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Southern University
La ACES Team
EXCELLE Experiment
(Experiment For Solar Cell Efficiency)
Tannus Joubert, Kristen Hypolite, Kevin James,
Laquonda Johnson, Michael Johnson, Shanta
McKinzie, Leslie Sanford
Preliminary Design Review (PDR)
March 18, 2005
Mission Objectives
 Measure the light conversion efficiency
 Output of an assortment of solar cells
throughout various levels of the atmosphere
 Results
– conclude whether future La ACES experiments
can be powered by the most efficient solar cells
found
SCIENCE GOALS
Understanding
 Solar Cell Efficiency
 The Solar Spectrum
– Its relation to the silicon solar cell material band
gap
 Energy
 Photons
 Wasted Heat
Types of solar cells
 Monocrystalline
– Made from pure silicon, most efficient (~24 % in
the lab), but most expensive since they are
difficult to make
 Polycrystalline
– Less efficient (18 % in the lab)
 Amorphous
– Least efficient (13%), used in watches, calculators
Technical Goals
 Measure the light conversion efficiency that
solar cells
– Research the condition the solar cells can
withstand
– Find the position that the sun is at the time of
launch and during launch to maximize the solar
power
– Deal with the rotation that maybe encountered
by the cord being tangled
Payload Design
 The payload will be surrounded with three
types of solar cells, so that energy
conversion efficiencies can be compared.
 DesignSubcategories:
 System
 Thermal
 Mechanical
 Electrical
 Software design
Principle of Operations
Photon Path
I
_
_
_
_N-Type _ _ _ _ _ _
Electric Field
+
Vo
+ + + + + ++ + + + ++ + + + + + +
P-Type
Load
_
Power
output
Possible challenges
 Rotation effects- may be dealt with by measuring position
of sun with respect to pay load
 Ultra-violet radiation- Will it damage the cells or be
beneficial by providing more energy?
 Pendulum motion of package- will it interfere with our data?
 Launching at dawn – how to maximize sunlight intake due
to low position of sun?
System Interface Components
 Main System:
 Basic Stamp Processor
 Subsystems:








Solar cells
User Interface
Real Time Clock
Analog-To-Digital Converter
Memory
Power
System Reset
Temperature Sensor
System Interface Components
*Real Time Clock provides accurate
date and time
Real
Time
Clock
Solar cells send
the charge
through charge
converter for
signal
acquisition by
the multiplexer.
Solar
Cells
Charge
Converter
User interface (Laptop) will
be used to upload and
download software and data.
User
Interface
System
Reset
Basic
Stamp
Processor
ADC converts analog to
a readable digital signal
Analog to
Digital
Converter
Memory
Multiplexer
Temperature
Sensor
Power
Basic Stamp
Processor is used to
control all data
acquisition and
processing.
Memory must
be
synchronized
with the ADC
to process the
data.
Electrical Design
 BalloonSat System
– 6V at 100mA
– 4 AA Li Batteries
 Charge Controller/Converter
– Convert current coming from each cell into voltage
– Convert excess voltage into heat, used to keep inside of
box warm
– Voltage signal/readings to be passed through an 8
channel multiplexer
 combine all the signals into one data stream
Electrical Design cont’d
 Onboard Temperature Reading
– Onboard ADC
– Voltage Regular Temperature Reading
– Operational Amplifier
 BASIC STAMP
– If memory is full Basic Stamp is able to turn itself off
– Power supply regulator is already built into the circuit
board
– LEDs will be used to confirm operations
Electronic Flowchart
SOLAR
CELLS
CHARGE
CONVERTER
MULTIPLEXER
ADC
RTC
BASIC STAMP
MEMORY
Thermal Design
 Flying payload to the height of approximately
30km at the temperature of -60oC.
 Location Palestine, Texas.
 Challenge is to design a payload to stay well
in the range of the operating condition of the
electronics.
 Overheating of the solar cell
Payload Operating at -60 oC
Overheating of the
Solar Cells
80oC
Overheating of Electronics
Thermal Schematic
Spacer
Mesh
Solar cells
cool by
radiation
Inner Temp maintained to
within 5 - 6oC with
induced convection with
fan
Air (R)
Qcond
Electronics
generate heat
Solar Cells (R)
Mesh (INS) (C)
Foam Core (C, R)
Inside Payload (R) (CV)
Air flow (-60oC)
where R- radiation, C-conduction, CV-Convection, and INS – Insulation
Recommendations
 Spacer-mesh combination to prevent
scorching of foam core
 May rely of rotational effects to radiate heat
from the box
 Test simulation will be done on electronic
and payload system to determine possible
thermal effects
Mechanical Design
We will focus on :
1. Creating a payload of a low weight, high thermal
stability, and a suitable degree impact resistance.
