AS1 MidTerm Design Review

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AS-1 Mid-Term Design Review

• Oct 17, 2007

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Fall 2007 Goals

• Functioning Ground Station
• Built and tested EPS board
• Built CDH board
• Built external structure
• Functioning primary comm system
• Designed secondary receiver
• Functioning antenna deployment mechanism
• First version of AS-1 software complete

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System Engineering
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Mass Budget
CDH
ADC
Structure
Comm
EPS
Payload
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Pin Header Budget

• Keep track of electrical interconnections within
  the satellite
• 2 of 40 pin headers

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Custom Printed Circuit Boards

• Board Template
• Standard size to fit CUBE
• Interconnections
• Consistent across all boards
• Flexibility
• Prototype
• Re-Design
• Final Build
• Powerful Software

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CDH Hardware

• Making component library in Eagle
• Transferring schematics to Eagle
• Consider pin budget

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Electrical Power System
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EPS

• Making component library in Eagle
• Transferring schematics to Eagle
• Decision on redundancy
• Decision on size of prototype board
• Decision on 90 degree pin headers

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CDH Software
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CDH Software

• Development Plan
• Design
• Define
• Implement
• Debug

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Design
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Define

• Completed
• Defined an API to simplify the logic
• Defined a log file format
• Defined a transmission standard

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Implement

• Completed
• Developed upper level logic
• Developed lower level functions
• Uncompleted
• Integrate all software on the microprocessor

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Debug

• Uncompleted
• Test and debug upper and lower functions
• Test and debug integrated software
• Test and debug software embedded on the
  microprocessor

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CDH Software

• So far
• Design
• Define
• Implement
• Left to do
• Debug Integrate

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Communications
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Communications

• Receive commands/data from the groundstation
• Transmit data to the groundstation
• Capable of receiving a transceiver shutdown
  command (FCC requirement)
• 435-438 MHz band, 1200 baud FM modulation

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Comm Block Diagram
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Antenna Switching Matrix
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Secondary Command Receiver
VCC
R101
C103
C105
C102
C106
TO ANTENNA SELECTION RELAY MATRIX
C104
L101
L102
L103
C101
C107
437 MHZ BANDPASS FILTER all these components are
chip inductors and capacitors
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Command Decoder
To Melexis IC demodulated output (note may
require level shifting interface circuitry)
Valid transmission indication Use TBD
These can be an 8 position DIP switch for
prototype, but will be shorted with wire jumpers
for final launch version.
To four critical control points in AS-1
mode circuitry These are latched outputs
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Structure
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Structure

• External structure
• Internal structure
• ADM (antenna deployment mechanism)
• Vibrations and thermal modeling testing

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External Structure

• External Structure
• Prototype is built
• 278 grams
• This first step prototype should accommodate
• Internal stack
• Antenna deployment mechanisms
• Vibration testing
• This integration is crucial to see how external
  design works

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External Structure
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External Structure

• Solar Cells
• Make cutouts for top/bottom plates
• Build side plate cutouts off of current antenna
  doors
• PCB material over cutouts to leads
• Epoxy cells to plates
• 90 headers

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Internal Structure

• Integration with the Internal Structure
• Board gaps because of pin headers?
• Procure 11.12mm pin headers
• This assumes equidistance between each of seven
  boards

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Internal Structure

• Spacers
• Unthreaded aluminum
• Dependant on gap between circuit boards
• Can be custom cut to right length

SPACER
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Internal Structure

• Battery Attachment
• Battery board will have cutouts for batteries
• Four aluminum brackets will secure boards
• Six bolts will provide fastening

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Antenna Deployment System
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Compliant Mechanism Overview
An applied force creates flexure in mechanism.
Compliant Mechanism
Nitinol antenna unfurls and straightens
When tension released, elastic mechanism resumes
original shape
Antenna is constrained by plastic tether tied
through PCB and around antenna. The tension
deforms mechanism.
A Nichrome heating element in contact with tether
severs the fishing wire and tension is released.
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Designs
Flap Thicknesses .25 and .5 mm Undeformed Angle
180
Flap Thicknesses .25 and .5 mm Undeformed Angle
110
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Material Considerations

• Antenna material selection
• Nitinol
• Measuring Tape
• Compliant material selection
• No outgassing
• Resistance to O3
• Space legacy
• Withstand stresses

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Hinge and Spring System
Springs attached from satellite structure to
hinged flaps
Exposed Top View
Fully Deployed System
Antennas are constrained with plastic wire to the
PCB. Tension is created by extension springs
attached to flaps and structure.
Side View shown with Top Plate
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Spring Selection
Spring 2
Spring 1
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Design Comparison

• Tolerances for compliant piece are too small to
  machine
• Issues of epoxy cracking on bendable surface of
  compliant part
• Spring and hinge system is more complex

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ADM Board Layout
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Epoxy Selection

• Comparison Matrix

• All epoxies pass NASA outgassing qualifications
• All epoxies are able to bond metal to most
  plastics

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Vibrations and Thermal Analysis

• Purpose
• To Validate Design
• Goals
• Determine FEA Software
• Create a Record of Procedure
• Create and Update Model of Aubie-Sat 1
• Create Test Environment
• Test Aubie-Sat 1 on Vibration Table

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Ground Station
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Surge Protection Grounding

• Surge Protection
• Coax cable
• Rotor cable
• Grounding
• Antenna
• Rotor
• Coax cable surge protector
• Rotor cable surge protector

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• Cables going Grounding
• into the building

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To grounding point on elevation rotor mounting
plate
To boom grounding point on 2 meter crossed yagi
antenna
To boom grounding point on 436 MHz crossed yagi
antenna
These can be taped to the mast for support
and cable management
Rotators Bottom of antenna mast
Load center grounding bar electrically bonded to
mast pipe or ground clamp such as McMaster 7599K76
To facilities ground point
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Transmission line to antenna AND boom grounding
strap
S/S Compression clamp with either some
sheet rubber underneath or put transmission line
in split automotive rubber fuel line to prevent
abrasion by clamp
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Rest of the semester

• Finish installing hardware on roof
• Confirm interface between hardware and software
• Track satellites
• Communicate with satellites