On November 13th, 2010, my UCSC friends and I helped about half a dozen Google employees launch 7 high altitude balloons into near space, each reaching an altitude in excess of 100,000 feet.
The balloons carried cameras (still and video), APRS beacons, radar reflectors, and several Google Nexus S cellphones.
Of these 7 balloons, 6 were recovered within a day of launch and one was found a month after launch.
We were able to track the progress of the balloons using a Microtrack 8000FA APRS beacon connected to a GT-320FW GPS for each payload. Each beacon transmitted a packet with the latitude and longitude of the balloon every two minutes. These packets were decoded by internet connected amateur radio stations and placed online where we could view them at aprs.fi. For each APRS beacon we used a flexible 2 meter J-Pole antenna. The radio and GPS were powered using 8 AA lithium batteries each. Lithium batteries were chosen as the more standard alkaline batteries don't perform well in the cold temperatures of near-space.
The balloons were equipped with various still and video cameras -- most notably a Canon G11 and several GoPro HD video cameras. Most of the GoPro cameras we used were mounted inside of the payload looking at Nexus S phones running various apps (Google Maps, Skymap, etc) although two were mounted externally: one looking at the horizon and one looking at the ground. Battery life was, of course, a major issue with these cameras. The GoPro's battery was supplemented with USB power provided by two AA litium batteries and an adapter. Most of the GoPro video cameras we flew ran out of storage space on their 16 gb SD cards and turned off before the balloons burst. One of the GoPros, which was given a 32 gb SD card, functioned throughout the entire flight.
The G11 camera was running CHDK and an intervalometer script to take a photograph every 12 seconds and powered using just its internal lithium ion battery pack. The G11 worked throughout the flight, taking several thousand photographs over a period of several hours.
One balloon was launched and recovered as a test of our systems on November 4th, with the remaining 7 launched on the 13th.
The decision of the launch location was a difficult one. The wind charts for that day showed that the high altitudes winds were predicted to push our balloon many miles to the South. We decided to launch as far North as we could, and picked a park in Ione, California, for our launch point.
After arriving at our launch site with our 7 helium tanks, 7 balloon payloads, boxes of balloons, radar reflectors, and the like, we began to inflate balloons. The first balloon, KJ6ELP-9, was launched at 10:19am. By monitoring its ascent via aprs.fi, we determined that the about 3 lbs of buoyancy we gave the balloon was insufficient and inflated the next few balloons with slightly more helium.
The last balloon was launched at 12:30pm. We inflated our 1200 gram kaymont balloons to a little more than 3 lbs of buoyancy with the payload attached. The balloons rose at about 6 meters/second until they reached a bit above 100,000 feet where they burst due to the expansion of the balloon in the low pressure of near space.
Landing and Recovery
As the balloons rose into thinner atmospheres they expanded to many times their original size until at about 100,000 feet, they popped and the payloads began to fall. Parachutes attached to the payload slowed the fall of the payload and the APRS beacons continued to broadcast their locations. When the balloons landed we were able to locate them based on the APRS data that these balloons broadcast.
4 payloads were recovered on the same day as launch with another 2 recovered the next day. The payloads all landed in the Central Valley, but many of them landed in wetlands South of Los Banos forcing recovery teams to hike through fairly difficult terrain.
The last of our payloads was recovered a month later when someone found KI6NKO-8 and called my number which I had posted on the side of the payload.
Overall, the project went very well. We did learn quite a bit about launching balloons, especially during our trial launch. A few notes:
Launch early: especially during late fall, the days are short. By launching early you give yourself more daylight hours to look for your payload and hopefully recover it on the same day. Also, once the balloons are launched, get right to planning out the recovery. It's tempting to take a break but the work is far from done.
Buoyancy matters: Make sure you have a way of measuring and modifying the amount of lift on your balloons. Also, more lift is almost never a bad thing.
A TNC is very helpful: If you can get your hands on a TNC, use it. Once our balloons were on the ground they could no longer hit any digipeaters and we didn't get any packets on aprs.fi. Without our TNC, we would have recovered far fewer of our payloads.
Plan ahead: once your payload is designed and built it's important to know where, when, and what parameters you're going to put into launching it. Do that right, and you've got a very high chance of recovery.
Along with the many cameras we sent up, several Nexus S and one Nexus One phone were sent up as dataloggers. Several hundred megabytes of data were generated, including accelerometer, gyroscope, GPS, and magnetometer readings. Additionally, we've got .kmz files of the flight paths of our balloons via APRS.fi.
The .kmz files are posted here and are viewable in Google Earth. Our flight paths are also visible here on aprs.fi.
This is a pretty easy project. If you're interested in doing it yourself, here are a few pointers to get you started: