Craig Cholar writes: > Here are the criteria that NASA uses to determine visibility... > 1) Apparent spacecraft elevation greater than 15 degrees > 2) Local solar elevation less than -6 degrees > 3) Spacecraft in sunlight > 4) Apparent spacecraft solar elongation greater than 90 degrees. These parameters should seem very conservative for most Seesat readers, and rightfully so. Remember that the average 'joe nasa-fan' doesn't have much skywatching experience, just interest in the shuttle and maybe having the opportunity to see it. By using extremely conservative parameters the odds of success are fairly high if the weather cooperates. And for unexperienced observers this is certainly justifyable. I would suspect that only a very small minority of the folks who read the NASA predictions have the capability, or inclination (no pun intended) to view anything dimmer than third magnitude. Instinctively, based on the launch time, I can give a guess as to when I'll start to have visible passes. The opening of the launch vehicle was constrained by sunrise on landing day at Edwards Air Force Base in California. Given the planned duration of the mission and time of year that resulted in the 10:41 AM EDT launch time. So since the shuttle launched at the beginning of the window it's logical to assume that the end of mission landing time (whether it's Florida or California) will be close to sunrise. And the passes before landing will be good visible passes, including the couple of days before landing. The SPAS platform aboard Discovery previously flew as the ORFEUS-SPAS on the STS-80 mission last November. And two days before landing I had an *incredible* pre-dawn pass of both the shuttle and SPAS going past the Moon and Mars (the only two celestial bodies bright enough to be seen that close to dawn that day). On the original planned landing day the weather was incredibly clear the pass before the planned landing and I saw the shuttle go across the sky. But was incredibly surprised to see it overtake another satellite going the same direction! It was obvious from the direction and brightness that it had to be either Hubble or GRO, and it turned out to be GRO. But the theory by one ex-astronaut Dave Leestma, was that it was the alien spacecraft coming to pick up Story Musgrave so he wouldn't have to return to Earth! Philip Chien [M1959.05.31/31.145//KC4YER@amsat.org]