> Actually, the X-axis is =parallel= to the ground with the Soyuz =trailing=. > Q. One more question about the attitude with the "LVLH". I assume it's PMA > forward - Z1 going to nadir - PMA-3 going to zenith, straight into the > flight direction? > A. No. PMA-3 is facing Earth. P6 is sticking up, facing the zenith and > wings flat. It's in the attitude you saw in the fly-around video when the > (STS)97 crew undocked from the station. It's in exactly the same attitude. This means the main arrays have surface normals that are pointing approximately toward nadir/zenith (i.e. the arrays are parallel to the velocity vector). If so, then solar glints off the main arrays can only occur when ISS is extremely low in the southwest in the evening, and about to enter the terminator, or extremely low in the southeast in the early morning having just exited the terminator (northern hemisphere viewing). There are 2 pairs of smaller solar arrays that appear to have their surface normals tilted slightly forward of nadir (slightly in the ram direction). If so, then these arrays CAN produce glints. The only favorable glint geometry for winter in the northern hemisphere would be a descending node pass in the early morning when ISS is traveling northwest to southeast. The amount of the tilt of these arrays would determine where in the pass that ISS glints. For a very shallow tilt, the glint occurs when ISS is past culmination and setting in the southeast. For a slightly greater tilt, the glint occurs earlier when ISS is closer to culmination. With a little more tilt still, the glint would occur before culmination while ISS is still rising out of the NW. Based on the picture at: http://spaceflightnow.com/ops/stage4a/001209snapshots/withearth.html it appears that the forward tilt is somewhere around 20-30 degrees, which would favor glints at fairly high satellite elevation angles. Whether ISS needs to pass northeast of your zenith or southwest of your zenith would depend on how high your latitude is. If you're pretty far north, then the descending ISS pass would need to culminate southwest of your zenith to produce a glint; at some magic north latitude (which changes with the seasons), a perfect NW to SE zenith path produces the correct geometry; south of this latitude, the ISS culmination needs to be in the NE. Note that the current geometry does not permit glints off these smaller solar panels in the early evening, only the morning. Best, Rob P.S. If someone can provide the tilt angle, I can make an adjustment to IRIDFLAR to provide glint timing information for ISS (but only a relative brightness estimate until enough observations have been made). ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Fri Dec 15 2000 - 19:41:55 PST