High-altitude balloons
| High-altitude balloons | |
|---|---|
| Main types | Latex "near space" flights; long-duration pico balloons |
| Latex flight altitude | Commonly 80,000 to 100,000 feet or more, before the balloon bursts |
| Pico balloon altitude | Roughly 30,000 to 45,000 feet, floating |
| Pico payload | Often 20 grams or less, including solar panels |
| Tracking | |
| Latex flights | APRS on 2 meters (144.390 MHz in North America) |
| Pico balloons | WSPR on HF, often 20 meters |
| Pico transmitter power | Milliwatts |
| US rules | FCC Part 97 for the radio; FAA Part 101 for the balloon |
High-altitude balloons carry small amateur radio payloads into the upper atmosphere, where their signals can be heard over enormous distances. Hams fly two quite different kinds. Latex balloon flights, sometimes called near-space flights, climb for a couple of hours to around 100,000 feet, burst, and parachute back to earth, usually tracked by APRS so a chase team can recover the payload. Pico balloons are small, sealed balloons carrying a solar-powered tracker weighing only a few grams. They float at airliner altitudes for weeks or months, drifting with the jet stream, and some have circled the globe many times while being tracked by WSPR signals on HF. Both are popular with clubs and schools as a way to combine radio, weather and engineering in one project.
Latex flights
A latex flight uses a weather balloon filled with helium or hydrogen. As it climbs, the surrounding air pressure falls and the balloon expands until it bursts, typically between 80,000 and 100,000 feet or higher, after which a parachute brings the payload down. The whole flight usually takes a few hours and covers tens of miles or more downwind.
The payload typically includes an APRS tracker that sends position and altitude every minute or so on 144.390 MHz in North America. From high altitude the radio horizon is several hundred miles, so digipeaters and internet gateways far from the launch hear the packets, and the flight appears on public APRS maps in near real time. Other common payloads include cameras, temperature and pressure sensors, SSTV transmitters sending pictures from the edge of space, and occasionally cross-band repeaters that briefly let hams work each other across several states. Chase teams use the APRS reports and flight-prediction software to be near the landing spot when the payload comes down, which can be a field, a forest or a rooftop.
Pico balloons
A pico balloon does not burst. It is a sealed, nonstretching balloon, often a foil party balloon or one made of clear plastic film, filled with just enough gas to rise to a chosen float altitude and stay there. The payload is tiny: a tracker board weighing a few grams, a set of thin solar panels and a wire antenna. Most carry no battery, to save weight, so they transmit only in daylight and fall silent each night.
The transmitter usually sends WSPR, a weak-signal mode designed for propagation testing, at power levels measured in milliwatts. Thousands of WSPR receiving stations around the world upload what they hear to a central database, so a balloon over a remote area can still be spotted many times a day. A standard WSPR message carries only a call sign, a four-character grid square and a power level, so trackers add a second, specially encoded transmission in which the fields actually carry a finer position, altitude, temperature and battery or solar voltage. Encoding schemes such as the one used by the QRP Labs U4B tracker, and open designs such as the Traquito, are widely used, and dedicated websites decode the spots and map each flight.
Some pico balloons carry APRS instead of, or as well as, WSPR. APRS works well over land with dense networks, such as North America and Europe, but there are few receivers over the oceans. Because the APRS frequency differs by region, such as 144.800 MHz in Europe, trackers often switch frequency automatically according to their position.
Circumnavigations
Winds at float altitude carry pico balloons eastward, and a balloon that survives long enough goes all the way around the world. In 2015 the ARRL reported that foil party balloons launched in Australia by Andy Nguyen, VK3YT, had circled the globe; one of them, PS-46, made its first circuit in about 12 days, tracked by WSPR and JT9 spots. Since then, many pico balloons have circled the world repeatedly, and flights lasting several months are no longer unusual. A flight ends when the balloon leaks, is damaged by storms or ice, or comes down, and pico payloads are rarely recovered.
Rules and safety
Amateur operation from a balloon is permitted under the normal Part 97 rules, including the requirement for station identification, which a WSPR or APRS tracker meets by sending its call sign. The balloon itself is regulated by the FAA under Part 101 of its rules for unmanned free balloons. Light payloads, generally a few pounds or less, with a suspension line that breaks under modest force, are exempt from most of its requirements; heavier payloads must meet rules on notifying air traffic control, lighting, and other matters. No flight may be operated in a way that creates a hazard to people, property or aircraft. Because a balloon can drift across national borders, flyers also need to consider where their payload will be transmitting.