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Astronomical Applications Department, U.S. Naval Observatory - Data Flow Diagrams (Page 2)

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Astronomical Applications Department, U.S. Naval Observatory - Data Flow Diagrams
Objective: use target catalog and knowledge
of spacecraft rotation to identify targets.
Calibrate raw pixel data.
known CCD effects (e.g., variations in
pixel sensitivity, etc.)
Identify type of object.
Check for anomalies.
Identify Targets
Objective: determine centroid & PSF
parameters for targets.
Task: using all events for a given star during
the same observation episode (the time
during which a given star is in the field of view
on successive rotations of the s/c), do
weighted least squares (WLS) fit of the
centroid and PSF parameters for each star.
WLS parameters
centroid model(s)
PSF model(s)
stellar parameters (spectral type,
star multiplicity analysis
Calculate residuals.
Flag anomalies.
Photometric fitting.
Spiral Fitting
Objective: a rigid spiral
Uncertainty in angular separations is small
compared to single-measurement
Yield: spacecraft rotation model for each
spiral segment.
Task: perform weighted least squares fit of
the spacecraft orbit and spin dynamics and
instrument parameters.
Integrate equations of motion.
Integrate variational equations.
Use a priori fiducial star coords, then
WLS parameters: see Spin Dynamics
Optimal spiral segment length TBD.
Spiral segment orientation not well known
(but that's okay for now).
Global Fitting
Objective: tie the spiral segment rotation
models together.
Yield: a single spacecraft rotation model.
Task: weighted least squares fit of fiducial
stars (or subset of fiducial stars).
WLS parameters
Fiducial star astrometric parameters
Spiral segment orientation parameters
Toss out (and replace) anomalous stars.
Check: repeat for different sets of fiducial
Inertial fram orientation.
Astrometric Fitting
Objective: determine astrometric parameters
for each target star
astrometric parameters
Look for peculiar motions (planets!)
Weighted least squares fit
Do one star at a time.
Use all observations (i.e., data span is
mission length).
Check PSFs for anomalies
color variations
size variations
Identify "interesting" stars (anomalous
Search residuals of "interesting" stars for

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