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SwRI Guided Implementation of CYGNSS's ADCS Subsystem

The CYGNSS ADCS consists of a Nano Star Tracker (NST), Magnetometer (Mag), Medium Sun Sensor (MSS), Coarse Sun Sensor (CSS), Reaction Wheel Module (RWM) containing three Reaction Wheels (RW), and three Torque Rods (TR). The components, along with the ADCS FSW developed by Draper Inc., allow the CYGNSS Observatory to be indefinitely controlled in Sun Point and Local-Vertical Local-Horizontal (LVLH) pointing modes as well as a Rate Damp mode. The NST serves as the primary sensor providing attitude knowledge measured in arcseconds. The MSS and Mag serve as secondary sensors. The MSS provides attitude information when the Sun causes NST outages. The Mag provides magnetic field measurements that are used primarily in rate estimation and momentum management. The CSS is only used in Sun Point as the primary sensor and is supplemented in that mode by Solar Array telemetry. The primary actuators are the three RWs contained in the RWM. These are oriented such that each wheel has a control torque about more than one of the Observatory body axes. If there is an unexpected issue with any one of the RWs the Observatory can operate with limited fidelity on any two RWs. The TRs serve as secondary actuators when in LVLH for the purposes of momentum management and primary actuators in Sun Point and Rate Damp modes when the RWs are not active. All ADCS components were selected by SwRI to be provided from external Vendors to best meet the requirements of the CYGNSS system. These requirements were developed by SwRI to guide the design of the ADCS subsystem and to provide the necessary platform for ADCS FSW to effectively control the Observatory in the context of the greater mission requirements.

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Related Links

Southwest Research Institute

Draper: Software

Blue Canyon Technologies: Star Tracker and Reaction Wheel Assembly

University of Michigan: Torque Rods

SpaceMicro: Sun Sensor

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