Ground Sphere CubeSat Ground Station

h1. Preliminary Design

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h3. 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.

h3. SkyCube Radio Details

*SkyCube* uses a Colony 2 (CII) radio from "AstroDev":http://www.astrodev.com/public_html2/.  The specific radio is the Boeing variation as documented in the following PDF ("CII_Specification_08042010.pdf":http://www.astrodev.com/public_html2/downloads/datasheet/CIIUserManual.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.  

h3. 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":https://opendesignengine.net/news/50)

*** Antenna

**** Dimensions ("source":https://opendesignengine.net/news/46)

***** 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":http://www.g0mrf.com/432LNA.htm

*** "RTL2832U SDR":http://www.realtek.com.tw/products/productsView.aspx?Langid=1&PFid=35&Level=4&Conn=3&ProdID=257

* 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>

h3. Software Design of Ground Sphere

* TR 1.1 Enable users to receive "space tweets"

** TR 1.1.1 Predict SkyCube flyover opportunities

*** Using "GPredict":http://gpredict.oz9aec.net for flyover prediction

** 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