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Hermes: Hemera Returning Messenger

Hermes: Hemera Returning Messenger A common issue for long-duration balloon flights in the polar area is high bit rate data transferring. Just a few hours after launch balloons are nor reachable with direct radio link, and often satellite links are not fast enough to allow the necessary transfer rate or, simply, too expensive. For this reason, stratospheric balloon borne experiments carry out on-board data recording. Data recorded need to be recovered after termination, which is, sometimes, a slow, difficult and expensive task. Not always it is easy or possible to reach the landing site, especially during the polar winter. The aim of the project is to provide an autonomous glider capable of physically carrying the data from the stratospheric platform to a recovery point on the ground. This can also transport physical objects (like air samples) collected at float or along the flight. We estimate that an electrical motorglider released in the stratosphere can fly for several hundreds of kilometers. The glider is installed on the balloon payload through a remotely controlled release system, and connected with the main computer to receive data and the geographic coordinates of the recovery point. The glider trajectory can be monitored with Iridium SBD (Short Burst Data), and simple commands can be issued as well as using Iridium. Keywords Stratospheric platform · UAV · LDB · Data recording 1 Introduction The launch of HERMES is part of the European project HEMERA [2, 3], born with the aim of improving the scien- We describe an affordable and easy to use vector able to tific activities in the stratosphere by offering to researchers safely transport scientific data and samples from the strat- an easy access to the space in individual or shared strato- osphere to the ground, a desirable tool for several scien- spheric payloads. tific measurements. Such a system was originally thought As part of this project, two calls for proposals have been for physically recovering data media from the Olimpo [1] organized to select eligible scientific experiments. Such pro- experiment, but it can be used as well for i.e. sampling the jects, including HERMES, were offered a free balloon flight. volcanic ash from ground to the stratosphere or to make bet- In the case of HERMES, the launch campaign will take ter and more complete sounding balloons because you are place at the Swedish space base of Esrange (Kiruna), and not forced to use expandable payloads with limited capacity, will be carried out by the Swedish Space Corporation (SSC). since the payload can be recovered and reused. With the HERMES project, a stratospheric platform The HERMES payload is a project funded and coordi- equipped with a glider was designed and developed. The nated by Agenzia Spaziale Italiana (ASI), and whose sci- glider, once released, is capable of transporting a copy of entific coordinator is Istituto Nazionale di Geofisica e Vul- the data of the scientific experiment hosted by the platform canologia (INGV). to a pre-established recovery point on the ground. This is achieved thanks to the presence on board the glider of a Solid State Drive (SSD) memory, connected to the payload flight computer. * Alessandro Iarocci This would allow the scientific data of the experiment alessandro.iarocci@ingv.it on board the balloon to be available within a few hours Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy and in an accessible place. This is of prime importance for Elettromeccanica Adobbato Pasquale, Montopoli, Italy scientific experiments on Long Duration Balloons (LDB) that take place on polar flights [ 4–9]. In fact, recovering the Dipartimento di Fisica, Università di Roma La Sapienza, Rome, Italy Vol.:(0123456789) 1 3 A. Iarocci et al. payload in these cases is rather difficult and expensive (there a compatibility test for the experiments hosted on the are special recovery teams dedicated to such activities), but same gondola. it is the only way to recover the scientific experiment data 3) The mechanics of the releasing system had to be tested set. Furthermore, during the landing of the payload, damage with an acceleration of 10 g, to allow (in case of failure to the same may occur, compromising the outcome of the in releasing) the glider attachment to resist the accelera- scientific experiment. tion induced by the parachute opening. Because of the first two points the system cannot share the gondola with other experiments and needs to be completely 2 Project History and Evolution autonomous, providing its own power and communication. A sketch of this configuration appears in Fig.  1, where the The project started from the ABACHOS (Automatic BACk absence of a common gondola has led to revisit the project, HOme System) [ https:// s tr at hosph er eff ect. com/ ABACH designing a self-consistent mechanics and modular electron- OS] platform modified to meet the HERMES needs. ABA - ics, which allows to easily compose the characteristics nec- CHOS is launched using inexpensive latex balloons and is essary for use on any gondola. All the modules that make recovered at launch point. The use of affordable latex bal- up the system are autonomous and can be easily integrated loons helped experiment with this design with more than 15 into any stratospheric experiments. flights. The analysis of an ABACHOS flight appears further in the article. The original platform was modified by adding some electronics (mass storage, communication, umbilical 3 System Description connector, battery heater) and a tail motor to increase the flight length. The glider is no longer released by the latex The system is composed of: payload (hosting HERMES balloon explosion but from a command issued by a ground electronics and the releasing system), glider and GROUND station and is tied to a releasing platform attached mechani- STATION. In its nominal configuration HERMES expects cally and electrically to the main gondola. The sketch of the the use of solar panels, as well as an external power source original releasing platform appears in Fig 3. Here, the glider from the main gondola. is held in place using a couple of brackets on the wings and In the case of short-term experimental flights (a few the releasing is assisted by a pushing arm who also helps hours), the system can operate exclusively by the on-board detaching the umbilical magnetic connector. battery. Some modifications had to be done to meet the SSC Figure 1 shows the overall view of the payload without requirements, linked to three considerations: the solar panels (short-term experimental configuration). The main modules that make up the payload handle bat- 1) The release of a load can change the mass center of the tery power and communications. Also present is the Flight gondola and be a source of disturbance. While the atti- Computer Simulator (FCS) and the glider release system tude variation can be tolerated on a large LDB (Long (RELEASER). All modules communicate over CAN (Con- Duration Balloon), where the weight of the glider is neg- troller Area Network) bus. ligible compared to that of the gondola, it is no longer The GROUND STATION can decide the flight termina- so in a small experimental flight. This problem cannot tion through a command via a satellite channel, after upload- be overcome by releasing the glider at the end of the ing the coordinates