UHF Communication SystemDevelopment for Nanosatellite

Avionics for satellites is a market which is continuously growing in these years. The
cost reduction enables many institutions to develop their own satellites. To evaluate
the feasibility of COTS components in space projects, some departments of
Politecnico di Torino developed a nanosatellite named PiCPoT. In order to greatly
reduce cost for further, the group began to develop a true modular satellite—AraMiS,
which allows a number of missions to share the same design.
A primary mission requirement of any satellite is the ability to exchange
information with a ground based command station. Similar as PiCPot, AraMiS has
two radio-frequency communication subsystems. One subsystem works in UHF
(437MHz) band, the other one works in S (2.4GHz) band. The two communication
subsystems are independent and their functions are interchangeable. Both channels
implement a half-duplex protocol, sharing the same frequency for downlink and
uplink.
The duty of this thesis is to develop the UHF communication subsystem. To get
the compatibility with amateur radios, this communication subsystem needs realize
AX.25 communication protocol. It consists of a micro-controller performing a TNC, a
transceiver, a power amplifier and an antenna. The micro-controller is TI
MSP430F149, which is low cost, low power and easy to operate. The transceiver is
CC1020, which is true narrowband, low voltage and power and easy to configure.
And it only needs a few external passive components. Still choose to use RFMD
RF2175 as the power amplifier, which can provides an +34dBm output power, while
using a helical antenna.
This paper copes with all the details to develop and verify the UHF
communication subsystem. Chapter 1 is an introduction of this final project,
addressing an general idea of the whole development process. In chapter 2, a brief
description of a space radiation environment, which largely affects the satellites’
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normal functionalites, is presented. From chapter 3 to chapter 5, development details
are exactly described. In chapter 3, detail the hardware development. After evaluating
several exiting solutions, our choice is addressed, including components selections,
circuits realizations and interface descriptions. Software development is shown in
chapter 4. The AX.25 protocol is firstly introduced, which involves how to transmit
and receive packets based on this protocol. Thereafter, softwares performing hardware
modules’ functionalities and their relations to exchange information are interpreted in
details. Since both hardware and software are designed, realization and test processes
are demonstrated in chapter 5. The PCB realization procedures are addressed and
experiments for test are established, while results are also reported. In chapter 6, a
conclusion is given to conclude this final project.