Camera Engineering

1
Camera Engineering

• LSST Directors Review
• Stanford Linear Accelerator Center
• March 8-9, 2006
• Martin Nordby
• Stanford Linear Accelerator Center

2
Outline

• System engineering
• Design overview
• Sub-assembly descriptions
• Environmental systems development
• Preliminary budgets
• Summary

3
Camera System Engineering

• Interface management
• Tightly integrated system
• Design development managed at the discipline
  level
• Results in design flexibility during development
  cycle
• Ultimately, the systems engineering effort will
  be formalized to include
• Requirements flow-down and control
• Metrics managementpower, mass, center of gravity
• Configuration control
• Implement configuration control by Camera PDR at
  start of FY2008

4
Camera Mechanical Overview
Utility Trunk
Cold Plates
BEE Module
Cryostat outer cylinder
Focal Plane fast actuators
Raft Tower (Raft with Sensors FEE)
L3 Lens in Cryostat front-end flange
Filter Changer rail paths
Shutter
Back End
L1/L2 Housing
Camera Base Ring
Front End
Filter Carousel main bearing
Filter in stored location
L1 Lens
Camera Housing
Cut-Away View of Camera Assembly(false-color
image)
L2 Lens
Filter in light path
5
Camera Layout and Stayclears
Filter
L3 Lens
L2 Lens
L1 Lens

• Camera mechanical package constrained by
• Bore diameter of M2 mirror
• M2-M3 light path on front end
• Size and locations of lenses
• Locations of optics was recently finalized
• Camera stayclear envelope is currently being
  worked out
• The working conceptual design includes radial and
  axial margin to our envelope

Camera Weights and Dimensions
Camera Optical Clear Apertures and Proposed
Stayclear Envelope
6
Focal Plane Array
Shack-Hartman Sensors (4 locations)

• Key parameters
• Pixel pitch 10 mm
• Pixel count 3.2 G-pixels
• Focal plane flatness 10 mm p-v
• Current work
• Developing prototype sensors with candidate
  manufacturers
• Laying out focal plane geometry
• Developing structural and thermal design concepts
• Reference talks by Veljko Radekaand Rafe
  Schindler

Guider Sensors (8 locations)
3.5 degree Field of View (634 mm diameter)
Curvature Sensors (16 locations)
Raft (21 in FPA)
Sensor Package (9 per Raft)
Focal PlaneWorking Dimensions
Focal Plane Array
7
Camera Electrical Overview

• Parallel handling of timing, control, and readout
• Science sensors are controlled and read out in
  parallel, by way of Front End Electronics (FEE)
  and Back End Electronics (BEE) modules
• Timing and Control module handles all control of
  science sensors
• Independent communication and control
• Systems are controlled independently by the
  Camera Control System (CCS)
• Reference talkby John Oliver

Camera ElectricalBlock Diagram
8
Sensor Package

• Key parameters
• 4-side butt-able packaging
• Sensor flatness 5 mm
• Sensor temperature uniformity 0.6 K
• Current work
• Prototyping thick-silicon CCD
• Developing packaging and mounting concepts
• Performed thermal analysis of sensor package
• Reference talk by Veljko Radeka

Thermal Strap
V-Mount blocks
85-Pin Connector
0.35 K uniformity across face of sensor
CCD sensor showing overhang for wirebonding
Aluminum-Nitride support structure
Aluminum-Nitride circuit board
Sensor PackageBack-side View
Sensor Package Temperature Profile(Single-Strap
Design)
Sensor PackageFront-side View
9
Rafts and Front End Electronics

• Key parameters
• All 9 sensors flat to 6.5 mm
• Raft and mount to Grid stable down to 173 K
• Minimize/eliminate dead area due to structure
• Current work
• Developing Raft and mount structural design
• Laying out sensor mount and packaging concept
• Developing sensor alignment methods and flatness
  metrology techniques
• Reference talks byVeljko Radeka,Rafe Schindler,
  and John Oliver

Raft mount points
Sensor Packages
Raft
Flex cables and Thermal Straps
FEE Boards
FEE cage
Raft TowerFront-side View
Aluminum-Nitride Raft structure
Thermal Straps
Partially Assembled RaftFront-side View
Sensor Package mounting balls
10
Wavefront Sensing

