HAB-1: Research, Development, and Construction

By Josh Eiland · December 6, 2014

Our high-altitude balloon project, abbreviated HAB-1, was launched from Sam Smith Park in Cartersville, Georgia on Saturday November 22nd. It landed in Candor, North Carolina approximately 6.5 hours later. A write-up of the full project process is included below.

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The balloon began as just an idea. We had heard about Google’s Project Loon and seen balloon projects from a couple of other hobbyist groups, and decided that making our own high-altitude balloon would be a great way to get hands-on experience and get as close to space as possible for people with our experience and resources. This entire process primarily served as just a test to get our feet wet, and see what we could do to improve before the Global Space Balloon Challenge in April.

Design

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The fundamental design of a high-altitude balloon is as follows: the balloon, of course, is at the top of the payload train, with the parachute below it. This allows the parachute to deploy with everything else underneath it after the balloon has popped. Below the parachute is the radar reflector, which is a light-weight device that is geometrically optimized to reflect radar signals in order to signify nearby receivers of the balloon’s presence and position. And finally, at the bottom of the train, is the payload itself. We based all design and measurements on an estimate of a 4 pound payload. The payload train was assembled with 43 pound rope, as the FAA requires that the payload train be able to be broken with 50 pounds of force.

Balloon

We used a 1200 gram latex balloon ordered from High-Altitude Science, which has a neck 14 centimeters in length and a nozzle 3 centimeters in diameter. This balloon worked well and was easy to tie off, however, we learned that exposure to sunlight will result in discoloration in the balloon, so it is best to keep the balloon out of direct light whenever possible. Although this balloon option was more expensive than some, especially those from Asia, we discovered in our research that they were much easier to tie off, and the material was a much higher quality, meaning that we could achieve a higher altitude with a smaller balloon.

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The balloon is advertised to lift a 5.0 pound payload above 87,000 feet, and we believe from the GoPro’s footage and from analysis of the flight pattern that our balloon reached an altitude of approximately 90,000 feet. However, if in the future we fly a payload of over 5 pounds, we will need to consider a 1600 gram balloon to achieve an optimal altitude. Based on our GPS coordinates, we predict that the balloon traveled around 275 miles East before it popped. This was far longer than predicted, and was caused by a slight issue we had with inflation and payload weight, which is described in our next blog post.

Parachute

We opted to purchase a 5-foot parachute from Sky Probe. This parachute had an estimated descent rate of 10.6 miles per hour for a 4.7 pound payload. We discovered this to be a good balance that maintains a safe decent speed while not drifting hundreds of miles away.

Radar Reflector

We built our radar reflector ourselves, using three squares of cardboard and foil tape. It is able to effectively reflect radar signals due to its many corners on all sides. A radar reflector is required by the FAA, and also ended up helping us locate the balloon upon landing because of the reflection from our flashlights.

Payload

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The outer shell of the payload was an orange triangle of PVC for stability and visibility. The triangle was assembled with rubber tubing, hose clamps, and a paracord safety line running through it. In one corner of the triangle we attached a SPOT3 GPS with zip ties. Opposite of the SPOT we mounted a GoPro Hero 2. The GoPro was almost exactly twice the weight of the SPOT and made it easy to adjust the center of gravity for stability.

A triangular lunch box was secured with paracord in the middle of the PVC triangle. We insulated the lunch box with styrofoam. Inside it housed our APRS setup as a secondary GPS tracker.

HAM Radio APRS Setup

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We decided to use an the Argent Data OpenTracker USB with a Baofeng UV-5R. We connected an ADS-GM2 GPS receiver to the OpenTracker USB serial ports. We programmed the OpenTracker USB with the software provided on their website, and then soldered the connections to 3.5mm and 2.5mm phone jacks to connect with the Baofeng. The OpenTracker USB was powered by a lithium 9V battery.