Objective: use target catalog and knowledge

of spacecraft rotation to identify targets.

Tasks:

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,

magnitude)

CCD

star multiplicity analysis

Calculate residuals.

Flag anomalies.

Photometric fitting.

**Centroid**

**Spiral Fitting**

Objective: a rigid spiral

Uncertainty in angular separations is small

compared to single-measurement

uncertainty.

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

bootstrap.

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

stars.

Inertial fram orientation.

**Astrometric Fitting**

Objective: determine astrometric parameters

for each target star

Yield:

astrometric parameters

residuals

Look for peculiar motions (planets!)

Tasks:

Weighted least squares fit

Do one star at a time.

Use all observations (i.e., data span is

mission length).

Check PSFs for anomalies

asymmetry

color variations

size variations

Identify "interesting" stars (anomalous

residuals).

Search residuals of "interesting" stars for

periodicities.