New Slip Ring Assembly Meets the High-voltage Needs of Satellites

The harsh environment of space requires that space engineers source specialized components and materials for robust and reliable satellites. Of these many specialized components, one of particular interest is the slip ring assembly, which negates wiring failures in a spinning satellite.

 

Scientists at Ecole Polytechnique Federale de Lausanne have designed a slip ring assembly said to triple the operational voltage of high-voltage satellites. Image used courtesy of EPFL

 

Recently, researchers from the Swiss Plasma Center (SPC) at Ecole Polytechnique Federale de Lausanne (EPFL) announced a newly designed slip ring assembly that can withstand the higher voltages of solar-powered satellites. In this article, we’ll discuss slip ring assemblies, their role in satellites, and the new research from SPC.

 

What Is a Slip Ring Assembly?

In many electromechanical devices, especially those that rotate, one significant reliability challenge is wiring. For example, in a device with stationary sensors mounted on a rotating surface, the wires that provide the sensors power and read I/O are likely to get twisted and eventually break in a normal configuration. Slip ring assemblies are important components to solve this issue.

 

Slip ring assembly protects wires in rotating devices. Image used courtesy of Moflon

 

A slip ring assembly is an electromechanical device designed specifically to supply power and signals from an immobile structure to a rotating device. A standard slip ring assembly consists of a series of solid metal rings around a rotating shaft. As the rings turn, a series of brush contacts, which are connected to input wires from the stationary device, maintain a constant connection with the rings, enabling the conduction of electrical signals. Each ring is then connected to output wires that are also rotatable on the shaft.

For satellites to operate and communicate with earth properly, they need to maintain the same orientation to earth. Since satellites are in orbit, their orientation will naturally change with time. To solve this problem, most satellites rotate at regular intervals to keep themselves aligned.

Slip ring assemblies allow a satellite to rotate freely without the risk of internal cables failing. In a satellite, a slip ring is used largely to provide power between the system’s onboard solar array to other components such as the onboard computer, sensors, or thruster systems. 

 

SPC Designs High-voltage Slip Ring Assembly

Slip ring assemblies operate at relatively low voltages; once a slip ring reaches 200 V, the chances of arcing increase significantly. Now, as satellites are growing more powerful and need higher voltages, the European Space Agency launched the APRIOM (Advanced sliP Ring for hIgh vOltage Mechanism) program to challenge engineers to come up with a better slip ring solution.

 

An internal look at a slip ring assembly. Image used courtesy of Fabricast

 

This week, researchers from SPC, in collaboration with Beyond Gravity and with the support of the European Space Agency, have successfully designed a new slip ring assembly that can withstand the higher voltages needed for satellites. The new ring is said to raise the voltage range of satellite slip ring assemblies from their current state of 28–100 V all the way up to 300–600 V. The ring has already functioned within 400–500 V and 8 A. 

Beyond high voltage, the slip ring assembly from SPC also exhibited high performance at low pressures resulting in a transferred power of up to 40 kW. SPC has yet to publicly release details about the specific design techniques used in the new slip ring technology.

 

The Challenges the New Slip Ring Assembly Solves

In addition to meeting the rising need for higher voltage in satellites, the SPC team's work on this slip ring assembly aims to surmount the risk of electrical breakdown in space—an event that could generate plasma that would critically damage the satellite.  

 

A satellite slip ring in the High Voltage Electrical & Power System Architecture Project (HV-EPSA). Image used courtesy of EPFL

 

Satellites undergo immense pressure changes from launch to the deep vacuum of space, which integrally affects electrical components that rely on vacuum conditions. While past solutions have relied on complex configurations of electrical circuits to manage this pressure, these circuits can interfere with the satellite's function. The new slip ring assembly can operate from extremely low pressures (10^-5 mbar) to critical pressure values (~1 mbar), solving this issue.

A ring must also make a number of turns each day—amounting to 11,000 turns after 30 years of operation—which can wear the component down over time. Yet, the new component demonstrated high mechanical reliability, maintaining operation after 25,000 turns—the equivalent of more than 60 years of standard operation in a geostationary satellite.