Spacecraft Bus / Platform

Transcription

1 Spacecraft Bus / Platform Propulsion Thrusters ADCS: Attitude Determination and Control Subsystem Shield CDH: Command and Data Handling Subsystem Payload Communication Thermal Power Structure and Mechanisms Communications Subsystem Up-link and Down-link Satellite FOV Frequency: S-band (2 GHz), X-band (8 GHz) and Ku (12 GHz). 1

2 TV Satellit 3000 W 200 W 2

3 Command and Data Handling (CDHS) Command node (Payload / Bus) Telemetry Housekeeping (HK) 3

4 Spacecraft Bus / Platform Propulsion Thrusters ADCS: Attitude Determination and Control Subsystem Shield CDH: Command and Data Handling Subsystem Payload Communication Thermal Power Structure and Mechanisms Orbit Perturbations Secular variations langsomt, lineært Short-period variations Long-period variations Element Cyclic variations Short Period Long Period Orbit Time 4

5 Attitude Determination and Control ADCS / ACS The attitude determination and control system (subsystem) - ADCS shall: Stabilize the spacecraft and Orient it is the desired direction Determine the attitude using sensors Control the spacecraft using actuators Spacecraft attitude Control Determination Attitude Attitude Determination Attitude sensor Attitude Control Attitude control torque 5

6 Spacecraft attitude Attitude Determination Attitude Control Attitude sensor Attitude control torque Control Determination Attitude Disturbance torques: Cyclic sinusoidal Secular drift Jitter noise Z Roll Attitude coordinate system: 3-axis Y Yaw X Looking along Z Pitch Pitch Yaw Roll 6

7 Attitude Determination Requirements Accuracy: How well is the orientation of the spacecraft known? Range: Range over which the accuracy must be met Attitude Control Requirements Accuracy: How well can the orientation of the spacecraft be controlled? Range: Range over which the control performance must be met Jitter: Short-term (high-frequency) motion Drift: Slow (low-frequency) motion Settling Time: The time needed to recover from maneuvers or upsets 7

8 Jitter: White noise Slow drift: Secular 8

9 Cyclic: Periodic Jitter: White noise 9

10 Slow drift: Secular Cyclic: Periodic 10

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13 Stability of a control system Spacecraft attitude Attitude Determination Attitude Control Attitude sensor Attitude control torque Control Determination Attitude Disturbance torques: Cyclic sinusoidal Secular drift Jitter noise A Simple Simulation of a Control System x( t dt) x( t) dx( t, dt) T ( x) x( t) dx( t, dt) ( x( t t) ) T S T t S T Gain for guiding Time delay for guiding Scatter on Attitude determination (sensor) Scatter on Attitude control (torque) 13

14 Attitude determination and no active attitude control 0.08, t 10 dt, 0, 0 S T Attitude determination and active attitude control 0.08, t 10 dt, 0, 0 S T 14

15 0.08, t 10 dt, 0, 0 S T 15

16 0.08, t 10 dt, 0, 0 S T 0.08, t 10 dt, 0, 0 S T 16

17 17

18 0.02, t 10 dt, 0, 0 S T 0.05, t 10 dt, 0, 0 S T 18

19 0.08, t 10 dt, 0, 0 S T 0.10, t 10 dt, 0, 0 S T 19

20 20 0 0,, 10.15, 0 T S dt t 0 0,, 2.00, 1 T S dt t T S t t x dt t dx t x dt t x ) ) ( ( ), ( ) ( ) (

21 21 T S t t x dt t dx t x dt t x ) ) ( ( ), ( ) ( ) ( 0 0,, 2.50, 0 T S dt t T S t t x dt t dx t x dt t x ) ) ( ( ), ( ) ( ) ( 0 0,, 2.15, 0 T S dt t

22 0.00, t 2 dt, 0, 0 S T x( t dt) x( t) dx( t, dt) ( x( t t) ) S T Spacecraft attitude Attitude Determination Attitude Control Attitude sensor Attitude control torque Control Determination Attitude Disturbance torques: Cyclic sinusoidal Secular drift Jitter noise 22

23 Attitude Control Modes Attitude Control Modes De-tumbling Momentum dumping Raw Attitude (power req.) 23

24 Attitude Control Methods Control Moment Gyros Momentum Wheels Reaction Wheels 24

25 ACS Sensors 25

26 Hubble's Instruments: FGS - Fine Guidance Sensors Hubble has three Fine Guidance Sensors (FGS'es) onboard. FGS Facts Instrument type Weight Dimensions Field of view Wavelength range Resolution Astrometric interferometers 220 kg 0.5x1x1.6 m 69 arcminutes (only 5x5 arcseconds at any one time) 4670 to 7000 Angstroms arcseconds 26

