High-altitude balloon stack

In this post it will be described what is the typical high-altitude balloon stack. In this and in the next posts the terms high-altitude balloon and near space photography will be used interchangeably.

Fig. High-altitude balloon stack (@Paulo Carmo)

The figure on the left shows a typical stack for high-ballooning. With stack we mean a pile or heap of sub-systems that together compose the high-balloon system:

Balloon (sometimes called envelope): the balloon is the device that provides the lifting force that allows the whole system to reach an high-altitude in the Earth's atmosphere. As the system rises the balloon expands until eventually it bursts and the whole system starts falling back into Earth's surface. It is filled-in with a gas lighter than the air, usually helium or hydrogen. Today helium is more used because it is less explosive than the hydrogen even though is more expensive.

Parachute: the parachute is activated after the balloon bursts and the whole system starts falling back into Earth's surface. Before this, the parachute is in tension between the balloon above and the radar reflector and payload bellow. When the balloon bursts, it stops providing the tension force for the parachute bellow and so the parachute naturally opens providing a drag force that decreases the falling velocity of the whole system.

Radar reflector: the radar reflector is a safety apparatus that is placed between the parachute and the payload and it serves the purpose of presenting an high radar reflectivity and in this way increasing the chances of the whole system being detected by a flying asset (air plane, ultra-light, etc) and consequently reducing the probability of an air collision.

Payload: the payload contains the whole purpose of the system, which is the set of equipment that will accomplish the mission. An example payload could be constituted by the following modules:

• Communications: this module is responsible for the communication with ground. Its major task is to communicate back the position of the system so that it can be tracked and found after landing; usually radio-frequency communication is used, but GSM communications is also employed;
• Sensors: this module contains any device that detects a physical condition in the world. It contains several sensors depending on the mission. Its primary sensor is the GPS receiver, but other sensors can be aboard like camera, temperature, pressure and others;
• Actuators: this module contains any device such as switches, that perform actions such as turning things on or off or making adjustments in the system; one practical example is an actuator that is able to move a camera to control the angle in which a photograph is taken;
• Computing: computing power is necessary to all sorts of things like:
• acquiring the sensor readings and storing and/or communicating them (through the communications module);
• controlling the electronics and other equipment;
• other.
• Power: this module will be responsible for the power to feed the equipments in the payload; it is wise to have separate and independent power lines in order that problems in one line does not affect other line.

It must be noticed that all components of the high-altitude stack must be tied up very securely. Depending on the components your are tying, different types of strings are used, like nylon string and others.

The balloon, the parachute and the radar reflector are sometimes named flight system. This means that the high-altitude balloon stack is in fact constituted by two major subsystems, the flight system (with the balloon, the parachute and the radar reflector) and the payload (with all its subsystems).