of the landing point to the autopilot. experiment, because the Swedish rules for testing UAVs (Unmanned Aerial Vehicle) limit the distance from the 3.1 The Launch Platform launch point, which would be exceeded after a few hours at altitude. Figure  2 shows the block diagram of the payload. It is 2) The balloon system telemetry (with transponder divided in two sections, the RELEASER who hosts the bat- included) is service telemetry of SSC which the payload tery charger and the parts to carry out the release, and the cannot use (the only communication facility provided to gondola frame which contains all the facilities we expect the payload was a relay contact to be used as emergency to have in a host gondola. The computer simulator, logi- release command). Therefore, HERMES had to provide cally part of the gondola frame, has been installed in the its own auxiliary telemetry in line of view. The gener- RELEASER to facilitate connections. ous use of equipment capable of generating RF (Radio The BATTERY PACK module manages the battery that Frequency) disturbances (two Iridium SBD modems powers the system. The battery, consisting of seven pure and two 1 GHz line-of-sight telemetry) to the balloon’s lead elements, was chosen for the extended temperature natural telemetry would require specific integration and range. A microprocessor manages the battery correctly by 1 3 Hermes: Hemera Returning Messenger Fig. 1 The overall view of the payload Fig. 2 Launch platform block diagram 1 3 A. Iarocci et al. Fig. 3 The glider release sequence charging it from the panels (using the MPPT algorithm) or connector (connector J21 in Fig. 2), powers the glider’s SSD, from some other dc source, taking into account the tem- recharges the glider’s batteries and maintains its temperature perature. The module powers the system through the CAN by means of a heater. connector and supplies a specialized power supply to the The FCS produces synthetic data with which to fill the glider's battery charger which is operated, before release, SSD, simulating the presence of a flight computer. In fact, to switch the glider's batteries from storage mode to full HERMES was designed to transport the data produced by a charge. The BATTERY PACK communicates all the values balloon borne experiment to the ground, and the FCS, since concerning the power supplies through the CAN bus. Using there is no real data, produces test data, which loads through two switches, the battery can be separated for transport and the umbilical connector on the SSD present on the glider. the system can be set up for battery operation only, ignoring These data are the video taken by a camera, active from the external power sources. moment of launch, and the house keeping data acquired by The COM and CONTROL module is responsible for all the modules and transferred through the CAN bus. managing satellite and line-of-sight communications. A reduced version of this module is designed to be housed on board the glider to allow commands to be sent over the 3.2 The RELEASER satellite network. The IMU (Inertial Measurement Unit) block contains the The RELEASER module, housed under the plate that holds inertial sensors (three-axis accelerometer, three-axis gyro- the glider, controls the servo motors that release the glider. scope), a three-axis magnetic compass, a barometric sen- The servomotors are controlled through a position signal sor and a GPS (Global Positioning System) receiver. The (PWM, Pulse Width Modulation) and through the power module, self-consistent for general use, allows to know the supply that can be supplied individually. The temperature payload’s attitude. of each servo and the overall current supplied are checked. The MONITOR and SD RECORDER module makes a As mentioned, three servomotors are used, of which two local acquisition of the log file of the CAN traffic and pro- free the wings and one activates a thrust mustache which vides an interface RS232-CAN helpful for debugging. helps release. Currently, the umbilical connection of the The GLIDER CHARGER and JUNCTION BOX mod- glider to the platform is obtained with a magnetic connec- ule manages the connection with the glider’s umbilical tor. Figure 3 shows the sequence of the glider release. 1 3 Hermes: Hemera Returning Messenger The presence of the aircraft on the platform is revealed 3.3 The Glider Electronics through a proximity sensor installed near the rear engine. A manual switch allows you to operate the servomotors for Figure 5 shows the glider block diagram. J21 is the magnetic installing the aircraft on the release platform. connector that connects the glider to the payload through the The releasing command can take place: (a) through a umbilical cable. command via the CAN bus (b) through a contact provided Through this connector the payload supplies the heater for by logistics telemetry, to be activated in the event of a the battery of the glider, keeps the battery charged, transfers defect in communications. (c) through a manual switch the backup data from the FCS to the SSD, and allows com- when installing the glider on the platform. munications with the glider through the CAN bus. Compared to the original design just described, the The possibility is foreseen that the glider can host a COM mechanics of the separation system has been modified to and CONTROL module (with IRIDIUM SBD), connected comply with the request of the Swedish authorities which via CAN with the autopilot, of which it reads the positioning requires that the system resist an acceleration of 10 g. system to allow you to track the glider when you are not in The original system was supported by two motorized line of sight. brackets that operated on the wings. Now, a safety screw It can load a new landing point on the autopilot and turn (Fig. 4) has been added to this system which secures the the engine on and off. fuselage to the RELEASER and which is unscrewed and extracted when the aircraft is released. The brackets that 3.4 Final Considerations support the wings have been maintained to keep the glider in position but they no longer have a support function. The The actual version of HERMES has been designed for sum- servo used to move the pushing mustache is now used only mer flights. Under these conditions, the main issue to con- to help detach the umbilical connector. sider is the poor heat dissipation provided by the atmos- phere (5 mb at the float altitude) and the internal pressure of Fig. 4 The mechanical drawing (on the left) and a detail of the assembly (on the right) of the safety screw Fig. 5 Glider electronics block diagram 1 3 A. Iarocci et al. electrochemical parts (i.e. batteries or capacitors). A thermal check of the modules in a vacuum chamber gives the confi- dence of a good performance in the stratosphere. A much more critical scenario is a flight during the winter in the polar regions, where the temperature reached may be of the order of – 80 °C [10]. These extreme conditions will put a strain especially on the mechanical parts and electronics. Note that HERMES payload modules are not pressurized, special attention should be paid to heating the batteries and electronics. Concluding, HERMES is built in the name of modularity. This permits to: – Make modules usable separately in other balloon pro- jects; – Make debugging easy; – Make the project updatable: if a module is technically obsolete it can be replaced with an updated module that respects the functionality, with a minimum redesign of both HW and SW; – Easily add new features. In fact, all modules communi- cate on the bus and use the same connectors so you can add functionality simply by adding a module. 