Last updated 22 Apr 2017

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Man made Satellite Orbit and Ephemerides Pages

Occasionally Artificial Satellites are picked up by chance from Great Shefford as they pass through the telescope/CCD field of view and noticed in near real-time as the images are being transferred from CCD to computer.

Low altitude satellites move very fast and traverse the entire field of view in a fraction of the length of a normal exposure and it is therefore impossible to determine the direction they are headed or at what speed, so any attempt at trying to follow them is hopeless.

However, some satellites move much slower, at speeds similar to Near Earth Asteroids when making very close approaches to Earth (e.g. anywhere from 100"/min up to 2,000"/min+). Although very unlikely, it cannot be ruled out immediately that the observed object may indeed be a natural Near Earth object (though rapid flashing tends to indicate an artificial object), so further positions are obtained to try and determine an orbit good enough to prove whether it is in a geocentric orbit and therefore almost certainly artificial.

These slower objects will be in the same field of view for several consecutive exposures, allowing an initial estimate of speed and direction of motion to be made. To have any chance of orbit determination the object needs to be followed immediately to allow further positions to be obtained. As these exposures are being taken Astrometrica is used to measure the exposures already made and these early positions then used to make a linear extrapolation for subsequent telescope positioning.

However, any object very close to the Earth will be either accelerating or decelerating fast as seen against the sky and a linear interpolation will often only suffice to keep up with the object for the first 10-20 minutes. This period can be extended significantly by fitting the observed RA & Declination co-ordinates to a quadratic rather than a linear fit, but sooner or later FindOrb is needed to calculate an initial orbit and ephemerides to predict further positions.

So far these exercises at Great Shefford have led to the determination of a number of geocentric orbits (see some examples below) but maybe one day a real NEO making a very close approach will be identified?

List of orbital elements and ephemerides:

Bill Gray's artificial satellite "Pseudo-MPEC" index page

GS733A = 1987-105D = NORAD 18704 (4th stage of rocket that launched COSMOS 1903 into a Molniya orbit on 21 Dec 1987)

GS697A = 1990-71D = NORAD 20745 (4th stage of rocket that launched Molniya 1-78 on 10 Aug 1990)

GS695A = 1994-48D = NORAD 23197 (4th stage of rocket that launched COSMOS 2286 into a Molniya orbit on 05 Aug 1994)

GS61LA = (unidentified, geocentric orbit)

GS436A = (unidentified, geocentric orbit)

GS428A  (link to Bill Grays' site) = (Unidentified Molniya

IMP8 (including J95-centric 'dark hours only' ephemeris covering 2010-08-12 to 2011-09-13).

1983-020A (including J95-centric 'dark hours only' ephemeris covering 2008-12-07 to 2009-12-16)

1983-020D (including J95-centric 'dark hours only' ephemeris covering 2008-12-07 to 2009-12-16)

Geotail (including J95-centric 'dark hours only' ephemeris covering 2009-01-17 to 2010-01-16)

WMAP (including J95-centric 'dark hours only' ephemeris covering 2009-02-18 to 2009-05-08)

2007-004B (THEMIS B) (including J95-centric 'dark hours only' ephemeris covering 2009-02-18 to 2009-05-08) and an equivalent ephemeris for 703 (Catalina Sky Survey). See here and here for more information on this unusual object. Orbit corrections appear to be made frequently, possibly every few weeks, making predictions difficult.

9O0DC57 (including J95-centric 'dark hours only' ephemeris covering 2010-12-05 to 2011-01-15). See also Bill Gray's 9O0DC57 page.

9U01FF6 (including J95-centric 'dark hours only' ephemeris covering 2010-04-13 to 2011-04-03).

2010-050B (including J95-centric 'dark hours only' ephemeris covering 2010-11-28 to 2011-11-29 and lightcurve obtained 2010-11-25). See also Bill Gray's 2010-050B page.

RW28E3B (including J95-centric 'dark hours only' ephemeris covering 2010-11-28 to 2011-01-08).


Special thanks to
Tony Beresford for providing identifications for many of the fast moving objects picked up at Great Shefford
Bill Gray for the many hours spent calculating orbits, for FindOrb, for Sat_ID and for providing data used on the MPCs Distant Artificial Satellites Observation Page.
Mike McCants for identifications and observational help in following up some objects.

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