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Jeremy Wright, 12/27/2013 07:16 am


Preliminary Design

Introduction

This document covers the preliminary design decisions for the Ground Sphere ground station. The document includes three sections: technical background on SkyCube's radio, hardware design of Ground Sphere, and software design of Ground Sphere. The design is structured in parallel with the Requirements Document to ensure all requirements are satisfied.

SkyCube Radio Details

SkyCube uses a Colony 2 (CII) radio from AstroDev. The specific radio is the Boeing variation as documented in the following PDF (CII_Specification_08042010.pdf).

The SkyCube radio operates at 915 MHz with a transmit power of 2 W. It has an omni-directional antenna which adds negligible gain.

Hardware Design of Ground Sphere

  • TR 1.1 Enable users to receive "space tweets"
    • TR 1.1.2 Receive radio signals on 915 MHz (link budget)
      • Antenna
        • Dimensions (source)
          • Phasing line: 2.7745" of RG-62 90 ohm coax cable
          • Ground plane: 6.3" diameter disk of conductive rip stop fabric
          • Ground plane radial arms: 2.3925" of rigid material (need not be conductive)
          • Aerial length (circumference): 13.7075" of 12ga copper wire or better
          • Distance between bottom of aerials and ground plane: 1.6475"
      • Preamp
      • RTL2832U SDR
  • TR 1.2 Be easy to assemble from kit components
    • TR 1.2.1 Time to assemble
      • Ground station will be shipped as a kit
    • TR 1.2.2 Tools for assembly
      • Preamp will ship already assembled, ground station structure will include all drill holes and all other component fabrications steps
  • TR 1.3 Have low shipping costs for the packaged kit
    • <insert max dimensions here?>
  • TR 1.4 Operate using a modern Windows PC
    • TR 1.4.3 Hardware must connect to PC using standard port(s)
      • The SDR connects to host computer through USB 2.0
  • TR 1.5 Hardware must be robust
    • All connectors will be designed to ensure long life (internally mounted, have adequate strain relief, etc)
  • PR 2.1 Budget
    • PR 2.1.1 Unit cost
      • <insert current materials cost here from BoM>

Software Design of Ground Sphere

  • TR 1.1 Enable users to receive "space tweets"
    • TR 1.1.1 Predict SkyCube flyover opportunities
    • TR 1.1.2 Receive radio signals on 915 MHz
      • SeeDeR software (provided by Southern Stars) can tune SDR to 915 MHz
    • TR 1.1.3 Decode "space tweet" message from SkyCube
      • SeeDeR software (provided by Southern Stars) can decode the BPSK-modulated, unencrypted AX.25 data packets sent at 9600 baud "space tweets" sent out by SkyCube
    • TR 1.1.4 Account for Doppler shift
      • SeeDeR software (provided by Southern Stars) will be updated to account for Doppler shift
  • TR 1.4 Operate using a modern Windows PC
    • TR 1.4.1 Software must run on Windows
      • GPredict runs on Windows 7
      • SDR drivers <get link from Aaron> run on Windows 7
      • SeeDeR runs on Windows 7
    • TR 1.4.2 Software must be easy to install
      • GPredict includes a Windows installer
      • SDR drivers include a Windows installer
      • Southern Stars will provide a Windows installer for SeeDeR

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