RE: X-37B: Altitude history of OTV 1-1 ad 2-1

From: Ted Molczan (
Date: Sun Dec 04 2011 - 03:52:51 UTC

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    Robert Clark wrote:
    >  When you type in the name OTV 2 in the search box, that brings up a page with the general
    > orbital elements of the satellite. This gives the perigee as 328.9 km. But then there is a
    > link on the page near the top: "Track it now!"
    >  This gives the real time position and altitude of the satellite. As you watch it, over the
    > 90 minute orbit it frequently dips down to around 296 km. But I'll email the maintainer of
    > the site to see where these real time numbers are coming from.
    I had another look, and spotted something I overlooked earlier: the TLE is from early June, which is seriously out of
    date. I have propagated the same TLE using SGP4 and obtained virtually the same real-time position and altitude that was
    displayed by the site. Since the object makes frequent manoeuvres to maintain the orbit against drag, using such an
    outdated TLE yields useless predictions.
    Ted Molczan
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