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28 Hubble's Instruments: FGS - Fine Guidance Sensors Resolution arcseconds Gyroscopes Hubble has six gyroscopes, or gyros, on board. Two of these are needed at all times to keep the telescope pointing in the right direction and to keep the telescope stable. Inside a gyro a wheel is spinning more than 19,000 times per minute (315 Hz) and there are electronics to detect the very small deflections of the wheel's axis. 28

29 Pioneer 10 Spin stabilized at 4.8 rpm (spin period near the end of the mission being 14.1 seconds). Attitude controlled by direction finding on communications radio beam. Hydrazine propulsion with 6 x 1-lbf thrusters. One star (Canopus) sensor and two sun sensors for attitude knowledge. 29

30 Voyager 1 and 2 Voyager 2 3-axis stabilized to within 0.1 deg. using hydrazine thrusters, star tracker (Canopus), sun sensors, and high-gain antenna. 30

31 Ørsted 3-axis stabilized Gravity gradient and magnetorquers Local orbit plane SIM: 1.2 arcsec ACS: ~ 5 degrees 31

32 Kepler Spacecraft Bus Kepler reaction wheels Kepler Star Trackers Kepler reaction wheel 32

33 Kepler Photometer 1.4 m diameter primary mirror 42 CCDs read every 3 seconds Focal plane electronics 15 minute integrations Sunshade 0.95 m diameter Schmidt corrector Focus mechanisms Radiator and heat pipe for cooling focal plane Graphite cyanate structure 105 sq deg FOV Focal plane assembly: CCDs, field flattening lenses fine guidance sensors Focal Plane Assembly 42 CCDs with Field Flattener Lenses 33

34 Focal Plane Assembly 42 CCDs with Field Flattener Lenses Four fine guidance sensor (FGS) CCD modules are mounted to the corners of the Invar substrate to gather additional pointing information for the Attitude Control System in order to attain the required <2.5 milli-pixel pointing accuracy Thermal Subsystem Heat and heat transport Passive and active thermal control Electronics operate at room temperature! (Venera, Mars Rovers, Russian sat.) Solar Panels, Batteries Surface coating/insulation and degradation Eclipses, Interplanetary journeys 34

35 Power Subsystem Power generation Solar 1367 W/m2 -- Radioisotope Thermoelectric (Voyager, Galileo ) Solar Arrays Batteries (NiCd, Li-Ion) Power Control Unit (PCU), Converter Structure and Mechanisms Structure and protection Release mechanism (separation) Centre of gravity, radiation shield Damping of oscillations. 35

36 Spin-stabilized Payload: Nuclear Detection 221 kg, 90 W Spin-stabilized Payload: Radiation Field 64.6 kg 36

37 Spin-stabilized Payload: Communication 523kg, 500 W Kepler Photometer 1.4 m diameter primary mirror 42 CCDs read every 3 seconds Focal plane electronics 15 minute integrations Sunshade 0.95 m diameter Schmidt corrector Focus mechanisms Radiator and heat pipe for cooling focal plane Graphite cyanate structure 105 sq deg FOV Focal plane assembly: CCDs, field flattening lenses fine guidance sensors 37

38 Sunshade 1.4 m Primary Mirror 38

39 1.4 m Primary Mirror 1.4 m Primary Mirror 39

40 1.4 m Primary Mirror 95 cm Schmidt Corrector 40

41 95 cm Schmidt Corrector 95 cm Schmidt Corrector 41

42 One Kepler CCD: 50x25 mm (2200x1024 pixels) Field Flattener Lenses at Focal Plane 42

43 Focal Plane Assembly 42 CCDs with Field Flattener Lenses Focal Plane Assembly 42 CCDs with Field Flattener Lenses 43

44 3-axis control Payload: Earth Observation 940 kg, 990 W 44

45 3-axis control Payload: Comminucations (TDRS) 2200 kg, 1700 W Rømer ( ) 100 kg ADCS: Attitude Determination and Control Subsystem Propulsion Thrusters Shield CDH: Command and Data Handling Subsystem Communication Thermal Power: 100 W Structure and Mechanisms 45