Electric propulsion systems work by converting electrical energy into thrust. They accelerate a propellant, often a noble gas like xenon, to very high speeds, generating the necessary force to move the spacecraft. While these systems produce lower thrust compared to traditional chemical propulsion, their efficiency is much higher, making them ideal for long missions where conserving fuel is critical. These systems can be broadly categorized into electrostatic thrusters, such as ion thrusters; electromagnetic thrusters, like Hall effect thrusters; and electrothermal thrusters, which heat a propellant electrically before expelling it to generate thrust.

Figure 1: How electric propulsion works (Credit: Purdue University) 

To ensure the success of such systems, highly efficient power electronics are essential. These electronics must operate reliably in the harsh environment of space, handling extreme temperatures, and radiation, and conform to the strict weight and size requirements. Historically, silicon-based semiconductors have been the go-to for power electronics in space applications. However, as mission demands grow more complex, the limitations of silicon—such as efficiency losses, thermal management challenges, and limited high-temperature operation—are becoming more apparent.

SiC has an edge in spacecraft power electronics

This is where SiC technology offers a significant advantage. SiC-based power converters represent a substantial leap forward in the performance of spacecraft power management systems. One of the primary benefits of SiC is its ability to operate at higher efficiencies compared to traditional silicon. This efficiency is crucial in space, where every bit of saved energy can extend the mission's duration. SiC devices achieve this by operating at higher frequencies and temperatures, which drastically reduces power conversion losses. For long-duration missions, where power management is a critical factor, this efficiency is invaluable.

Another significant advantage of SiC is its superior thermal performance. Unlike silicon, SiC can function effectively at much higher temperatures. This characteristic reduces the need for complex cooling systems, which are typically required to prevent silicon devices from overheating. By simplifying thermal management, SiC contributes to overall system reliability and longevity, which are essential for missions that extend far into space.

The miniaturization potential of SiC-based electronics is another crucial benefit. SiC allows for the development of smaller, lighter power systems, which is particularly advantageous in space missions where every kilogram saved can be used for additional fuel or scientific instruments. The reduced size and weight of SiC-based systems directly translate into increased payload capacity, longer mission durations, or the ability to explore further into space.

SiC in electric propulsion systems

Specifically, in electric propulsion systems, SiC-based converters ensure stable and reliable thruster operation over extended periods. These systems need to be both efficient and durable, given the long-term nature of most deep-space missions. The high efficiency of SiC devices also means less heat is generated during power conversion, which is critical in the vacuum of space, where dissipating heat is particularly challenging. By minimizing heat production, SiC helps maintain the spacecraft's thermal balance, further enhancing mission reliability and longevity.

In high-voltage applications, such as those required by ion and Hall effect thrusters, SiC excels due to its high breakdown electric field strength. SiC devices can handle the elevated voltages necessary for these thrusters more effectively than traditional silicon devices. This capability allows for the development of more powerful and efficient thrusters that can operate at higher voltages without compromising the system's reliability. The ability to manage high voltages is particularly important for extended missions, where component failure due to voltage stress could jeopardize the entire mission.

Additionally, SiC's inherent radiation resistance makes it ideal for deep-space missions. Spacecraft operating far from Earth are exposed to high levels of radiation, which can degrade or damage traditional electronic components. SiC's robustness against radiation ensures that the spacecraft's power systems remain operational, even in the harshest environments. This radiation hardness is critical for maintaining the integrity of high-voltage power supplies in electric propulsion systems, ensuring the spacecraft's continued operation throughout its mission.

Precision in thruster control is another area where SiC technology shines. The superior switching performance and faster response times of SiC devices enable more accurate voltage and current control, which is essential for fine-tuned adjustments during space maneuvers. The compact nature of SiC-based electronics also allows for easier integration into spacecraft designs, reducing the length of power cables and associated power losses. This precision and compactness are particularly valuable in missions that require detailed orbital adjustments or extended periods of thrusting.

Moreover, SiC-based inverters and motor drives are critical for the efficient operation of propellant feed systems, which are necessary for delivering propellant to the thrusters in electric propulsion systems. SiC inverters can operate at higher frequencies, improving the efficiency of these motor drives and allowing for a reduction in the size of passive components like inductors and capacitors. The reliability of SiC, combined with its superior thermal properties, ensures the consistent operation of propellant feed systems, which is crucial for mission success.

Reliability of SiC in Thermal Stress and Radiations

The integration of SiC technology into electric propulsion systems has far-reaching implications for the capabilities of modern spacecraft. The increased efficiency, reduced size and weight, and enhanced reliability provided by SiC allow for more ambitious mission designs. Missions can be extended in duration, as the higher efficiency and reduced power losses ensure that spacecraft can operate longer without depleting their energy reserves.

The weight savings achieved through the use of SiC-based power electronics can be redirected towards carrying additional scientific instruments or payloads, thereby increasing the scientific return of the mission. The precise control enabled by SiC also allows spacecraft to perform more complex maneuvers with greater accuracy, which is essential for missions requiring detailed mapping of celestial bodies or precise positioning in orbit. Furthermore, the high reliability of SiC in the face of radiation and thermal stress significantly reduces the risk of mission failure due to power system malfunctions, making it a cornerstone of modern spacecraft design.