Page:SATCON2 Algorithms Report.pdf/5

 In brief, the SATCON1 recommendations call for the ability to flag, mask and repair satellite trails affecting astronomical data (a software tool we call TrailMask), to predict when satellite trails may or will affect specific observations (which we call PassPredict), and to simulate the effects of satellite trails so that the community can assess the scientific impact of those effects on astronomical research.

Our main focus is on ground-based optical images of all kinds. However, we also considered space-based images and spectroscopy. We did not consider the (important) effects of satellite constellations on radio astronomy, although the PassPredict tools should work for single-dish radio observations to the extent that sidelobes are not important.

We are mostly concerned with the large low-Earth orbit (LEO) satellite constellations. However, spacecraft at near-lunar distance are regularly seen by asteroid surveys, so we should consider MEO and GEO (medium Earth orbit and geosynchronous Earth orbit) cases too. Note that the fainter magnitude of high-orbit satellites is offset by their lower apparent angular velocity, leading to larger effective exposure time on a streak pixel.

In Figure 1 we note that the counts in a satellite streak will tend to be independent of exposure time, and so the measured magnitude of the streak will be fainter for longer exposures.



''Figure 1. Effect of trailing on the effective magnitude of a satellite. Red: visual magnitude at zenith of an example satellite as a function of orbit altitude. Blue to Green: observed magnitude of the same satellite accounting for trailing, for a series of increasing exposure times and assuming a 1-arcsecond resolution element. In a given telescope/instrument, as exposure time increases, the number of counts detected from a faint (e.g., 15th magnitude) star will increase, but the number of counts in the satellite trail will not, assuming that the satellite crosses the field of view in a time that is short compared to the exposure time. Thus, the apparent brightness of the satellite trail will be comparable to stars of increasingly faint magnitude with increasing exposure. We assume this is a small telescope, so the spatial extent of the satellite (defocus + resolved size) is not accounted for.'' Rh