Solar Dynamics Observatory

Transcription

1 Solar Dynamics Observatory Solar Dynamics Observatory System Concept Review Helioseismic and Magnetic Imager Draft Presentation 21 March 2003 Hansen Experimental Physics Laboratory Stanford, CA Lockheed Martin Space Systems Company Solar & Astrophysics Laboratory Palo Alto, CA - Scherrer 1

2 Science Objectives B Solar Dynamo J Sunspot Dynamics C Global Circulation 60 Latitude I Magnetic Connectivity -1 v (km s ) Year A Interior Structure -1.4 D Irradiance Sources 2.0 B (kg) -2.0 Flux (kg) Ic to disk center 10Mm H Far-side Imaging E Coronal Magnetic Field NOAA 9393 Far-side G Magnetic Stresses F Solar Subsurface Weather - Scherrer 2

3 Top Down View of Science Requirements NAS/NRC and NASA Roadmap Living With a Star SDO Mission Investigation Science Objectives Science Data Products Observations Observables Instrument Data Instrument Concept Instrument Requirements - SDO interface SDO S/C Concept Ground System - Scherrer 3

4 Science Objectives Convection-zone dynamics and the solar dynamo Structure and dynamics of the tachocline Variations in differential rotation Evolution of meridional circulation Dynamics in the near surface shear layer Origin and evolution of sunspots, active regions and complexes of activity Formation and deep structure of magnetic complexes of activity Active region source and evolution Magnetic flux concentration in sunspots Sources and mechanisms of solar irradiance variations Sources and drivers of solar activity and disturbances Origin and dynamics of magnetic sheared structures and d-type sunspots Magnetic configuration and mechanisms of solar flares Emergence of magnetic flux and solar transient events Evolution of small-scale structures and magnetic carpet Links between the internal processes and dynamics of the corona and heliosphere Complexity and energetics of the solar corona Large-scale coronal field estimates Coronal magnetic structure and solar wind Precursors of solar disturbances for space-weather forecasts Far-side imaging and activity index Predicting emergence of active regions by helioseismic imaging Determination of magnetic cloud Bs events - Scherrer 4

5 Science Data Products Science Data Products High-level data products which are input to the science analyses. These are time series of maps of physical quantities in and on the Sun. Internal rotation Ω(r,Θ) (0<r<R) Internal sound speed, cs(r,θ) (0<r<R) Full-disk velocity, v(r,θ,φ) and sound speed, cs(r,θ,φ) maps (0-30Mm) Carrington synoptic v and cs maps (0-30Mm) High-resolution v and cs maps (0-30Mm) Deep-focus v and cs maps (0-200Mm) Far-side activity index Line-of-Sight Magnetic field maps Vector Magnetic Field maps Coronal magnetic Field extrapolations Coronal and Solar wind models Brightness Images Context Magnetograms - Scherrer 5

6 Science Observations Science Objectives Implies Science Data Products Implies Observations, e.g. HS-3 Requires Observables Table shows which Observations are needed for which Science Data Products which are needed for which Science Objectives Rows are Science Objectives Columns are Science Data Products Text in cells identifies Observation types - Scherrer 6

7 Observables Requirements - Scherrer 7

8 Observables Requirements - Scherrer 8

9 Observables Requirements - Scherrer 9

10 Source of Requirements Investigation Science Objectives Duration of mission Completeness of coverage Science Data Products Roll accuracy Time accuracy (months) Observations Duration of sequence Cadence Completeness (95% of data sequence) Noise Resolution Time accuracy (days) Observables Sensitivity Linearity Acceptable measurement noise Image stability Time rate (minutes) Completeness (99.9% of observable data in 90s) Orbit knowledge Instrument Data Accuracy Noise levels Completeness (99.99% of data in filtergram) Tuning & shutter repeatability Wavelength knowledge Image registration Image orientation jitter Instrument Concept Mass Power Telemetry Envelope Sub-system requirements CCD: Thermal environment ISS: pointing drift rate, jitter Legs: pointing drift range to SDO Interface Requirements Ground System Processing System Data Distribution - Scherrer 10