4 The Glider The glider has been designed and made on purpose. It is built of foam reinforced with carbon fiber tubes. All parts are obtained by machining a foam block with a numerically controlled hot wire cutting machine (Fig. 6). Fig. 7 Mechanical drawing of the glider In Fig. 7, there is the mechanical drawing, while in Fig. 8, there are some pictures of the glider during the machining process. a range of connectivity options. The open-source nature of this device allows the users to have access to the source The glider is equipped with a commercial autopilot for navigation (Pixhawk). The system combines advanced sen- code, and this enables us to modify and customize the code to meet specific needs. sors, including an accelerometer, gyroscope, magnetom- eter, barometer, and GPS, a powerful microcontroller, and In Fig. xx, it is visible how the glider, during an experi- mental flight, correctly gets into flight attitude at an altitude of 22,000 meters. Normally, the autopilot controls the aircraft through the left and right ailerons, and receives commands from the radio telemetry (connection with the glider control station) and from the remote radio (remote control for landing in line of sight). Usually in planning a mission, the Home Position is set as the location where the aircraft is armed. This is the mode used in the experimental flights carried out so far. Alternatively, there is the possibility to use waypoints to set up an alternative return point. The control station of the glider (telemetry in line of sight) permits entering new way- points, setting geographic coordinates (latitude, longitude) Fig. 6 The hot wire cutting machine 1 3 Hermes: Hemera Returning Messenger and altitude. This is the mode we are developing for the next payload configuration, where the glider will also have an Iridium SBD modem on board. A balloon flight is unpredictable in the long term. The flight has to be continuously monitored from a ground team who decides if to release the glider. The glider will be released if (1) there is the necessity to recover the data (2) there is the possibility to land to a safely reachable place. In this case, the landing point is uploaded to the glider, and the releasing command is issued. Once released, the glider is able to autonomously reach the landing point. In any case, in the final phase of land- ing, when the glider is visible to the operator, there is the possibility of manually taking control of the aircraft (RC commands). From the point of view of logistics, when the command release has been executed, the flight support team travels to the prearranged location, now just expect to see the glider in line of sight and then manually take control of it with radio command to land it. To facilitate its contact with the ground, a carpet of plastic material (about ten meters long) is spread where it will land. 5 Experimental Flights As previously mentioned, the tests carried out so far have been performed with latex balloons. Figure 9 shows the launch phase and the re-entry phase of an experimental flight conducted with a latex balloon. Experimental results show the glider, after releasing, gets in attitude between 10 and 20 km height. The length of the flight depends on the attitude height, the efficiency and, if the tail propeller is used, on the efficiency of the thruster and on the battery Fig. 8 The glider during the assembly process capacity. A 100 Wh battery can increase the flight length of roughly 50 km. If in attitude at 20 km the glider can fly for more than 100 km in calm air. This distance can be Fig. 9 a Launch phase; b Re- entry phase of an experimental flight 1 3 lo lo lon n n lla att A. Iarocci et al. Ma Ma Max x x height height height time : 120.8 minutes time: 152 minutes Free Free Free fall fall fall 20 height : 28.6 km 30 30 30 ascent height : 12.8 km Flight Flight Flight atti atti attitude tude tude -20 25 25 25 -40 free fall glide 20 20 20 -60 -80 time: 125 minutes malfun malfun malfunct ct ction ion ion 15 15 15 height 21.6 km -100 free fall -120 10 10 10 15,60 15,60 15,60 Free Free Free fall fall fall 15,47 15,47 15,47 -140 cras cras crash h h 15,34 15,34 15,34 110 120 130140 150160 5 5 5 15,21 15,21 15,21 time (minutes) Tak Tak Taking ing ing of of offff 15,08 15,08 15,08 14,95 14,95 14,95 0 0 0 41,0 41,0 41,0 41,2 41,2 41,2 Fig. 10 Plot of the vertical speed 14,82 14,82 14,82 41, 41, 41,4 4 4 Fig. 12 A 3D plot of the engine powered flight distance from base height -5 -20 -10 0102030405060708090100110120130140150160170 time (minutes) Fig. 11 Plot of the distance from the base and of altitude Fig. 13 Glider efficiency vs. height further increased using the tail propeller and choosing a descent path to take advantage of the wind. The result of the flight test with the tail propeller con- The presence of the RC pilot to facilitate the landing is ducted in 2019 in Benevento, suggests that the presence of not mandatory although safer. The glider can land nicely the engine also helps the aircraft to get into flight attitude on a flat surface (like the snow or ice we expect to have in (22 km) 2 km higher than the best flight without engine. polar areas). However, the memory stick containing data can Figure  10 shows the plot of the vertical speed in the survive even in case of a bad landing. experimental flight of the glider equipped with the engine. In order to be able to compare the flight described above Figure 12 shows a 3D plot of the flight path and Fig.  11 with a flight performed without an engine, an experimental shows the plot of the distance from the base and of the flight performed on is now analyzed. First of all it is shown altitude of the flight. Figure  13 shows the glider efficiency in Fig.  14, the altitude-time diagram of the flight, which (horizontal speed/vertical speed) vs. height, calculated shows how the glider gets in attitude at 20,000 meters. from the flight test data. The graph shows an apparent The same graph is shown on a three-axis Cartesian system (the engine was on) efficiency greater than 20 at 13 km: (Fig. 15), where on the (x,y) plane, we have the geographical unfortunately a malfunction occurred during this promis- coordinates, while on the z axis, we have the height. With ing flight and it was not possible to examine the prototype this representation, all phases of flight from launch to land- to understand the cause of the malfunction. ing are clearly visible. 