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- For COARSE accuracy we require about 10-arcminute fidelity, corresponding to about 1 km at the satellite. For FINE accuracy we would like arcsecond fidelity, corresponding to meter-level knowledge of the cross-track satellite position.
- The along-track angular velocity of the satellite is large, the time to cross the field of view being on the order of a second. The along-track requirements on the prediction accuracy may be somewhat weaker, but confirming this requires a more accurate calculation involving the transverse angular velocity of the streak in the detector frame.
- Requirements on the observatory parameters are similar to those on the satellite: kilometer for coarse, meter for fine.
- Requirements on the observation parameters include at least 1 second absolute accuracy on the exposure start and end time, to match the coarse requirement for satellite position.
Accuracy requirement on methods (and so outputs):
- For FINE accuracy refraction and aberration must be accounted for.
- For brightness calculations in advanced mode, 0.1 magnitude is probably more than good enough to assess the scientific impact of streaks.
3.2.2. Modes
PassPredict will have three modes:
- Simple mode, predicting position but not brightness. This should include support for a browser-based interface as well as an API.
- Advanced mode, predicting brightness of the satellite as well.
- A posteriori mode, for identifying streaks or (importantly) possibly compromised fiber spectra — in archives.
- Note that post facto operator ephemerides are often more accurate than predictive ones, in contrast to two-line elements (TLEs) which are never improved retrospectively.
One could separate out the “position [and optionally brightness] of satellite vs time” part from the “what does the streak look like on the image?” part and make them two separate programs.
3.2.3. PassPredict: Considerations for the ephemeris database
The ephemeris database will be an interface to a variety of data inputs:
- The list of satellites to be considered. Each satellite (with a few exceptions that we aren’t interested in) may be labelled by its number in the US satellite catalog. This is a 9-digit integer (currently all but a few objects use only 5 digits, but that’s about to change). Tables are available to look up the satellite name and owner as a function of catalog number, and to look up which catalog numbers are currently in orbit rather than re-entered. Note that
SATCON2 Algorithms Working Group Report
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