Instrument Overview and Systems Engineering Robert Besuner UCB

Instrument Overview and Systems Engineering Robert Besuner (UCB) DESI Project Engineer/Systems Engineer 17 June 2015 R. Besuner Director’s Review for CD-2 P 3 1

Outline • Systems Engineering — Overview — Completed phases — Requirements Tracking — Resource Management — Interfaces — Quality Assurance — Configuration Control • DESI Instrument Overview — Corrector — Focal Plane — Fiber System — Spectrographs — Instrument Control System R. Besuner Director’s Review for CD-2 P 3 2

Systems Engineering Overview • Systems Engineering focuses on how to design and manage complex engineering systems over their life cycles. • The DESI Systems Engineering approach, defined in DESI 0301, encompasses: — Alternatives analysis — Baseline design definition — Development of subsystem requirements — Resource allocation and tracking — Interface control — Quality assurance — Configuration control R. Besuner Director’s Review for CD-2 P 3 3

Systems Engineering Overview • Systems Engineering focuses on how to design and manage complex engineering systems over their life cycles. • The DESI Systems Engineering approach, defined in DESI 0301, encompasses: E N O — Alternatives analysis — Baseline design definition — Development of subsystem requirements — Resource allocation and tracking — Interface control — Quality assurance — Configuration control D R. Besuner Director’s Review for CD-2 P 3 4

Alternatives Analysis (Trade Studies) • • • Site Selection (DESI-0311) Targeting Alternatives Selection (DESI-0375) Atmospheric Dispersion Compensator (DESI-0306) Wide-Field Corrector Alternatives (DESI-0302) Focal Plate and Fiber Positioner E N — Monolithic versus “petal” (DESI-0758) — Focal Plate Material (DESI-0452) — Positioner type (DESI-0716) • O D Spectrograph — Spectrograph design survey (DESI-0755) — Reflecting versus transmissive (DESI-0757) — Number of channels (DESI-0756) R. Besuner Director’s Review for CD-2 P 3 5

Baseline Design Development • DESI-0318 Three stages of requirements development L 1 -Science Requirements — Flowdown — Flowup — Redistribution • L 2 -Dataset Requirements E N Performance predictions by simulation L 3 -Technical Requirements — Instrument parameters — Non-instrument parameters — Output • O D Resource Allocations — — Mechanical tolerances Optics specs Barrel mass Inter-exposure time • Iteration… • Results: — Baseline design — Preliminary Subsystem Requirements — See Conceptual Design Report (DESI -0315) R. Besuner Candidate Baseline Design(s) Throughput Estimates Resource Allocations Exposure Time Calculation Baseline Design Corrector Optics Focal Plane/ Positioners Detectors/ Front End Electronics Corrector Barrel Instrument Control System Cryostat Cage/ Hexapod/ Ring/Spider Fiber System Spectrograph Director’s Review for CD-2 P 3 6

Subsystem Requirements Development E N O D R. Besuner Director’s Review for CD-2 P 3 7

Requirements Tracking (DESI-0579) • DESI requirements tracked in requirements tracking spreadsheet (DESI-0579) — By element — By project phase R. Besuner Director’s Review for CD-2 P 3 8

System Resource Management • Galaxy light throughput from sky to detector — Key managed DESI resource — Dictates survey speed/duration/cost — e. g. minimize fiber optic length to limit light absorption • Implementation/Resource allocation — Mass, Electrical Power, Cooling • • Prime Focus Spectrograph Room Computer Room Cassegrain Cage — Observation Timeline — Data capacity (bandwidth, storage) R. Besuner Director’s Review for CD-2 P 3 9

Throughput Tracking Spreadsheet (DESI-0347) • • • Current Best Estimates of performance of all elements of telescope + instrument Summary table feeds into simulation tools for exposure time calcs Same tool used to allocate tolerances and resources as needed Wavelength 10 R. Besuner Director’s Review for CD-2 P 3

Interfaces • Where major subsystems come together and where the instrument meets the existing Kitt Peak hardware. — Mechanical — Electrical — Thermal — Data • Governed by Interface Control Documents (ICDs) R. Besuner Director’s Review for CD-2 P 3 11