• Investigating 2 options for wavefront sensing
• Shack-Hartmann sensorsre-image on pupil plane,
  focus light through lenslet array to sense
  wavefront gradients, and reconstruct wavefront
  phase (4 sensors)
• Curvature sensorslocate detectors above and
  below focal plane to sense wavefront curvature,
  and reconstruct wavefront phase (16 sensors)
• Issues being worked in analyzing options
• Stellar densityhow much area do we need to
  achieve desired performance
• Reconstruction algorithmsensor noise,
  atmospheric bias
• Methods to improve efficiency of SH FP
  usageoptimize footprint, broaden acceptable FOV
  investigate steerable SH sensors
• WFS use area in the focal plane, so this
  investigation impacts coverage of science sensors

Shack-Hartman Sensor Concept
Focal plane
CurvatureSensor Concept
11
Cryostat Assembly

• Key parameters
• Cryostat and contents are vacuum compatible
• Control of contamination and offgassing
• Focal plane held and moved stably at operating
  temp in all orientations
• Current work
• Developing complete conceptual designs
• Running stress/deflection analyses
• Establishing strawman assembly and servicing
  methods
• Reference talk by Rafe Schindler

Focal Plane Fast Actuators
Feedthrough Plate
Cold Plates
Grid(a.k.a. Integrating Structure)
L3 and Flange Stress Analysis
L3 Lens mounted in vacuum-tight flange
Outer cylinder
Cut-Away of Cryostat AssemblyFront-side View
12
Grid Structure (a.k.a. Integrating Structure)

• Key parameters
• Hold focal plane flat to 10 mm for all
  orientations
• Thermally and structurally isolate Rafts
• Current work
• Laying out Grid design around the packaging
  constraints of Rafts, WFS, FEE, and fast
  actuators
• Working with silicon-carbide manufacturers to
  specify material properties, and prototype
  material and fabrication methods

Fast Actuators mounted at corners
Pockets for Curvature Sensor access
Empty Grid StructureFront-side View
Grid with Raft and Fast ActuatorsFront-side View
Empty Grid First Mode Shapef1 463 Hz
13
Back End Electronics and Cryostat Back End

• Key parameters
• Packaging and board design is mechanically and
  thermally constrained
• Current work
• Developing packaging concepts in conjunction with
  board design
• Working routing and access for fiber optics and
  cabling to feedthrough flange
• Laying out mechanical design and mounting concept

Feedthrough flange 1 optical fiber and Micro-D
feedthrough per Raft
FEE Module mounted to 153 K Cryo Plate
Any Grid Bay is accessible without removing
feedthrough flange
BEE Module mounted to 233 K Cool Plate
Cryostat Back EndBack-side View
14
L1/L2 Assembly

• Key parameters
• Support lenses over operating temperature and
  pressure ranges and in any orientation
• Maintain air-tight seal
• Current work
• Analyzing support methods to understand impact on
  deflections
• Determining allowed deflections and distortions
  of L1 and L2 as part of optical design effort
• Reference Scot Oliviers talk

Double-bladed flexure
Mount block epoxied to lens
L1 Mounting Flexure Detail
L2 Lens
Support structure
2 m/fringe
L1 Lens
Flexure mount
Z-Deflection of L1 Under 1g Z Load
L1/L2 Sub-AssemblyFront-side View
15
Shutter

• Key parameters
• Maximum variation in exposure time 0.1
• 106 cycles/year
• Constrained between filter and L3
• Large field-of-view large shutter
• Roll-up shutter is first-of-a-kind
• Current work
• Completed preliminary fatigueanalysis and
  operations concept
• Packaging Shutter around L3
• Establishing Shutter requirements
• Developing drive train prototype

Filter
Shutter
L3 Flange
Tensioner Reel
Take-up Reel
Shutter aperture cut into thin sheet
Structural frame
Shutter Packaging Concept
Section of Shutter in Camera F.O.V.
16
Filter Changer and Carousel

• Key parameters
• 2000 changes/year
• 10,000 revolutions/year of Carousel
• Filter position accuracy appears relatively loose
• Need provision for an 8-hour manual filter swap
• Current work
• Comparing track vs linkage vs articulating arm
  actuation
• Defining stayclear volumes, required filter
  motions, and packaging with neighboring components