1 3 km vertical speed (km/h) height (km) height (km) height (km) Hermes: Hemera Returning Messenger Fig. 14 Plot of the altitude vs time Fig. 16 The ground projection of the descent spiral Fig. 15 Plot of height in a three-axis system Fig. 17 The perspective view of the descent spiral Once close to the ground, the glider spirals until manual control is taken. On the figures below, there is the ground projection of the several improvements that will make this technique afford- descending spiral (Fig. 16) and the perspective view of the able and usable. The tail propeller showed to be a good way spiral with the starting point of the manual piloting highlighted to increase the flight length, and a higher efficiency means (Fig. 17). a bigger choice of landing points and a longer flight time to To determine the acceleration to which the glider is sub- collect samples during the descent. Retractable wings (to be jected, the log data relating to the inertial platform (IMU) are deployed after entering the troposphere) will help in this task now analyzed. as well as a better energy management and a better propul- The diagram of Fig. 18 shows a plausible baseline at 9.8 m/ sion efficiency. High efficiency space-grade solar panels may s with occasional fluctuations below 1/2 g on takeoff, a bump be hosted on the wing surface without significantly affecting at 10 g on release and some spikes to 2 g on landing. the weight and may increase the time of flight and (more important) keep communications alive allowing tracking the glider even in case of a delayed recover. 6 Future Developments The experimental flights showed the glider sets itself in flight attitude at various altitudes, making the flight length The use of autonomous stratospheric gliders is a promis- unpredictable. A better autopilot algorithm or a glider design ing method for collecting and transporting scientific sam- should make this height known in advance and therefore the ples and data. The results of experimental flights suggest flight length more predictable. The autopilot actually relies 1 3 A. Iarocci et al. Table 1 10-pin connector pin diagram PIN Photovoltaic Power Servo (with heater) 1 + Photo + Batt Heater 2 + Photo + Batt Heater 3 + 9 4 + 5 servo 5 + 5 + 5 + 5 therm 6 + CAN Servo 7 Therm –CAN Therm 8 Gnd th Gnd Gnd th 9 Gnd Gnd Gnd 10 Gnd Gnd Gnd Table 2 4-pin connector pin diagram Fig. 18 The Z-axis acceleration plot PIN CAN USB 1 CAN power (9 V) nc on the magnetic compass. When in the polar areas, the hori- 2 + CAN USB + zontal component of the magnetic field becomes unreliable 3 –CAN USB– and modification of the autopilot algorithm will be manda- 4 Gnd Gnd tory to overcome this problem 1. Connect the photovoltaic panel and the panel thermom- Appendix eter to the battery pack module. There is only one con- nection of this type (panels to J1). Photovoltaic column General Info and Power/Digital Interfaces in the table. 2. Carry power (direct battery, 9v stabilized and 5v stabi- The mass of the entire payload is of about 16 Kg (weight lized) and CAN signal. There is only one connection of 156,8 N), of which 3 Kg (29,4 N) is the glider. this type [from J3 (battery pack) to J20 (glider charter + Total average power consumption: 10W. junction box)]. The CAN I/F is the one that allows all the modules to 3. Connect the release system servos (version with heater, communicate with each other and with the glider. from J15 to J18). The USB I/F manages the data transfer between the FCS and the SSD on board the glider before its release. See Tables 1, 2, 3. Speaking of power interfaces, the Battery Pack and the The 4-pin connectors connect all the modules by carrying Glider Charger and Junction Box modules have on-board the USB or CAN signal and 9 V voltage. To avoid conflicts step down converters that generate stabilized 9V and 5V. in the event of incorrect insertion, the USB connectors (on These supply voltages are distributed to all modules and to the modules) are not connected to the power supply. the glider. These leads connect J2-J26; J27-J4; J5-J9; J10-J11; J25- J24; J12-J22. J21 is the magnetic connector that connects the glider Connections Between Modules to the payload through the umbilical cable. Through it the payload supplies power (5 V) and data (USB interface) to All system modules communicate with each other via CAN the SSD memory on board the glider. bus. Only 2 types of connectors (except glider umbilical J21 In addition, this cable supplies the glider battery mainte- and RF connectors J6, J7, J8) are used for communications: nance voltage, the power to the heater (to keep in tempera- a 4-pin connector and a 10-pin connector. The connectors ture the glider battery) and CAN signals. The latter allows can have different purposes but the connections are arranged landing coordinates to be loaded onto the autopilot before so that inserting a connector incorrectly does not cause an releasing the glider. electrical fault. Connector J13 refers to the cable carrying the release The 10-pin connectors are used for: command coming from the host telemetry. This is a 1 3 Hermes: Hemera Returning Messenger included in the article's Creative Commons licence, unless indicated Table 3 Magnetic connector PIN Magnetic connector otherwise in a credit line to the material. If material is not included in (J21) pin diagram the article's Creative Commons licence and your intended use is not 1 nc permitted by statutory regulation or exceeds the permitted use, you will 2 nc need to obtain permission directly from the copyright holder. To view a 3 Glider battery charger copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . 4 nc 5 nc 6 Heater References 7 USB power (SSD power) 1. https:// olimpo. roma1. infn. it/. Accessed 27 Mar 2023 8 Gnd 2. https:// www. hemera- h2020. eu/. Accessed 27 Mar 2023 9 Gnd 3. Volpe, A., et al.: Italian Space Agency Balloon Borne Research 10 Gnd Activities and Programmes. 25th ESA Symposium on European 11 USB– (SSD data) ROCKET & BALLOON programmes and related research. 1–5 May 2022 - Biarritz-France (2022) 12 USB + (SSD data) 4. Volpe, A. et al.: “OLIMPO & LSPE/SWIPE missions: innova- 13 CAN power (9 V) tive instrumentations for astrophysical observations”, Proceedings 14 –CAN of the XXV AIDAA International Congress of Aeronautics and 15 –CAN Astronautics, Casa Editrice Persiani 3, 1800–1807 (2019) 5. de Bernardis, P., et al.: SWIPE: a bolometric polarimeter for the Large-Scale Polarization Explorer. In Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VI, redundant command, in case the Iridium release command volume 8452 of Proceeding SPIE, page 84523F (2012) 6. Peterzen, S., Masi, S., de Bernardis, P.: Polar stratospheric sent by the Ground Station fails. research platforms—ballooning in the Polar Regions. In 38th Connector J14 refers to the cable carrying the glider pres- COSPAR Scientific Assembly, volume 38 of COSPAR Meeting, ence signal. p 4 (2010) 7. Iarocci, A., et al.: PEGASO: an ultra light long stratospheric pay- load for polar regions flights. Adv. Space Res. 42, 1633–1640 Funding Open access funding provided by Istituto Nazionale di Geofi- (2008) sica e Vulcanologia within the CRUI-CARE Agreement. 8. Ronchi, E., et al.: STRADIUM: a telemetry & telecommand sys- tem for LDB flights. Mem. Soc. Astron. Ital. 79, 926–931 (2008) 9. https:// lspe. roma1. infn. it/ index. html?. Accessed 27 Mar 2023 Declarations 10. Piacentini, F., Coppolecchia, A., de Bernardis, P., Di Stefano, G., Iarocci, A., Lamagna, L., Masi, S., Peterzen, S., Romeo, G.: Win- Conflict of Interest On behalf of all authors, the corresponding author ter long duration stratospheric balloons from Polar regions. Mem. states that there is no conflict of interest. Soc. Astron. Ital. 75, 282–286 (2018) Open Access This article is licensed under a Creative Commons Attri- Publisher's Note Springer Nature remains neutral with regard to bution 4.0 International License, which permits use, sharing, adapta- jurisdictional claims in published maps and institutional affiliations. tion, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aerotecnica Missili & Spazio Springer Journals

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Abstract

