6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 1 Building on NEAT concept M. Gai – INAF-OATo (a) Extension of science case (b) Payload implementation options [aspects not necessarily coincident]

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 2 Proposed science topic: Solar System dynamics Implementation: relative astrometry of Solar System objects vs. reference stars Goals: very high precision ephemerides of planets [deep space navigation] - Fundamental Physics tests – gravitation theories, PPN ,  Context: Best current ephemerides from IMCCE (INPOP) and JPL - ranging data on Jupiter expected from JUNO (2017), JUICE (2033) - ranging data on Saturn from Cassini adequate to current precision

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 3 Hints on Solar System planet observation feasibility NEAT scale: EFL = 40 m  s  5"/mm …thus mapping 50 mas on the sky over a 10 µm pixel Planet typical size: 10" ÷ 40"  N px  200 ÷ 800 pixel … larger individual CCD required, ≥ 1 k pixel Magnitude dilution:  2.5 log N px 2 = 11.5 ÷ 14.5 mag …planets readable as not-too-bright stars Requirement: readout of significant areas [binning feasible] Minor planets: also feasible, smaller size, comparable brightness

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 4 Photon limited astrometric performance [approximate] Planets: diameter / SNR few µas Stars: diffraction size / SNR few µas …for intermediate magnitude stars,  1 hour total exposure Systematic errors: Planets: illumination / mass distribution uncertainty < 1 mas TBC Stars: Gaia catalogue error few ten µas Planet model improvement required  planetary science Expected improvement on ephemerides: one – two orders of magnitude

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 5 Operation requirements Ephemerides approach: global “Grand Fit” of Solar System Many measurements over a few years to cover a reasonable fraction of orbits Side benefit: average systematic errors and astrophysical noise Targets: Jupiter, Saturn, Uranus, Neptune, …? Expected impact on observing time: 5% to 10%

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 6 Payload option: Multiple Field Superposition Rationale: look for reference stars over significant area, with limited size focal plane Concept: Field Of View FOV 2 pivoting around FOV 1, roughly centred on science target Field size: dR  dR Area covered:  2πR  dR

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 7 Field multiplicity: 2 to 4 Field size: ~0º.1 2 fields  strip width 0º.1 4 fields  strip width 0º.3 Expectation on reference stars: Larger number Brighter magnitude

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 8 Rationale for moderate size focal plane detector Impact of primary ionising radiation reduced significantly even with simple shielding [few mm Al] Radiator design adapted to match shielding requirements Fully static detector design Target/reference acquired by satellite pointing Possible implementation: 3  3 mosaic 2k  2k CCDs 10 to 15  m pixels (with focal length tuning)

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 9 Multiple Field Superposition Implementation 4-way beam combiner on a common telescope from GAME concept [M. Gai, SPIE ] Caution: incomplete beam superposition along the optical path  static beam walk (metrology / calibration)  OK for relative measurement  differential astrometry

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 10 Reference star availability assessment Data from GSC II catalogue Target selected for magnitude V ≤ 10 mag total 1,967 objects Reference selected for magnitude V ≤ 12 mag total 320,446 objects Sky region avoiding 3º around poles and zero declination for simpler numerical implemen- tation [1,934 targets; 317,640 reference stars]

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 11 Referenced targets: fraction and density Radius  Base Angle 2 fields: radius ≥ 1º for probability >90% of at least one reference star 4 fields: > 90% at radius ≥ 0º.5; more reference stars radius = 2º % targets with ≥ 1 reference star Histogram: # reference stars / target

6/11/2012 Building on NEAT concept - M. Gai - INAF-OATo 12 Referenced targets: magnitude of reference stars radius = 2º field = 0º.3 radius = 2º field = 0º.1 Histogram of the three brightest reference stars for each target in the sample  1 mag brighter reference stars using 4 fields (0º.3 strip width) vs. 2 (0º.1)

6/11/2012Building on NEAT concept - M. Gai - INAF-OATo13 Conclusions NEAT science case may include Solar System dynamics Reasonable impact on detector requirements (larger field of individual CCD) observing time allocation (≤10%) Technical options Multiple field superposition: improve on density / brightness of reference stars for any target simpler, smaller detection system benefit for shielding against ionising radiation