Onboard and Ground Station Telemetry Architecture Design for a LEO Nanosatellite

摘要

This paper details the communication system architecture for a 3U hyperspectral imaging cubesat. The paper begins with discussions on objectives of and requirements from the communication system. Based on these, an architecture has been proposed. The architecture has been designed to ensure that the system works even in the case of emergencies, including, but not limited to antenna deployment failure or other component failures. This has been done by introducing multiple redundancy provisions. The architecture is broadly classified into three sections - Uplink, Downlink and Beacon transmission. The satellite implements a full-duplex UHF-VHF architecture using Gaussian Minimum Shift Keying (GMSK) modulation scheme for data downlink and uplink, while a Morse coded, simplex, On-Off Keying (OOK) scheme is used for beacon transmission. Onboard the satellite, a single monopole antenna is used for receiving uplink, while the other antenna doubles as a turnstile and dipole for downlink and beacon transmissions respectively. All the components to be used in the system, both onboard the satellite and at the Ground Station (GS) have been discussed. The reasons for selecting and details regarding interfacing of these components have been elucidated. The paper also describes the flight plan for TTC and how the microcontroller switches between the modes of operations. Entry and exit conditions for each mode are defined. Discussions on terrestrial testing of individual modules and architecture of the system have been included. All of the conducted tests were satisfactorily passed and the proposed architecture was proven to be a viable option for use in the satellite.