Reusable High Altitude Balloon, the goal of the development is to build a rigid device that can be used in multiple missions time to time. This could provide a reliable insulation capsule ready to fly and no need of capsule development and building before missions.
What is higy altitude ballooning?
At the beginning of the 20th century for measurment of meteorological data unmanned balloons was started to use. First these devices was followed with bare eye observing the wind in different heights. Later the balloons were equipped with measurement and data storage units collected temperature and air pressure values. The recovered capsules were collected and sent back by civilians. Thanks to the more advanced radio technology returning the capsules was no longer needed. The measurment data was sent back via wireless communication. Nowadays meteorological services launch unmanned balloons in dayly basis.
In the early seventies radio amateurs spread the hobby of high-altitude balloon launching and hunting. The first modern mission developed under the command of Bill Brown (WB8ELK) as a part of Ilmari Program in 28th of May 1967. Finnland. The evolution of positioning systems the HAM balloons became more and more trackable and reusable. Spread of the digital cameras and camcorders opened new horizons in amateur ballooning. Breathtaking pictures could be taken from the edge of space thanks to these developments. High altitude ballooning often called the ‘Poor man’s space program’ due to the low costs of the projects.
For the flight a balloon made of latex is filled with some light gas (typically with Helium). This balloon lifts the payload. The reason it won’t end up on the surface of the Moon, is that the balloon pops out due to the decreasing air pressure outside the balloon. Well adjusted or controlled inside balloon-pressure could help increase the length of the flight. There are Zero Pressure Balloons available typically for long duration missions.
Usually a flight takes to 2 to 3 hours and the balloon reaches 25-30,000 meters (82-100,000 ft). The capsule typically descends with a parachute, but there are special missions, where the capsule is so lightweight the parachute is not needed, it could descend safely with the remains of the balloon.
Finding the returning measurement unit is the tricky part of the mission. Usually GPS tracking is used. Logging the GPS data has some limits: the consumer GPS chips usually have a 18-20,000 meter (60-65,000ft) height limit. Nowadays GPS units are available that are able to work over up to 35,000 meters (115,000ft).
During the flight the main complicating factor is the temperature. In the stratosphere the temperature could drop under -50°C (-58°F). The electronic units usually are placed in an insulation capsule typically made of polystyrene or styrofoam. Sometimes sensitive equipments need to be heated. The appropriate temperature inside of the insulation capsule could be provided by heater coil connected to the specific instrument and controlled by the measured house-keeping data, or by uncontrolled chemical heater that heats the whole instrument-box.
In some countries, the regulation requires the installation of flight breaker unit. It usually a cord cutter device that separates the capsule from the balloon. Usually it is activated by a separate timer unit or controlled by the flight computer.
The main goal of the ReHAB capsule is to introduce engineering students to the development of fault-tolerant measurement units. Near-space projects are good basics for aerospace and space developments, because conditions and regulations are similar.
The capsule is a multi-layer insulation box with aluminium frame. This forms lightweight but robust structure. The descent speed is reduced by a parachute and GPS receiver helps finding the recovery module. Beside the position data, the altitude, speed, internal and external temperature and battery voltage data are also collected. These build up the house-keeping telemetry messages sent by the radio communication module. During the flight a two way radio contact provides the continuous communication. This helps us to monitor the payload real time during flight.
Various cameras can be mounted on the capsule. The plan is to monitor the external experiments and sensors, the balloon and take pictures and videos of the landscape. The cameras are controlled by the flight computer and some of them are able to send back the pictures by radio or processed on board.
The flight computer has a redundant data storage for measurement data and creates a more detailed log of the flight than the sent back telemetry. These data could be downloaded after successful recovery of the capsule.