Risk Assessment and Experimental Light-Balloon Deployment of a Stratospheric Vertical VLF Transmitter
Abstract
:1. Introduction: VLF Emitted from Airborne Sources
2. VLF Theory of Propagation from High Altitudes
2.1. Mode Magnitudes
2.2. Mode Excitation Efficiencies
2.3. Modes’ Attenuation: Hypothesis of Apparent Frequency Decrease
3. Mission Specifications
4. Risk Assessments
4.1. Mechanical
No. | Description | Probability | Severity | Probability × Severity | Mitigation |
---|---|---|---|---|---|
M1 | Antenna wire break | 4 | 2 | 8 | Division of antenna wire into radiating wire (metal) and supporting tether (poliethylene, multi-thread), with mandatory strength against breaking <230 N |
M2 | Cable disconnections | 4 | 3 | 12 | Screw connections, cables threaded through circuit boards to remove loads from the solderings |
M3 | Excessive loads on the mission components | 5 | 2 | 10 | Entire mission designed as a linear structure, with all tethers connected to each other’s ends |
M4 | Equipment detachment in flight | 4 | 2 | 8 | Additional tethers to external equipment (if needed) |
M5 | Explosion due to lack of degassing | 4 | 2 | 8 | Avoidance of creation of sealed spaces—addition of small air drains |
M6 | Early balloon burst | 3 | 2 | 6 | Choice of high-quality balloon |
M7 | Damages due to balloon burst deceleration | 2 | 3 | 6 | Affixation of components resistant to high accelerations |
M8 | Damages due to landing deceleration | 2 | 4 | 8 | Affixation of components resistant to high accelerations |
M9 | Damages due to landing on uneven terrain | 2 | 4 | 8 | Sufficiently thick and shock-absorbing walls of the gondola |
M10 | Loss of gondola integrity | 5 | 1 | 5 | Temperature- and shock-resistant gondola hatch |
4.2. Thermal
No. | Description | Probability | Severity | Probability × Severity | Mitigation |
---|---|---|---|---|---|
T1 | Loss of glue joints performance in freezing temperatures | 5 | 1 | 5 | Use of low-temperature-resistant substances/qualified for space use |
T2 | Shattering of cable insulation due to freezing temperatures | 4 | 1 | 4 | Exclusion of low-resistant insulations for all insulated cables |
T3 | Freezing temperature on the frequency generator | 4 | 3 | 12 | Sufficient passive thermal control—surrounding insulation |
T4 | Freezing temperature on the upper navigation unit | 3 | 3 | 9 | Sufficient passive thermal control—surrounding insulation |
T5 | Freezing temperature on the lower navigation unit | 3 | 3 | 9 | Use of stratosphere-qualified commercial-off-the-shelf navigation transmitter |
T6 | Freezing temperature on the battery pack | 4 | 3 | 12 | Sufficient passive thermal control—surrounding insulation |
T7 | Excessive temperature on the power amplifier | 4 | 4 | 16 | Heat sink attached to the power amplifier’s transistors |
T8 | Excessive temperature on the power amplifier components | 4 | 4 | 16 | Affixation of heat bridges connected to the main heat sink |
T9 | Uneven temperature distribution on the transistors | 3 | 3 | 9 | Power amplifier with multiple transistors and load resistors; use of a common heat sink |
T10 | Fire breakout onboard the gondola | 5 | 1 | 5 | Sufficient electrical insulation on high-voltage and prone-to-overload circuits, efficient heat transfer from hot components |
T11 | The Joule-Thompson effect during the re-entry phase | 4 | 4 | 16 | Sufficient passive thermal control—surrounding insulation |
4.3. Electrical
No. | Description | Probability | Severity | Probability × Severity | Mitigation |
---|---|---|---|---|---|
E1 | Short-circuit due to condensed water | 4 | 1 | 4 | Affixation of silica-based desiccants inside the gondola |
