What is near-space ballooning?
Near-space ballooning involves using a latex weather balloon, usually filled with Helium, to carry payloads through the Earth's atmosphere to very high altitudes. Payloads typically include command systems (such as GPS receivers and radio transmitters) and experiments designed for testing in near-space environments. Many balloons also include cameras to take pictures of the ground, space, or the curvature of the earth. What payloads are carried is dependent on the mission: for example, a weather balloon may carry environmental sensors and a transmitter to broadcast the data. The balloon may carry a single payload box underneath it, or a chain of payload boxes/components.
How high does the balloon go?
This depends on how much helium is put in the balloon. Typically, a balloon is inflated to about 6 feet in diameter on the ground. As the balloon ascends, the atmosphere gets thinner, and the balloon expands until it bursts. If less helium is put in the balloon, then the balloon will be able to go higher before it bursts. The balloons launched by UCSD reach altitudes of approximately 85000 feet above sea level. Even higher altitudes (up to 100,000 feet) could be achieved if less helium were put in the balloon, but this would result in a slower ascent rate and less certainty in the landing zone. (See question below).
How do you steer the balloon?
The balloon cannot be actively steered, and its ground track is determined primarily by its ascent rate, burst altitude, and the wind conditions throughout the atmosphere. Prior to launch, balloon teams check weather forecasts and use software to predict where their balloon will go. By putting more or less helium in the balloon, the ascent rate of the balloon and the expected burst altitude can be adjusted. More helium and a lower burst altitude equal a smaller predicted landing zone, while less helium and a higher burst altitude equals a larger predicted landing zone. To ease this process, some balloons are equipped with cut-down devices to release the latex balloon from the payload at a specified altitude in order to prevent to balloon from going too high.
What happens to the payload after the balloon bursts?
When the balloon bursts (or is released using a cut-down mechanism), the payload begins to free-fall through the upper atmosphere. A parachute is attached to the top of the payload, but there is not enough air in the upper atmosphere for the parachute to function. As the payload falls, it reaches denser air, and the parachute begins to provide some drag to slow the descent rate. Eventually the parachute is fully functional, and the payloads land at about 15 mph. The balloon team tracks the payload as it descends, and collects the payload if it lands in a recoverable area.
How are balloons regulated? Can you put anything on a balloon?
Near-space balloons must comply with regulations dictated by the Federal Aviation Association (FAA), specifically those stated in Federal Aviation Regulations part 101 (FAR 101). To minimize the required involvement with the FAA, balloons and payload chain must weigh 12 pounds or less, with each payload box weighing 6 pounds or less. All components should be ingestible into a turbine engine without causing detrimental damage to the engine. There are many things to consider when designing an experimental payload, but as a general summary: hazardous materials are not permitted on these balloons, and objects cannot be intentionally dropped or fired from the balloon.
Where does UCSD launch their balloons?
The balloons are launched in the desert areas to the east of San Diego, typically near Plaster City. The exact launch location is determined hours before the launch, and is selected based on predicted balloon trajectory. On windy days, the balloon can be expected to travel further, and the team must carefully select a launch location which will minimize the chance that the balloon will land in Mexican territory. In addition, the team must try to select a location which will reduce the chance that the balloon will land in restricted military areas. To accommodate these constraints, the team must be flexible and capable of launching from remote locations. The balloon and all required launch equipment is carried in trucks and SUVs to allow the team to traverse unkempt roads and desert to reach adequate launch sites.