Constructing a payload that will withstand such
stresses is also a key factor in our design.
2. The method of attaching solar cells to the
payload and interfacing them with the rest of
the electronics.
3. Preflight worthiness test .
Mechanical Design
The box concept for now is simply rectangular
payload with which consist of two modules:
1. Inner module
2. Outer module
Mechanical Design
The functions of the outer module are:
1. To serve as a primary encase
for the second module.
2. Provide a protective covering
against acceleration, deceleration,
shock, and impact.
15.5 cm
3. To provide a surface for the
attachment of the solar cells
and framed mesh.
4. To provide a barrier against the
cold temperatures experienced by the payload.
18 cm
17 cm
Mechanical Design
The functions of the inner module are:
1. To provide a containment for the electronics.
2. To hold the batteries.
3. To serve as a second line of defense
against impact, shock and gravitational
forces.
15 cm
4. To help optimize the heat transfer of the
payload.
6 cm
14 cm
Mechanical Design
•The solar cells will be mounted on a
sheet of mesh framed with Popsicle
sticks.
•The removable frame will
then be attached to the
payload by screwing the
frame into half inch nonconducting standoffs that
will already be attached to
the box.
•By mounting the solar cells
on this structure, the heat
that will dissipate from the
solar cells will be able to
flow freely away from the
payload.
Back view of framed mesh.
Non-conducting
standoff
Front view of framed mesh.
Mechanical Design
Weight Budget of the Pay Load:
Weight limit:
500 g
• Balloon Sat:
63.55 g
• One monocrysitaline solar cell:
• Batteries:
0.5g x 3 x 4 =
6.00 g
8.3 x 4
33.3 g
=
• Inter and outer modules:
+
• Frame
• Mesh
• Standoffs
160 g
< 237.15 g
500 g - 262.85 g =
237.15 g
Futuristic Payload Development
 Charge Converter System
 Control Solar System
– Circuit
 Mechanical Systems
– Screws
 Thermal Control System
– Too Hot???
 Finishing Software
 Build Prototype
– Find circuits that work interface with software
Payload Construction Plan
 Electronics- planning, development, and
implementation
 Mechanical and thermal- Planning,
development and implementation
 Software systems
 Documentations
 Flight Implementation
Electronics
Mechanical
Thermal
Software
Integration
BalloonSat
Foam Core
Electronics
Basic Stamp
Inner Module
Modules
Sensors
Solar cells
Basic Stamp
Thermal
ADC Converter Outer Module
ADC program Electronics
Flight
BalloonS
Mechanical Basic Sta
ADC Conv
Multiplexer
Spacers
Mesh
Control
Software
Multiplex
Sensors
Mesh
Foam Core
Interfaces
Interfaces
Sensor
Interfaces
Solar cells
Interface
Hardware Fabrication
 Solar Cells
– Testing
– Framework
 Charge Converter Circuitry (Separate Boards)
– Circuitry
– Multiplexer
 Box Structure
– Shock and Thermal Testing
– Drop Test
 Battery (Power System)
– Location
– Interfacing to Whatever Needs Power
Integration Plan
 To test the connections between electronics
and software.
 Stabilize Power Connection
 Ensure that the Mechanical structure is able
to hold the batteries, boards, and other
system ancillaries.
 Take Thermal Test to ensure that
components are working properly due
changes in temperature.
Software Implementation and
Verification
 The Software designed will calculate and
measure the current and voltage output by
the cells and store the data
 The software will decide from which set of
cells the signal is being read, and process
each accordingly. The software will be used
to calculate voltage and power produced by
the cells as a function of altitude.
ADC
Time
Stamp
Function
Not T
Not 1
Not 2
Temperature
Inputs
the Data
T
Reads the
ADC value
1
Solar
Cell
Identifier
Reads the
ADC value
Solar
Cell
Identifier
2
Solar
Cell
Identifier
3
Reads the
ADC value
Calculates
the
Voltage
After completion of flight, memory is downloaded to obtain
data and for the analysis of results.
