Download Slide 1 - project team

The Active Optics System
S. Thomas and the AO team
The Active Optics System
• Maintain system alignment
• Maintain surface figure on three mirrors
 Focal plane map
 Sensitivity matrix
 Prior knowledge of the
system
 Bending modes
 Catalog
 Calibration Product
Crosstalk
Camera DAQ corrected
images
for WFS
images
Science
images
from DM?
Crosstalk
corrected
images
Wavefront Sensor
Estimation (WEP)
For each detector:
- Instrument Signature Removal
- Source Selection
- Masters computation
- Compute the Zernike
Coefficients
Zernike
Coefficients
for each
detectors
M1M3 Controller
Active Optics
Control System
-
Optimal estimator
Control algorithm using a
cost function
M2 Controller
Forces
M2 hexapod
Controller
Camera hexapod
Controller
2
WEP
Curvature sensing enables
significant flexibility in selecting
sources due to the large field of
view of the area sensors
split sensors: because of the fast
f-number (f/1.23) and crowded
focal plane, using a beam
splitter and delay line or
physically moving the detector
will not work.
LSST WFS challenges
- 61% Central Obscuration
- f/1.23
- Off-axis Distortion & Vignetting
(~1.7o)
- Field Dependence (covering
1.51° to 1.84°)
Use multiple sources to
increase S/N, to help
average out atmosphere
noise, and to alleviate
problems due to vignetting.
The defocus for the WFS detectors is +/- 1mm (TBC)
3
WEP Status
- Publication of the update to the basic curvature
sensing algorithm by Bo Xin (large central
obscuration, small f/number, distortion and
vignetting)
- Requirement document close to completion
- Understand interfaces
- Understand calibrations
- WEP translated from Matlab to Python
- Start to include the WEP in the DM stack
4
On sky tests
Chuck Claver and Bo Xin had a one-night observing run on Magellan (3/30/2015)
• To test LSST curvature wavefront sensing software
• IMACS f/2, SLOAN r filter, 26.5% central obscuration
• Piston secondary mirror to get defocused donut images
• Nominal setup: 3.5mm image defocus.
• Analysis of wavefront was done in real time.
• Good agreement in general between system input and the curvature wavefront estimates
5
AOCS Status
• An algorithm written in Matlab exists and Paul
Lotz will be in charge of the translation in
Labview.
• Include the telescope models and use PhoSim
to built the look-up-table (temperature,
elevation and azimuthal angle).
• “closed-loop” done using Zemax simulations
and bending modes of the mirrors
• Need to close the loop using PhoSim
6
7
Data Quality Control
• In the WEP:
– Source Selection
– Master
Consequence: The Zernike coefficient for the specific
wavefront sensor is truncated.
• In the AOCS:
– Check forces sent to the various controllers
Consequence: TBD?
8
Future Work
• Write the ICDs for the different mirrors and
hexapods, and also with Data Management
• Include the telescope models in the look-uptable (temperature, elevation and azimuthal
angle).
• Include the AOS code in the DM software
stack (one first step is to add the code on
github)
9
Issues
- Should we send the offsets to the mirrors or
the actual forces
- Need to update the interface documents (to
the mirrors and hexapods)
- How to make this system automatic and
robust?
- Still a few unknown, some of which we won’t
know before going on sky (such as how often
do we want to update the forces)
10
11
Wavefront sensor camera
ICD provides specifications and tolerances:
• Offset distance for intra/extra focal sensors
+/- 2mm??
• Flatness
10 microns rms
• Placement wrt science FPA
+/- 20 microns in along z-axis
• Sensor noise and QE
Matches science sensors
• Useable effective sensor area
80 arcmin2 x two halves
• Data exchange and format
12
Image quality drives AOS
related requirements
•
Science Requirements Document (LPM-17)
LSST System Requirement (LSE-29)
–
–
•
Observatory System Specifications (LSE-30)
–
–
–
–
–
•
Optical prescription
Allocates 0.30 arcsec to the Camera
Allocates 0.25 arcsec to the Telescope
Additional AOS error is captured fully in the Telescope allocation
Mean slew and settle time of 5 sec. between visits
Telescope and Site Requirements (LSE-60)
–
–
•
Mandates 0.4 arcsec FWHM from the system (Telescope + Camera)
Plate scale control not required
AOS functional requirements
Alignment and Compensation
Detailed Image budgets
– Telescope & Site image budget (LTS-123, LTS-124)
– Camera System (LCA-17)
TMA Review • Tucson, Arizona • May 9-10, 2013
Title
13
Covariance Analysis
(Algorithmic
+
atmospheric)
Covariance
matrix
Total covariance is almost entirely
dominated by atmosphere
– Diagonal elements (lower left) similar
– Singular values (lower right) also similar;
some increase for low singular values
Variance
Singular values
14