A common issue for long-duration balloon flights in the polar area is high bit rate data transferring. Just a few hours after launch balloons are nor reachable with direct radio link, and often satellite links are not fast enough to allow the necessary transfer rate or, simply, too expensive. For this reason, stratospheric balloon borne experiments carry out on-board data recording. Data recorded need to be recovered after termination, which is, sometimes, a slow, difficult and expensive task. Not always it is easy or possible to reach the landing site, especially during the polar winter. The aim of the project is to provide an autonomous glider capable of physically carrying the data from the stratospheric platform to a recovery point on the ground. This can also transport physical objects (like air samples) collected at float or along the flight. We estimate that an electrical motorglider released in the stratosphere can fly for several hundreds of kilometers. The glider is installed on the balloon payload through a remotely controlled release system, and connected with the main computer to receive data and the geographic coordinates of the recovery point. The glider trajectory can be monitored with Iridium SBD (Short Burst Data), and simple commands can be issued as well as using Iridium. Keywords Stratospheric platform · UAV · LDB · Data recording 1 Introduction The launch of HERMES is part of the European project HEMERA [2, 3], born with the aim of improving the scien- We describe an affordable and easy to use vector able to tific activities in the stratosphere by offering to researchers safely transport scientific data and samples from the strat- an easy access to the space in individual or shared strato- osphere to the ground, a desirable tool for several scien- spheric payloads. tific measurements. Such a system was originally thought As part of this project, two calls for proposals have been for physically recovering data media from the Olimpo [1] organized to select eligible scientific experiments. Such pro- experiment, but it can be used as well for i.e. sampling the jects, including HERMES, were offered a free balloon flight. volcanic ash from ground to the stratosphere or to make bet- In the case of HERMES, the launch campaign will take ter and more complete sounding balloons because you are place at the Swedish space base of Esrange (Kiruna), and not forced to use expandable payloads with limited capacity, will be carried out by the Swedish Space Corporation (SSC). since the payload can be recovered and reused. With the HERMES project, a stratospheric platform The HERMES payload is a project funded and coordi- equipped with a glider was designed and developed. The nated by Agenzia Spaziale Italiana (ASI), and whose sci- glider, once released, is capable of transporting a copy of entific coordinator is Istituto Nazionale di Geofisica e Vul- the data of the scientific experiment hosted by the platform canologia (INGV). to a pre-established recovery point on the ground. This is achieved thanks to the presence on board the glider of a Solid State Drive (SSD) memory, connected to the payload flight computer. * Alessandro Iarocci This would allow the scientific data of the experiment alessandro.iarocci@ingv.it on board the balloon to be available within a few hours Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy and in an accessible place. This is of prime importance for Elettromeccanica Adobbato Pasquale, Montopoli, Italy scientific experiments on Long Duration Balloons (LDB) that take place on polar flights [ 4–9]. In fact, recovering the Dipartimento di Fisica, Università di Roma La Sapienza, Rome, Italy Vol.:(0123456789) 1 3 A. Iarocci et al. payload in these cases is rather difficult and expensive (there a compatibility test for the experiments hosted on the are special recovery teams dedicated to such activities), but same gondola. it is the only way to recover the scientific experiment data 3) The mechanics of the releasing system had to be tested set. Furthermore, during the landing of the payload, damage with an acceleration of 10 g, to allow (in case of failure to the same may occur, compromising the outcome of the in releasing) the glider attachment to resist the accelera- scientific experiment. tion induced by the parachute opening. Because of the first two points the system cannot share the gondola with other experiments and needs to be completely 2 Project History and Evolution autonomous, providing its own power and communication. A sketch of this configuration appears in Fig.  1, where the The project started from the ABACHOS (Automatic BACk absence of a common gondola has led to revisit the project, HOme System) [ https:// s tr at hosph er eff ect. com/ ABACH designing a self-consistent mechanics and modular electron- OS] platform modified to meet the HERMES needs. ABA - ics, which allows to easily compose the characteristics nec- CHOS is launched using inexpensive latex balloons and is essary for use on any gondola. All the modules that make recovered at launch point. The use of affordable latex bal- up the system are autonomous and can be easily integrated loons helped experiment with this design with more than 15 into any stratospheric experiments. flights. The analysis of an ABACHOS flight appears further in the article. The original platform was modified by adding some electronics (mass storage, communication, umbilical 3 System Description connector, battery heater) and a tail motor to increase the flight length. The glider is no longer released by the latex The system is composed of: payload (hosting HERMES balloon explosion but from a command issued by a ground electronics and the releasing system), glider and GROUND station and is tied to a releasing platform attached mechani- STATION. In its nominal configuration HERMES expects cally and electrically to the main gondola. The sketch of the the use of solar panels, as well as an external power source original releasing platform appears in Fig 3. Here, the glider from the main gondola. is held in place using a couple of brackets on the wings and In the case of short-term experimental flights (a few the releasing is assisted by a pushing arm who also helps hours), the system can operate exclusively by the on-board detaching the umbilical magnetic connector. battery. Some modifications had to be done to meet the SSC Figure 1 shows the overall view of the payload without requirements, linked to three considerations: the solar panels (short-term experimental configuration). The main modules that make up the payload handle bat- 1) The release of a load can change the mass center of the tery power and communications. Also present is the Flight gondola and be a source of disturbance. While the atti- Computer Simulator (FCS) and the glider release system tude variation can be tolerated on a large LDB (Long (RELEASER). All modules communicate over CAN (Con- Duration Balloon), where the weight of the glider is neg- troller Area Network) bus. ligible compared to that of the gondola, it is no longer The GROUND STATION can decide the flight termina- so in a small experimental flight. This problem cannot tion through a command via a satellite channel, after upload- be overcome by releasing the glider at the end of the ing the coordinates of the landing point to the autopilot. experiment, because the Swedish rules for testing UAVs (Unmanned Aerial Vehicle) limit