11 Key Requirements - Scherrer 11

12 Instrument Concept The instrument is an evolution of the successful Michelson Doppler Imager instrument which has been operating on the SOHO spacecraft for over seven years. The raw observables are filtergrams of the full solar disk taken with a narrow band (~ 0.1 A bandpass) tunable filter in multiple polarizations. The primary science observables are Dopplergrams, line-of-sight magnetograms, vector magnetograms and continuum images computed from a series of filtergrams. Some of the key instrument design drivers include maintaining uniform image quality and performance through detailed optical and thermal design and rigorous testing. The vector magnetic field measurements are best decoupled from the helioseismology measurements, and a two camera design results to maintain image cadence and separate the two primary data streams. - Scherrer 12

13 Optical Layout - Scherrer 13

14 Optics Package Layout - Scherrer 14

15 Design Improves on MDI The common design features based on MDI: Front window designed to be the initial filter with widest bandpass. Simple two element refracting telescope. Image Stabilization System with a solar limb sensor and PZT driven tip-tilt mirror. Narrow band tunable filter consisting of a multi-element Lyot filter and two Michelson interferometers. Similar hollow core motors, filterwheel mechanisms and shutters. The improvements from MDI: The observing line is the Fe I nm absorption line instead of the Ni I nm line. This observing line is used for both Doppler and magnetic measurements. Rotating waveplates are used for polarization selection instead of a set of polarizing optics in a filterwheel mechanism. An additional tunable filter element is included in order to provide the measurement dynamic range required by the SDO orbit. The CCD format will be 4096x4096 pixels instead of 1024x1024 pixels in order to meet the angular resolution requirements. Two CCD cameras are used in parallel in order to make both Doppler and vector magnetic field measurements at the required cadence. The is no image processor all observable computation is performed on the ground. - Scherrer 15

16 Subsystems Optics Package Structure The optic package structure subsystem includes the optics package structure, the mounts for the various optical components and the legs that mount the optics package to the spacecraft. Optics Subsystem Includes all the optical elements except the filters Filter subsystem The filter subsystem includes all the filters and Michelsons Provides the ability to select the wavelenght to image Thermal Subsystem Controls the temperature of the optics pkg., the filter oven, CCDs, and the front window. Implements the decontamination heating of the CCD. Image Stabilization Subsystem Consists of active mirror, limb sensor, precision digital & analog control electronics It actively stabilizes the image reducing the effects of jitter Mechanisms Subsystem The mechanisms subsystem includes shutters, hollow-core motors, calibration/focus wheels, alignment mechanism, and the aperture door CCD Camera Subsystem The CCD camera subsystem includes 4Kx4K CCDs and the camera electronics box(es) Electronics Subsystem Provides conditioned power and control for all subsystems as well as C&DH hardware Software Subsystem The software subsystem includes the C&DH interface to the spacecraft and controls all of the other subsystems - Scherrer 16

17 Functional Block Diagram CCD CCD CCD Driver Card (2) Clock & sequencer CDS/ADC Command / Data Interface IEEE 1355 PWB LVDS Camera Camera interface Interface (SMClite) ) Buffer Buffer memory Memory (2x4Kx4Kx16) x x x 16) Housekeeping Housekeeping ADC, ADC, & master & Master clock Clock DC DC -DC- DC power Power converter Converter PWB Mechanism Mechanism & & heater Heater controllers Controllers Control Camera data PWB Data Data compressor Compressor / & Buffer AEC Camera Electronics Box Image Stabilization System Limb Sensor & Active Mirror Mechanisms: Focus/Cal Wheels (2) Polarization Selectors (3) Tuning Motors (4) Shutters (2) Front Door Alignment Mechanism Filter Oven Control Structure Heaters Housekeeping Data Optics Package PWB ISS ISS (Limb (Limb tracker) tracker) Control PWB ISS ISS (PZT (PZT drivers) drivers) PWB Housekeeping data Data acquisition Acquisition Control Control ISS data PWB PC/local PC/local bus bridge/ Bus Bridge EEPROM PWB Central Central processor Processor/ EEPROM Electronics Box Buffer Spacecraft memory Interface PCI Bus PWB Power converters Converters SDO SDO Spacecraft Spacecraft - Scherrer 17

