Aaron J. Dando Principle Supervisor: Werner Enderle Australian Cooperative Research Centre for Satellite Systems (CRCSS) at the Queensland University of Technology (QUT) Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 1
Overview Introduction JAESat Mission Attitude Control System Concept Simulation Results and Discussion Conclusion Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 2
Introduction The Attitude Control System Concept for the Joint JAESat is a joint project between the Queensland University of Technology (QUT) and the Australian Space Research Institute (ASRI) QUT is responsible for the JAESat project since late 2003 The JAESat micro-satellite project main objectives are: Design, develop, manufacture, test, launch and operate a microsatellite Develop payloads with a technological and scientific relevance Use JAESat as a sensor in space and GNSS technology demonstrator Educate young engineers in space activities Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 3
JAESat Concept Formation Flying of Two Micro-Satellites Master is 390mm cube Slave is 390mm x 390mm x 195mm Tray based structure (see image left) Master Three-axis Stabilized Slave is Gravity-Gradient Stabilized Power generated by Master: 22 Watts (Orbit average) Power generated by Slave: 10 Watts (Orbit average) Polar Sun-Synchronous Orbit (800 km) Operational Lifetime: 12 15 month Operations via Ground Station at QUT Master Slave Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 4
JAESat Experiments Testing and evaluation of QUT GPS receiver SPARx Position, Velocity and Time On-board Orbit Determination based on GPS Three-axis Attitude Determination based on GPS Testing of a new integrated Star Sensor / GPS navigation sensor concept for three-axis attitude determination Relative navigation between JAESat Master and Slave satellites In orbit testing and validation of JAESat ACS concept Atmospheric research limb sounding Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 5
Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 6
ACS Requirements Attitude Control Accuracy (per axis) Master: < 5 deg (3σ) Slave: < 10 deg (3σ) Attitude Det. Accuracy (per axis) Master: < 0.5 deg (3σ) Slave Satellite Gravity-Gradient Stabilized No Libration/Nutation Damper and No Extendable Boom No Attitude Sensors or Actuators Mission Requirement for an Inter-Satellite Link is a Key Driver for the ACS Concept Inter-Satellite Link Uplink/Downlink Master Satellite Three-Axis Stabilized (Zero Momentum) Capable of Frequent and Precise Attitude Maneuvers using Magnetic Coils Very Accurate QUEST AD using Star Sensor Observations Optional GPS Based AD for Technology Test and Validate Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 7
JAESat ACS Modes Detumble Mode Damp the satellite rates prior to slewing/tracking maneuvers Master/Slave are coupled Ground station contact established when rates are sufficiently low Reorientation Mode Satellite performs an attitude maneuver to achieve an earth-pointing attitude Master and slave are coupled Once required attitude is achieved the separation sequence is executed Normal Mode Master and Slave are separated Inter-satellite link for communications Master is three-axis stabilized in earthpointing orientation Slave is gravity-gradient stabilized Test and validate the innovative star sensor / GPS attitude sensor concept Conduct relative navigation experiments Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 8
JAESat Master Satellite ACS Configuration 4 x GPS Antennae (+z face) Sensors Time & Orbit Propagator Target Motion Quaternion & Magnetic Field Model Actuators 1 x Star Sensor (+z) GPS Attitude Sensor Star Sensor Sensor Selection Attitude Determination Control Law Magnetic Coils ACS Input ACS Output 3 x Magnetic Coils (+x, +y, +z) Kayser-Threde KM1301 Star Sensor GPS Attitude Sensor Antenna Array Magnetic Coils (Air Coils) Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 9
Operational Mode Sensors Actuators Control Laws Attitude Determination Algorithms Comments Detumbling Star Sensor 3 x Magnetic Coils B-Dot N/A Rates < 0.2 deg/sec (end of detumbling) Reorientation Star Sensor 3 x Magnetic Coils Sliding Mode Tracking Law or Optimal Tracking Law QUEST Algorithm Angular rate estimation based on internal algorithm or by considering attitude motion b/w sampling epochs Normal Star Sensor GPS Attitude Sensor 3 x Magnetic Coils Sliding Mode Tracking Law or Optimal Tracking Law or QUEST Algorithm (Star Sensor) Least Squares Algorithm (GPS) Testing of the GPS attitude sensor requires frequent attitude maneuvers to test sensitivity to rotation rates. LQR Control Law Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 10
Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 11
Attitude Determination of JAESat based on GPS SD Measurements 3 Antennas, 2 Baselines Baseline length 36 cm (each) Multipath error on SD 5 mm Attitude determination error is < 1 deg per axis Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 12
Detumbling Reorientation Normal Mode Simulation Mode Simulation Spacecraft Variable Reorientation structure rates Mode are control damped law law with Attitude B-Dot error control is error < 0.1 lawis deg < 0.05 (3σ) per deg Resulting axis (3σ) per rates axis are < 0.2 deg/sec per Settling axis time is approx. 2 orbits Actuator LQR control power law consumption may be usedis reasonable very low! Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 13
Conclusion & Future Directions for Research Novel ACS concept/design for JAESat has been proposed which meets performance requirements Next step is to integrate and test ACS software with flight computer GNC research will be performed in the following areas: Optimal controls for large-angle attitude tracking maneuvers Efficient and robust star identification techniques, and star sensor based attitude determination Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 14
Special thanks to the CRCSS and all project partners for their valuable contributions to the JAESat project. Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 15
If you would like to know more about JAESat, please visit the JAESat web site or contact the JAESat Project Manager Assoc. Prof. Werner Enderle Phone: +61 7 3864 1436 Email: w.enderle@qut.edu.au http://watt.lab.eese.bee.qut.edu.au/jaesat/ Aaron Dando, CRCSS/QUT, 19 th AIAA/USU Small Satellite Conference, Logan, Utah, USA, 8-11 Aug 2005 16