Europa Orbiter Spacecraft to Lander Frontier Radio Relay Communications

A versatile relay communications system has been implemented on the highly capable low size, weight, and power (SWaP) space-grade Frontier Radio platform for use on the NASA Europa Clipper mission and other possible future missions. The Frontier Radio, developed by JHU/APL, has been used for traditional Earth-to-spacecraft communication links and has now been enhanced to implement relay communications between two Frontier Radios for use on Europa missions. NASA has been studying a future Europa Lander mission, one variation of which required relay links to a Carrier and Relay Stage (CRS) as well as to the Europa Clipper spacecraft. The relay communications are at X-band, using the same Frontier Radio already in use for direct-to-Earth (DTE) communications. By exploiting the software-defined nature of the Frontier Radio, a new software protocol "relay personality" was created for relay communications. The process of relay-session establishment, loss of lock actions, and emergency communications contingencies are discussed here. The radios each perform self-acquisition by internally sweeping their receivers to lock onto the incoming signal and has a feature to implement Doppler predicts instead of relying on a ground station to sweep the uplink signal frequency as in DTE links The protocol leverages the existing flight computer/command and data handling (C&DH) similar to the DTE links. The concept of operations (CONOPS) for the Europa relay links nominally uses scheduled passes preloaded from contact parameter tables, but unscheduled passes are also supported where either node can initiate. These protocols and processes were implemented in flight software running on a Microprocessor without Interlocked Pipeline Stages (NIPS) core located in the radio's field programmable gate array (FPGA). The constraints imposed on the design of the relay communications and the current implementation of this relay protocol is covered in this paper.