• design
• graphical user interface
• platform
• realization
• tethered balloon

Since the beginning of the twentieth century, balloons have been used for a wide variety of applications.
Tethered balloons, in particular, were utilized for the study of the lower atmosphere and for military purposes. With the miniaturization of the electronics, they have become an attractive technology to be used as platform for various new concepts. The Space Laboratory of the University of Pisa is developing this concept in the frame of the Poiana project (Piattaforma per Osservazione In Ambito Naturalistico ed Ambientale), for the observation of agricultural fields with the aim of optimizing water management and the health state of the plant. Tethered balloons have many advantages compared to a drone: cost reduction, long service life, higher load capacity, high reliability of processed data and higher stability. In addition, the use of new technologies capable of exploiting a wide-ranging communication protocol and low power consumption such as the LoRa protocol and the advent of Internet of Things (IoT) devices easily manageable and controllable through the use of the internet, allows for the development of efficient monitoring and management platforms attached to balloons at altitudes of tens of meters, directly controllable from anywhere in the world.
The work carried out in this thesis proposes the development (design and realization) of a prototype of a modular platform, for tethered balloons equipped with: a system capable of stabilising the platform in terms of angular velocity and angular position around the yaw axis by means of a momentum wheel; a camera monitoring system, steerable with a servo-motor, to control the status of the platform, the connection with the balloon and the payload; a system capable of monitoring the internal conditions of the platform in terms of temperature, humidity, power consumption etc…; a system for data reception with a LoRa communication protocol. All these subsystems have been placed and assembled on a newly designed PCB, in order to achieve a high-order of platform integration. Moreover, the modularity of the platform allows to equip the platform with different payloads for various applications, such as a high-resolution, swivelling ground observation camera and/or an electronic system with solar cells capable of self-powering the platform itself. In addition, thanks to the Internet Connectivity, to control the platform and view the data in real time, a Graphical User Interface (GUI) has been developed.
This work demonstrates the successful development of a tethered balloon platform, equipped with an attitude control system for the yaw axis, with a system characterising the internal conditions of the platform, monitoring the external conditions of the platform with a swivel camera, and a telecommunication system capable of receiving data from the sensor on the ground using the communication protocol LoRa.
The platform weights about 2 kg, thus has still a great improvement potential for hosting more advanced and diverse sensors and subsystems, such as solar cells to charge the battery after discharge or a payload with a swivel camera for ground observation.
The attitude control system meets the requirement on aiming capability (in module < 5°), swinging the yaw angle in ±3.8° about after reaching the target.
The system of monitoring the external conditions of the platform allows to frame the platform itself and the interface with the balloon through the cables, allowing thanks to the angular range and resolution of the camera, to view the condition of the balloon itself and a possible payload interfaced with the underlying part of the platform.
The realization of a closed structure made the electronics and the interior of the platform itself, especially the reaction wheel, much less vulnerable to the conditions of the external environment.
Moreover, the realization of an integrated circuit and the use of a single micro-processor capable of managing all the subsystems has allowed to further simplify the system, greatly reducing the use of cables and jumpers for the connection, as well as making it more integrated and more compact.
In addition, the possibility of connecting to the Internet directly the Raspberry Pi, has allowed to interface quickly and efficiently with the platform itself, thanks to the graphical interface of Blynk, allowing its use in real-time from anywhere in theworld: in particular, the implementation of commands such as the control of the pointing direction of the platform, the possibility of blocking the attitude control system or the possibility of rotating the camera and taking photos and videos. At the same time, streaming widget via Blynk still needs to be fixed. VNC or other types of desktop sharing services, can be, however, used as alternatives to implement this feature.
In addition, the synchronization of services on the Raspberry still has to be made robust, and sometimes it is necessary to stop the service on the attitude control and restart it from the terminal.
Despite the excellent results obtained, there is always the great possibility of improving the system in future works. A list is given below:
• implement a main software to organize and manage the subsystems routines of the platform, in order to increase its robustness;
• introduce in the HAT 4G module for Raspberry Pi, a SIM IoT Card, to allow the connection to the internet without having to connect to a Hot Spot of an additional device;
• use other servers capable of streaming the camera, such as Remote.it that would allow to use SSH and VNC communication protocols from anywhere in the world;
• improve the controller of angular velocity and angular position with respect to the yaw axis, through a more performance study on the choice of gains or by introducing a PID (Proportional-Integral Derivative) controller instead of a PI;
• improve the aiming with respect to the target, reducing the oscillation in terms of angular position with respect to the yaw axis, by introducing a brushless motor with its driver;
• replace the reaction wheel made of PLA, with a reaction wheel made of aluminium, while maintaining the inertia with respect to the axis of rotation, so as to reduce the diameter and thickness of the wheel by a small increase in weight, but above all, to have less imperfections than that in PLA for the quality of 3D printing and less oscillations during the rotation by designing a more robust interface for the motor shaft adapter;
• introduce another PCB or by modifying the present one, the appropriate electrical connections to connect to the Raspberry Pi a multi-camera adapter, to which it is possible to connect more than one interchangeable diagnostic camera, in order to frame the payload from different directions, possibly adjustable;
• attach in the underlying part of the interface, a payload with a high resolution camera possibly adjustable, for ground observation;
• attach in the underlying part of the interface, a payload with solar cells swivelling appropriately, with its electronics, so as to recharge the battery at each discharge cycle, to extend the service life to weeks or months;
• introduce inside the platform a GPS or take advantage of the Hat 4G module for the location of the platform and a parachute at the interface with the tethered balloon to cope with a possible shearing of the cables or braking the balloon.