I also saw this morning's very lovely pass. I missed them comming out of shadow but suddenly found them about 45 deg up in the WSW through thin clouds. They were nearly equal in brightness at about -1. They passed 30 deg NW of the zenith. Even then they comfortably fit in the field of view of 7x50s. I estimated the same ~5 second seperation that others seeing this pass have reported. Within a few seconds they both started to fade, especially the Shuttle (leading object!) I had nearly lost the shuttle by late in the pass (~20 elev, NNW) but ISS was still there at about mag 2. During the entire pass they were ducking in and out of scattered altostratus (or cirrus?) that I later realized was the outer fringe of huricane Gordon's influence. These clouds make the brightness/fading behavior a little tricky to quantify. On Mon, 18 Sep 2000 Mir16609@aol.com wrote: > In a message dated 9/18/00 2:19:48 PM EDT, DeHBeaver0@aol.com writes: > ... [confusion over which object leads after undocking] > ... > I made the same mistake during a Mir docking mission in 1997. The shuttle > should always lead after undocking and the fly around. > > Ref: > http://www2.satellite.eu.org/seesat/Sep-1997/0455.html > http://www2.satellite.eu.org/seesat/Sep-1997/0456.html > > Thing work the opposite as you would expect in orbital dynamics. When you > "speed up" or boost your orbit your ground track slows down because your > orbit now has a larger circumference. And a slower mean velocity in its orbit, even if it happens to be a bit faster near perigee. > Conversely when you "Slow down" you drop into a lower orbit and your ground > track speeds up. Because Atlantis dropped into a lower orbit it will lead > the ISS because the circumference of the orbit is now smaller. It's mean > motion has increased by going into the lower orbit. > > Rather than using Heavens Above for relative position, try using Dave > Ransom's STS Plus program (www.dransom.com) and use the most recent TLEs from > OIG. It clearly shows that Atlantis leads the ISS. Getting the right TLE to use for the Shuttle after undocking can be tricky. The Shuttle doesn't just head off on its own way, there is a fly-around and inspection after undocking first. This can be rather cursory (half a loop and AWAY!) or quite detailed (1 1/2 or 2 complete loops before departure), so it can take from 1 to 3+ hours after undocking before the Shuttle actually makes its sep burn. So you can't just use the first post-undock TLE to predict/reconstruct the departure. And yes, the Shuttle always moves into a lower orbit after departing ISS or MIR. It seems like there may have been a single exception back in the very early days of operations with MIR. Also the brightgness predictions have fooled some people. Real satellites are not uniform spheres, they are irregular in shape e.g. roughly cylindrical, and with surfaces that may give specular reflections. So those brightness estimates are only a general guide. Actual brightness depends on the illumination and viewing geometry in a much more complex manner than simply described by the phase angle, and on satellite attitude. > Q2 - My Shuttle TLEs from the Spacelink e-mail list stopped arriving about > 2-3 days ago. Anyone else suffer the same fate? Yes, I've noticed this too. I've had to get elements from OIG. Although as has been pointed out in other posts, the predicted TLEs on the NASA SPACEFLIGHT webpage were just about spot on! (There seems to have been a further update to their predictions late friday or early saturday but the difference was only a few seconds at the time of undock.) Richard Clark rclark@lpl.arizona.edu 38.99N 76.83W Toto, I don't think we're in Tucson any more! ----------------------------------------------------------------- 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 : Mon Sep 18 2000 - 18:15:56 PDT