Stores into
Memory
End
Flight Certification Testing
 Upon the completion of the total payload, we will start flight certification
testing. We will do both temperature and shock testing.
 Temperature testing of the payload :
We will place the payload in a ice chest which will contain dry ice and
run the electronics as if in actual flight.
 Shock Testing of the payload:
To test the durability of the payload. We will drop the payload (about
10ft) to make sure the electronics are safely contained and will good
conditions to take post-flight measurements.
We will analyze the data for both test and make the necessary
changes needed for a successful flight mission.
Mission Operations
*Synchronize our Real Time Clock
with the Global Positioning System
*Erase all test data before flight
Flight Requirements and Operations
*Flight duration of approximately 4 hours
*Reach approximately 100,000 before
falling
*Temperatures ranges from -60 to 85
degrees Celsius.
*Ascent of balloon is expected to be
smooth
*Turbulence is expected during the fall.
Launch Requirements
*Synchronize RTC with GPS.
*Computer to communicate with
the Basic Stamp.
Data Acquisition and Analysis Plan
Data to be collected:
*Charge from solar cells
*Product of current and voltage
will allow us to compute the
power output by each cell
group.
*Temperature inside the payload
*Time stamp generated RTC
Data needed:
GPS system data: Longitude, Latitude, Altitude.
This data will be gathered after the flight. The data will then be
correlated to the data collected on the payload.
*All data will be stored on board using EEPROM memory.
Organization and Responsibilities
La Aces Program Office
Team Leader
(T. Joubert)
Project
Management
(T. Joubert)
Payload
Design
System
Design
(K. James )
Data Analysis
(L. Johnson)
Mechanical
Design
(L. Sanford )
Documentation
Calibrations
Software
Design
(T. Joubert )
Thermal
Design
(M. Johnson)
Parts/Budget
Flight Data
Analysis
Electrical
Design
(S. McKinzie )
Scheduling
(K. Hypolite)
Results
Interface Control
Software Interfaces
(Electronic) Needs
to know when to
read data; how often
to read data.
Thermal Interfaces
Depends on the
mechanical design for
cooling of solar cells,
temperature inside the
box.
All electronic components
on the payload will need
to endure extreme
temperature changes
Interface
Control
Electronic Interfaces
(System) Need to know
much voltage is coming in
various components.
Circuits needs to checked
for connections to software
and system components
System Design
Needs to be able to
communicate with all
components.
Mechanical Interfaces
Needs to be able supply an
adequate amount of space for all
components.
Materials used in construction
depend on thermal testing.
To provide a suitable degree of
impact resistance.
Master Schedule
Activity
Mission Objectives/Project Management
Start
Finish
2/28/2005
3/9/2005
Payload Design
3/2/2005
4/12/2005
Payload Development
3/9/2005
4/12/2005
Payload Construction Plan
3/9/2005
3/9/2005
Master Budget/ PDR
3/10/2005
3/13/2005
Submit Complete PDR
3/17/2005
3/17/2005
Preliminary Design Review
3/18/2005
3/18/2005
Spring Break
3/21/2005
3/29/2005
Submit Complete CDR
4/12/2005
4/12/2005
Critical Design Review
4/15/2005
4/15/2005
Flight Readiness Review
5/23/2005
5/24/2005
Launch Trip
5/22/2005
5/26/2005
Work Break Down Schedule
 Time Schedule
 Milestones
Budget
Name
Vendor
Source
Solar Cells
Radio Shack
Went to
store
Multiplexer
Digi-Key
Glue
TBD
EEPROM
Digi-Key
Catalog
1 week
1
AT27BV25612JC-ND
2.32
2.32
Batteries
RadioShack
Went to
Store
In Stock
1
4 AA
3.99
3.99
Foamcore
ACES
Program
In Stock
1
ADC
Digi-Key
Popsickles
Wal-Mart
Standoffs
Digi-Key
Construction
Tools
ACES
Program
Total So Far
TBD
Delivery
Time
In Stock
Qty
6
Part No.
276-124
TBD
Price per
quantity
10.00
Price
10.00
TBD
TBD
Catalog
Catalog
TBD
TBD
TBD
100
1 week
10
TBD
1902ck-nd
$5.24
5.24
In Stock
$21.55
RISK MANAGEMENT
Levels of Risk
High
Medium
Low
Transfer of Responsibility