Re: Formations/groups

From: Björn Gimle (b_gimle@algonet.se)
Date: Tue Jul 15 2003 - 04:59:03 EDT

  • Next message: Peter Wakelin: "SATOBS 2003 July 14"

    > First, is there a FAQ or other good resource about general terms and
    info
    > about orbits and tracking?
    >
    http://www.satobs.org
    http://www.satobs.org/faq.html
    and/or http://home.att.net/~sue.worden/SeeSat-FAQ/
    
    > 1.  What is 'OIG' ?
    >
    > 2.  I see a lot of rows of numbers posted on these messages.
    > Assuming they are orbital elements, why are there 2 different
    > formats, what is the difference between them, and what does
    > the information do for me (or anyone else reading it), and
    > how do I use that info?
    >
    When you see lines of this format:
    KH 9-19 ELINT    0.3  0.9  0.0  7.5 v
    1 15071U 84065C   03150.89915022  .00001550  00000-0  19410-3 0    04
    2 15071  95.9080 216.8521 0003000 126.4264 233.5734 14.82343294    07
    they are orbital elements (TLE).
    Only Pierre Neirinck uses a different one, but rarely posts on SeeSat-L.
    The format is described at http://www.satobs.org/element.html and many
    other places.
    The US STRATCOM Space Control Center (formerly NORAD) number (15071)
    and(or) Intl.ID (84065C)
    and(or) name (KH 9-19 ELINT) is used to identify the object.
    Occasionally, you may want to know about a specific element, like the
    inclination (because it narrows down at what latitudes it is most easily
    seen); or compare series of elsets (element sets) for one object for
    errors or abnormal changes.
    But mainly they are for users who run prediction programs
    (http://www.satobs.org/tletools.html) on their own computers instead of
    connecting to http://www.heavens-above.com/
    
    As Kevin remarked, you can also find observation reports (used for
    analyses with some of the programs found on the satobs pages).
    The most common format is the IOD/ObsEntry format:
    24680 96 072A   8305 G 20030711034641530 56 35 1947947+702738 35 S
    Mainly by British observers:
    2420 0307 0.211 1204
    13
    9305501 220718.88 200440+232809 5.5 5.5 0 S
    or:
    IntlId SiteYYMMDDHHMMSSss  Sss  TCHHMMmm   DDddd  Ddd E             MMm
    9607201211503062021491402  020  13121881  -0064   007 5
    
    > 3.  What are orbital 'planes'?
    >
    The orbits are ellipses in a plane through Earth's centre
    (approximately). The plane rotates slowly around the polar axis, but if
    the size (14.82343294) , shape (0003000) and inclination (95.9080) for
    two orbits are close, they maintain their relative positions. The Right
    Ascension of the Ascending Node (216.8521) defines where on the celestial
    sphere the orbit currently crosses the equator, going S-->N.
    
    > 4. When you say "52 Globalstar satellites at 52 degrees", what does
    > that mean?
    > Is there a correspondence with the number of satellites and the orbits?
    > Are they all at '52 degrees'?  What is that measured from -
    > the ground, azimuth, etc?
    >
    That is the inclination of the orbital plane to the equator plane (see
    above).
    The 52/52 and 86/86 pair was just an unusual coincidence - actually I
    find 90 Iridiums in the TLE files.
    
    -- b_gimle@algonet.se (home)  http://www.algonet.se/~b_gimle --
    -- COSPAR 5919, MALMA,    59.2576 N, 18.6172 E, 23 m         --
    -- COSPAR 5918, HAMMARBY, 59.2985 N, 18.1045 E, 44 m         --
    
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