RE: Low perigee question

From: Ted Molczan (
Date: Tue Feb 17 2009 - 15:52:05 UTC

  • Next message: Kevin Fetter: "Superbird A, Superbird A1 and Skynet 4A video and ppas report"

    Björn Gimle responded to David Brierley:
    > > If I remember correctly, the Molnija 2s were placed in 
    > > slightly different orbits so that their perigee height 
    > > tended to increase rather than decrease.
    > If that were an inherent, constant property of the orbit, it 
    > would never decay !?
    > IMHO, it varies with Moon/Sun positions relative to the apogee.
    Dr. Desmond King-Hele discussed this in his memoir, A Tapestry of Orbits, on pages 162-163. [(P) Cambridge University Press, 1992, ISBN 0-521 39323 X]. He explained that the controlling influence of luni-solar perturbations on Molniya orbital life is strongly dependent upon the initial orbital parameters, especially the initial value of the longitude of the node, denoted by the symbol Ω (capital omega, in case this is mangled through plain text e-mailing). Numerical integration is required for precise predictions of lifetimes, but he developed a simpler approximate method, useful when great precision was not required:
    "For Molniya satellites at 65 deg inclination, as for most of those then launched [I believe he meant up to about 1975], the lifetime was between 1 and 7 years, according to the initial value of Ω. If Ω was 250 deg initially, for example, the lifetime would be between 3 and 4 years; for Ω = 0, the lifetime would be between 5 and 7 years. For Molniyas in orbits of 63 deg inclination, as in most subsequent launches, the theory was more difficult and the answers were less clear-cut. If the initial Ω was between 90 deg and 270 deg, the lifetime was likely to be between 9 and 13 years; for other values of Ω, decay is quite likely between 12 and 20 years after launch, but it is possible that the perigee may librate about the southern apex and, if so, no limit can be set to the lifetime."
    Ted Molczan
    Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive:

    This archive was generated by hypermail 2b29 : Tue Feb 17 2009 - 15:53:37 UTC