Part one here.
High Altitude Balloons (HABs) are a unique system that are capable of carrying payloads to near space at a low cost. HABs are made up of many different components, the most significant of these are the balloon, parachute and payload.
Their are two types of balloons. The most common is a simple balloon made of latex. Some higher end projects need the better performance of a super pressure balloon. These balloons often dwarf their much smaller latex counterparts, with the largest super pressure balloons made of 8,000 square meters (8,700 square miles) of material. Balloons of this size are capable of lifting payloads weighing as much as 2,700 kg (6,000 lbs). Unlike latex balloons, super pressure balloons do not burst at high altitudes due to the much stronger material used in their construction. This allows them to stay in the air for much longer until gas leakage causes them to slowly descend. The main drawback of super pressure balloons is their cost, even a small super pressure balloon can cost thousands of dollars.
Regardless of the type of balloon, it is filled with a lifting gas before launch. Helium and hydrogen are the most common, although methane is occasionally used. Helium is a rare gas, making it more expensive than hydrogen. Helium is also denser, which means more gas has to be used to achieve the same amount of lift, increasing the cost of using helium even more. The only downside to hydrogen, is that it is highly flammable and explosive when combined with oxygen (the space shuttle’s main engines are fueled by a mixture of hydrogen and oxygen).
The parachute is one of the most important parts of the HAB. It is used to slow it down to a safe landing speed as it falls. With out a working parachute, the payload would free fall, quickly reaching a speed fast enough to destroy it. The most common parachute design is a simple round canopy that is attached to the cable partway between the balloon and the payload. This configuration prevents the parachute from opening during the payload’s ascent. When the balloon bursts, the payload starts to fall, forcing air into the parachute and inflating it. Some advanced HABs use springs, CO2 or pyrotechnic charges to deploy the parachutes from a canister.
The payload hangs at the end of the cable that is attached to the balloon and parachute. Payloads are made from a wide range of materials; anything from styrofoam to metal can be used. The payload can carry lots of different scientific instruments such as cameras, sensors and more. Some payloads have specialized flight computers to perform more advanced actions during flight. All payloads carry a GPS tracker that relays it’s coordinates to the ground allowing the payload to be found after it lands. Some trackers also transmit telemetry and data from the payload such as temperature and altitude.