E2 | Excessive electric potential on electronic components due to pyroelectric behaviour of water | 4 | 1 | 4 | Affixation of silica-based desiccants inside the gondola |
E3 | Corona appearance on the transmitter circuitry | 4 | 2 | 8 | Lacquering of the circuitry, use of lower voltages |
E4 | Corona apearance on the antenna wire | 3 | 5 | 15 | Corona dischargers concentrating the discharges away from the wire |
E5 | Transmitter overload due to corona appearance | 4 | 4 | 16 | Automatic detection of overloading with transmitter decoupling/low antenna-transmitter coupling |
E6 | Transmitter overload due to lightning strike | 5 | 2 | 10 | Automatic detection of overloading with transmitter decoupling/low antenna-transmitter coupling |
E7 | Flashover on the main antenna insulator towards the main gondola | 4 | 3 | 12 | Proper design of the ‘mushroom’ upper insulator |
E8 | Interference with other instruments onboard the gondola (near field of the VLF antenna) | 3 | 2 | 6 | Design of the instrumentation within the constraint of operation in the VLF near-field (shieldings, additional filters, digital protocols) |
E9 | Low stability of the frequency generator | 3 | 3 | 9 | Additional frequency stabilization circuit, passive thermal control around the generator |
E10 | Loss of power on transmitter subsystems | 4 | 2 | 8 | Division of power source into multiple, separate, independent power sources |
E11 | Transmitter malfunction (other) | 4 | 2 | 8 | Transmitter ground testing on a dummy load |
E12 | Transistor gate breakdown | 4 | 1 | 4 | Choice of transistor type with high durability heritage; multiplication of transistors in the power amplifier |
E13 | Electrical discharge from the system during landing | 2 | 1 | 2 | Corona dischargers concentrating the discharges away from the wire |
4.4. Operational
No. | Description | Probability | Severity | Probability × Severity | Mitigation |
---|---|---|---|---|---|
O1 | Incorrect antenna deployment | 4 | 2 | 8 | Elaborated antenna launch procedure |
O2 | Antenna damage during deployment | 4 | 3 | 12 | Proper choice of launch/deployment site, with sufficient clearance |
O3 | Air traffic hazard due to antenna length | 5 | 2 | 10 | Affixation of radar reflectors, optical warning systems and a double system of navigation/transponder units (on both ends of the antenna) |
O4 | Low optical- and radar visibility of the mission | 5 | 2 | 10 | Affixation of large radar reflectors and optical warning signs colored in red or bright orange |
O5 | Parachute coiling | 5 | 1 | 5 | Sufficiently long parachute tethers |
O6 | Antenna wire coiling during descent phase | 3 | 3 | 9 | Use of antenna end-weight for movement and re-entry stabilization |
O7 | Loss of mission tracking | 4 | 2 | 8 | Redundant navigation system |
O8 | Loss of landing site location | 4 | 2 | 8 | Redundant navigation system, live mission tracking, repeated flight/landing predictions |
O9 | Landing on water | 4 | 1 | 4 | Positive buoyancy of the gondola |
O10 | Landing on high-voltage power lines | 5 | 1 | 5 | Antenna wire breaking when subjected to high-voltage short-circuit |
O11 | Landing on a frequented road | 4 | 1 | 4 | High visibility of the entire flight train |
O12 | Inflicting damage on external environment when landing | 4 | 1 | 4 | Hard flight train components and main gondola built from/shielded with softened/elastic materials |
O13 | Reduced amount of delivered RF data due to E5 and E6 risk mitigation | 4 | 3 | 12 | Employment of a large amount of reception points/locations with sensitive receivers and large/ferrite antennas |
4.5. Analysis of Highest-Grade Risks
No. | Description | Probability | Severity | Probability × Severity | Mitigation |
---|---|---|---|---|---|
E5 | Transmitter overload due to corona appearance | 4 | 4 | 16 | Automatic detection of overloading with transmitter decoupling/low antenna-transmitter coupling |
