C H A P T E R

N ° 32

Modern vs. Autonomous Aircraft (Part 1)

Activities occurring on the Sun (i.e., solar activity) can create space weather influencing the performance and reliability of space-borne, air-borne, and ground-based technological systems. Additionally, in some instances, it can even endanger human life and health. The future indicates an ever-growing dependency on advanced technologies to enable a plethora of services and capabilities. This is especially within critical infrastructures like the aviation industry, which is on a trajectory to provide fully autonomous air vehicles (aircraft) in the future.

Some aircraft are already close to being semi-autonomous. Modern aircraft, particularly long-haul airliners, utilize semi-autonomous systems. These systems are used for much of the routine flight tasks, allowing pilots to focus on more complex aspects of flight and contingency management. While fully autonomous flights are still in development for commercial aircraft, the technology for semi-autonomous and even fully autonomous flight already exists. 

In Hoplon’ articles; C H A P T E R  N ° 27-30, we provide an introduction to the relation between space weather and the aviation industry, exploring the interaction between space weather and the Earth’s natural planetary defence systems, avionics, and aircrews. Additionally, we discuss the associated risks of financial losses caused by space weather impact and some of the currently available mitigation measures. Lastly, we discuss the effectiveness of radiation protection measures for aircrews and aircraft.

Today’s article will be the second of four articles focused on exploring the topic of autonomous aircraft and how space weather may affect them. Throughout this mini-series, we will look closer at how autonomous aircraft are classified and how they work. Additionally, we will discuss the risks and vulnerabilities of such inventions starting by looking at how space weather interacts with the data transferring process from satellites to receivers on ground and in air. Moreover, we will look at specific space weather impacts on aircraft comparing modern and autonomous air vehicles, and provide examples. Lastly, we will look closer at some of the currently available mitigation measures and the complexity of mitigation measure for autonomous vehicles.

Image Credit: Unsplash/kent_pilcher, rparmly.

How Space Weather affects modern vs. autonomous aircraft

Space weather can significantly impact air vehicles directly and indirectly through its dependency on satellite services. These vulnerabilities will only increase with the creation of autonomous aircrafts, despite the level of automation. An increase in the vulnerability of the aircraft increases the risk of potential safety issues for autonomous aircraft operations. In modern aircraft, space weather can impact in following ways:

The data transferring process

Understanding space weather impact on technologically advanced inventions such as fully autonomous aircraft demand an awareness and understanding of the signal transferring process between satellites, ground receivers, and the receivers onboard the aircraft in air, and this process in relation to space weather.

Satellites orbiting Earth are floating computers in the vast reaches of space with their primary task being to gather and disseminate information, forming an intricate constellation of data exchange. They typically send signals back to a satellite operating station on the ground, or ground receivers that furtherly transmits the data to the next satellite, which at some point in the transferring process ends up at the receiver onboard the aircraft located in air. Most communication satellites sending data back to Earth use radio frequencies (i.e., radio waves) or optical communications (i.e., Optical Communication Terminals (OCTs) (i.e., thermal radiation)).

It is through these signal transferring capabilities, that satellite data is transmitted from the space environment to ground receivers and further to ground operating stations, aircraft receivers, or other satellites. They enable services such as radio broadcasts, military communication, mobile phones, ham radio, and wireless computer networks, like the 5G networks.

*To learn more about radio waves and radiation on Earth contra radiation in space, please read: C H A P T E R  N ° 3  The Outer Space Environment: Radiation vs Space Radiation.*

However, satellites use radio frequencies and optical communication to transfer data to and from ground receivers. These are both a type of electromagnetic radiation. Similarly, space weather comprises electromagnetic energy in many wavelengths. Additionally, it is capable of emitting streams of radiation comprising electrically and magnetically charged particles into the near-Earth space environment, and through the Earth’s magnetic field and down into its atmosphere.  

During this process, the particles emitted from the Sun are capable of interfering with already present particles, changing the space and atmospheric environment. Through this change, the particles in the atmosphere are able to bend the path of radio waves or scatter them completely at some frequencies and absorb them at other frequencies. A consequence of this, is that it can cause things such as loss of Global Positioning System (GPS) signals and telecommunication blackouts.

The signal transferring process between satellites, ground receivers, and receivers onboard aircraft depending on the process carried out by the electromagnetic radiation (i.e., visible light, radio wavs, ultraviolet, gamma rays, and high energy X-rays) sent from a satellite to a receiver are, therefore, significantly vulnerable to space weather.

* To learn more about space weather, the relation between space weather and the ionosphere and the rest of Earth’s atmospheric layers, please read: C H A P T E R  N ° 1, 6 & 13. *

Image Credit: NASA: The electromagnetic spectrum (EM).

Single Event Effects (SEE)

Space weather can cause Single Event Effects (SEE), which are malfunctions in electronic devices caused by an interaction between a technological device and a single energetic particle. A single energetic particle refers to a particle, like an electron or proton, with a high kinetic energy capable of causing significant effects when interacting with a material. They are often found in space and can penetrate spacecraft materials.

Like Galactic Cosmic Rays (GCRs) and high-energy protons, these particles can deposit energy in semiconductor materials, potentially causing changes in the device's state leading to functional failures or permanent damage. Single Event Effects (SEE) can be destructive, like Single Event Latchup (SEL) or Single Event Burnout (SEB), or non-destructive, such as Single Event Upsets (SEUs).

