by Jon Pearce, WB2MNF & Mike Thompson , KG4JYA

The Clubhouse was closed for general use today but Doug, Mike and I got there before 8 to set up another radio-carrying balloon test. Our objective this time was to use a sealed balloon (as opposed to the vented balloon in the last test) and to see how high it would go before failure. Failure could occur in one of three main ways :

• The Mylar® party balloon would definitely burst at some point since they’re not strong enough to handle the pressure differential at high altitude
• The battery (which we’re using for these tests because it’s cheaper than solar cells and will give a consistent voltage to the telemetry radio) will run down, or
• The battery will freeze and stop working.

We set up the balloon in the same way as last week’s except that we sealed the inflation port with its own sealer and then wrapped in Kapton tape. We then took it outside and had a very successful launch, watching on a clear, virtually windless day as it disappeared into the sky to the southwest.

But back inside we heard no telemetry, which is broadcast every 10 minutes. It missed the 9:22, 9:32, 9:42 and 9:52 transmissions at which point we concluded that the battery had come unsoldered and the radio had quit. As we were castigating ourselves for not ground-testing the radios before launch when we suddenly received a WSPR signal at 10:02 followed shortly by a telemetry signal showing that the balloon had reached 13,780 feet and was moving south at about 45 mph. Recriminations ceased and we began tracking its course and watching the telemetry.

The balloon rose steadily for the next two hours, reaching a maximum altitude of 27,625 feet, far higher than last week. During that ascent we watched the reported temperature drop from 41 degrees F to 1.4 degrees F and the battery voltage dropped from 3.2 volts to 3.05 volts. After that telemetry ceased. We concluded that the battery had frozen as expected and that we might never hear from the balloon again unless we were fortunate enough to catch a transmission as it ultimately descended.

An hour later, though, another transmission appeared on the WSPRnet site that was picked up by two stations followed ten minutes later by a single reception from a station in Maryland. No telemetry accompanies those receptions (it takes two WSPR packets to send the identification and telemetry data) so we didn’t know its altitude or location, but we did know that the battery had un-frozen sufficiently to allow transmission so it was much lower than previously.

Finally two hours later we received a single decoded telemetry transmission showing that the balloon was on the ground in grid square FM29ef, which centers between Smyrna and Dover Delaware. It’s on the ground or suspended somewhere down there. Unfortunately a 6-digit gridsquare is too broad for a search to be practical so we’ll never see that balloon again (not that we expected to recover it anyway). Over the past few hours it has transmitted several times with the battery voltage again dropping to about 3 volts. It may continue to transmit occasionally until the battery runs out.

We’ve tried to estimate how high the balloon rose after the battery froze, and it’s possible that it made it into the mid-30,000 foot altitudes with about 39,000 feet being proclaimed as the highest altitude generally attained by these types of balloons when filled with helium (hydrogen-filled balloons go a little higher). Our tracking was successful although we did learn the lesson of patience after declaring failure and then seeing the ultimate telemetry showing success.

The next balloon launch attempt will be next Saturday August 3, planned for noon weather and other factors permitting. We’ll be launching one of the super-pressure balloons that we don’t expect to burst along with the ZachTek tracker powered by two 5 volt solar cells. Come on out to the Clubhouse if you’d like to watch. If all goes well we’ll email tracking information in case you’d like to check the status of this balloon yourself. And hopefully we’ll have some good news to present at the General Membership Meeting on August 7.