Final Design Review for

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Final Design Review for CubeSat Base Electrical
Subsystem April 1, 2008 Bryce Wheeler Jeff
Brady Josh Karren
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Presentation Outline

• Overview
• Electrical Power Subsystem (EPS)
• Command Data Handling
• Communications
• Payload (Science Sensors)

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Overview
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What is the CubeSat

• CubeSat is a type of space research satellite
  with standard dimensions of 10 x 10 x 10 cm
• Weighing no more than one kilogram
• Typically used in commercial off-the-shelf
  electronics components

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What is the CubeSat

• Used in the realm of space science and
  exploration
• Most carry one or two scientific instruments as
  their payload

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Electrical Power Subsystem (EPS)
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Power Subsystem Requirements
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Off-The-Shelf Parts

• Clyde Space
• EPS
• Solar Panels
• Batteries (li-poly)

Power Board Batteries
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EPS Block Diagram
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Solar Cell Suppliers

• Emcore has 1500 minimum purchase fee
• Spectrolabs has 500 minimum purchase fee.
• Winner? Spectrolabs!

Price indicates what it would cost to cover one
side of CubeSat
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Solar Cells
Each side of the CubeSat will have one panel of
dual-junction solar cells which consists of two
cells in series. Each cell is 3cm x 7cm for a
total area of 21 cm2. I/V characteristics per
panel Vout 4.1V (max) Iout 300 mA
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DC-DC Converter (Max 641)

• Requirements
• Accept wide input voltage ( 1V to 4.5V)
• Adjustable output to 6.5V
• High temperature operating range

Specs
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Battery Requirements

• Supply up to 1A of current
• Store at least 700 mAh
• Withstand high temperature fluctuations
• Reliable
• Low mass
• Low volume

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Battery Options
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Why Ni-MH Batteries?

• Higher energy density than Ni-Cd
• Easier to charge than Li-ion
• Longer charge-cycle life than Li-ion
• More heritage in space
• More reliable

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Command Data Handling (CDH)
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CDH Requirements

• Handle multiple inputs and outputs in real-time
• Allow for modularity in subsystems (SPI, I2C, )
• Work in harsh space environment
• Incorporate redundancy to compensate for errors
• Have sufficient clock speed

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MCU Options
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Microcontroller Solution

• ARM2103 Features
• Real-time clock
• Low power consumption
• 2 UARTs
• 2 SPI busses
• 2 RS232 ports
• 3.3 V supply pins
• 32 General I/O
• 82mm x 62mm x 25mm
• 20 MHz operating frequency
• 32 KB of flash memory
• 8 KB of RAM

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Software Flowchart
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Software Solutions

• Operating System freeRTOS
• Small memory usage (less than 236 bytes)
• Simplifies interrupts
• Free!
• Already ported to ARM7 microcontroller

• IDE
• GNUARM (GCC ARM cross compiler)
• C programming language
• Flash-magic (Flash programming tool for hex file)

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Communications
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Communication Requirements

• Minimum 1200 Baud data rate
• UART or RS-232 interface capable
• Utilize 70cm Amateur Radio satellite
  frequencies (435MHz - 438MHz)
• Simple communications protocol
• Low power consumption
• High RF output

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Communications Block Diagram
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Communication Alternatives

• Transceivers
• Microhard Systems Spectra 2400
• MaxStream 24XStream
• Kenwood TH-D7A(G)
• Yaesu VX-2R

• Terminal Node Controllers (TNC)
• PacComm PicoPacket
• Kenwood TH-D7A(G) - integrated
• Tigertronics, Inc. RTX-12OEM
• Byonics TinyTrak4

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RF Modem Specifications

• Power Output 500mW_at_5V, up to 1W max
• RF Effective Rate 1200bps
• Communication Mode Half-duplex
• Frequency Band 400MHz470MHz (customized)
• Channel 8
• Interfaces COM1TTL/UART , COM2RS232 standard

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RF Modem Interface
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RF Modem Interface
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RF Modem Channels

• Band Plan for 70cm reserves 435MHz 438MHz
  for satellite communications
• Satellite frequencies are assigned by the
  Amateur Radio Association
• Channels are programmed with half megahertz
  increments between channels
• Channels allow for greater flexibility

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Hardware Software Protocols

• Hardware based on Gaussian Frequency Shift
  Keying (GFSK) modulation to achieve low Bit
  Error Rate (BER) and to provide resistance to
  both transient interference and random
  interference
• Software based error detections are handled
  with CRCs and checksums, etc.
• Data communication protocol is handled with
  software generated data packet (header, data
  bits, stop bits, etc.)

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Link Budget
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Link Budget
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Link Budget
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Link Budget
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Antenna Requirements

• Durable collapsible construction
• Easily deployed
• 50-Ohm impedance
• Four ?/4 monopoles
• Constructed from blue spring steel
• Currently under development by mechanical
  engineers

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Payload (Science Sensors)
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Payload Requirements

• Operate in LEO space (Lower Earth Orbit)
• Use no less than I (min) equal to 1µA.
• Use no more than I (max) equal to 250 mA
• Use no more than 70 mW of power

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Payload Options

• Use 16-bit shift registers for converting
  serial-to-parallel data transfer.
• Connect Payload Sensors to the microcontroller
• Use temperature sensors MAX6633/34/35 for the
  temperature payload

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Payload Solution

• DS1624 Digital Thermometer and Memory
• Temperature range between -55C to 125C
• Temperature accuracy up to 13-bits
• Serial interface

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Block Diagram

• Architecture of the DS1624
• Address and I/O Control
• Temperature Sensor
• Status Register and Control Logic
• EEPROM Memory

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Pin Description
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Command Set
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Data Storage
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Payload System

• The payload system has data being stored in the
  DS1624 Temperature Sensor
• Data stored as 13-bits in the DS1624 Temperature
  Sensor is sent from the SDA pin (Serial Data I/O)
  to PIC18F MCU.
• PIC18F MCU takes 13-bits data, converts data from
  serial-in to parallel-out
• Data after conversion is sent to ARM
  Microprocessor