RE: Shenzhou 6 return details

From: Ted Molczan (seesat@rogers.com)
Date: Sun Oct 16 2005 - 04:01:55 EDT

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    Dear Jin,
    
    > >Ted Molczan wrote:
    > >
    > >I estimate that retrofire is planned for 2005 Oct 16, about 19:46:35
    > >UTC, over 24.1 S, 7.0 E, with touchdown near 20:32 UTC..
    > 
    > From the current orbit, it seems that Shenzhou 6 will pass
    > Beijing at about 20:20 UTC, which is just about 30 minutes 
    > after the estimation time of retrofire. So what would that 
    > influence the orbit and observation condition in
    > Beijing?
    
    I do not have the means to accurately model a de-orbit, but I have made some
    guesses, which I hope are reasonable. 
    
    I have assumed that the effect of retro-fire will be to reduce perigee height to
    zero km, which would result in the following orbit at the location and time of
    retro-fire:
    
    1 70000U 70000A   05289.82361112  .00000000  00000-0  00000-0 0    05
    2 70000  42.4137 358.3221 0259300 142.5721 180.3360 16.39300000    08
    
    Without any drag, this orbit would rise above the horizon at Beijing at 20:14:53
    UTC, at azimuth 284 deg, and the spacecraft would be 92 km high. In reality,
    however, the effects of drag will already have been felt, so some altitude will
    have been lost, delaying the rise above the horizon.
    
    I estimate that the landing site, Dorbod Xi, is located near 41.9 N, 116.65 E.
    Its azimuth relative Beijing is 301 degrees. Without any drag, the above orbit
    would reach that azimuth at 20:16:09 UTC, and it would be 6 deg above the
    horizon. Of course, in reality the full effects of drag will already have
    occurred, and the spacecraft will land near 20:32 UTC. So, from Beijing, the
    spacecraft will not even reach 6 deg elevation during the re-entry pass. I am
    not certain that it will rise at all, but if it does, it will be very low.
    
    If anything is to be seen from Beijing, it will occur somewhere between azimuth
    284 and 301 degrees, and probably no more than one or two deg above the horizon.
    Atmospheric extinction would be severe, so I doubt much could be seen.
    
    If it were me, and I had good view of the horizon, and if the weather forecast
    was for exceptionally good visibility, I might have a look, but my expectations
    would be low.
    
    I would be interested in comments or advice from anyone on the list, especially
    from anyone who understands de-orbit trajectories.
    
    
    > By the way, some current observations:
    > 
    > The weather in Beijing was bad for Oct. 13 morning.
    > 
    > My colleagues and some amateurs watched Shenzhou 6 and its
    > rocket in Oct. 14 morning at Juyongguan Great Wall, took some 
    > pictures and also video (via Watec 902H). Paul 
    > Maley was also there and made his observations. At that time 
    > I was on a train from 
    > Hefei to Beijing, and should be passing some place near 
    > Tianjin, and I did see the 
    > spaceship through the window before it reached the Big Bear, 
    > but then the train turned around and I could not see the 
    > later path. The weather was quite good.
    > 
    > It was also very clear for next day (Oct. 15 morning) and I
    > went to Juyongguan Great Wall with my colleages. Everything 
    > was okey and we saw the spaceship and the rocket, also with 
    > camera and video.
    > 
    > This morning (Oct. 16) we went to Bei'anhe and made similiar
    > observations. It was cloudy after midnight but was clear 
    > before the prediction time.
    > 
    > The predictions are quite accurate and the objects seems 1-2
    > magnitude brighter than expected. My colleagues should post 
    > the link for pictures etc. later. Some already presented on 
    > newspapers and TV programs.
    > 
    > Thanks for the helps!
    
    I am glad that you and your colleagues and Paul Maley had some good views, and
    am pleased to have been able to help out.
    
    I look forward to the crew's safe return.
    
    Best regards,
    Ted
    
    
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