Detailed Desctipion - Eros Flyby Historical Background - The original mission plan for Eros orbit insertion called for a series of 4 rendevous burns beginning on Dec 20, 1998 that would conclude on Jan 10, 1999 when the spacecraft would enter Eros orbit. This plan was altered when on Dec 20, 1998, Rendezvous burn 1 aborted after 1 second. The project lost contact with the spacecraft for over a day, but an intermittent signal was eventually picked up. After hasty analysis contact was reestablished. Since the burn had not executed, the spacecraft was still moving at a large velocity relative to Eros. It would fly past Eros on Dec 23, midday EDT. Project allowed a flyby imaging sequence to be built and sent to the spacecraft as this might be the only chance we would have to image Eros. Imaging design for the flyby was dependent on knowing the uncertainty in location of Eros relative to the spacecraft. Just as in the Mathilde flyby, each time you cover this region of sky with images, you hopefully capture one view of Eros somewhere within that mosaic. Unfortunately, the size of the uncertainty region for this flyby was uncertain! Navigation only had a little bit of doppler following the aborted burn to work with. The spacecraft had been tumbling, and its trajectory was uncertain. Nevertheless, using their best estimate of the uncertainty region, together with analysis with our visualization software, we determined that a 2x2 mosaic would likely cover this region through the flyby. Turns out this was a little less conservative than should have been because Eros was actually sitting outside that region. Despite that, serendipity and geometry allowed the first half of the imaging (through closest approach) to capture Eros within the mosaics. Some time after closest approach we lost Eros in the 2x2 target region. The images returned from this flyby allowed development of a 5 degree shape model of Eros to be constructed for the portions of Eros illuminated during the flyby. Prior to the flyby we only had the triaxial ellipsoid determined from ground-based lightcurves. Solar illumination on Eros during the flyby was southerly (sub solar latitude was -32 deg), hence, much of the north side of Eros was not visible at the time of the flyby. The model interpolated over those areas and the result was a volumne estimate that turned out to be good to about 15%. We also got a good calibration on the spin phasing of Eros. This was a trememdous help for planning of the orbital mission that would begin in Feb, 2000. Sequence Design Eros Flyby Sequences performed on 1998/357 includes the following three parts. NIS data was taken simultaneously with the MSI sequences. SatSrch1_contingency - A pre-flyby satellite search consisting of a 4x4 mosaic through the clear filter. At each position in the 4x4, four manual exp images were taken (4, 999, 999, 4 ms), fast compression. Pointing: mosaic centered on Eros' most-probable location. MultispecRot_contingency - This was a set of observations that went on for over 5.5 hours, more than one full spin period of Eros, and was intended to repeatedly image Eros plus trajectory uncertainty region. This main sequence began with 11 1/2 executions of the following pair of observations: 1) 7 filters with fov centered on Eros most-probable location (1x1), 2) 7-filters at each position in a 2x2 mosaic centered on Eros' most-probable location. The pair was repeated every 13 minutes. After 11 executions of the pair, plus one additional 1x1, we scheduled a 4x4 mosaic through the clear filter. The sequence was timed to occur at the predicted closest approach time as a backup in case we had been too conservative with the uncertainty ellipse size. In other words, in case the 2x2's were not large enough, hopefully we would at least capture an image of Eros at closest approach in this 4x4. Following the 4x4 mosaic, we resumed with the execution of the 1x1 plus 2x2 7 filter sequence pairs as above. Fourteen more pairs were executed. SatSrch2_contingency - Immediately following the above, a post-flyby satellite search was performed, similar to the pre-flyby sat search. This consisted of a 4x4 mosaic through the clear filter. As above, 4 clear filter manual exposures were taken for at each of the 16 positions (4, 999, 999, 4 ms). (no plot available for this one, but the mosaic looks exactly like satsrch1_contingency.gif) *********IMPORTANT NOTE about files available for Eros Flyby! ******* An imagelist, and plots are available for the above activities. They are located in /eros/98357/erosflyby_imagelist.txt /eros/98357/mosaicname.gif ..... The gif plot names correspond to the mosaic names as noted in the imagelist. Plots exist for all of the 1x1s, about 1/3 of the 2x2s, satsrch1, and the 4x4 at closest approach. Please note that as these were PREDICT plots, they display Eros at its most likely location as we believed it to be prior to the flyby. We targeted the mosaics to be centered on that most probable location of Eros. Eros' actual location was not at this point. Therefore, in the actual images, Eros will at a different position than where these plots indicate. The rotational state of Eros should be pretty good. Mosaic shape and frame-to-frame overlap should also be good. ************ADDITIONAL NOTES!!******* 1) Satsrch2 looks identical to satsrch1. I did not have a satsrch2 plot so I i linked the satsrch1 plot to Satsrch2 observation. 2) There are multiple plots for Multispecrot_contingency. Only the first plot is linked from the predict column. You must go to directory eros/98357/ to access the others.