Abstract: Data collection system (DCS) is a telemetry instrument using satellite as a relay station for transmissing the earth environment data,DCSof near-earth satellites,such as that of landsat and Tiros-N,are alb designed by means of the random access principle.For the design of the systems,the law of message collision which is concerned with the capacity of the systems is an important problem.In this paper,the theoretical representations which agree with the simulation results are given.Computation of probability of the message collision for various scheme are presented.