Post on 03-May-2018
Beyond The Grid Square --
Fox# Experiments
Mark Spencer, WA8SME ARRL Education and Technology Program
My Purpose Today
• To make the opportunities afforded by the Fox satellites accessible to schools outside the immediate University of interest, and to the general ham population
• Outline: 1. WRAPS portable antenna rotor system to access Fox
and other satellites [Now] 2. Attitude Determination Experiment (Wobbler)
[Tomorrow at 1055] 3. Maximum Power Point Tracking (MPPT) [Tomorrow
at 1345]
WRAPS Design Goals
Battery operated, portable satellite antenna rotor system
Affordable alternative to the Yaesu G5500 Reproducible using commercial-off-the-shelf
parts, minimum mechanical work, common hand tools only
For work with ARROW or Elk hand held antennas Target audience: Schools to access Fox
telemetry; and the Portable satellite operator Fulfill a Bucket List goal
WRAPS Design Result • Power source: 12V DC battery (Yes! It works well and
for a good long time on a single 9-volt battery) • Affordable (all relative)
– G5500: $730, LVB Tracker $200, Cabling $100 – Total $1,000
– WRAPS: Parts minus shipping costs $275 • Rotor control interface is organic to unit
– USB 9600 baud – FTDI driver set/stable but some noise (unacceptable for
packet reception I found out) • New update – XBee link
– SatPC32/EasyCom/SAEBreTrack protocol
WRAPS Limitations (What WRAPS is NOT)
• Small, light weight antennas ARROW/Elk only • Not weather proof • Not intended for 24/7, unattended operation
– Used beside operator and mounted on camera tripod – limited safety shut off limit switches
• As designed is 360 degree AZ/90 degree EL – Can be modified for 180 degree EL
• Added mechanical stress and complication – Switch selectable North-stop/South-stop to mitigate
90 degree EL limitation • Requires SatPC32 Rotor Set-up change
90 Degree EL Limitation Mitigation
• If satellite will pass through the North – Set WRAPS for South-stop – Set SatPC32 for South-stop, 90 degrees EL – Park antenna at 180 AZ/0 EL, Point antenna south
• If satellite will pass through the South – Set WRAPS for North-stop – Set SatPC32 for North-stop, 90 degrees EL – Park antenna at 180 AZ/0 EL, Point antenna south
• Results in no AZ wrap around problems
Attitude Determination Experiment (Wobbler)
“In addition to the communications package, Fox-1 will host an experiment payload. AMSAT is sponsoring a capstone project at Penn State University for the 2011-2012 academic year... The project will involve designing and constructing an attitude experiment based on a 3-axis, micro-electro-mechanical gyroscope. The experiment data will measure the performance of the satellite’s magnetic stabilization system...”
Attitude Determination Experiment (Wobbler Experiment)
• Use gyroscopes to directly monitor satellite rotation around the X, Y, and Z axes – Precedence has been to infer
rotation rate from solar panel voltage/currents
• Gyroscopes contain an oscillating driving mass – Oscillation proportional to
direction and rate of rotation – Oscillation converted to
voltage
Wobbler In-classroom Simulator • Simulator uses actual
gyroscope devices to be flown
• Mounted on rotator to simulate on-orbit behavior
• Data linked off-platform like the actual satellite – Manipulate the Wobbler
board and see what data results
– Capture real satellite data and see the Wobbler board gyrations that produce similar data
Wobbler Ground Station GUI
• GUI displays data transmitted by Wobbler board
• GUI also used to control rotator behavior (direction and rate of rotation)
• GUI dumps data to Excel for exploitation and graphing
Data Analysis, the real value
-2 -1 0 1 2 3 4 5 6 7
0 100 200 300 400 Ro
tatio
n De
g/Se
c
Time in Seconds
Level CCW 1 RPM
X
Z(X)
Y
Z(Y)
-2
0
2
4
6
8
10
0 100 200 300 400
Rota
tion
Deg/
Sec
Time in Seconds
Tilt Around X CCW 1 RPM
X
Z(X)
Y
Z(Y)
-2
0
2
4
6
8
10
0 100 200 300 400
Rota
tion
Deg/
Sec
Time in Seconds
Tilt Around Y CCW 1 RPM
X
Z(X)
Y
Z(Y)
MPPT Task
Rochester Institute of Technology (R.I.T.) engineering students have tackled the task of developing a maximum power point tracking (MPPT) system for use on the AMSAT Fox-2 satellite (see March/April 2013 AMSAT JOURNAL). Their task was to prototype a system that optimizes the power delivered by the satellite’s solar panels.
MPPT
• Solar panel output dependent on illumination and operating temperature
• There is a sweet spot where output power is optimum
• Experiment purpose is to find and then keep the panels operating at the sweet spot
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0 1 2 3 4 5 6
Wat
ts (W
)
Curr
ent (
A)
Voltage (Load)
I
Watts
Optimum panel output
MPPT In-classroom simulator
• Allows students to experiment with solar panels to find power production curves and the sweet spot
• Develop circuitry to find and then operate the solar panel at the sweet spot
• Anticipated grade level 8-9
• Anticipated grade level 13-14 pre-engineering
MPPT Circuit in Operation
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0 1 2 3 4 5 6 W
atts
(W)
Curr
ent (
A)
Voltage (Load)
I
Watts
FET control voltage
Panel operated in sweet spot
MPPT Classroom Simulator Components
• Controlled illumination source and solar panel
• MPPT Circuitry and computer interface
MPPT Illumination Source
• LEDs mounted inside of a PVC coupler fitting
• Portable and sealed to prevent outside light from getting to the solar panel – You put the unit in
controlled temperature environments
– I used my refrigerator
Solar Panel Side
• Solar panel with temperature sensor probe mounted in the other end of the PVC fitting
MPPT Circuitry
• Use a VOM and screw driver to vary the load on the solar panel and measure the output current/voltage
• Collect readings on a data table to generate the solar panel profile
MPPT GUI
• Displays temperature of the solar panel
• Allows for automatic MPPT operation based on temperature profile algorithm
• Allows for manual input of max/min voltage limits
Conclusion
• My Purpose: to make the Fox experiments more accessible beyond the Universities, including the average ham satellite enthusiast
• I have the hardware with me for up-close show-and-tell if you are interested
• If you would like the specifics and details of any of the systems, send me a note at mspencer@arrl.org and I will provide a DropBox link to the information I have on hand.
Sponsors
• The efforts I detailed yesterday and today were made possible by: – A grant from the ARRL Foundation – An award from the YASME Foundation
• My thanks to them for their support
• Questions that I can try to answer?
• If not, thanks for your attention and I will be around for one-on-one if you like.
• Mark Spencer, WA8SME mspencer@arrl.org or 860-460-1139