Please see the Disclaimer page before attempting to launch a balloon. If you are interested in duplicating this project, or would like some ideas for a modified balloon project, here's a quick and dirty DIY to get you started. Refer to the payload page and pictures on this site for visual reference. Half the fun of doing a project like this is from figuring things out on your own, so I'll just hit the highlights. Each section also contains a "things we learned list." You should read these if you are going to try this and learn from our mistakes!
This is the easy part, but you need to figure out a couple of important decisions. First, you'll need to know how big your payload is going to be. Our payload was about 1.7-2.0 lbs, including parachute. For this size payload, we used a Kaymont 600 gram sounding balloon. In order to lift the balloon at an appropriate lift rate (600-900 feet per minute), we filled it up to about 5-6 feet in diameter. That required about a quarter of a tank of helium (the big ones used at party stores). A full helium tank will cost about $80-100 plus any rental fees and deposits. Look for gas supply stores (welding supplies) in your area and tell them what you are doing. If they know it's for an educational project they might cut you a deal.
Things we learned:
1) Don't tie your balloon nozzle until you know you have enough helium to lift the payload. We failed to do this twice and it's a pain to untie the balloon and add more helium. We used zip-ties and kite string to seal the balloon.
2) A lighter payload will require less helium to lift, which means you can under-inflate the balloon a little. This will allow the balloon to rise higher before bursting. When let go, the balloon is 5 feet in diameter. At 100,000 feet, it grows to over 20 feet before bursting! More helium=faster climb but a quicker/lower burst.
3) Get as big a balloon as you can. 600 grams is pretty big, but they make bigger, and bigger means higher.
The camera is the trickiest part of the project and presents you with the toughest decisions. First of all, buy a Canon digital camera only after familiarizing yourself with the CHDK software web page: http://chdk.wikia.com/wiki/FAQ (you have to use a Canon camera because you need to add features that give it proper functionality and the software only works with Canon cameras). Spend a lot of time on this page. You will find a list of usable cameras to choose from, and you should consider things such as weight, megapixles, price and features. The CHDK software is easier than it looks and requires that you first install the software onto an SD memory card. The next step is to upload a "script" to the camera that adds an intervalometer feature and allows you to turn off the lcd display to conserve battery power. A copy of the script we used is attached below; you can open it using a text reading program like Notepad. It's a basic programming language script designed specifically for the Canon a470 and a530, although it will probably work with other Canon cameras.
1) The Canon a470 is a tank. It worked spectacularly, but it is a little heavier than other cameras. It's the camera the MIT guys used and it worked well for them too.
2) Two cameras were one too many and cost us some altitude. For an introductory flight, it was nice to have redundancies, but if I launch again, I'm only sending the a470.
3) Use the camera in "manual" mode and adjust the settings using the CHDK menus and the regular menus. We used an exposure time of 1/800 sec. and that gave us the best pictures. Set the focus to infinity.
4) Go with at least 7.1 megapixles and choose a camera that uses AA batteries. This allows you to get away with a 4GB memory card and use Energizer Ultra Lithium batteries (last 8X longer). Set the intervalometer to snap a shot every 10 to 15 seconds. If you want more pictures (we got about 1200 per camera per flight) you'll need a bigger card. You don't need all the USB cables for your camera, you can dump the program and scripts directly onto the memory card.
Our design was: Balloon---Parachute---Payload. Very simple and very efficient. We bought our parachute from Rocket Man Enterprises for 40 bucks. This might seem like a great place to save a little money, but I wouldn't recommend skimping here. The parachutes from RME are extremely high quality and make setting things up really easy.
1) Use Carabiners to attache the parachute to the balloon above and to the payload below. Small ones can be purchased all over the place.
2) For our payload, a 3 foot parachute worked fine but with the windier conditions of our second flight, it got a little twisted up and descended a little faster than we would have liked.
3) The design of the RME parachute made it less likely to get stuck high in a tree, and easy to retrieve when it got stuck 25 feet up at the end of the second flight.
We used a Styrofoam beer cooler with the top half cut off to save weight. This gave us plenty of room for all of our equipment. Holes were cut in the sides for the camera lenses to poke through and hot gule guns were used to affix the equipment. Two pieces of rope were run through small holes cut in the sides of the cooler and tied into loops. The loops helped to hold the top on and pulled together to attach to the carabiner. Duct tape was used to seal the top. Toe warmers were stuck to the equipment where the battery compartments were. An additional toe warmer was thrown in for good measure.
1) Don't try to make a snazzy woven basket to attach the payload to the parachute. Do what we did. It works perfectly.
2) Aim your cameras down a little bit. If you aim them straight out, you will get a lot of pictures of the sky, but miss the horizon.
3) Try to balance the payload so it doesn't tilt too much. Having two cameras helped with this, but with one, you might want to experiment with different configurations.
Tracking and GPS
Get the Boost Mobile/Motorola i290 phone. You have to have this to recover your payload after it lands. It has a built-in GPS, and as long as it has a cell phone signal, it can broadcast its position to a service called instamapper.com (requires you install software on the phone, instructions are somewhere online). You will need to spend some time on the instamapper web site to set up this service, but it's free and relatively painless. We also put a Garmin Forerunner 305 in the payload to record flight path and altitude. We had a back-up battery charger for the phone but didn't need it.
1) Make sure you have a cell phone coverage at the launch site and preferably along the entire flight path (in case you land prematurely), but it is ABSOLUTELY REQUIRED that you have a signal where you anticipate landing. Use the Near Space Venture site and play around with different assent rates, burst altitudes and descent rates so you know where your payload might land. If it lands out of cell range, you will not find it. Your best chance then is to include a note with your phone number in case someone finds it and is nice enough to return it.
2) We think the Garmin GPS (thanks Cristy for a wonderful birthday gift!) was fairly accurate, but it seemed to have some issues at high altitude with accuracy. For some reason, the device stopped recording data for 17-19 minutes above 78,800 feet.
3) After you launch your balloon, log on to instamapper and use the data to calculate an accurate ascent rate. Then you can recalculate your flight path at Near Space Ventures for better accuracy. You will find that you lose cell phone coverage at about 3000 feet, but that gives you plenty of readings to figure out how fast you are climbing.
You should familiarize yourself with regs that apply to unmanned balloons. Avoid controlled airspace, and keep your payload under 4 lbs. Disclaimer: I am not an authority on this. You are responsible for anything bad that happens. You must follow all rules and regs if you want to do this. We did.
That's it. Not everything you will need to know, but a good bit. Good luck!