After the success of the KD4STH launch in September, we decided to do it again! A new group formed for San Francisco High Altitude Balloons (SF-HAB), and we started scheming. The hardware and time stars finally aligned on Sunday March 8th, and we decided to launch from the Berkeley Marina. Unbeknownst to us, this was only a few days before the whole world shut down due to COVID-19. Great timing!
The balloon was a Kaymont 3kg balloon, and we used an entire K-sized tank of hydrogen for lift. Unlike some previous launches, we didn't use weights to carefully measure/specify the ascent rate, we just used the whole tank. During the chase, we calculated our ascent rate at about 1400 ft/min, which was faster than our target of 1000 ft/min. Faster ascent means the balloon is not being pushed around by the wind as much, but it will burst at a lower altitude if the balloon is overfilled. Since this was a 3kg balloon, it was not overfilled.
The primary mission of this launch was to fly a cross-band repeater. The uplink was on 145.525 MHz (with PL tone) and the output was 445.525 MHz. The hardware was a Wouxun KG-UV8D running with a regular internal battery, and it worked much better than I thought. The radio was packaged in a spherical styrofoam ball, with a short piece of coax and a standard HT rubber duck antenna hanging upside-down out the bottom. The outside of the styrofoam ball had copper tape on the outside, as a pseudo ground plane.
The cross-band repeater frequencies were advertised with local clubs before launch, so there was quite a bit of activity with standard QSOs happening, all while the chase teams were using it as their coordination frequency. Listening in, the furthest station I heard was from Mt. Shasta City, which is about 225 miles north. Not bad for 1 watt of RF power!
My XYL and Ted K5KZ were riding with me, and we meandered around Pittsburg and Antioch as the balloon meandered over the delta gaining altitude. Our equipment was my dual-band mobile rig for voice (crossband-repeater) comms, my APRS receiver ammo box hooked up to a laptop running Windows XP and APRSPoint, and another APRS HT.
The max altitude was 119,323 ft, and it burst over the Montezuma Hills. The predicted landing was near the small town of Rio Vista, so we headed that way as the balloon fell. The balloon actually fell just south of Highway 12 in a field. That area is home to the huge Shiloh wind power plant, which can generate over 1 GW of electricity at max output. The winds that day were light, but the turbines were still generating power.
Looking at the train with Martin W6MRR at the landing site, we realized we didn't leave enough line in between the payloads, parachute, and balloon. All the pieces became tangled after balloon burst, which meant that the parachute was wrapped up, and the entire package just fell with nothing to slow it down when it got closer to the ground and the air density increased.
Based on the last few APRS packets, we calculated that the payload was falling at 44 feet/sec, or about 30 MPH when it hit the ground. Ouch! Luckily the payloads were pretty light, and packaged in styrofoam or soft-sided containers. Lesson learned for next time, leave a lot of string between the payloads, balloon, and parachute.
Back at the car, we powered off the payloads, let the people following the recovery on the local repeater know that we successfully recovered it, and discussed lunch plans.
We decided to get lunch in Rio Nido, and plan our next launch.