Re: USA ###?

From: Björn Gimle (
Date: Mon Jan 31 2000 - 22:58:37 PST

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    > What are the objects designated as USA ###<(two or three digit number)?  Are they just
    > unidentified (obviously US) satellites?  I see the Lacrosse radar imaging satellites
    They are US military satellites.
    > listed often in the elsets, but rarely see visual imagery satellite(s) (like the KH
    > series) listed.  Why is this?  Is it because they change their orbit more often or more
    > radically and are lost to amateur observers?   Also, is there a list somewhere that 
    There are several reasons:
    1. They are in sun-synchronous orbits, so when they are in shadow at your latitude, the condition can last for many months.
    2. Many imaging satellites, like USA 116, have one noon and one midnight pass, making the situation worse.
    3. The KH satellites have a rather low perigee, so elsets are very unreliable after 1-2 months.
    4. Their orbits are raised 2-3 times per year to counteract drag and synchronize them to each other.
    The last two points certainly call for them to be observed and reported with elsets MORE often than Lacrosse and others !
    > identifies which of the _many_ cosmos objects are intelligence gathering satellites?
    A nice list is the bi-weekly "Jonathan's Space Report"
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