t, a, d

A minimum of three observations are required to determine the orbit of a satellite. Preferably, these observations should be at least a few degrees apart. It is highly recommended that Equatorial coordinates (R.A. and Dec.) be used since they are truly inertial coordinates.

Since many of us do not have ranging installations (such as radar) in our backyards, we have to rely on optical observations using angles only. It is recommended that images of the satellite be used rather than eyeball observations since the observation errors will be much lower when using image analysis.

The example tracking data presented in the table below has time in UTC and Equatorial coordinates in J2000.0. To use this method, both the R.A. and Dec. have to be in degrees. To convert the R.A. coordinate from hours to degrees, use the simple equation below:

ai (o) = [15o/hr] [ai (hms)]

where i = the observation number (1, 2 or 3).

The geodetic location where the observations were made also have to be known. These are provided in the second table for this example. The convention for longitude is negative for west of the Prime Meridian and positive for east.

 Obs Time (UTC) - January 3, 2012 Right Ascension (J2000.0) Declination (J2000.0) hh:mm:ss.sss hh mm ss.s o o  '  " o 1 23:00:00.00 15  30  49.6 232.70667 +49 59 56 +49.998889 2 23:05:28.22 00  31  45.6 7.9400000 +44 20 08 +44.335556 3 23:11:10.00 02  38  40.7 39.669583 -32 11 58 -32.199444

 Longitude (°) Latitude (°) Altitude (km) -76.889444 +44.121944 0.079

 SITE MAP Step 1: Tracking Data Was Last Modified On September 23, 2013