Re: Low perigee question

From: David Brierley (
Date: Tue Feb 17 2009 - 10:17:13 UTC

  • Next message: B Gimle @ComHem: "Re: Low perigee question"

    I was very interested to read this topic.  Back in the 1970s and 80s there 
    was a whole series of Molnija 1s and their rockets which decayed in this 
    way.  I spent hours with a Moonwatch telescope making precise positions on 
    them.  Because apogee was close to N apex, there was excellent visibility 
    from the UK.
    Peter Wakelin was posted to the Falkland Islands for a while, and could see 
    them near perigee, but illuminated passes were few and far between.
    If I remember correctly, the Molnija 2s were placed in slightly different 
    orbits so that their perigee height tended to increase rather than decrease.
    ----- Original Message ----- 
    From: "Greg Roberts" <>
    To: <>
    Cc: <>
    Sent: Wednesday, February 11, 2009 6:41 AM
    Subject: Re: Low perigee question
    > Morning
    > This is not uncommon - many of the high altitude objects- especially those 
    > in GTO orbits have a low perigee and a high apogee and decay rapidly.  The 
    > mechanics of how the orbit decays is quite interesting-I think it was 
    > discussed on SeeSat quite some time ago - Im not an expert on this so had 
    > best not say too much but the orbit tries to circularize with apogee 
    > coming down very rapidly whilst perigee height tries to increase but 
    > eventually the satellite looses its battle..
    > On the 23 Jan 2009 I reported to SeeSat an observation of an Atlas 5 
    > Centaur rocket - 08016B- catalog number #32764.
    > At the time of observation the prediction program used gave an apogee of 
    > 4300 kms but a perigee of 87 kms and doing 10 revs/day. Ive just checked 
    > on this object and the program reports "Object decayed" . At the end of 
    > Jnauary it had decreased its orbital period to around 14 revs/day and had 
    > an enormous drag term.
    > Guess this could make an interesting amateur observation program -- try 
    > and observe objects like this as they speed through perigee - just how low 
    > can one go without being destroyed ? For the bigger/brighter objects it 
    > might even produce quite a spectacular display - there are plenty of 
    > objects to watch ....
    > Cheers
    > Greg
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