T7 | Excessive temperature of the power amplifier | 4 | 4 | 16 | Heat sink attached to the power amplifier’s transistors |
T8 | Excessive temperature of the power amplifier components | 4 | 4 | 16 | Affixation of heat bridges connected to the main heat sink |
T11 | The Joule-Thompson effect during the re-entry phase | 4 | 4 | 16 | Sufficient passive thermal control—surrounding insulation |
E4 | Corona appearance on the antenna wire | 3 | 5 | 15 | Corona dischargers concentrating the discharges away from the wire |
M2 | Cable disconnections | 4 | 3 | 12 | Screw connections, cables threaded through circuit boards to remove loads from the solderings |
T3 | Freezing temperature on the frequency generator | 4 | 3 | 12 | Sufficient passive thermal control—surrounding insulation |
T6 | Freezing temperature on the battery pack | 4 | 3 | 12 | Sufficient passive thermal control—surrounding insulation |
O2 | Antenna damage during deployment | 4 | 3 | 12 | Proper choice of launch/deployment site, with sufficient clearance |
E7 | Flashover on the main antenna insulator towards the main gondola | 4 | 3 | 12 | Proper design of the ‘mushroom’ upper insulator |
O13 | Reduced amount of delivered RF data due to E5 and E6 risk mitigation | 4 | 3 | 12 | Employment of a large amount of reception points/locations with sensitive receivers and large/ferrite antennas |
O3 | Air traffic hazard due to antenna length | 5 | 2 | 10 | Affixation of radar reflectors, optical warning systems and a double system of navigation/transponder units (on both ends of the antenna) |
O4 | Low optical- and radar visibility of the mission | 5 | 2 | 10 | Affixation of large radar reflectors and optical warning signs colored in red or bright orange |
M3 | Excessive loads on the mission components | 5 | 2 | 10 | Entire mission designed as a linear structure, with all tethers connected to each other’s ends |
E6 | Transmitter overload due to lightning strike | 5 | 2 | 10 | Automatic detection of overloading with transmitter decoupling/low antenna-transmitter coupling |
5. Experimental Deployment
5.1. Mission Design
5.2. Flight Performance
6. The Analysis of Flight Results
6.1. Experimental Signal Coverage
6.2. The Evolution of the Antenna Radiation Pattern
6.3. Simulated Signal Coverages
7. Discussion
7.1. Simulations vs. Experimental Signal Coverage
7.2. Comparison with Low Frequency Experiments
7.3. Possible Ameliorations and System Employment
8. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
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Severity | Probability | ||
---|---|---|---|
1 | No/minor damage | 1 | Extremely low |
2 | Damage not affecting performance | 2 | Low |
3 | Loss of performance | 3 | Medium |
4 | Subsystem shutdown | 4 | High |
5 | Mission destruction | 5 | Very high |
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Miś, T.A.; Modelski, J. Risk Assessment and Experimental Light-Balloon Deployment of a Stratospheric Vertical VLF Transmitter. Sensors 2023, 23, 1073. https://doi.org/10.3390/s23031073
Miś TA, Modelski J. Risk Assessment and Experimental Light-Balloon Deployment of a Stratospheric Vertical VLF Transmitter. Sensors. 2023; 23(3):1073. https://doi.org/10.3390/s23031073
Chicago/Turabian StyleMiś, Tomasz Aleksander, and Józef Modelski. 2023. "Risk Assessment and Experimental Light-Balloon Deployment of a Stratospheric Vertical VLF Transmitter" Sensors 23, no. 3: 1073. https://doi.org/10.3390/s23031073
APA StyleMiś, T. A., & Modelski, J. (2023). Risk Assessment and Experimental Light-Balloon Deployment of a Stratospheric Vertical VLF Transmitter. Sensors, 23(3), 1073. https://doi.org/10.3390/s23031073