Orbit determination

Orbit determination is the use of a set of techniques for estimating the orbits of objects such as moons, planets, and spacecraft. Determining the orbits of newly observed asteroids is a common usage of these techniques, both so the asteroid can be followed up with future observations, and also to verify that it has not been previously discovered.

Observations are the raw data fed into orbit determination algorithms. Observations made by a ground-based observer typically consist of time-tagged azimuth, elevation, range, and/or range-rate values. Telescopes or radar apparatus are used, because naked-eye observations are inadequate for precise orbit determination.

After orbits are determined, mathematical propagation techniques can be used to predict the future positions of orbiting objects. As time goes by, the actual path of an orbiting object tends to diverge from the predicted path (especially if the object is subject to difficult-to-predict perturbations such as atmospheric drag), and a new orbit determination using new observations serves to re-calibrate knowledge of the orbit.

For the US and partner countries, to the extent that optical and radar resources allow, the Joint Space Operations Center gathers observations of all objects in Earth orbit. The observations are used in new orbit determination calculations that maintain the overall accuracy of the satellite catalog. Collision avoidance calculations may use this data to calculate the probability that one orbiting object will collide with another. A satellite's operator may decide to adjust the orbit, if the risk of collision in the present orbit is unacceptable. (It is not possible to adjust the orbit every time a very-low-probability situation is encountered; doing so would cause the satellite to quickly run out of propellant.) When the quantity or quality of observations improves, the accuracy of the orbit determination process also improves, and fewer "false alarms" are brought to the attention of satellite operators. Other countries, including Russia and China, have similar tracking assets.

...
Wikipedia