Designing a Communications System for Eagle

Lisa FergusonDr. Gary Yale, Dr. Ed Post

Arizona Statewide Symposium AnnouncementsApril 12, 2014

Overview

• System Definition

• Research Objectives

• Design Process

• Packet Radio Communications

• Friis Equation / Link Budget

• Current Status

• Future Development

Communications System Definition

•Responsible for up-linking commands to and down-linking data from the satellite

•Provides a means of contact and control from the ground station

•Comprised of a ground segment and a space segment

Research Objective

Develop a communications system that will establish a communication link over amateur radio frequencies between EagleSat and the satellite ground station at Embry-Riddle on the Prescott campus.

Design Process

• Requirements Definition

• System Design

• Develop Prototype

• Preliminary Testing

• Final Prototype

• Validation

Data Packet Protocol – AX.25 w/out Acknowledge

• AX.25 Packet Radio Protocol• Packet will not be resent or rejected if

containing errors• Error correction will be attempted by the

computer software• All packets down-linked from satellite will

be attempted to be received by the ground station

• UI packet

AX.25 UI Packet Structure

ReceiverCall Sign

SenderCall Sign

Control Bit

PID Data Checksum

SSID

Current Status

• Prototype developed and in operation for > three weeks

• PCB designed and ready for fabrication

• On schedule for testing on HASP

Schematic

Communications System• Software written in C

• Control via On-board Computer (OBC) PIC 24FJ256GA110-16 MIPS processor

• Modem converts audio tones to digital signals for both transmit and recieve

• Audio tones 1200 / 2200 Hz

• Non-return-to-zero inverted signals

System Diagram

GPS

Payload

EPS

PIC24F Modem Transceiver

Link Budget

• Used to determine the amount of power necessary to establish a connection between a satellite and the ground station

• Satellite transmit power is 500 mW

• Final link budget TBD

Friis EquationR

Pt

Ae

Gt Gr Pr

~

2

2

2

2

44 R

GGP

R

DGPP rttttr

log10log204log20

log20

R

dBGdBGdBmPdBmP rttr

Range vs Antenna Gain Plot

0 5 10 1550

100

150

200

250

300

350

400

450

500R

ange

(km

)

Rcv ant gain (dB)

3 dB fade margin

0 dB transmit gainISS = 400 km

Preliminary EagleSat Link Budget

Results of Friis Equation Analysis• Preliminary calculations suggest that

the range possible and the range needed for communication do not correlate

• Increased power and antenna gain will improve range and connectivity

• Link budget will be calculated to include all factors

Future Development

• Complete Link Budget

• Integrate with HASP payload

• Fly on HASP

• Integrate with EagleSat

• Test

• Launch 2016

Thank You

• Dr. Gary Yale

• Dr. Ed Post

• Mr. Jack Crabtree