Accurate astrometry is crucial for determining orbits of near-Earth-asteroids (NEAs) and therefore better tracking them. This paper reports on a demonstration of 10 mas level astrometric precision on a dozen NEAs using the Pomona College 40 inch telescope, at the JPL's Table Mountain Facility. We used the technique of synthetic tracking (ST), in which many short-exposure (1 s) images are acquired and then combined in postprocessing to track both target asteroid and reference stars across the field of view. This technique avoids the trailing loss and keeps the jitter effects from atmosphere and telescope pointing common between the asteroid and reference stars, resulting in higher astrometric precision than the 100 mas level astrometry from traditional approach of using long exposure images. Treating our ST of near-Earth asteroids as a proxy for observations of future spacecraft while they are downlinking data via their high rate optical communication laser beams, our approach shows precision plane-of-sky measurements can be obtained by the optical ground terminals for navigation. We also discuss how future data releases from the Gaia mission can improve our results.

The Habex study, commissioned by NASA in preparation for the 2020 Decadal Survey, is evaluating a 4 meter space telescope for high contrast imaging and spectral characterization of extrasolar terrestrial planets. Its off-axis configuration, active structural metrology, and low-disturbance pointing control provide an optimal system for coronagraphs. We present predictions of the Habex performance using a charge 6 vortex coronagraph that have been obtained using numerical modeling techniques developed for the WFIRST coronagraph. The models include realistic optical surface and polarization-induced aberrations, pointing jitter, and thermally-induced wavefront variations. Wavefront control using dual deformable mirrors is simulated to create a dark, high-contrast hole around the star. The results show that current technologies can closely approach the Habex performance goals, and with some additional development in key areas (e.g., deformable mirror surface quality, low-polarization coatings, etc.) over the next few years they should reliably meet them.

We observed the episodically active asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and found that it is no longer active after its recent outbursts at the end of 2018 and the start of 2019. The inactivity during this apparition allowed us to measure the absolute magnitude of Gault of H r = 14.63 ± 0.02, G r = 0.21 ± 0.02 from our secular phase-curve observations. In addition, we were able to constrain Gault’s rotation period using time-series photometric lightcurves taken over 17 hr on multiple days in 2020 August, September, and October. The photometric lightcurves have a repeating ≲0.05 mag feature suggesting that (6478) Gault has a rotation period of ∼2.5 hr and may have a semispherical or top-like shape, much like the near-Earth asteroids Ryugu and Bennu. The rotation period of ∼2.5 hr is near the expected critical rotation period for an asteroid with the physical properties of (6478) Gault, suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spin-up by the Yarkovsky–O’Keefe–Radzievskii–Paddack effect.

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