Filter in Carousel load position
Filter in Field of View
Filter Motion Study.wmv movie file (in ppt,
click to view)
17
Camera Environmental Systems

• Three requirements drive the design of the Camera
  environmental systems
• Low noise and stability of sensor quantum
  efficiency
• Sensors operate at 173 K
• Sensor temperatures held stable
• Very flat focal plane
• Structurally stable at temperature
• Minimize gradients in structures
• Clean environment to protect optical elements
• Use materials that will not contaminate silicon
  or fog optics
• Environmental systems must keep camera clean
• How do we plan to meet these requirements
• Thermally isolate sensors via cold sink and trim
  heaters
• Thermally isolate Grid
• Use parallel cooling paths for process heat
• Match expansion coefficient of silicon
• Maximize conductivity and specific stiffness of
  structures
• Test and approve all materials
• Provide cleansing environments
• Studying option of operating focal plane at a
  higher temperature when using Y-Band filter

18
Thermal System Design

• Five camera thermal zones
• Zone 1, Focal plane 173 K 0.6 K uniformity
  across sensor 2.0 K uniformity across FPA
• Zone 2, FEE 153 K
• Zone 3, BEE 240-260 K
• Zone 4, Optics and camera body actively
  controlled to match ambient
• Zone 5, Utilities Trunk external on-camera
  crates, controlled to match ambient
• Thermal isolation and insulation ? why a vacuum?
• Using an insulating vacuum reduces heat load to
  only radiation through L3, which will be very
  stable, and essentially eliminates other
  secondary convection paths around the perimeter
  of the Cryostat

Camera Power
19
Thermal System Layout
Thermal SystemBlock Diagram
Chiller Specifications
20
Vacuum System Design

• Cryostat forms the vacuum vessel
• L3 serves as vacuum window
• Focal plane at 5 x 10-6 Torr vacuum
• Vacuum zones match the thermal zones in the
  Cryostat
• Baffles/chicanes between vacuum zones reduce
  conductance ? reduces molecular flow of
  contaminants
• Sensor surfaces are not the coldest surface
  within the cryostat
• Cryo Plate is the coldest surface, and provides
  some amount of cryo pumping
• On-board pumps will provide holding capacity in
  each of the vacuum zones
• Ion pumps
• Molecular sieves
• Charcoal
• Investigating options for roughing pumps

Accounting of Materials in Cryostat Vacuum
21
Purge System and Contamination Control Plans

• Two purge systems in the Camera
• Cryostat back-fill system
• Camera housing purge system
• Purge systems are one of 5 contamination controls
  we plan to implement
• Materials testing
• Materials and process controls
• Contamination controls
• QA oversight
• Active purging to maintain clean environments
  during assembly and operations

22
Budget Development Efforts

• Bottoms-up budgets are being developed in
  conjunction with the conceptual design and
  requirements
• Budgets presented here
• 3.2 Systems Engineering and Integration
• 3.5.2 Utilities
• 3.5.3 Camera Body and Mechanisms

23
3.2 Systems Engineering and Integration
24
3.2 Systems Engineering and Integration (cont.)
Forward-loading in FY07 shows early emphasis on
Systems Engineering prior to PDR
Budget Estimate of 4.97M(Fully loaded, FY07 ,
no contingency)
25
3.5.2 Utilities
Early spike shows pre-production completion of
Materials Test Facility at SLAC
Budget Estimate of 3.7M(Fully loaded, FY07 ,
no contingency)
26
3.5.3 Camera Body and Mechanisms
Double-humped profile shows prototype development
prior to CDR, then full production in FY09
Budget Estimate of 5.3M(Fully loaded, FY07 ,
no contingency)
27
SummaryTowards a Baseline Design

• Prototyping high-risk technologies and designs
• Silicon sensor research
• Focal plane metrology methods
• Distilling the key requirements
• See LSST-1153 LSST Camera Requirements and
  Working Parameters
• Developing a complete working design
• Including tracking needed trade studies and
  prototypes
• Laying out an assembly plan and subsystem
  deliverables
• Identifying development risk and mitigation plans
• We are in the middle of the process of bringing
  the Camera design together into one
  self-consistent design
• The result of this process will be a baseline
  design suitable for our project execution plan,
  proposal, and CD-1