Courier was a United States Army experimental communications satellite. The objective of the Courier program was to develop a satellite of higher capacity and longer life than SCORE, which could be used for communication tests and assessments of traffic handling techniques. The concept was similar to SCORE in that the primary operating mode was store-and-dump using onboard tape recorders. A real-time mode was also available. Unlike SCORE, Courier was a self-contained satellite and had both solar cells and rechargeable batteries for power supply. Except for the final amplifiers of the transmitters, the electronics were all solid state.