The main hardware we are developing are our probes. The probes are actual electromechanical payloads tied below the balloon with a tether, collecting, processing, and transmitting data. A lot of effort goes into designing and producing a good probe. We need everything to be as efficient as possible. This means we need ultra-low power consumption, ultra-low mass, and low manufacturing cost.
We designed and manufactured 10 different probe generations. The last probe version that has flown in a mission is the version 8.3.0. You can see this probe in the image below.
The work on the probes is divided into work on specific subsystems. All of them are covered in depth below.
¶ Power Supply
Power supply is the highest priority subsystem. Without it, nothing can function. The task of the power supply subsystem is to deliver clean, stable power for years, while costing little money and payload mass. It also should be environmentally clean and not include dangerous chemicals (which many batteries do).
Because of these requirements, the best power supply for this use is clearly solar power. There is more than enough solar energy in the Picoballoon cruising altitude. Therefore, all our probes from generation 7 and up include a solar cell array as the power source. Of course, a good power source needs to be paired with a good power storage element. Currently, we are using supercapacitors because of their light weight and very high electrical and environmental endurance. On the picture below, you can see the current solar board, which includes 4 solar cells (power source), a supercapacitor (power storage element) and a spectral sensor.
With more R&D funding in the future, we plan to experiment with rechargeable cells, which would allow for overnight operation. We are also already starting to experiment with flexible solar cells, which can be integrated into the balloon itself for higher durability.
¶ Power Distribution
The power distribution system takes care of distributing the available power to all the other systems accordingly. The highest priority subsystem is the processor, which is turned on at all possible times. If the current state allows so, the processor can enable other subsystems, otherwise they stay disabled and isolated.
¶ Processor
The processor collects data from sensors, monitors the power supply, backups data, makes changes according to the probe location and takes care of interfacing with other probes and ground stations trough the communications subsystem. In our current probe design, the processor is placed alongside the communications IC in a single silicon SoC.
¶ Communications
The communications subsystem is responsible for all the communications with the external devices, which are either probes or ground stations. We do not create the communication circuits themselves; these are mostly premade ICs. Our job is mainly to select, implement and test the right ones and create the frequency conditioning and frequency switching circuitry. Virtually all our past probes used the LoRa modulation, in the 868 – 920 MHz band for their communication.
We receive all the data through LoRaWAN, a worldwide network of thousands of cloud-connected community ground stations, which instantly forward all the received data to us. Soon we want to start experimenting with different frequency plans and modulations to give us more options though.
¶ Positioning
The positioning system takes care of getting the location, altitude, bearing and speed of the probe. There are various ways to achieve this, ranging from tracking of the sun to tracking the Earth’s magnetic fields. Despite this, we used, are using and most certainly will continue using GNSS. This is because using satellites is the most accurate positioning method, it requires very little R&D and is affordable enough. Our current probes use commercially available, highly integrated 72-channel GNSS SiPs. We get the location of the probes from the GPS and GLONASS satellite constellations.
¶ Sensorics
The sensorics subsystem is the most diverse one. It contains all the sensors of a probe. These are very important, because they collect all the actual scientific data, other than the probe’s location and movement parameters.
We use many kinds of sensors. We can split them into a couple of different categories. These are basic meteorology sensors (temperature, humidity, pressure), ray sensors (UV, IR, visible spectrum, charged particles…) and gas sensors (oxygen, CO2, NO2…).
There is also one special kind of sensors, utility sensors. These collect system data about the probe and flight performance. These can include IMU-s (measuring orientation and acceleration), tension sensors (measuring mechanical tension of the balloons) and internal balloon pressure sensors.