the distance from the 3.1 The Launch Platform launch point, which would be exceeded after a few hours at altitude. Figure  2 shows the block diagram of the payload. It is 2) The balloon system telemetry (with transponder divided in two sections, the RELEASER who hosts the bat- included) is service telemetry of SSC which the payload tery charger and the parts to carry out the release, and the cannot use (the only communication facility provided to gondola frame which contains all the facilities we expect the payload was a relay contact to be used as emergency to have in a host gondola. The computer simulator, logi- release command). Therefore, HERMES had to provide cally part of the gondola frame, has been installed in the its own auxiliary telemetry in line of view. The gener- RELEASER to facilitate connections. ous use of equipment capable of generating RF (Radio The BATTERY PACK module manages the battery that Frequency) disturbances (two Iridium SBD modems powers the system. The battery, consisting of seven pure and two 1 GHz line-of-sight telemetry) to the balloon’s lead elements, was chosen for the extended temperature natural telemetry would require specific integration and range. A microprocessor manages the battery correctly by 1 3 Hermes: Hemera Returning Messenger Fig. 1 The overall view of the payload Fig. 2 Launch platform block diagram 1 3 A. Iarocci et al. Fig. 3 The glider release sequence charging it from the panels (using the MPPT algorithm) or connector (connector J21 in Fig. 2), powers the glider’s SSD, from some other dc source, taking into account the tem- recharges the glider’s batteries and maintains its temperature perature. The module powers the system through the CAN by means of a heater. connector and supplies a specialized power supply to the The FCS produces synthetic data with which to fill the glider's battery charger which is operated, before release, SSD, simulating the presence of a flight computer. In fact, to switch the glider's batteries from storage mode to full HERMES was designed to transport the data produced by a charge. The BATTERY PACK communicates all the values balloon borne experiment to the ground, and the FCS, since concerning the power supplies through the CAN bus. Using there is no real data, produces test data, which loads through two switches, the battery can be separated for transport and the umbilical connector on the SSD present on the glider. the system can be set up for battery operation only, ignoring These data are the video taken by a camera, active from the external power sources. moment of launch, and the house keeping data acquired by The COM and CONTROL module is responsible for all the modules and transferred through the CAN bus. managing satellite and line-of-sight communications. A reduced version of this module is designed to be housed on board the glider to allow commands to be sent over the 3.2 The RELEASER satellite network. The IMU (Inertial Measurement Unit) block contains the The RELEASER module, housed under the plate that holds inertial sensors (three-axis accelerometer, three-axis gyro- the glider, controls the servo motors that release the glider. scope), a three-axis magnetic compass, a barometric sen- The servomotors are controlled through a position signal sor and a GPS (Global Positioning System) receiver. The (PWM, Pulse Width Modulation) and through the power module, self-consistent for general use, allows to know the supply that can be supplied individually. The temperature payload’s attitude. of each servo and the overall current supplied are checked. The MONITOR and SD RECORDER module makes a As mentioned, three servomotors are used, of which two local acquisition of the log file of the CAN traffic and pro- free the wings and one activates a thrust mustache which vides an interface RS232-CAN helpful for debugging. helps release. Currently, the umbilical connection of the The GLIDER CHARGER and JUNCTION BOX mod- glider to the platform is obtained with a magnetic connec- ule manages the connection with the glider’s umbilical tor. Figure 3 shows the sequence of the glider release. 1 3 Hermes: Hemera Returning Messenger The presence of the aircraft on the platform is revealed 3.3 The Glider Electronics through a proximity sensor installed near the rear engine. A manual switch allows you to operate the servomotors for Figure 5 shows the glider block diagram. J21 is the magnetic installing the aircraft on the release platform. connector that connects the glider to the payload through the The releasing command can take place: (a) through a umbilical cable. command via the CAN bus (b) through a contact provided Through this connector the payload supplies the heater for by logistics telemetry, to be activated in the event of a the battery of the glider, keeps the battery charged, transfers defect in communications. (c) through a manual switch the backup data from the FCS to the SSD, and allows com- when installing the glider on the platform. munications with the glider through the CAN bus. Compared to the original design just described, the The possibility is foreseen that the glider can host a COM mechanics of the separation system has been modified to and CONTROL module (with IRIDIUM SBD), connected comply with the request of the Swedish authorities which via CAN with the autopilot, of which it reads the positioning requires that the system resist an acceleration of 10 g. system to allow you to track the glider when you are not in The original system was supported by two motorized line of sight. brackets that operated on the wings. Now, a safety screw It can load a new landing point on the autopilot and turn (Fig. 4) has been added to this system which secures the the engine on and off. fuselage to the RELEASER and which is unscrewed and extracted when the aircraft is released. The brackets that 3.4 Final Considerations support the wings have been maintained to keep the glider in position but they no longer have a support function. The The actual version of HERMES has been designed for sum- servo used to move the pushing mustache is now used only mer flights. Under these conditions, the main issue to con- to help detach the umbilical connector. sider is the poor heat dissipation provided by the atmos- phere (5 mb at the float altitude) and the internal pressure of Fig. 4 The mechanical drawing (on the left) and a detail of the assembly (on the right) of the safety screw Fig. 5 Glider electronics block diagram 1 3 A. Iarocci et al. electrochemical parts (i.e. batteries or capacitors). A thermal check of the modules in a vacuum chamber gives the confi- dence of a good performance in the stratosphere. A much more critical scenario is a flight during the winter in the polar regions, where the temperature reached may be of the order of – 80 °C [10]. These extreme conditions will put a strain especially on the mechanical parts and electronics. Note that HERMES payload modules are not pressurized, special attention should be paid to heating the batteries and electronics. Concluding, HERMES is built in the name of modularity. This permits to: – Make modules usable separately in other balloon pro- jects; – Make debugging easy; – Make the project updatable: if a module is technically obsolete it can be replaced with an updated module that respects the functionality, with a minimum redesign of both HW and SW; – Easily add new features. In fact, all modules communi- cate on the bus and use the same connectors so you can add functionality simply by adding a module. 