DESI Block Diagram (DESI-0448) • Many elements. Many collaborators. Many interfaces. R. Besuner Director’s Review for CD-2 P 3 12

Interface Matrix (DESI-0379) Populated cells show type of interface and DESI document number of ICDs tracked in DESI-0532 13 R. Besuner Director’s Review for CD-2 P 3

Quality Assurance • QA encompasses ensuring functional requirements are met, which includes ensuring the safety of the hardware itself (hardware cannot function if damaged) • Project follows LBNL/PUB-3111 for QA which provides Guidance in planning, executing, verifying and improving work product — Work Process • • Work done to established standards and administrative controls (procedures, etc) Proper use of hardware Workers responsible for quality of their work Line management responsible for ensuring quality achieved — Hardware/software development • • Use sound engineering processes (ref LBNL Engineering Process Guide) Design to appropriate standards (IEEE, ASTM, ANSI, ASME. . . ) Document analyses Hold team meetings Hold design reviews Employ configuration management Track requirements and their verification R. Besuner Director’s Review for CD-2 P 3 14

Subsystem Quality Assurance Plans • Corrector — Corrector element specifications verified by lens acceptance data package • • — Assembly and alignment • • • Cameras: PSF test with microscope objective Coatings accepted by witness sample Thermal cycles • Collimators — — — Collimators and Cameras accepted individually (acceptance test) VPH gratings tested individually for diffraction efficiency, scattering and wavefront Integrated spectrograph test • Operational temperature range athermalization testing Mechanical/optical functional testing of each positioner shortly after manufacture for rapid response to any quality issues Acceptance, and short form functional testing after electronics integration Electronics — Short and/or long form functional tests Detectors — — • Wavefront testing (just a sphere) Positioners — — • Survival range for each camera (glue joint) — • • Contact metrology Optical testing Spectrograph — — — • Profile Radius of curvature Wedge Wavefront (if applicable) Dark current QE Read noise Cosmetics Fibers — — Prior to integration into PFA, measure FRD of each fiber (pass/fail) Installation into slit Measure alignment Splice fiber and measure FRD, cleave and re-splice if necessary Throughput: every ~100 fibers TBD R. Besuner Director’s Review for CD-2 P 3 15

Machine Protection (Hardware Safety) • • Machine Protection is part of Quality Assurance Tracked in Machine Protection Plan (DESI-0928) Sergio Zimmermann BO 5. 3 R. Besuner Director’s Review for CD-2 P 3 16

Configuration Control • Software versioning managed in SVN and in Git. Hub • Other documents managed in Doc. DB — Sequential version numbers — Archived older versions — Required approvals depend on type of document • Level 4 Requirements and ICDs between subsystems Change Control Board includes Sys. E, PM, and L 2 Manager(s) of affected subsystem(s) • Level 5 Requirements/Specs/Drawings — Managed by L 2 Subsystem Manager R. Besuner Director’s Review for CD-2 P 3 17

Systems Engineering Preliminary Design • Iterative development and flow-down/flow-up of requirements leads to the DESI Instrument Preliminary Design R. Besuner Director’s Review for CD-2 P 3 18

DESI Instrument Overview • • • Corrector Focal Plane Fiber System Spectrographs Instrument Control Proto. DESI R. Besuner Joe Silber P 4 Jerry Edelstein P 5 Dick Joyce BO 4. 4 Director’s Review for CD-2 P 3 19

DESI Hardware Overview • • • Collect light from Mayall 4 m primary mirror Focus onto repositionable fiber optic tips Pipe the light off the telescope to spectrographs Take spectra of 5000 objects simultaneously Identify spectral features to determine redshifts Corrector Focal Plane System Primary Mirror Fiber View Camera Spectrographs Readout & Control Fiber System R. Besuner Director’s Review for CD-2 P 3 20

Prime Focus Corrector • • 3. 2˚ diameter field of view Wavelength bandpass 360 – 980 nm Four fused silica lenses Two borosilicate lens/prisms: Atmospheric Dispersion Compensator (ADC) Peter Doel BO 2. 1 R. Besuner Director’s Review for CD-2 P 3 21

