3.4 Observing Moving Targets during Cycle 4

Once SOFIA achieves its nominal operating capabilities, it will be able to observe solar system targets by (i) guiding on the object itself, (ii) offset guiding from field stars, or (iii) predictive tracking based on accurate ephemerides. As of this writing, the non-sidereal tracking capabilities have been implemented, but have not been fully tested. Consequently, programs requesting non-sidereal tracking will inherently involve greater risk. Nevertheless, the SOFIA project will make every attempt to observe Solar System targets in highly ranked proposals.

Successful guiding on a moving target requires it to be bright at visible wavelengths, where the guider cameras operate. Our current estimate is that we will be able to guide on solar system targets with R ≤ 10 and that have a non-sidereal angular speed of 1'/s or less. The minimum acceptable solar elongation for a target is limited by the lower elevation limit of the telescope and the rule that no observations can be acquired before sunset or after sunrise. For Cycle 4, the minimum solar elongation is 25 degrees.

Identification of solar system targets will be done manually by the Telescope Operator by inspecting images obtained with the FPI. The ephemerides of the proposed target must be accurate enough to allow for unambiguous identification. While the required accuracy could vary somewhat based on the complexity of the background star field, it should in general be better than about 30\arcsec.

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