High Altitude Photo System

Overview

  • Tracking System - James Coxon
  • Photo System - Doug Ellison

Payload Deck

  • The payload deck is a 15cm x 30cm carbon fibre sheet with an anchor hole on each corner. The lines from the corners extend up to a central point where they are attached to the parachute lines and also the balloon main line.
  • Below it the antenna ground plate is attached on 4 foam blocks
  • Each section of the payload has 15cm x 15cm deck space.

Tracking System

  • The tracking system for HAPS-1 is based around a Gumstix verdex and prototype goliath board (kindly donated by Gumstix Inc.). For more information check out my Goliath wiki page.
  • Onboard there is:
    • Ublox Neo-4 GPS module
    • Siemens MC75 GSM/GPRS module
    • UBC1400 Audio
    • USB Host

GPS

  • The Ublox Neo-4 doesn't have a true altitude limit instead it doesn't work if both the altitude limit and the speed limit are exceeded (Unlike the SIRF III which doesn't work above 24km due to calculation errors)
  • It is connected to the Gumstix via usb and so requires the cdc-acm module to work, it then appears as ttyACM0
  • The code:
    • Reads ttyACM0 (acting like a serial port)
    • Parses the NMEA and gets all the important data values
    • Logs it to gps.log
    • Every 10 minutes this log file is backed up separately (so we don't strain the filesystem with a very large file)

GSM

  • The GSM module is also attached by usb and also uses the cdc-acm module appearing as ttyACM1
  • The best way to communicate with a GSM module is via AT commands, to simplify this I've used Gnokii.
  • Every 2 minutes Gnokii is called to take the last line out of the log file and send it by sms to base.
  • GSM doesn't work at altitude (due to the horizontal facing cell tower antenna) and so stops working after about 1km altitude, therefore the GSM module won't send any sms and will just timeout. Once the payload descends back down below this level it'll be able to send sms messages again. While attempting to send every 2 minutes is an inefficient method (the alternative would be to only try and send sms messages when the payload was below a certain height) it is very reliable.

Radio

  • The radio is a Radiometrix NTX2 module that transmits on a frequency of 434.650 at 10mW. Its 'Data In' pin is connected directly to audio out port of the goliath board, a GPIO is used to control the 'Enable' pin just before transmitting data.
  • The tracking system is trialing two different methods of transmitting data; Packet Radio and SSTV.
  • The general radio sequence is:
    • 30 loops of packet radio every 15 seconds with the coordinates (during this time a picture is taken and then processed)
    • “Sending Picture” is sent
    • The image is transmitted via SSTV (Martin 1)

Packet Radio

  • This is based around soundmodem which is a userspace program that uses a soundcard to encode and decode packet radio. On linux this is coupled with AX.25 libraries and tools.
  • Packet Radio is best used when there is both and downlink and an uplink (something for the future) as you can have a complete TCP based network however we only have a downlink so are using 'beacon' to send the coordinates.
  • A complete data string is sent every 15 seconds at 1200baud.

SSTV Radio

  • SSTV stands for Slow Scan TV and is a method of transmitting images over radio.
  • dj1yfk on #hamradio on freenode wrote some code in an afternoon which converts a jpeg image into a sstv wav file which can then be played with a normal audio player through the sound card.
  • Generation of the wav file takes about 5 minutes while transmission takes just under a minute.
  • The original plan was to have a camera onboard that had a remote capture feature however I managed to break the camera while stripping it down to reduce weight.
  • Instead a test jpg will be used and will undergo the same processes as if it had come off the camera.
  • In the future I'll add in the camera.

Code

OLD CODE

  • gpsparser3.pl - reads the gps serial port and parses the NMEA
  • gpslogrotate.pl - rotates the logs and gzips them to save space.
  • cutdownpolygon.pl - reads the gps log and decides if payload has exceeded the cutdown polygon
  • smsloop.pl - send SMS of coordinates using AT commands to the Telit module

* downlink

Backup Beacon

  • This uses a CDPTX04 radio module which operates at 10mW on a frequency of 434.075Mhz and is attached to a 555 timer setup to pulse every second.
  • The system runs off 2 AAA lithum batteries

Photo System

  • Based around a modified Canon A560 running the CHDK firmware.
  • The camera is set to take 15 seconds of video and then multiple stills every minute.
  • Encased in a foam insulation
  • Also has a SIRF III based independent data logger to act as a backup gps track after the flight.

Ground Station

  • The radio is attached to a MacBook running OS X and the data is decode via TrueTTY (running in wine) and MacRobotSSTV.
  • TrueTTY logs very slowly (every 3 mins) so akawaka (#highaltitude on freenode) wrote a program to use the DXSOFT.DLL of TrueTTY to access the Rx buffer more often and log to file.
  • MGroundControl is a RubyCocoa program that reads the log file, parses it and then uploads it to the online tracker
  • Also a IRC bot reads the log file and sends updates to #highaltitude99 on freenode.
  • Also on the tracker is a ustream webcast of the launch, a webbased IRC client, twitter display and also will display any pictures that are recieved by SSTV.
  • MControl RubyCocoa Source
    • radio1.txt needs to be placed on the Desktop
    • Pictures are downloaded from the MacRobotSSTV MemoryBank directory

 
missions/haps/haps-1.txt · Last modified: 2008/08/27 16:17 by jamescoxon
 
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