The aim of this work was to use my finder camera to produce calibrated light curves for satellite passes. The finder camera has a 135mm f2.8 lens and uses a 1004XA board camera with a 1/3" BW Sony EXviewHAD chip. Tis chip has a 0.003 LUX rating and can capture stars down to about magnitude7.0. The field dimensions are 125.4'x94.0' making it easy to keep the satellite in view during tracking
To calibrate the camera I wrote a calibration tool for the AutoTrack program which finds stars of any desired magnitude from the bright star catalogue and points the LX200 at them. The user then clicks on the star and the program calculates a brightness. The brightness is the sum of all pixels in a box round the star after subtracting the sky background (mean plus 3.5 standard deviations).
The camera model is therefore
magnitude = M0 - k log10(brightness)
M0 is the magnitude for unit brightness
Lacrosse 2 Result
Modelling the Magnitude
The estimated magnitude is a curve fit to the measured magnitude. The basic equation for the curve is
magnitude = A + B*log10(range/1000)+C*log10(I)+D*log(max(1,Fmax-F))
A is the magnitude at 1000km, fully illuminated and not flaring
The curve fit for Lacrosse 2 above has A=2.34, B=5 and C=-1.56. Due to the bad data in the middle I fixed A and C manually although my program has a least squares capability for all parameters. D is not used here because no flare occurred.
Here is a screen shot from the light curve program. The graph is rudimentary but the results can be saved to a CSV file for use in XL.
ERS 2 Dimensions
ERS 1 Dimensions
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