0.041 \pm 0.005 is derived. The Near-Earth Asteroid Thermal Model (NEATM) has been fitted to the measured fluxes to derive a geometric visual albedo p_v = 0.046 \pm 0.014, effective diameter at the observed aspect D_eff = 1.68 \pm 0.25 km, and beaming parameter {\eta} = 1.15 for phase angle {\alpha} = 11.7{\deg}. The Advanced Thermophysical Model (ATPM) has been fitted to the measured fluxes to derive a more accurate effective diameter D_eff = 1.71 \pm 0.07 km and albedo p_v = 0.044 \pm 0.004. Based on the ATPM results, assuming the same albedo for primary and secondary, we derive a primary mean spherical diameter D_p = (1.69 +0.18/-0.12) km, secondary diameter D_s = 0.51 \pm 0.03 km, and a secondary orbital semi-major axis a = (2.8 +1.7/-0.7) km. A low surface thermal inertia {\Gamma} = 120 \pm 50 J m^-2 s^-1/2 K^-1 was also derived, suggesting a dusty surface and raising questions as to the binary formation mechanism of this asteroid. These physical properties are used to predict a Yarkovsky drift in semi-major axis of (-60 +31/-45) m yr-1.

Cite as: 1108.1831v1 [astro-ph.IM]

Link: Paper (PDF format)


Measurement requirements for a near-Earth asteroid impact mitigation demonstration mission 

Authors: Stephen D. Wolters, Andrew J. Ball, Nigel Wells, Christopher Saunders, Neil McBride (Submitted on 21 Jul 2011)

Abstract: A concept for an Impact Mitigation Preparation Mission, called Don Quijote, is to send two spacecraft to a Near-Earth Asteroid (NEA): an Orbiter and an Impactor. The Impactor collides with the asteroid while the Orbiter measures the resulting change in the asteroid's orbit, by means of a Radio Science Experiment (RSE) carried out before and after impact. Three parallel Phase A studies on Don Quijote were carried out for the European Space Agency: the research presented here reflects outcomes of the study by QinetiQ. We discuss the mission objectives with regards to the prioritisation of payload instruments, with emphasis on the interpretation of the impact. The Radio Science Experiment is described and it is examined how solar radiation pressure may increase the uncertainty in measuring the orbit of the target asteroid. It is determined that to measure the change in orbit accurately a thermal IR spectrometer is mandatory, to measure the Yarkovsky effect. The advantages of having a laser altimeter are discussed. The advantages of a dedicated wide-angle impact camera are discussed and the field-of-view is initially sized through a simple model of the impact.

Cite as: 1107.4229v1 [astro-ph.IM]

Link: Paper (PDF format)


Ultra-Low Delta-v Objects and the Human Exploration of Asteroids 

Authors: Martin Elvis, Jonathan McDowell, Jeffrey A. Hoffman, Richard P. Binzel (Submitted on 20 May 2011 (v1), last revised 15 Jun 2011 (this version, v2))

Abstract: Missions to near-Earth objects (NEOs) are key destinations in NASA's new "Flexible Path" approach. NEOs are also of interest for science, for the hazards they pose, and for their resources. We emphasize the importance of ultra-low delta-v from LEO to NEO rendezvous as a target selection criterion, as this choice can greatly increase the payload to the NEO. Few such ultra-low delta-v NEOs are currently known; only 65 of the 6699 known NEOs (March2010) have delta-v <4.5 km/s, 2/3 of typical LEO-NEO delta-v. Even these are small and hard to recover. Other criteria - short transit times, long launch windows, a robust abort capability, and a safe environment for proximity operations - will further limit the list of accessible objects. Potentially there are at least an order of magnitude more ultra-low delta v NEOs but, to find them all on a short enough timescale (before 2025) requires a dedicated survey in the optical or mid-IR, optimally from a Venus-like orbit because of the short synodic period for NEOs in that orbit, plus long arc determination of their orbits.

Cite as: 1105.4152v2 [astro-ph.IM]

Link: Paper (PDF format)


Detection of radiation pressure acting on 2009 BD 

Authors: Marco Micheli, David J. Tholen, Garrett T. Elliott (Submitted on 03 Jun 2011)

Abstract: We report the direct detection of radiation pressure on the asteroid 2009 BD, one of the smallest multi-opposition near-Earth objects currently known, with H ~ 28.4. Under the purely gravitational model of NEODyS the object is currently considered a possible future impactor, with impact solutions starting in 2071. The detection of a radiation-related acceleration allows us to estimate an Area to Mass Ratio (AMR) for the object, that can be converted (under some assumptions) into a range of possible values for its average density. Our result AMR = (2.97 \pm 0.33) x 10^(-4) m^2 kg^(-1) is compatible with the object being of natural origin, and it is narrow enough to exclude a man-made nature. The possible origin of this object, its future observability, and the importance of radiation pressure in the impact monitoring process, are also discussed.

Cite as: 1106.0564v1 [astro-ph.IM]

Link: Paper (PDF format)
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