Placing SOFIA in the central flash for the 29 June 2015 Pluto Occultation

We report on the astrometry prediction process carried out for the 29 June 2015 occultation of an 11.9 magnitude star by Pluto. The occultation star, UCAC2 139-209445 was first identified in 2013 as a good candidate for an occultation to be observed with Stratospheric Observatory for Infrared Astronomy (SOFIA) due to the circumstances of the event. In addition, the event's proximity to the New Horizons encounter with Pluto made the event even more timely. We were awarded time on SOFIA for the Pluto occultation in 2014. From mid-2014 up through the night of the occultation, we tracked Pluto's position. We collected astrometric data from four telescopes: the SARA-CT telescope located in Cerro Tololo International Observatory, Chile; the Lowell Observatory 42-inch Hall telescope; the Lowell Observatory 4.3-m Discover Channel Telescope, both in Flagstaff, AZ; and the USNO 1.55-m Kaj Strand telescope in Flagstaff, AZ. The objective of the astrometric observations was to improve the prediction enough to place the aircraft within the central flash zone (approximately ±75 km, 5mas, from the center line of the Pluto shadow).The prediction uncertainties included those of the star position and proper motion, Pluto ephemeris offset, potential zone-dependent offsets in the reference catalog, unknown stellar duplicity, and center-of-mass to center-of-light offsets. Over the two years since we identified this event as promising, we worked to steadily decrease each of the sources of uncertainty.We communicated prediction updates to the SOFIA flight planning team. We provided a pre-take-off update, which was then followed by a later in-flight update that necessitated a change in the flight plan of 320 km. The crew were able to implement this change and SOFIA was able to capture the central flash of this event (Bosh et al., and Person et al., this conference).