4 The Glider The glider has been designed and made on purpose. It is built of foam reinforced with carbon fiber tubes. All parts are obtained by machining a foam block with a numerically controlled hot wire cutting machine (Fig. 6). Fig. 7 Mechanical drawing of the glider In Fig. 7, there is the mechanical drawing, while in Fig. 8, there are some pictures of the glider during the machining process. a range of connectivity options. The open-source nature of this device allows the users to have access to the source The glider is equipped with a commercial autopilot for navigation (Pixhawk). The system combines advanced sen- code, and this enables us to modify and customize the code to meet specific needs. sors, including an accelerometer, gyroscope, magnetom- eter, barometer, and GPS, a powerful microcontroller, and In Fig. xx, it is visible how the glider, during an experi- mental flight, correctly gets into flight attitude at an altitude of 22,000 meters. Normally, the autopilot controls the aircraft through the left and right ailerons, and receives commands from the radio telemetry (connection with the glider control station) and from the remote radio (remote control for landing in line of sight). Usually in planning a mission, the Home Position is set as the location where the aircraft is armed. This is the mode used in the experimental flights carried out so far. Alternatively, there is the possibility to use waypoints to set up an alternative return point. The control station of the glider (telemetry in line of sight) permits entering new way- points, setting geographic coordinates (latitude, longitude) Fig. 6 The hot wire cutting machine 1 3 Hermes: Hemera Returning Messenger and altitude. This is the mode we are developing for the next payload configuration, where the glider will also have an Iridium SBD modem on board. A balloon flight is unpredictable in the long term. The flight has to be continuously monitored from a ground team who decides if to release the glider. The glider will be released if (1) there is the necessity to recover the data (2) there is the possibility to land to a safely reachable place. In this case, the landing point is uploaded to the glider, and the releasing command is issued. Once released, the glider is able to autonomously reach the landing point. In any case, in the final phase of land- ing, when the glider is visible to the operator, there is the possibility of manually taking control of the aircraft (RC commands). From the point of view of logistics, when the command release has been executed, the flight support team travels to the prearranged location, now just expect to see the glider in line of sight and then manually take control of it with radio command to land it. To facilitate its contact with the ground, a carpet of plastic material (about ten meters long) is spread where it will land. 5 Experimental Flights As previously mentioned, the tests carried out so far have been performed with latex balloons. Figure 9 shows the launch phase and the re-entry phase of an experimental flight conducted with a latex balloon. Experimental results show the glider, after releasing, gets in attitude between 10 and 20 km height. The length of the flight depends on the attitude height, the efficiency and, if the tail propeller is used, on the efficiency of the thruster and on the battery Fig. 8 The glider during the assembly process capacity. A 100 Wh battery can increase the flight length of roughly 50 km. If in attitude at 20 km the glider can fly for more than 100 km in calm air. This distance can be Fig. 9 a Launch phase; b Re- entry phase of an experimental flight 1 3 lo lo lon n n lla att A. Iarocci et al. Ma Ma Max x x height height height time : 120.8 minutes time: 152 minutes Free Free Free fall fall fall 20 height : 28.6 km 30 30 30 ascent height : 12.8 km Flight Flight Flight atti atti attitude tude tude -20 25 25 25 -40 free fall glide 20 20 20 -60 -80 time: 125 minutes malfun malfun malfunct ct ction ion ion 15 15 15 height 21.6 km -100 free fall -120 10 10 10 15,60 15,60 15,60 Free Free Free fall fall fall 15,47 15,47 15,47 -140 cras cras crash h h 15,34 15,34 15,34 110 120 130140 150160 5 5 5 15,21 15,21 15,21 time (minutes) Tak Tak Taking ing ing of of offff 15,08 15,08 15,08 14,95 14,95 14,95 0 0 0 41,0 41,0 41,0 41,2 41,2 41,2 Fig. 10 Plot of the vertical speed 14,82 14,82 14,82 41, 41, 41,4 4 4 Fig. 12 A 3D plot of the engine powered flight distance from base height -5 -20 -10 0102030405060708090100110120130140150160170 time (minutes) Fig. 11 Plot of the distance from the base and of altitude Fig. 13 Glider efficiency vs. height further increased using the tail propeller and choosing a descent path to take advantage of the wind. The result of the flight test with the tail propeller con- The presence of the RC pilot to facilitate the landing is ducted in 2019 in Benevento, suggests that the presence of not mandatory although safer. The glider can land nicely the engine also helps the aircraft to get into flight attitude on a flat surface (like the snow or ice we expect to have in (22 km) 2 km higher than the best flight without engine. polar areas). However, the memory stick containing data can Figure  10 shows the plot of the vertical speed in the survive even in case of a bad landing. experimental flight of the glider equipped with the engine. In order to be able to compare the flight described above Figure 12 shows a 3D plot of the flight path and Fig.  11 with a flight performed without an engine, an experimental shows the plot of the distance from the base and of the flight performed on is now analyzed. First of all it is shown altitude of the flight. Figure  13 shows the glider efficiency in Fig.  14, the altitude-time diagram of the flight, which (horizontal speed/vertical speed) vs. height, calculated shows how the glider gets in attitude at 20,000 meters. from the flight test data. The graph shows an apparent The same graph is shown on a three-axis Cartesian system (the engine was on) efficiency greater than 20 at 13 km: (Fig. 15), where on the (x,y) plane, we have the geographical unfortunately a malfunction occurred during this promis- coordinates, while on the z axis, we have the height. With ing flight and it was not possible to examine the prototype this representation, all phases of flight from launch to land- to understand the cause of the malfunction. ing are clearly visible. 1 3 km vertical speed (km/h) height (km) height (km) height (km) Hermes: Hemera Returning Messenger Fig. 14 Plot of the altitude vs time Fig. 16 The ground projection of the descent spiral Fig. 15 Plot of height in a three-axis system Fig. 17 The perspective view of the descent spiral Once close to the ground, the glider spirals until manual control is taken. On the figures below, there is the ground projection of the several improvements that will make this technique afford- descending spiral (Fig. 16) and the perspective view of the able and usable. The tail propeller showed to be a good way spiral with the starting point of the manual piloting highlighted to increase the flight length, and a higher efficiency means (Fig. 17). a bigger choice of landing points and a longer flight time to To determine the acceleration to which the glider is sub- collect samples during the descent. Retractable wings (to be jected, the log data relating to the inertial platform (IMU) are deployed after entering the troposphere) will help in this task now analyzed. as well as a better energy management and a better propul- The diagram of Fig. 18 shows a plausible baseline at 9.8 m/ sion efficiency. High efficiency space-grade solar panels may s with occasional fluctuations below 1/2 g on takeoff, a bump be hosted on the wing surface without significantly affecting at 10 g on release and some spikes to 2 g on landing. the weight and may increase the time of flight and (more important) keep communications alive allowing tracking the glider even in case of a delayed recover. 