Space exploration requires robust, reliable, and long-lasting technologies, especially for human-safety-critical systems utilized on extended missions. While the safety-critical systems have traditionally leveraged simple-and-dependable, tried-and-true solutions, significant performance and SWaP (size, weight, and power) gains can be realized by leveraging the vast improvements in computing power and electronics’ reliability in the past few decades.
These advances have shifted the focus toward digital and software controls, enabling step changes in performance. Hydraulic or pneumatic legacy systems are replaced with electrical systems and mechanical means of flow control, such as valves are replaced with variable speed motors.
This shift of electrification and optimization is highlighted by some of the recent improvements in the environmental controls on the International Space Station (ISS). The makeup of the breathable atmosphere must be managed, and trace contamination must be reduced to acceptable levels.
The Four Bed Carbon Dioxide Scrubber (FBCO2) system currently in advanced development and testing on the ISS is the latest iteration of the CO2 removal system. The FBCO2 system draws air from the cabin and separates water and CO2, which can then be reused for other purposes or vented as waste. Within the FBCO2 system, the Calnetix In-line blower/circulator is the mechanism which drives air flow through the system.
The In-Line blower system, which includes a compact blower on magnetic bearings and an integrated dual controller, leverages a variable high-speed permanent magnet (PM) motor and active five-axis active magnetic bearing (AMB) system. This system represents a step change toward electrification and optimization. Previous CO2 removal solutions utilized passive gas foil bearings that float the rotor on a layer of gas once the rotor is spinning.
While this was a simple solution from a controls perspective and requires no electronics to manage the bearing system, gas bearings can be susceptible to contaminants in the process airstream, are prone to wear with many start/stop cycles, and require a minimum process gas pressure and rotor speed to operate. Conversely, AMBs require relatively complex electronic and software controls, but can function at very high speeds, provide significantly improved life with no mechanical limits on cycles, are tolerant to particle contaminants in the process airstream, and can operate when exposed to vacuum.
The main design challenge was to fit the new magnetic bearing blower into the same space as the gas-bearing-supported heritage blower. The AMB system with position sensors and backup bearings had to be miniaturized to fit into a highly constrained space.
To circulate environmental air through the FBCO2 system, the blower leverages an overhung radial impeller spinning at up to 60,000 rpm. From the impeller, flow is directed through the housing and around the centrally located motor section. Keeping the motor effectively sealed from the process flow keeps the motor and bearing components free from erosion or accumulation of contaminants.
Process flow around the motor and magnetic bearings cavity also provides heat rejection for thermal management of the stator. Backup bearings provide a mechanical backup function in the case of shock loads exceeding the load capacity of the magnetic bearings, or any time the active magnetic bearing system experiences a fault or loss of power.
To take advantage of the frictionless magnetic bearings system, the PM motor can operate at very high speeds, providing improved volumetric and gravimetric power density. The radial flux surface-mount PM rotor utilizes a carbon fiber sleeve to provide rotor-dynamic stiffness and magnet retention while providing improved permeability. With windage as the only major mechanism for loss, a motor such as this can exceed 98 percent efficiency.
From a controls perspective, the AMB is significantly more complex than legacy mechanical bearings or air bearings. Speed and position sensors in the stator are utilized to determine velocity and orientation of the rotor. Electromagnetic actuators provide the force to center the rotor, counteract dynamic loads, and safely maintain rotor position with five axes of control. Permanent magnets can be used to bias the AMB system to offset static loads and reduce control current.
The Calnetix dual electronic controller ties all of this together, taking inputs from the sensors, driving the speed of the motor, and controlling the relative position of the rotor. The added complexity comes with the advantages of the ability to actively tune the performance of the motor, real-time motor status monitoring, and prognostic health monitoring of the blower as well as the connected system.
Long-duration human habitation in space or on other planets will require efficient, robust, and highly reliable solutions for the processing of breathable atmosphere and other health-critical systems. “The unique blower system was successfully installed by NASA on ISS and has been operating continuously since February 2023,” said Vatche Artinian, CEO, Calnetix Technologies.
“This is the first time a five-axis, magnetically levitated system has been commissioned for use in an orbital application and shows promise as a technology, which can be used across many other applications, such as fluid pumps, reaction wheels, and gyroscopes that challenge conventional bearing technologies,” Artinian added.
Following the validation phase in the current ISS system, AMB and related high-speed PM motor technologies could further be utilized in future space missions, such as Artemis, Orbital Reef, and Mars missions.
This article was written by Matthew Farides, Director of Business Development, Calnetix Technologies (Cerritos, CA). For more information, visit here .