D

With the coordinates of the GlobalStar M047 satellite predicted, it is often beneficial to compare these coordinates with actual observation. This is normally done to measure how trustworthy the propagation equations are for different satellite orbit types and different observation conditions.

Using Steps 1 to 14 we calculated the following coordinates for the GlobalStar M047 satellite:

a = 00^h 50^m 35^s.95
d = +45^o 20' 02".84

The original CASTOR image of the GlobalStar M047 satellite was used to determine the observed coordinates:

a_obs = 00^h 49^m 26^s.6
d_obs = 45^o 56^' 10^"

The errors of each coordinate were then calculated by subtracting the observed from the measured. These values are commonly known as "Residuals" and are also used in Orbit Determination.

Da = 1^m 9^s.35 = 12' 15".57
Dd = -36' 07".16

The total error was then calculated using the following equation:

cosD = sindsind_obs + cosdcosd_obscos [15^o/hr (a - a_obs) ]

D = 0^o 38' 05".58

The image above shows an illustration of the predicted satellite streak location vs. the actual satellite streak detected by CASTOR. The dot at the endpoint of the predicted streak depicts the predicted location of the GlobalStar M047 satellite at the time selected for this example. The white arrow denotes the apparent direction of satellite travel in both cases.

This error would certainly enable the CASTOR wide-field camera (11.3 degrees FOV) to successfully detect this object using the predicted satellite coordinates calculated in this example. For a higher accuracy prediction, a higher precision orbit element propagator model would be required.

This single orbit propagation example is an introduction to the steps that automated orbit propagators contain in order to give you satellite location predictions based on your location and selected observation time(s). These steps are followed by every satellite prediction software and service that you use.

Contact CASTOR with your questions, comments and possible corrections.

BACK TO STEP #14