Built by Defense Systems Inc. (DSI) for the Defense Advanced Research Projects Agency (DARPA), the 12-sided Microsats (a.k.a. SCS, Small Communications satellite) measured 10 cm by 48 cm and weighed 22 kg each. They were designed to assess the use of low-earth orbit for global communications.

Each satellite operated in UHF, using an analog transponder for FM radio relay of voice communications and a digital transponder to relay data, message, facsimile and modest video traffic. The spacecraft with overlapped footprints provide near continuous communications, which would be global for three planes. The system was intended to provide data for ArcticSat, a system for communicating with nuclear submarines under the polar cap. The microprocessor-controlled digital communications payload was similar to the one used in MACSAT, but with less redundacy and less memory.