Research Terms
Mechanical Engineering Aerospace Engineering
This three-flywheel assembly reduces attitude jitter caused by momentum actuators in satellites, improving its on-orbit pointing stability. Spacecraft with momentum actuators suffer form attitude jitter and high frequency oscillations due to imbalance in the rotors of momentum actuators. These problems can interfere with a satellite’s orientation, imaging, and scientific experimentation, sometimes causing the whole spacecraft to become nonfunctional. Existing jitter control using active isolation techniques help to address some of the effects of jitter but are only effective in a localized area and cannot prevent wear and tear on the entire space system. Further, these systems are expensive and require a sophisticated control system. The three-flywheel assembly developed by researchers at the University of Florida provides continuous jitter control for higher performance and longer use. The three-flywheel assembly replaces the single-flywheel system and hence provides continuous on-orbit balancing capability. Existing systems with one flywheel may suffer from increased jitter over time due to imbalance growth, sometimes rendering the satellite inoperative. The use of multiple flywheels addresses this issue and the further adds layers of protection to the overall system, allowing for continued use of the satellite if one or even both of the other flywheels fail. The system also provides a cost advantage over existing active isolation techniques.
A three-flywheel assembly reduces jitter and increases satellites’ performance
University of Florida researchers have developed a three-flywheel assembly that reduces jitter in small satellites. The system includes two similarly balanced flywheels to counter the effect of residual imbalance from the first one. It cancels out jitter at the source to minimize static and dynamic imbalances while adapting to minor changes in the individual rotor imbalances that occur over time. The redundancy of multiple flywheels increases reliability and reduces the amplitude of jitter by manipulating phase difference using controlled balancing techniques.
This automated measuring device obtains spectral data from various azimuth and elevation angles around a specific object to generate a bidirectional reflectance distribution function (BRDF) so that scientists can better understand, view, and predict the physical location of the object if it were in orbit with Earth. Simply put, objects look different when viewed from different angles and when illuminated from different directions. BRDF is the technical, objective measure of reflectance and illumination that causes those different views and is a critical step in space situational awareness (SSA), which involves tracking objects in orbit with Earth. The space community is seeking more efficient approaches for BRDF characterization due to increasing space debris and launches of small satellites. Available devices for BRDF are based on a fixed item and a mobile camera taking images from different elevation angles, which does not efficiently calculate a BRDF. Researchers at the University of Florida have developed a device that uses fixed multiple cameras coupled with a rotary table for moving the item with respect to the camera, thus reducing the time required for complete imaging of an object and increasing the overall productivity of BRDF measurements.
Automated generation of BRDF measurements
This BRDF measuring device consists of spectroscopes attached to a rigid structure that defines the angle and elevation for each spectroscope. The object of interest is placed on a turntable illuminated by a xenon arc lamp, and it is incrementally rotated to the desired azimuth angles to attain accurate spectral measurements. These measurements are recorded at every azimuth angle and processed to calculate the BRDF. A BRDF describes how much light is reflected when light makes contact with a certain material and is a critical step in determining how the object will behave and interact in space. This device increases productivity and provides a new approach for scientists to quickly learn the BRDF of any object.
