designing a communications system for eagle lisa ferguson dr. gary yale, dr. ed post arizona...
TRANSCRIPT
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