18 Optics Subsystem 1 arc-sec diffraction limited image at the sensor Requires 14 cm aperture Requires 4096x4096 pixel sensor Solar disk at the sensor 4.9 cm For sensor with 12 um pixels Focus adjustment system with ±3 (TBC) depth of focus range and 16 steps Provide calibration mode that images the pupil on the sensor Provide beam splitter to divide the telescope beam between the filter oven and the limb tracker Provide telecentric beam through the Lyot filter Provide beam splitter to feed the output of the filter subsystem to two sensors Minimize scattered light on the sensor - Scherrer 18

19 Filter subsystem Central wavelength 6173Å Fe I line Reject 99% of solar heat load from the OP interior Total bandwidth 76mÅ FWHM Tunable range 500 må Very high stability and repeatability required (to be quantified) The required bandwidth obtained by cascading filters as follows Front window 50Å Blocker 8Å Lyot filter (5 element 1:2:4:8:16) 306 må Wide Michelson 172 må Narrow Michelson 86 må Tuning range requires use of three co-tuned elements Narrowest Lyot element Wide Michelson Narrow Michelson - Scherrer 19

20 MDI Lyot Elements and Michelson Interferometers - Scherrer 20

21 Thermal Subsystem Optics package thermal control Operating temperature range 15 to 25 C Active control to ±0.5 C Control loop in software Filter oven Operating temperature range 35 ± 4 C Temperature accuracy 0.5 C Temperature stability 0.01 C /hour Changes in internal temperature gradients as small as possible Dedicated analog control loop in controlled thermal environment Sensor (CCD detector) thermal control Operating 100 C to 30 C Stability over an orbit xx C? Decontamination mode raise CCD to 20 to 40 C (may need to be wider because of unregulated power) Front window thermal control Minimize radial gradients Return to normal operating temperature within 60 minutes of eclipse exit - Scherrer 21

22 Image Stabilization Subsystem Stability (over TBC second period) 0.1 arc-sec Range ± 14 arc-sec Frequency range 0 to 50Hz Continuous operation for life of mission - Scherrer 22

23 Mechanisms (1 of 2) Shutters Repeatability 100 us Exposure range 50 ms to 90 sec Knowledge 30 us Life (5 year) 40M exposures Hollow core motors Move time (60 deg) <800 ms Repeatability 60 arc-sec Accuracy 10 arc-min Life (5 year) 80M moves - Scherrer 23

24 Mechanisms (2 of 2) Calibration / focus wheels Positions 5 Move time (1 step) 800 ms Accuracy XX arc-min Repeatability XX arc-min Life (5 Years) 20K moves Alignment system Movement range ± 200 arc-sec Step size 2 arc-sec Aperture door Robust fail open design - Scherrer 24

25 CCD Camera Subsystem Format 4096 x 4096 pixels Pixel size 12 um Full well >125K electrons Readout noise 40 electrons Readout time <3.4 seconds Digitization 12 bits Dark current 10 e/sec/pixel at 60 C - Scherrer 25

26 Electronics Subsystem Provide conditioned power and control for all subsystems Provide processor for: Control all of the subsystems Decoding and execution of commands Acquire and format housekeeping telemetry Self-contained operation for extended periods Program modifiable on-orbit Provide stable jitter free timing reference Provide compression and formatting of science data Provide interface for 55 Mbps of science date Provide spacecraft 1553 interface Commands 2.5 kbps Housekeeping telemetry 2.5 kbps Diagnostic telemetry 10 kbps (when requested) - Scherrer 26

27 Operations Concept The goal of operations is to achieve a uniform high quality data set of solar Dopplergrams and magnetograms. A single Prime Observing Sequence will run continuously taking interleaved images from both cameras. The intent is to maintain this observing sequence for the entire SDO mission. Short calibration sequences are run on a periodic basis (daily or weekly) in order to monitor instrument performance parameters such as focus, filter tuning and polarization. Every six months, coordinated spacecraft maneuvers are performed to determine the end-to-end instrument flat-field images and measure solar shape variations. commanding requirements will be minimal except to update internal timelines for calibration activities and configuration for eclipses. After instrument commissioning, it is anticipated that a single daily command load will be sufficient. - Scherrer 27

28 Dataflow Concept } Pipeline - Scherrer 28

29 Data Analysis Pipeline - Scherrer 29

30 Completed Trade Studies Observing Wavelength 6173 Å vs Å: 6173 Å selected CPU RAD 6000 vs. RAD 750 vs. Coldfire: RAD 6000 selected (from SXI) High-Rate Telemetry Board Single Board or to include a redundant board: Redundant concept selected Sensor Trade CMOS vs. CCD Detector: CCD selected - Scherrer 30

31 Trade Studies In Progress Inclusion of redundant mechanisms in Optic Package Increased reliability vs. Increased cost & mass Have allocated volume to not preclude additional mechanisms Inclusion of redundant power supply in Electronics Box Increased reliability versus Increased cost and mass Just started this trade Camera Subsystem - evaluating two options Build in-house an evolution of a Solar-B FPP Camera Procure from RAL an evolution of a SECCHI Camera CCD Configuration Evaluating operation in front side or back side illuminated mode - Scherrer 31

32 CCD and Camera Electronics Baseline CCD vendor is E2V Specification drafted - includes capabilities that allow more optimal camera electronics design and requires less power SHARP and to use identical CCDs E2V to be given a design phase contract ASAP Two principal paths for development of camera electronics Develop cameras in-house => evolution of the Solar-B FPP FG camera Procure cameras from RAL => evolution of the SECCHI camera Key Considerations for decision on approach Schedule => very critical Cost => RAL approach less expensive if already doing SHARPP cameras Performance => both good enough but RAL better Recommendations if camera electronics are procured from RAL Baseline same camera for SHARPP and Have separate RAL subcontracts from LMSAL and NRL Continue to study FPP-option through Phase A Recommendation if camera electronics are developed in house Do not provide cameras for SHARPP Keep informed on RAL-for SHARPP camera status and vice versa - Scherrer 32

33 Current Optics Package 3D view - Scherrer 33

34 Optics Package Layout Current Layout Envelope (20 Mar 2003) X = 1114 mm Y = 285 mm Z = 696 mm Y X Z Origin - Scherrer 34

35 Electronics Box Layout SPARE CAMERA INTERFACE/BUFFER 7.7 in CAMERA INTERFACE/BUFFER 14.2 in COMPRESSOR/HIGH RATE INTERFACE A COMPRESSOR/HIGH RATE INTERFACE B LIMB TRACKER PZT DRIVERS MECHANISM & HEATER CONTROLLERS MECHANISM & HEATER CONTROLLERS MECHANISM & HEATER CONTROLLERS PCI/LOCAL BUS BRIDGE/1553 Interface 9.5 in Current Layout Envelope (20 Mar 2003) X = 361 mm Y = 241 mm Z = 234 mm HOUSEKEEPING DATA ACQUISITION RAD 6000/EEPROM Power supply adds 1.1 in in one dimension X Internal cabling for I/O connectors requires 3 in one dimension Y 9.2 in End View Z Top View Z - Scherrer 35

36 Resources Mass Estimates Mass no margin included 20 Mar 2003 Optics Package (OP, w/lmsal-ceb): 35.3 kg (TBC) Electronics Box (HEB): 15.0 kg (TBC) Harness: 3.0 kg (TBC) OP Assumptions Includes mass of redundant mechanisms in OP Includes larger OP for additional mechanisms, and ease of integration and alignment 1.5 kg mass reduction in OP possible if RAL CEBs are substituted HEB Assumptions Includes additional compression/high speed bus interface boards Includes thinned walls to account for spacecraft shielding 1 kg mass reduction in HEB power supply possible if RAL CEBs are substituted Does not include redundant power converters Harness Assumptions Harness mass presumes a length of 2 meters - Scherrer 36

37 Resources Inertias & CGs OP 20 Mar 2003 Ixx: 1.00 kg-m 2 (TBC) Iyy: 4.30 kg-m 2 (TBC) Izz: 3.48 kg-m 2 (TBC) these estimates are about the CG along OP axes so are therefore NOT principal axes, i.e. there are also some small inertia products CG (x,y,z) = 487 mm, 145 mm, 21 mm (TBC) HEB 20 Mar 2003 Ixx: 0.79 kg-m 2 (TBC) Iyy: 0.22 kg-m 2 (TBC) Izz: 0.97 kg-m 2 (TBC) these estimates presume the HEB is symmetrical about the center vertical axis so these are about principal axes through the CG, i.e. there are no inertia products CG (x,y,z) = 180 mm, 110 mm, 98 mm (TBC) - Scherrer 37

38 Resources - Average Power 20 Mar 2003 Operational Mode (1) Eclipse Mode (2) Survival Mode Early Ops (3) EB Electronics 30.5 W 30.5 W 0 0 OP Oven Control 1 W 1 W 0 0 OP Filter Oven 3 W 3 W 0 0 subtotal 34.5 W 34.5 W 0 0 PC Inefficiency 14.8 W 14.8 W 0 0 subtotal 49.3 W 49.3 W 0 0 Survival Heaters W 45 W CCD Decontam Heaters W Operational Heaters (4) 13 W 23 W 0 0 subtotal 62.3 W 72.3 W 45 W 67 W CEB (LMSAL) 30 W 30 W 0 0 Margin 15W 15W 9W 9W TOTAL W W 54 W 76 W 1 10 Watt reduction possible if RAL CEB is substituted 2 Preliminary allocation of 10 W additional heater power for window 3 CCD decontamination heaters only (TBC) 4 Operational heaters for OP, presume no power for HEB & CEB - Scherrer 38

39 Resources Mass Estimates Mass no margin included 20 Mar 2003 Optics Package (OP, w/lmsal-ceb): 35.3 kg (TBC) Electronics Box (HEB): 15.0 kg (TBC) Harness: 3.0 kg (TBC) OP Assumptions Includes mass of redundant mechanisms in OP Includes larger OP for additional mechanisms, and ease of integration and alignment 1.5 kg mass reduction in OP possible if RAL CEBs are substituted HEB Assumptions Includes additional compression/high speed bus interface boards Includes thinned walls to account for spacecraft shielding 1 kg mass reduction in HEB power supply possible if RAL CEBs are substituted Does not include redundant power converters Harness Assumptions Harness mass presumes a length of 2 meters - Scherrer 39

40 Resources - Telemetry Telemetry Data Rate Nominal science data: 55 Mbits/sec (Split between two interfaces) Housekeeping data: 2.5 kb/sec Diagnostics data: 10 kb/sec Command uplink: 2.6 kb/sec (max) - Scherrer 40

41 Spacecraft Resource Drivers Data Continuity & Completeness Capture 99.99% of the data (during 90 sec observing periods) Capture data 95% of all observing time Spacecraft Pointing & Stability The spacecraft shall maintain the reference boresight to within 200 arcsec of sun center The spacecraft shall maintain the roll reference to within TBD arcsec of solar North The spacecraft shall maintain drift of the spacecraft reference boresight relative to the reference boresight to within 14 arcsec in the Y and Z axes over a period not less than one week. The spacecraft jitter at the mounting interface to the optical bench shall be less than 5 arcsec (3 sigma) over frequencies of 0.02 Hz to 50 Hz in the X, Y and Z axes. Reference Time Spacecraft on-board time shall be accurate to 100 ms with respect to ground time (goal of 10 ms) - Scherrer 41

42 Heritage The primary heritage is the Michelson Doppler Imager instrument which has been successfully operating in space for over 7 years. Between launch in December 1995 and March 2003, almost 70 million exposures have been taken by MDI. Most of the sub-systems are based on designs developed for MDI and subsequent space instruments developed at LMSAL. Lyot filter has heritage from Spacelab-2/SOUP, SOHO/MDI, Solar-B/FPP instruments. Michelson interferometers will be very similar to the MDI Michelsons. Hollow core motors, filterwheel mechanisms, shutters and their controllers have been used in SOHO/MDI, TRACE, SXI, Epic/Triana, Solar-B/FPP, Solar-B/XRT, Stereo/SECCHI. The Image Stabilization System is very similar to the MDI design, and aspects of the ISS have been used in TRACE and Stereo/SECCHI. The main control processor planned for is being used on the SXI and Solar-B/FPP instruments. - Scherrer 42

43 Design Heritage The design is based on the successful Michelson Doppler Imager instrument. - Scherrer 43

44 Mechanisms Heritage - Scherrer 44

45 Technology Readiness Level - Scherrer 45

46 Assembly & Integration Flow Entrance filter Telescope structure Calibrate filter Integrate & align telescope Operations & Analysis Optics fabrication Lyot element fabrication Verify optics performance Assemble/align Lyot cells Assemble/cal. Lyot filter Fabricate optical elements Verify optics performance Fabricate Optics Package Launch & commissioning Michelsons fabrication Oven & controller fabrication Calibrate Michelsons Test oven & controller Assemble/test filter oven system Assemble & align on optical bench Assemble & align in optics package Spacecraft I&T calibration Fabricate mechanisms Test mechanisms environmental test Fabricate focal plane Integrate focal plane Calibrate focal plane Test & calibrate ISS Integrate electronics, software, & OP functional test CCD detector Camera electronics Fabricate ISS Fabricate electronics Develop Software - Scherrer 46

47 Environmental Test Approach In general environmental test will be done at the integrated level to protoflight levels & durations The preferred order of testing is: LFFT SPT for Calibration SPT for Sunlight Performance EMI/EMC LFFT Sine & Random Vibration Electronics & Optics Package separately Powered off LFFT Thermal Vacuum / Thermal Balance LFFT SPT for Calibration SPT for Sunlight Performance in vacuum Mass Properties Delivery - Scherrer 47

48 Instrument Calibration Approach Critical subsystems will be calibrated at LMSAL prior to integration these include The CCD cameras The Michelsons The Lyot filter Mechanisms Other optical elements The completed will be calibrated at LMSAL using lasers, the stimulus telescope and the Sun The completed will be calibrated at LMSAL in vacuum using both the stimulus telescope and the Sun - Scherrer 48

49 Functional Test Approach will use a structured test approach so that the test at each point in the program can be appropriate to the need and consistent test results can be obtained The tests will be controlled by STOL procedures running in the EGSE and will use released test procedures The Aliveness test will run in less than 30 minutes and will do a quick test of the major subsystems The Short Form Functional Test (SFFT) will run in a few hours and will test all subsystems but will not test all modes or paths. It will not require the stimulus telescope The Long Form Functional Test (LFFT) will run in about 8 hours and will attempt to cover all paths and major modes. The SFFT is a subset of the LFFT. The LFFT will require the use of the stimulus telescope Special Performance Tests (SPT) are tests that measure a specific aspect of the performance. These are detailed test that require the stimulus telescope or other special setups. They are used only a few times in the program - Scherrer 49

50 Functional Test on Observatory SFFT / LFFT / SPT are derived from Instrument level tests We assume that GSFC will provide an interface to the EGSE so the same EGSE system can be used to test after integration onto the spacecraft We will use the stimulus telescope to verify calibration while is mounted on the spacecraft We recommend the inclusion of a spacecraft level jitter compatibility test - Scherrer 50

51 Schedule and Critical Path - Scherrer 51

52 Risks Assessment Instrument Development Filter performance: The Lyot filter and Michelson interferometers are the heart of the instrument. Although we have previously built these filters for the MDI instrument, there are relatively few vendors with the specialized skills necessary for their fabrication. We are working aggressively to develop detailed filter specifications and identify potential vendors. Mechanisms longevity : Although the hollow core motor and shutter planned for have significant flight heritage, the required number of mechanism moves is of concern. Lifetests of the hollow core motors and shutters are planned to validate their performance for the planned SDO mission duration. Thermal performance: The thermal stability of the instrument is critical to achieving it s ultimate performance. Detailed thermal modeling and subsystem thermal testing will be used to optimize the thermal design. - Scherrer 52

53 Risks Assessment - Programmatic camera electronics has potential schedule/cost impact: Obtaining SECHHI derived camera electronics from the Rutherford Appleton Laboratory in the UK is a viable option for, but the development schedule is not know in detail. If this option is chosen, we feel it is best that we obtain the camera electronics directly from RAL. A modified Solar-B/FPP camera electronics developed by LMSAL will also meet the requirements. This option has less schedule risk, but costs and camera power and mass are higher than the RAL camera. Timely negotiation of Product Assurance Implementation Plan - Scherrer 53