- Ascent - This is the easy part (we think). We buy a weather balloon, put our camera and other electronics gear in some sort of styrofoam box, attach the box to a parachute and attach the parachute to the weather balloon. Then we fill our balloon with enough Helium to lift the payload (camera, styrofoam box, parachute, etc) plus 1 lb to 1.5 lbs of extra lift. Dale found a chart that shows what the ascent rate should be based on how much extra lift you have. I'll get that from him and will link it here. I found one balloon site where the group was using Hydrogen to provide lift. Didn't the Germans give that a try a few years ago? :) I like having eyebrows so I think we'll stick to Helium.
- Descent - At some point the weather balloon will burst due to the expansion of the Helium. Of the other balloon project websites that we've read the highest launch was to 117k feet. That's pretty darn high if you stop and think about it! I know I'll be very happy if we get anywhere close to that. Anyway, once the balloon pops you need a parachute to get your payload back on the ground in one piece. Parachutes from model rockets seem to be the popular choice. We haven't ordered one yet because we don't know how much our payload is going to weigh.
- Camera - Obviously we want something digital and we need a way for the camera to take pictures without any user intervention. The easiest thing to do is buy a camera that has an intervalometer feature which allows you to set the camera to take a picture every X seconds. The other option is to rig some sort of mechanical device to push the shutter button every X seconds. Dale has tracked down a free camera for Project-WARPED but it doesn't support invervalometer so we will have to rig a mechanical solution. Here's a great website for some more information on time lapse photography.
- Tracking - This is the tricky part. If you launch a balloon to 100k feet and take lots of cool pictures you need a way to recover the camera when the balloon finally lands. We will be using Automatic Position Reporting System (APRS) to track the balloon's location. In a nutshell, APRS is implemented by using a GPS receiver that attaches to a RF transmitter which in turn transmits the GPS coordinates via packet radio (this is why we needed our ham radio licenses). We will pick up the RF signal from our transmitter (the Micro-Trak 300) by using a RF scanner on the ground. The headphone output from the RF scanner feeds into a laptop's microphone input which decodes the data from the scanner into a digital format containing the GPS coordinates of the balloon. Doing this last part on the laptop is something we don't have working yet. The following powerpoint presentations have more detail on APRS and how it ties into ballooning:
Monday, September 24, 2007
One of our motivations for blogging this project is that we haven't been able to find any good "from start to finish" documentation on how to launch a camera with a weather balloon and recover it. We found several other balloon blogs but none of them gave much detail on how they did everything. We're going to try to document as much as we can so that hopefully someone can use this blog as a reference for their own balloon project. That said, here is a rough overview of how we think this will work. We're learning as we go though so I'm sure this will change.