  IITMSAT is a student-built nano satellite mission of Indian Institute of
Technology Madras, Chennai, India. The objective is to study the precipitation
of high energy electrons and protons from Van-Allen radiation belts to lower
altitude of 600-900 km due to resonance interaction with low frequency EM
waves. The unique communications system design of IITMSAT evolves from the
challenging downlink data requirement of 1 MB per day in the UHF band posed by
the mission and the satellite's payload, SPEED (Space based Proton and Electron
Energy Detector). To ensure continuous downlink data stream in the short Low
earth Orbit passes, a robust physical layer protocol was designed to counter
time-varying aspects of a Space-Earth telecom link. For the on-board
communications system, two types of design alternatives exist for each module.
The first option is a custom design wherein a module is developed from scratch
using discrete components.The other option is an integrated design wherein an
electronics COTS module can be directly plugged into the subsystem. This module
is evaluated by carrying out vibration and thermal tests. If an integrated
module is low-cost and meets the design requirements, it is preferred over a
custom design. In order to carry out performance tests under simulated link
conditions, an RF attenuation test setup was designed that can work at extreme
temperatures. Burn-In tests for 72 hours at ambient and extreme temperatures
were carried out. Integrated tests indicate all IITMSAT design requirements
have been met. Hence a robust communications system has been validated. The
time taken for development of on-board telecom and GS was less than a year and
was achieved at a low cost which agrees to a LeanSat approach.