Corrector Mechanical • Lenses mounted in cells that are in turn mounted in the stiff barrel structure – DECam heritage • Barrel supported in cage on a movable hexapod to compensate for temperature, gravity, and misalignment – DECam heritage Cage Spiders • Cage suspended from telescope trusses by a ring and spiders – DECam similarities Gaston Gutierrez BO 2. 2 Upper Ring R. Besuner Director’s Review for CD-2 P 3 22

Focal Plane System • Focal plane system — Attaches to the back of the corrector barrel — Carries the focal plate assembly consisting of. . . — Ten Petals, each supporting. . . • 500 fiber positioners • 12 illuminated fiducials • 1 Guide/Focus/Alignment sensor 10 copies Joe Silber BO 2. 3 R. Besuner Director’s Review for CD-2 P 3 23

Fiber Positioner • 5000 positioners, 500 on each focal plate petal • Place fiber optic tip to commanded position within 5µm rms • 10. 4 mm pitch hexagonal array • 12 mm diameter patrol disk Greg Tarlé BO 2. 4 C. Bebek 2014/09/09 CD-1 Review P 3 24

Focal Plane System • Guide / Focus / Alignment sensors – 1 per petal — Guide star tracking feedback to telescope – 6 units — Focus and alignment data for hexapod – 4 units • Illuminated fiducials – 12 per petal — Precisely surveyed to GFA sensors — Provide optical distortion and mechanical deformations data when imaged with Fiber View Camera • Fiducials are the blue and red dots Fiber view camera (FVC) — Observes illuminated fiducials … — … and backlit fiber positioners — Provides feedback to positioners to align fibers to galaxies R. Besuner Director’s Review for CD-2 P 3 25

Focal Plate Petal Assembly (10 x) Joseph Harry Silber Director’s Review for CD-2 - BO 2. 3 26

Fiber System • 500 fibers per cable — Unitized with focal plane petal assemblies • • Fiber core size –Φ 107 μm (1. 47 arcsec on sky) Ten cables run down telescope structure and pivots to fixed spectrographs ~35 m Claire Poppett BO 3. 5 R. Besuner Director’s Review for CD-2 P 3 27

Spectrograph • 10 spectrographs each take 500 simultaneous spectra — Unitized with a focal plate petal and fiber cable • • • Located in climate controlled ‘shack’ in Large Coude Room 3 -channel, reflective collimator, refractive cameras One 4096 x 4096, 15 μm pixel CCD per channel CCD Camera Collimator R. Besuner Fiber Slit Pat Jelinsky BO 3. 1 Director’s Review for CD-2 P 3 28

Instrument Readout and Control • • Instrument and observation control, and telescope interface Builds on DECam – same people, same components Spectrograph and GFA Data Modules Hardware Software Modules Online Data Analysis Mayall Interface R. Besuner Director’s Review for CD-2 P 3 Klaus Honscheid BO 3. 6 29

Proto. DESI • • • Summer 2016, subscale focal plane assembly with DESI positioners, illuminated fiducials, and guider installs on existing Mayall prime focus corrector Uses DESI Fiber View Camera and DESI Instrument Control System (no spectrograph) Mitigates technical and commissioning risk by: — Guiding to specific guide star on a specific guider pixel position — Closing the loop on the guiding/fiber view camera/fiber positioner/sky mapping system • Bridges the gap between individually-proven components and the overall system DESI Fiber View Camera Proto. DESI Focal Plane Assembly (FPA) with DESI positioners, fiducials, guider Fiber Photometry Camera and Back-Illuminator (in place of spectrograph) R. Besuner DESI Instrument Control System Dick Joyce BO 4. 4 Director’s Review for CD-2 P 3 30

Conclusions • Preliminary instrument design meets the scientific and technical requirements for the survey, documented in the TDR. • Detailed throughput estimates for all identified items in signal chain are tracked. • System resources, interfaces, and requirements are being managed and tracked. • Quality Assurance, including Machine Protection, is managed by Systems Engineering. • Proto. DESI will help mitigate DESI technical risks and develop DESI commissioning procedures. R. Besuner Director’s Review for CD-2 P 3 31