Session
Poster Session 3
Location
Salt Palace Convention Center, Salt Lake City, UT
Abstract
Small satellites have become prevalent within the aerospace industry due to their ability to provide an inexpensive and easily accessible platform for technology demonstrations. Reaction wheels are typically selected for these missions’ attitude and rate control due to their small form factor. Their downside, however, is high cost, upwards of thousands of dollars, which does not align well with the low budget of many small satellites. To address this issue, alternative momentum-actuator technologies can be implemented that, similar to traditional reaction wheels, impart torques for actuation but require much less mass, volume, power, and money. This manuscript discusses the implementation and testing of one such low-cost alternative, a hard disk drive (HDD) reaction wheel system, on Sailing to the Stars, a 1U CubeSat testing various deployers for shape-memory alloy light sails onboard the International Space Station (ISS). To mimic a spin-stabilized spacecraft, Sailing to the Stars spins about its major axis at a rate of 4 rad/s. This is achieved through the implementation of a 2.5-inch HDD reaction wheel system and inertial measurement unit (IMU). Two types of controllers were implemented on the HDD: a closed loop controller and in case of hardware failure, an open loop controller. The closed loop controller uses gyroscopic feedback from the IMU to calculate a stabilization torque with a proportional control law. The gain is applied to the change in spin speed of the HDD directly proportional to the torque that the HDD imparts onto the deployer. This results in a PWM value for the HDD ranging from 1000 μs to 2000 μs and is sent to the HDD via an Electronic Speed Controller (ESC). In case of IMU failure, the system triggers open loop control commanding a fixed final PWM value calculated using conservation of angular momentum. The reaction wheel system hardware consists of the HDD, IMU, ESC, and Feather M0 microcontroller. The HDD’s electrical capabilities were initially characterized through current draw and voltage measurements at various PWM values. The engineering design unit was assembled and tested in a simulated environment consisting of fishing line stabilizing the deployer about its major axis and attached to a swivel hook to allow for free rotation about this axis. A secondary test bed was developed via an air bearing to simulate a zero-gravity environment with no motion constraints about any of the satellite’s axes. Testing was conducted to tune the proportional gain heuristically until desired rise time, settling time, and steady state error were achieved. These tests were augmented with disturbances including imitation of external torques resulting from astronauts holding and releasing the deployers. These tests showed promising results with successful rate control of the deployer using the HDD reaction wheel system. Sailing to the Stars will be launching to the ISS in 2025 at which point the HDD performance in a true zero-gravity environment can be assessed to demonstrate the viability of the HDD reaction wheel system for future small satellites.
Document Type
Event
Hard Disk Drive Reaction Wheel System for CubeSat Architecture
Salt Palace Convention Center, Salt Lake City, UT
Small satellites have become prevalent within the aerospace industry due to their ability to provide an inexpensive and easily accessible platform for technology demonstrations. Reaction wheels are typically selected for these missions’ attitude and rate control due to their small form factor. Their downside, however, is high cost, upwards of thousands of dollars, which does not align well with the low budget of many small satellites. To address this issue, alternative momentum-actuator technologies can be implemented that, similar to traditional reaction wheels, impart torques for actuation but require much less mass, volume, power, and money. This manuscript discusses the implementation and testing of one such low-cost alternative, a hard disk drive (HDD) reaction wheel system, on Sailing to the Stars, a 1U CubeSat testing various deployers for shape-memory alloy light sails onboard the International Space Station (ISS). To mimic a spin-stabilized spacecraft, Sailing to the Stars spins about its major axis at a rate of 4 rad/s. This is achieved through the implementation of a 2.5-inch HDD reaction wheel system and inertial measurement unit (IMU). Two types of controllers were implemented on the HDD: a closed loop controller and in case of hardware failure, an open loop controller. The closed loop controller uses gyroscopic feedback from the IMU to calculate a stabilization torque with a proportional control law. The gain is applied to the change in spin speed of the HDD directly proportional to the torque that the HDD imparts onto the deployer. This results in a PWM value for the HDD ranging from 1000 μs to 2000 μs and is sent to the HDD via an Electronic Speed Controller (ESC). In case of IMU failure, the system triggers open loop control commanding a fixed final PWM value calculated using conservation of angular momentum. The reaction wheel system hardware consists of the HDD, IMU, ESC, and Feather M0 microcontroller. The HDD’s electrical capabilities were initially characterized through current draw and voltage measurements at various PWM values. The engineering design unit was assembled and tested in a simulated environment consisting of fishing line stabilizing the deployer about its major axis and attached to a swivel hook to allow for free rotation about this axis. A secondary test bed was developed via an air bearing to simulate a zero-gravity environment with no motion constraints about any of the satellite’s axes. Testing was conducted to tune the proportional gain heuristically until desired rise time, settling time, and steady state error were achieved. These tests were augmented with disturbances including imitation of external torques resulting from astronauts holding and releasing the deployers. These tests showed promising results with successful rate control of the deployer using the HDD reaction wheel system. Sailing to the Stars will be launching to the ISS in 2025 at which point the HDD performance in a true zero-gravity environment can be assessed to demonstrate the viability of the HDD reaction wheel system for future small satellites.
