Inappropriate analogy. Trains are on tracks. You know where the train is going and you know whether or not you are on the track with the train. If you are on the track when the train goes through the probability of collision is 100%. If you are even a few feet off the track in either direction the probability of collision is zero. This is not the case with debris trajectories.

Quote from: Jorge on 03/14/2009 05:47 pmInappropriate analogy. Trains are on tracks. You know where the train is going and you know whether or not you are on the track with the train. If you are on the track when the train goes through the probability of collision is 100%. If you are even a few feet off the track in either direction the probability of collision is zero. This is not the case with debris trajectories.It basically becomes an excercise in covariance analysis, right?

Quote from: vt_hokie on 03/14/2009 06:17 pmQuote from: Jorge on 03/14/2009 05:47 pmInappropriate analogy. Trains are on tracks. You know where the train is going and you know whether or not you are on the track with the train. If you are on the track when the train goes through the probability of collision is 100%. If you are even a few feet off the track in either direction the probability of collision is zero. This is not the case with debris trajectories.It basically becomes an excercise in covariance analysis, right?Pretty much. The state vector itself defines a "mean" trajectory and the covariance matrix essentially defines an ellipsoid in space about the mean, within which there is a given probability of finding the actual object.If a train's trajectory were defined not by the track but by a diffuse "probability cloud" around the track, which way do you jump in order to avoid the train?

Doesn't matter, as long as you get several sigma out from the center of the elipse, before the train gets there!