> Despite your high-precision analysis of Earth-Sun and perigee relations, I see no consideration for the precession of the ISS orbit plane (-5.1 degrees/day). You're absolutely right! (I figured somebody'd find something wrong with my analysis...) I've archived the daily ISS TLEs since February of this year, but I'd never examined the values they contained in any detail (except for the purpose of "digesting" them programmatically). So, what would account for such a huge precession of the plane of orbit? The most significant torque (or force acting in a non-center-directed way) on the ISS would seem to be gravitational tugging by the moon & sun (which I'd think would largely balance out, over the course of an orbit), atmospheric drag, and the solar wind. With respect to the latter two, I assume that the solar panels are always facing essentially toward the sun, which could result in some overall torque- though I'd think it would depend on the orientation of the orbit relative to the sun, and so would not result in such a nearly constant amount of daily precession (or even a consistent direction of precession)... Do more compact satellites (such as Hubble, for example) have a similar orbital precession? I see that on day-of-year 346 the RAAN of the ISS's orbit will be about 203; it had been this value on about DOY 60 as well (having precessed 2 revolutions in that time), which gives an average of 1 revolution each 71.5 days, or 5.11 revolutions for each orbit of the sun. The fractional revolution (.11) therefore corresponds to about 7.75 days, which is in good agreement with the adjustment you suggest- and of course improves the prospects for folks like Michael Gill (and maybe Roland Stalder :-). Anyhow, when I have a bit of time, I'll try again using the adjusted date. Of course, there'll still be a problem of longitudinal fuzziness of the transit tracks (not to mention the fact that the grounding of the Shuttle will likely result in a continuing decay of the orbit), which may not come into good focus until a month or so before the event. However, it might be interesting go generate transit tracks based upon this analysis, as well as current TLEs, and see how things come into better focus as time progresses. ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Thu Dec 04 2003 - 12:51:46 EST