Satellite Search Design 


We performed two  types of satellite searches. The only one of the first type was Satellite search A.    
Sat searches B, C and D fell into the second catagory. In the first design type we stop at each position 
in the mosaic and perform tiny 2x2 pixel slews while imaging. In the second type we slew continuously 
along the columns of large mosaics, and take sets of images along the way.





1. Satsearch design 1:

SatSrchA  - (2000-13/0415)

see /eros/00010/msi_satsrcha.gif

Sat Search A was intended to be a reconaissance of the region of space within which the spacecraft would be orbiting.
We needed to do this far enough out so that if we saw something inside +/-1000 km region, we would have a few weeks 
to react.   At greater distances it was easier to image larger areas with small mosaic, however the trade-off is
that it's more difficult to see smaller objects.  The software intended to analyze these data required that multiple
images be taken of the same region. 

Sat Search A design ==> At each of 6 mosaic positions within a 2x3 mosaic pattern (2 columnsx3rows) 8 clr filter images
(999ms man exp, fast) are taken spaced 4 seconds apart while Eros is slewed slowly across a 2.5x2.5 pixel diagonal. 
Position order: 1) upper left, 2) upper right, 3) middle right, 4) middle left, 5) lower left, 6) lower right. The 2x3 
was repeated 5 additional times for a total 6 executions.

The little scan at each position moves the fov  .0003402 deg/sec in the horizontal, or short pixel direction and 
.0005765 deg/sec in vertical, or long pixel direction. Slew duration is 40 seconds which means that total slew length is 
2.5 short pixels horizontally by 2.5 long pixels vertically. The imaging covers 32 seconds of that 40 second scan, and is 
centered within the scan (imaging start is delayed to begin 4 seconds after start of the scan, and ends 4 seconds before 
the end of the scan).  Direction of scan is such that Eros should move to the left and up relative to the field of view 
during the scan.

2. Satsearch design 2:


SatSrchB -  (2000-28/0810) 
SatSrchC -  (canceled because of a problem that occurred in 00031, never executed)
SatSrchD -  (2000-41/0145)

See /eros/00024/msi_satsrchb.gif
and /eros/00038/msi_satsearchd.gif

Satellite Searches B and D were performed as close as possible to rendezvous so we could see the smallest objects possible.
We originally had planned to perform this search three times so that if any potential satellites were discovered, we might be 
able to determine a trajectory.  Satellite search C had to be canceled due to some unexpected spacecraft problems.
We still might have been able to do that with these two searches.

As we drew closer to Eros, the solid angle of the region of influence grew very large relative to the MSI fov. The 
objectives were to cover at least about +/-125 Eros radii in each satellite search, keep smear less than 1 pixel for max 
exposure (999ms).  Satsearch B is a 6x7 mosaic (colxrow) and Satsearch D is an 8x13. Design was to slew along the vertical 
columns within the large mosaic patterns at a slew rate of .01 deg/sec. Direction of slewing is so that the fov moves 3 
long pixels vertically (up or down) for every 50 microradians to the right (in the short pixel direction) relative to 
background stars.  Along each scan take a set of 4 clear filter images every 207 seconds. This includes 1 autoexposure 
and 3 manexp 999ms, spaced 3 seconds apart.  The 207 seconds gives 15% vertical overlap between 4-image sets.  In the plot, there 
are actually 4 frames at what looks like each single fov. The purpose for taking the three 1 second exp images is twofold.  
First, for any object to be unambigously identified it would need to appear in at least 2 frames (to distinguish from 
noise or cosmic ray hit).  Second, we needed three to accomodate for the the dark column problem.  There are 25 microrad ??
wide vertical dark regions that occur every other pixel across the ccd (no light collection in these regions). For 1 
second exposures, this scan rate will give a star trail that's about the length of the long dimension of a pixel during 
the exposure, and moves .18 of a short pixel width horizontally. The frames are taken 3 seconds apart, meaning the 3 vertical 
star trails are displaced from each other horizontally on the CCD by 3x.18 = .5 short pixels. This means any satellite is 
guaranteed to NOT be in a dark column for at least two out of those three images. The horizontal part of the scan does slightly 
skew the mosaic but not much.  Column-to-column overlap is 15% of the long (horizontal) side of the fov.  Mosaic pattern: start 
upper left, slew fov down during 1st column, reposition to right, slew up for 2nd column, reposition right again, slew down in 
3rd column, etc.