6 Future Developments The experimental flights showed the glider sets itself in flight attitude at various altitudes, making the flight length The use of autonomous stratospheric gliders is a promis- unpredictable. A better autopilot algorithm or a glider design ing method for collecting and transporting scientific sam- should make this height known in advance and therefore the ples and data. The results of experimental flights suggest flight length more predictable. The autopilot actually relies 1 3 A. Iarocci et al. Table 1 10-pin connector pin diagram PIN Photovoltaic Power Servo (with heater) 1 + Photo + Batt Heater 2 + Photo + Batt Heater 3 + 9 4 + 5 servo 5 + 5 + 5 + 5 therm 6 + CAN Servo 7 Therm –CAN Therm 8 Gnd th Gnd Gnd th 9 Gnd Gnd Gnd 10 Gnd Gnd Gnd Table 2 4-pin connector pin diagram Fig. 18 The Z-axis acceleration plot PIN CAN USB 1 CAN power (9 V) nc on the magnetic compass. When in the polar areas, the hori- 2 + CAN USB + zontal component of the magnetic field becomes unreliable 3 –CAN USB– and modification of the autopilot algorithm will be manda- 4 Gnd Gnd tory to overcome this problem 1. Connect the photovoltaic panel and the panel thermom- Appendix eter to the battery pack module. There is only one con- nection of this type (panels to J1). Photovoltaic column General Info and Power/Digital Interfaces in the table. 2. Carry power (direct battery, 9v stabilized and 5v stabi- The mass of the entire payload is of about 16 Kg (weight lized) and CAN signal. There is only one connection of 156,8 N), of which 3 Kg (29,4 N) is the glider. this type [from J3 (battery pack) to J20 (glider charter + Total average power consumption: 10W. junction box)]. The CAN I/F is the one that allows all the modules to 3. Connect the release system servos (version with heater, communicate with each other and with the glider. from J15 to J18). The USB I/F manages the data transfer between the FCS and the SSD on board the glider before its release. See Tables 1, 2, 3. Speaking of power interfaces, the Battery Pack and the The 4-pin connectors connect all the modules by carrying Glider Charger and Junction Box modules have on-board the USB or CAN signal and 9 V voltage. To avoid conflicts step down converters that generate stabilized 9V and 5V. in the event of incorrect insertion, the USB connectors (on These supply voltages are distributed to all modules and to the modules) are not connected to the power supply. the glider. These leads connect J2-J26; J27-J4; J5-J9; J10-J11; J25- J24; J12-J22. J21 is the magnetic connector that connects the glider Connections Between Modules to the payload through the umbilical cable. Through it the payload supplies power (5 V) and data (USB interface) to All system modules communicate with each other via CAN the SSD memory on board the glider. bus. Only 2 types of connectors (except glider umbilical J21 In addition, this cable supplies the glider battery mainte- and RF connectors J6, J7, J8) are used for communications: nance voltage, the power to the heater (to keep in tempera- a 4-pin connector and a 10-pin connector. The connectors ture the glider battery) and CAN signals. The latter allows can have different purposes but the connections are arranged landing coordinates to be loaded onto the autopilot before so that inserting a connector incorrectly does not cause an releasing the glider. electrical fault. Connector J13 refers to the cable carrying the release The 10-pin connectors are used for: command coming from the host telemetry. This is a 1 3 Hermes: Hemera Returning Messenger included in the article's Creative Commons licence, unless indicated Table 3 Magnetic connector PIN Magnetic connector otherwise in a credit line to the material. If material is not included in (J21) pin diagram the article's Creative Commons licence and your intended use is not 1 nc permitted by statutory regulation or exceeds the permitted use, you will 2 nc need to obtain permission directly from the copyright holder. To view a 3 Glider battery charger copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . 4 nc 5 nc 6 Heater References 7 USB power (SSD power) 1. https:// olimpo. roma1. infn. it/. Accessed 27 Mar 2023 8 Gnd 2. https:// www. hemera- h2020. eu/. Accessed 27 Mar 2023 9 Gnd 3. Volpe, A., et al.: Italian Space Agency Balloon Borne Research 10 Gnd Activities and Programmes. 25th ESA Symposium on European 11 USB– (SSD data) ROCKET & BALLOON programmes and related research. 1–5 May 2022 - Biarritz-France (2022) 12 USB + (SSD data) 4. Volpe, A. et al.: “OLIMPO & LSPE/SWIPE missions: innova- 13 CAN power (9 V) tive instrumentations for astrophysical observations”, Proceedings 14 –CAN of the XXV AIDAA International Congress of Aeronautics and 15 –CAN Astronautics, Casa Editrice Persiani 3, 1800–1807 (2019) 5. de Bernardis, P., et al.: SWIPE: a bolometric polarimeter for the Large-Scale Polarization Explorer. In Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VI, redundant command, in case the Iridium release command volume 8452 of Proceeding SPIE, page 84523F (2012) 6. Peterzen, S., Masi, S., de Bernardis, P.: Polar stratospheric sent by the Ground Station fails. research platforms—ballooning in the Polar Regions. In 38th Connector J14 refers to the cable carrying the glider pres- COSPAR Scientific Assembly, volume 38 of COSPAR Meeting, ence signal. p 4 (2010) 7. Iarocci, A., et al.: PEGASO: an ultra light long stratospheric pay- load for polar regions flights. Adv. Space Res. 42, 1633–1640 Funding Open access funding provided by Istituto Nazionale di Geofi- (2008) sica e Vulcanologia within the CRUI-CARE Agreement. 8. Ronchi, E., et al.: STRADIUM: a telemetry & telecommand sys- tem for LDB flights. Mem. Soc. Astron. Ital. 79, 926–931 (2008) 9. https:// lspe. roma1. infn. it/ index. html?. Accessed 27 Mar 2023 Declarations 10. Piacentini, F., Coppolecchia, A., de Bernardis, P., Di Stefano, G., Iarocci, A., Lamagna, L., Masi, S., Peterzen, S., Romeo, G.: Win- Conflict of Interest On behalf of all authors, the corresponding author ter long duration stratospheric balloons from Polar regions. Mem. states that there is no conflict of interest. Soc. Astron. Ital. 75, 282–286 (2018) Open Access This article is licensed under a Creative Commons Attri- Publisher's Note Springer Nature remains neutral with regard to bution 4.0 International License, which permits use, sharing, adapta- jurisdictional claims in published maps and institutional affiliations. tion, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are 1 3

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Aerotecnica Missili & SpazioSpringer Journals

Published: Jun 1, 2023

Keywords: Stratospheric platform; UAV; LDB; Data recording

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