The CSSWE team chose a half-duplex communications architecture operating in the 70cm band, primarily to reduce the complexity of the system. Given the size of the data product and the minimal amount of commanding required for CSSWE, sharing the uplink and downlink does not have a significant negative impact on the link budget.
The communications system onboard the spacecraft utilizes the AstroDev Lithium (Li-1) radio, which operates over a wide range of frequencies and temperatures, is 40% power-efficient, and can output 34dBm of radio-frequency (RF) power. Additionally the Li-1 radio supports the AX.25 packet radio protocol at a rate of 9.6kbps across the RF link and up to 115.2kbps between the radio and C&DH over the serial link. Assuming 21.75 minutes of communications time per day, calculated using Satellite Took Kit for our nominal orbit and a ground station in Boulder, we have the capacity to downlink 1.2MB/day, providing almost 50% more link capacity than is required for the mission.
A monopole was selected for the satellite antenna configuration after testing numerous options. The total length of the deployed antenna is 48.3cm. The matching and tuning of the antenna provided excellent performance over our operating frequency with a maximum antenna gain in excess of 2dBi for a reasonably omnidirectional antenna. The image below shows the measured gain pattern of the CSSWE COMM system before and after antenna deployment. The deployed gain drops below -5dBi only in the regions along the axis of the antenna, as well as at the small nulls near ±125° from the exposed end of the antenna. The results of orbit simulations indicate that CSSWE is rarely in an attitude and at a range where the link cannot be closed through this null in the pattern. Given our testing and analysis we are confident that the communications system will operate as designed and will meet all the mission requirements for commanding and data throughput.