Friday, November 16, 2007

wind, wind, go away

Ok yeah it's supposed to be rain - but our launch date just got scrubbed due to wind :( Note the projected path has the balloon landing in the Atlantic. Hrm, it's a bit chilly to be swimming.

Thanks to project SABLE folks who pointed out that our GPS was one that would not work above 60000 feet (oops). We ordered a new Garmin GPS (see parts list) to replace the Byonics GPS. Here is the list we found for GPS receivers that work at >60k ft.

We had another 2 crammed work days: setup up new GPS; soldered the new power connection to a DB-9 connector (for connecting GPS to RF transmitter); bought and setup a 2nd RF scanner; setup a 2nd laptop for 2nd chase vehicle; setup a spreadsheet to do all our math calculations (helium needed, ascent rate, burst altitude); tied ropes to connect parachute to cooler; punched holes through the cooler for the camera lens, antenna, and the GPS receiver; setup styrofoam shipping wedges to hold the camera in place in the cooler; created S- hooks with 90 degree turns to attach the ropes to the threaded rods on the cooler; and we've run a lot of simulations on ballon track with our spreadsheat numbers to decide if we should launch this saturday or not (tomorrow). For now we've scrubbed the launch. I suddenly have a lot more sympathy for why NASA is always moving the shuttle launches.

We've also decided that in hindsight, the parachute is too large. We don't need it to land like a feather - we just need the cooler and camera to survive. Our current payload estimate is 3lbs and our chute was rated for 3.5-8lbs (R7). We'll try to exchange the chute for a smaller one - maybe something in the 1.5-2.5lb (R3 or R4) range. Thanks to the folks at Rocketman for their advice here.

Monday, November 5, 2007

Software Recap

We are using several different bits and pieces of software for this project. We can split these apps up into a few different categories:

Pre Flight
  • Ascent Rate & Burst Altitude calculator - This is a handy spreadsheet for calculating the ascent rate and burst altitude for your balloon. These numbers are needed in order for the tool below to calculate the balloon's flight path.
  • Balloon Track for Windows is a software package that will project the flight path for your balloon. You tell the tool where you want to launch from, the ascent rate, the burst altitude, the descent rate and the wind data for your launch date and it models when and where your balloon should land. This is designed to give you a rough idea of where your balloon will go so you can avoid things such as your local airport and large bodies of water...such as the Atlantic Ocean :) If you have Microsoft MapPoint installed you can generate an image of the projected flight path. The green line shows the flight of the balloon during ascent and the red line is for descent. This shows us landing close to the ocean so we'll have to head west for our launch.


Our payload is pretty simple, we don't have an onboard computer so the only software application we are using is for our camera. CHDK is open-source 3rd party software that runs on several different digital cameras. We need to use CHDK to program our Canon A610 to take pictures on some set interval for an extended period of time. The default canon firmware has some time-lapse photography ability but it is limited to 100 pictures. We would like to take as many pictures as we can on a fully charged set of batteries thus the 3rd party software.

Chase Vehicle
  • AGW Packet Engine - This is the software that listens to "line in" on your PC for the audio coming from your receiver. It translates the audio into a digital packet format that can be used by other windows applications.
  • AGW Tracker then listens to the packets from AGW Packet Engine. These packets contain the GPS coordinates of our balloon which allows AGW Tracker to plot the location of the balloon on a map. If you have Internet connectivity you can just use google maps but if not you will need Microsoft MapPoint. We won't have Internet connectivity in our chase vehicle so we'll be using MapPoint.
Post Flight
  • Google Earth - Free software (mostly) that will let you do some very cool stuff in terms of displaying the path of some object based on GPS data.
  • GPS Visualizer - If you give GPS Visualizer a text file with the GPS coordinates of your balloon over time it can generate several different plots of the flight path. The best results are via a Google Maps image and a Google Earth file. Here is an example of a hang glider flight path in Google Earth:
  • PixGPS - I haven't used this yet but PixGPS will let you tag your pictures with GPS coordinates in the EXIF data. This way you know exactly where the picture was taken which makes it possible for tools like Google Earth to display the pictures on a map based on where they were snapped.