Single Event Latchup (SEL) is a destructive phenomenon in Complementary Metal-Oxide-Semiconductors (CMOS) integrated circuits and is characteristically triggered by Single Event Upsets (SEUs). It occurs when a single energetic particle (e.g., heavy ions from Galactic Cosmic Rays (GCRs) or protons from solar flares) passes through a sensitive region of a Complementary Metal-Oxide-Semiconductor (CMOS) device, creating a type of parasitic that acts like a thyristor. A thyristor is a solid-state semiconductor device that acts as a latching electronic switch, primarily used for controlling AC power. This structure provides a low-resistance path between the power supply and ground, leading to a potentially destructive latch-up condition causing loss of functionality or permanent damage to the device. 

Single Event Latchup (SEL) is a significant threat to aircraft electronics due to its potential to cause permanent damage and system failures. The risk of a potential latch-up condition can lead to a complete failure of the affected system. In an aircraft’s, this could involve flight control, navigation, or communication systems. A complete failure in any or a combination of those systems could pose serious safety risks. Unlike non-destructive Single Event Effects (SEE), such as Single Event Upsets (SEUs), Single Event Latchup (SEL) often requires power cycling (i.e., turning the device off and then back on) if the device is not permanently damaged, or, in case of permanent damage, a replacement of the damaged component.

Single Event Burnout (SEB) is a catastrophic failure in high-voltage electronic devices. It is caused by a single energetic particle (e.g., Galactic Cosmic Ray (GCR) or alpha particle) passing through a semiconductor device. When passing through, the particles interact with the device creating a localized region of high current within the device. If this current is sustained long enough, it can lead to localized heating and melting of the device, consequently resulting in permanent damage. A Single Event Burnout (SEB) can lead to complete failure of the device, potentially causing malfunctions in electronic systems. This can have serious consequences for aircraft systems, potentially leading to catastrophic failure.

Modern aircraft and autonomous aircraft, particularly those exploring concepts like ‘More Electric Aircraft (MEA)’ and ‘All-Electric Aircraft (AEA)’, utilize high-voltage electrical systems. These high-voltage systems are crucial for supporting advanced propulsion and onboard systems. However, the high-voltage electrical systems rely on power semiconductors for various functions, such as inverters and DC-DC converters. The increasing use of electric and hybrid-electric propulsion systems in aircraft increases the reliance on power electronics. This increased dependency on power electronics increases the potential vulnerabilities and risks of space weather impact causing Single Event Burnout (SEB) in semi and fully autonomous aircraft.

*An inverter, in an electrical system, is an electronic device that converts direct current (DC) electricity into alternating current (AC) electricity. *

*A DC-DC converter is an electronic device that transforms a direct current (DC) voltage from one level to another. *

Single Event Upsets (SEUs) is a type of disruption in electronic circuits primarily caused by energetic particles (e.g.,neutrons, protons and other heavy ions) that interact with the semiconductor material in electronic devices. When these particles pass through a circuit, they can generate a large number of electron-hole pairs, which can alter the electrical charge in a sensitive region of the circuit (like a memory cell). This change in charge can flip a memory bit from 0 to 1 or vice versa, or cause a logic gate to temporarily switch its output. 

*In a semiconductor, an electron-hole pair refers to the simultaneous generation of a free electron and a positively charged "hole" when an electron is excited from the valence band to the conduction band. This occurs when an electron absorbs enough energy, such as from light or heat, to break free from its covalent bond and move to a higher energy level, leaving behind a vacancy where it was previously located. This vacancy is the "hole". *

*A memory cell in a circuit is a fundamental building block of memory, designed to store a single bit of binary information (either a 0 or a 1), whereas a memory bit in a circuit represents the smallest unit of data storage, capable of holding a single binary digit (either 0 or 1). *

*In digital circuits, a logic gate is a fundamental building block that performs a basic logical operation on one or more binary inputs (0 or 1) to produce a single binary output. *

While Single Event Upsets (SEUs) does not usually cause permanent damage, they can lead to temporary errors in data storage or processing, potentially affecting the functionality of electronic systems. It can occur in various electronic devices, such as computer memory (RAM), microprocessors, and in Field Programmable Gate Arrays.

*A Field Programmable Gate Array (FPGA) is a type of integrated circuit that can be configured by a user after manufacturing. Field Programmable Gate Arrays (FPGAs) can be reprogrammed to implement different digital logic functions. This allows for flexibility in design and the ability to update functionality after deployment. *

In avionic systems, Single Event Upsets (SEUs) can affect flight control systems and navigation systems. The consequence of Single Event Upsets (SEUs) effects on aircraft could lead to a false reading, a temporary malfunction, or, in rare cases, a more significant issue impacting flight safety. 

Single-Event Effects (SEE), destructive or non-destructive, can present a significant risk to autonomous air transportation by disrupting critical systems like navigation, communication, and onboard decision-making algorithms. These disruptions, caused by temporary faults or permanent damage to flight control systems, can potentially lead to loss of control or system failure. Given that autonomous air vehicles depend heavily on sensors, communication links, and real-time data processing, Single-Event Effects (SEE) can compromise the accuracy and reliability of these components, affecting overall safety and mission success.

To be continued…

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