A low-volume low-mass low-power ultra-high-frequency radio transceiver for future planetary missions is described. The project targets a volume of less than 10 , mass of less than 50 grams, and power consumption of 50 mW on receive and 100 mW, 300 mW, or 3 W on transmit (for 10 mW, 100 mW, and 1 W output options). The transmitter design supports convolutionally coded binary phase-shift keying (BPSK), RC-BPSK, and quadrature phase-shift keying transmission from 1 to 256 kbps. Command/control instructions can be received at 2 or 8 kbps, with a sensitivity of better than 120 dBm. In addition to its low volume/mass/power features, temperature compensation to 100 C and radiation tolerance to 100 krad allow operation outside of thermally controlled, shielded enclosures, further reducing the mass and complexity of exploration vehicles. The design is described in a top-down format, beginning with system requirements and proceeding through digital modem algorithm development, discussion of the silicon-on-sapphire CMOS process used and elaboration of key blocks in the radio-frequency (RF) integrated circuit design. Techniques to address coupling between high-sensitivity RF and on-chip digital circuits are also presented, and test results are given for prototypes of all major functions. Although designed for the Martian environment, the transceiver is expected to be useful in other proximity links where a small low-power radio compatible with Prox-1 space-link protocols is desired.