This paper presents busy/idle signal" scheme for control channel in mobile satellite communication systems. In the design of channel access schemes in mobile satellite communication systems, the following three factors must be taken into account: (1) a control channel is shared by call setup signals and response signals, (2) differences in propagation delays occur depending on the distance between the satellite and the mobile stations, (3) the number of retransmissions of a call setup signal is limited. Traffic performance measures of the proposed channel access scheme, such as throughput, mean setup delay and mean response delay, are compared with those of the random access scheme and the framed access scheme. A numerical method is presented for obtaining these measures, and the method's accuracy is demonstrated by comparing results with those obtained by simulation. This numerical method is very simple and is applicable to channel access schemes for mobile satellite communication systems with the above three factors. Using the numerical method, the proposed scheme is shown to be superior to other schemes.