The purpose of the device is to refine the accuracy of a dark trajectory estimate of a meteor through introducing corrections to the flow of air masses during the meteor's flight in the atmosphere. As a consequence the elliptical impact area of the meteor on Earth's surface should reduce.
Data on atmospheric currents will be acquired by a weather balloon deflated immediately after the detection of a bolide flyby through the atmosphere. The balloon launch site should be chosen automatically based on the meteor trajectory estimate and known coordinates of the balloon silos in the network.
An important part of the system is the fully robotized discharged station (balloon silo), enabling the discharge of balloon from known coordinates without human intervention. A by-product of such development will be a device capable of future automation of classical meteorological radiosonde discharge.
The ground balloon network station would consist of compact box containing technology needed to discharge the balloon sonde. The device must be able to withstand (in order of several years) the standby mode and wait for the command to release the sonde.
Most of the electronics is composed of MLAB brick system modules.
At the same time, an equipment for telemetry reception of signal from other discharged radiosondae 2) from other stations is necessary.
STM32F10xRxT01A module meets the aforementioned requirements.
The ground discharge box is constructed to be able to run under various weather conditions. It has a shape of triangular prism with one side standing on a raised platform and the other two covered with photovoltaic cells supplying energy to the electronics. After the discharge, they can be used to check the correct slide-down of the roof panels. The monitoring of the supplied power during the day also enables to check for the occurrence of solid obstacles in the vicinity of the station.
The material used for construction is welded polyethylene, making the station waterproof and resistant to dirt entry, that could damage the balloon.
Most of the actuators should be designed with an emphasis on maximal reliability. Therefore, they would probably be springs with burnable plastic fuses (silicon fiber or ribbon burned by a powerful resistor). NFET4X01B module can be used To switch the current to resistors.
Helium management in the box must be designed to prevent the loss of helium by diffusion through porous materials like plastics or rubber. The main inlet valve must therefore be made of metal and ideally placed directly on the neck of the bottle.
An interesting idea would be to make use of bernoulli efect, when a low-pressure gas, like chemically produced hydrogen, would be sucked inside by a flow of the compressed helium, similar to inflation of this air pad.
In the case of our functional prototype, we have experimented with compressed helium as a source gas for the balloon filling. Preferred option, in this case is the use of disposable cartridges with compressed helium. Such packed helium is however quite expensive (700 Kč/0,1m³) and hydrogen is probably not available in this form.
An interesting solution seems to involve a chemical reaction to produce hydrogen directly in the discharge box. Discovered in 2007, a reaction of gallium and aluminum alloy with water produces hydrogen without an extensive heat production 3).
The course of the reaction is demonstrated in this video. You can purchase the necessary metals here:
It would be then sufficient to dry the hydrogen produced by this method by cartridge with silicagel.
Experiments with this metod showed difficulty in obtaining the galium back in order for it to be re-used.
Ferrosilicon method makes use of a reaction between the sodium hydroxide, water and a ferrosilicon.
Another option is a catalysed decomposition of the Sodium_borohydride.
In all cases, the volume of the carrier gas should be optimised with respect to required lift and the rate of climb.
To ensure the running of independent processes the use of ChibiOS/RT is a viable option.
A non-flying prototype of the balloon will be developed using MLAB modules.
GPS carried by the balloon should be kept in FIX state in order to avoid a delay while waiting for a fix. At the same time, there also exist doubts concerning the accuracy of the GPS in higher altitudes, where the deviation of the measured altitude from the actual one can reach hundreds of meters.
The GPS must by chosen to function correctly at higher altitudes as well.4).
The solution to the problem of low temperature at higher altitudes could involve the preheating of the balloon at startup.
The rules for free unmanned balloon flights are defined in the aviation regulations “L-2 Pravidla létání”, appendix 5 and R.
The balloon should be of B2 class, that is defined as a free balloon with the volume under 3,25 m^3 and none of the dimensions exceeding 2m when inflated to its maximal size.
An useful load refers to all the objects and materials that could, in an event of a collision with an aircraft, cause a damage to the aircraft (especially sparkles, glowstics,LEDs etc.) and any load exceeding a weigh of 0.1 kg. Due to this definition, a permission must be obtained in order to operate the balloon. All the information concerning the flight (like date, time and place of discharge, useful load, etc.) has to be published in Aeronautical Information Publication (AIP). In the case of special instances, like an unexpected observation, a warning must be issued in the form of a NOTAM notice, at least 24 hours before the balloon's take-off.
The balloon must not be filled with flammable and explosive gases, with the exception of a permission issued by CAA (http://www.caa.cz/index.php?lang=2). Restrictions on the materials used for antennae and batteries are not specified. Such restrictions are not specified for the materials used for the balloon as well, but when using a balloon with high luminosity or made of materials with high light or radar reflectivity, it must be reported to nearest air traffic control centre. A material (a rope, a thread) connecting the balloon with the sonde must not tolerate a force exceeding 230N.
The restrictions include all Prohibited, Restricted and Dangerous areas, as well as temporarily activated areas during their use, except when a permit has been issued by Civil Aviation Authority or when the area is reserved for the flight of the balloon in question. Operations close to the state borders or airports are problematic and as such are not recommended.
The configuration and the control of the network should be provided by an universal framework for distributed measurements.
The launch of the balloons must be planned automatically with regard to the effectiveness of the measurement and the air traffic safety as well.
Other maps are mostly scanned versions of originally paper aviation maps and so are not suitable for automatic planning.
The project's technical documentation is saved in SVN repository at MLAB: http://svn.mlab.cz/svnmlab/Designs/Measuring_instruments/ABL01A/
For tasks management and supervision of their implementation we use Redmine.
Documents and presentations concerning project management are stored here:
svn co https://lynx1.felk.cvut.cz/svn-students/pto/pto-13138-1 svnPTO
The project is carried out by the team of several ČVUT students from Department of Measurement and Department of Cybernetics.
Most parts of the project were provided by Universal Scientific Technologies s.r.o.
Suppliers of the construction equipment: