Engineering Overview and the Key Design Space for MSE

Transcription

1 Engineering Overview and the Key Design Space for MSE 29 to 31 July, First Annual MSE Science Team Meeting Kei Szeto, MSE Project Engineer - On behalf of the international design team H. Bai, S. Bauman, D. Crampton, N. Flagey, P. Fouque, P. Gillingham, X. Gong, K. Ho, A. McConnachie, S. Mignot, R. Murowinski, D. Salmon, Will Saunders, P. Spano,

2 Outline (1) The engineering overview presentation is a progress report of the work of the international engineering team. The focus has been developing a system-level observatory configuration that meets the MSE science mission and requirements. The physical observatory hardware consists of four major subsystems Observatory building and facilities the existing summit building, mechanical and electrical plants, and inner pier retrofitted to meet the MSE design requirements Calotte enclosure selected design for MSE Telescope - optics and telescope structure Instrument components between fiber input focal plane delivered by the telescope to the spectrograph system that generates the scientific data Design work has been progressing in parallel for all four subsystems, this presentation highlights the engineering work within their own design space. 2

3 Outline (2) Since the progress on telescope and instrument is most relevant to the science requirements, today I will present their design progress in context with the Science Requirement Document (SRD) groupings. Etendue and sensitivity how the telescope optical design affects collecting area and FOV Multiplexing how instrument configurations have been developed to allow efficient observations at different spectroscopic resolutions and with different number of targets Wavelength range how to establish feasible wavelength coverage at R3000 spectroscopic resolution In addition, I will give a summary progress on Systems Engineering work on system budgets and flow-down of science requirements. 3

4 Design Space Constraints (1) Redevelopment assumptions Reusing the existing inner pier to support telescope on its 4 th floor Reusing the existing summit building as the enclosure pier on its 5 th floor Retaining exterior appearance of the observatory Maintaining the spherical shape by using a Calotte style enclosure Limiting dimensional increase to 10% of the current value These limit the size of the new telescope. Outer Building Inner pier Outline of 10% larger Calotte enclosure superimposed over existing CFHT dome 4

5 Design Space Constraints (2) No connectors in the fiber relay between the fiber positioner unit and spectrograph input Maximize throughput Preserve spectrograph stability and repeatability This imposes considerations on the placement of telescope structural members and servicing procedures for installation and removal of the fiber positioner unit together with the fiber relay Given the current advances in fiber optics technology, usage of connectors (~3% loss) and field splicing (~1% loss) will be reevaluated in order to facilitate system integration. 5

6 Design Space Constraints (3) Utilize existing designs and technologies in order to minimize technical risks and meet the project schedule and budget ELT technologies on M1 segment system Fiber positioner designs Spectrograph designs The MSE design approach is to maximize utilization of existing designs and minimize development of new technologies. TMT M1 segment and support assembly LAMOST fiber positioner Echidna fiber positioner 6

7 Design Progress Observatory Building (1) Observatory building and facilities include building, mechanical and electrical infrastructure, and equipment required to support MSE operation and observations. Revised building layout to reorganize existing facilities and support equipment has been developed. Heavy industrial equipment located at the basement Thermal and vibration management As much as possible redeploying existing equipment to reduce cost New basement floor plan 7

8 Design Progress Observatory Building (2) Revised floor plans for 1 st, 2 nd and 3 rd F/L of summit building and inner pier Floor plan - outer building 1 st F/L Floor plan outer building 2 nd F/L Floor plan outer building 3 rd F/L 4 th F/L of the summit building is intentionally left empty to create a buffer zone to minimize heat dissipation into the enclosure 8

9 Design Progress Observatory Building (3) 4 th F/L of inner pier supports the new telescope 5 th F/L, observing floor, of the summit building is modified Central part of the exist floor is removed to accommodate new telescope Structural engineering to confirm viability of modification, along with the associated seismic upgrade required, has been completed From left to right: outer building complete, section view of new telescope and enclosure (elevation), inner pier complete, section view of new telescope and enclosure (isometric) 9

10 Design Space Enclosure (1) CFHT SUBARU KECK GEMINI Based on detailed trade study conducted by the TMT project of different enclosure designs, the advantages of Calotte design over other enclosures for the same telescope size are identified. Low construction and operation costs due to lighter structural mass Superior ventilation control to minimize seeing when using CFHT style ventilation modules 10

11 Design Space Enclosure (2) Based on these advantages the Calotte design is selected. It presents the best-match option over other enclosure designs. Aperture Base Cap Cap Axis Zenith Angle = 30 Zenith Angle = 60 Existing pier 11

12 Telescope and Instrument Block Diagram Telescope Optics WFC/ADC Fiber Positioner Unit - instrument input Fiber Handling & Cable Wrap Unit Fiber Relay Unit Spectrographs - low, medium and high resolution Telescope Instrument: De-rotating Instrument: Stationary 12

13 Telescope Design Space Telescope Optics WFC/ADC Etendue and Sensitivity Elements Fiber Positioner Unit - instrument input Fiber Handling & Cable Wrap Unit Fiber Relay Unit Spectrographs - low, medium and high resolution Telescope Instrument: De-rotating Instrument: Stationary 13

14 Design Space M1 Size (1) Etendue and sensitivity SRD requirement for A-Omega 118 m 2 deg 2 In context of a segmented primary mirror with 1.44 m size segments with a 1.5 deg 2 FOV The minimum aperture required is 60 segments* with an effective diameter of 10 m** Telescope aperture of m These define the minimum size of M1 and FOV. M1 size is also constrained by cost m M1 *Without central segment **Including allowance for top end obscuration 14

15 Design Space M1 Size (2) M1 size and FOV are key design parameters for MSE An often asked question: What is the optimal telescope configuration? > m? > 12.3 m? A trade study was conducted to determine the optimal telescope configuration. This is a system-level assessments starting with the optical performance. 15

16 Requirements and Goals Optical design requirements Image quality 0.35 EE80 diameter at 0 zenith Over the central 90% of FOV, including all optics Image quality 0.45 EE80 diameter at 50 zenith Telescope is expected to operate up to 60 zenith angle but with graceful degradation in optical performance 5% vignetting over the central 90% of FOV 15% vignetting at 10% edge of the field Light baffle design must be included as part of the optical design Goals Telecentric fiber feed Principal rays normal to the focal surface Maximize system throughput Including effects of the length of fiber relay, especially at the blue end Optimal atmospheric dispersion correction to maintain image size given the nm* wavelength range *More discussion on wavelength range to follow 16

17 Telescope Optical Designs The international design team developed four optical designs representative of the design space for evaluation in the trade study: National Research Council - Herzberg prime-focus (PF) Australian Astronomical Observatory PF Nanjing Institute of Astronomical Optics & Technology quasi-pf (QPF) Australian Astronomical Observatory Cassegrain-focus (CF) NRC PF NIAOT QPF AAO CF AAO PF 17

18 Optical Design Trade Study (1) Trade study was based on comparison of optical performance and non-optical attributes evaluated from an overall system perspective. How does a telescope based on each optical design would impact the overall observatory design and operation? CAD models of the MSE observatory are developed for each optical design in order to facilitate the evaluation. NRC PF AAO CF NIAOT QPF AAO PF 18

19 Optical Design Trade Study (2) Since the trade study is a quantitative comparison of the four telescope optical designs, a decision matrix was produced to facilitate the assessment process. The decision matrix contains 8 categories with 45 items to evaluate optical designs and analyze their impacts at the observatory level Optical performance Observatory building design Enclosure design Telescope structure design System performance Instrument maintenance Observatory operation Project programmatic Examples of categories and items in the decision matrix 19

20 Description of Optical Design (1) The two PF designs are similar m, 60 segments M1 with an overall optical path length of 18.5 m ±1% Telescope length fits within the proposed MSE enclosure Item NRC PF AAO PF M1 f/# f/1.83 f/1.63 Conic constant Fiber input f/# f/2.2 f/1.83 Effective M1 dia m 10.1 m NRC PF EE80 IQ* on-axis at 0 zenith EE80 IQ* at edge at 0 zenith 0.09 arcsec 0.38 arcsec 0.24 arcsec 0.30 arcsec % vignetting** at edge 25% 12% *Overall IQ of as-designed optics at λ= 0.55 um **Field dependent vignetting with respect to on-axis, due to WFC lens size AAO PF 20

21 Description of Optical Design (2) *Aspheric surface * The two PF designs differ in their WFC/ADC concepts Lens design and materials The difference in % vignetting is due to the available blank sizes for the WFC lenses NRC WFC L1 aperture is limited to 1 m AAO WFC L1 aperture is limited to 1.2 m Atmospheric dispersion correction NRC PF AAO PF AAO ADC operation for 60 zenith - 40 telescope pointing (dashed line shows telescope axis) - 30 um refocus and tilt of WFC/ADC unit (red arrow and dot) tilt of L2 (blue arrow and dot) - Motion exaggerated by a factor of 10 for clarity 21

22 Description of Optical Design (3) The two other designs are also similar 12.3 m, 66 segments M1, with short optical length Both are compact optical designs with sizable central obstructions NIAOT QPF M2= 3.45 m and AAO CF M2 light baffle = 3.8 m Item NIAOT QPF AAO CF M1 f/# f/1.23 f/1 7 central segments are used Conic constant Fiber input f/# f/2.8 f/3.0 Effective M1 dia m m EE80 IQ* on-axis at 0 zenith 0.17 arcsec 0.32 arcsec EE80 IQ* at edge at 0 zenith 0.26 arcsec 0.25 arcsec NIAOT QPF % vignetting** at edge 4% 2% *Overall IQ of as-designed optics at λ= 0.55 um **Field dependent vignetting with respect to on-axis AAO CF 22

23 Description of Optical Design (4) Axial ADC at 0 zenith touching the focal plane Axial ADC at 50 zenith away from focal plane Focal plane *Aspheric surface Focal plane WFC/ADC concepts NIAOT QPF No WFC required Novel axial ADC design Composes of 9 cemented sections* LLF1 PSK3 *Curvature of section exaggerated in figure AAO CF Three element WFC/ADC design with L1 aperture at 1.31 m NIAOT QPF AAO CF AAO ADC operation for 60 zenith - telescope pointing (dashed line shows telescope axis) - 3 mm translation and 0.1 tilt of M2-1.0 tilt of L1 (axis about blue circle) - 21 mm translation of L3 23

24 Highlight of Trade Study Findings: PF Optical Designs Advantages Simple optical design with M1 only Open telescope structure facilitates access and servicing, mirror and dome flushing, and does not impose complex requirements on observatory building and enclosure Low cost and programmatic risks Disadvantages Blank size availability of optics leads to vignetting Longer telescope length may require 10% increase in enclosure size Telescope more vulnerable to dynamic disturbances Potentially longer fiber bundle routes NRC PF AAO PF 24

25 Highlight of Trade Study Findings: Non-PF Optical Designs Advantages NIAOT QPF - Excellent image quality and no WFC AAO CF - Simple three element WFC design Compact telescope structure less vulnerable to dynamic disturbances such as wind shake due to lower moment of inertia and top-end far away from external wind at aperture opening Potentially shorter fiber bundle routes Disadvantages Challenging M1 optics Compact telescope structure that does not facilitate access and servicing, mirror and dome flushing, and imposes additional operational requirements on observatory building, enclosure and telescope Servicing of instrument, M2 and M3 systems Additional costs of M1 segments, M2 and M3 systems without significant increase in effective M1 diameter NIAOT QPF AAO CF 25

26 Conclusion of Trade Study (1) Based on the decision matrix, the PF optical designs are advantageous over the non-pf designs. 26

27 Conclusion of Trade Study (2) After analysis of the four optical designs and their impacts on overall system m prime-focus optical design is the optimal telescope configuration 10 m effective M1 diameter meets SRD requirements A prime-focus telescope with larger M1 does not fit inside the MSE enclosure Even if a larger enclosure is permissible, WFC blank size limits will lead to unacceptable vignetting. Non-PF designs do not result in significant increase in effective collecting area Effective Diameter NRC PF AAO PF NIAOT QPF AAO CF m m m m Due to large central obstruction, e.g. 3.8 m M2 light baffle for CF Non-PF designs incur significant higher costs due to additional optics m prime-focus telescope design is adopted moving forward! 27

28 Multiplexing Design Space Telescope Optics WFC/ADC Fiber Positioner Unit - instrument input Multiplexing Elements Fiber Handling & Cable Wrap Unit Fiber Relay Unit Spectrographs - low, medium and high resolution Telescope Instrument: De-rotating Instrument: Stationary 28

29 Design Space Multiplexing (1) SRD requirements for multiplexing 3,200 spectra at R3,000 and R6,500 1,000 spectra at high resolution (R20K-40K) The design space for multiplexing is to determine the optimal combinations of fiber positioner technology and fiber relay configuration to deliver the required number of spectra to the low, medium and high resolution spectrographs. A trade study was conducted, to select from 12 possible combinations, the most promising multiplexing configurations for detailed design development. Similar in methodology and at the same level of detail as the telescope trade study Screen capture of the multiplexing trade matrix 24

30 Design Space Multiplexing (2) After examining all practical combinations of positioner technologies, fiber relay configurations, spectrograph slit input arrangements and spectrograph concepts. Six design studies including two for different positioner technologies are identified for further development. At the completion of these studies, an optimal multiplexing configuration fully meeting the SRD requirements will be identified. Details of the trade study will be presented on Friday. See Shan s presentation SPLINE STICK & SLIP MOTION GENERATED BY SAW-TOOTH VOLTAGE PULSES Echidna Positioner Array Phi-Theta Positioner Array 30

31 Wavelength Range Design Space Telescope Optics WFC/ADC Fiber Positioner Unit - instrument input Telescope Fiber Handling & Cable Wrap Unit Fiber Relay Unit Spectrographs - low, medium and high resolution Wavelength Range Elements Instrument: De-rotating Instrument: Stationary 31

32 Design Space Wavelength Range (1) SRD requirement for wavelength range at R3000 is 360 nm to 1300 nm, with a goal of 1800 nm. Blue end - system performance will be optimized for wavelengths longer than 370 nm and with degraded sensitivity at 360 nm LR spectrographs located on telescope structure to maximize blue throughput by minimizing the fiber length Red end management and engineering challenges to extend the system design from nm to 1800 nm at first light Availability and performance of broadband AR coatings for large optics Availability of large format NIR detectors More importantly, the challenges of operating refrigerated spectrographs will impose extra requirements Optical and opto-mechanical designs for extended temperature range Thermal control and management for spectrograph stability Air handling and humidity control for frosting and condensation Spectrograph thermal enclosure design to ensure uniform temperature distribution Integration procedures for optical alignment and assembly How to align for subzero temperature at room temperature Work flow between room temperature and subzero temperature 33

33 Design Space Wavelength Range (2) Given the extra challenges realized for extending the R3,000 spectroscopic wavelength range from 1,300 to 1,800 nm Need understanding of the acceptable impacts on overall performance, e.g. accepting lesser throughput and poorer performance over the wider band due to greater demands on coating and WFC/ADC design Currently investigating upgrade path to H-band after first light Adding a standalone cryogenic NIR branch by replacing the warm slit input with a cold slit unit in front of the existing spectrograph Cryogenic H-band spectrograph Warm spectrograph Cold slit, collimator and dichroic 3 4

34 Systems Engineering Progress Systems Engineering work in progress Flow-down of Level-0 Science Requirements Document (SRD) to Level-1 requirement documents Observatory Architecture Document (OAD) Observatory Requirements Document (ORD) Operation Concepts Document (OCD) OCD-1 OAD-1 SRD-0 ORD-1 Level-2 design requirements documents for observatory building and facilities and enclosure Level 1 system budgets Throughput budget Noise budget Image quality budget Pointing error budget Plate scale stability budget Identify and understand the contributors and their relationships with SRD requirements for sensitivity, spectral stability and calibration Verification of sensitivity (SNR) based on the throughput and noise budgets 35

35 Summary of Engineering Accomplishments Observatory building and facilities architectural concept completed Enclosure design selected Telescope optical configuration identified Instrument configurations defined Systems engineering is in place to support the upcoming design work. System definitions and Level-1 requirements related to the four major subsystems are in place for their conceptual designs to move forward. 36

36 Thank you - Questions?

37 Design Space Multiplexing (3) Six multiplexing design studies identified for further development 1. Phi-Theta positioner system design Delivering two 3468 fiber bundles to LR/MR and HR spectrograph systems Phi-Theta-Theta option delivering one 1156 fiber bundle to HR spectrograph system 2. Echidna positioner system design Delivering one 3468 fiber bundles to LR/MR spectrograph system Delivering one 1156 fiber bundles to HR spectrograph system 3. Low and medium resolution spectrograph design Modular design with total 3468 spectra capacity 4. High resolution spectrograph design Modular design with total 1156 spectra capacity 5. Optical switch study Ability to switch from 3468 fiber inputs to 1156 fiber outputs 6. Fiber transmission system design At the completion of these studies, an optimal multiplex configuration fully meeting the SRD requirements will be identified. 28