TMT.SEN.PRE.13.040.REL01 Development and validation of vibration source requirements for TMT to...
23
TMT.SEN.PRE.13.040.REL01 Development and validation of vibration source requirements for TMT to ensure AO performance Hugh Thompson and Doug MacMartin AO4ELT3 Conference, Florence, Italy 26-31 May 2013
TMT.SEN.PRE.13.040.REL01 Development and validation of vibration source requirements for TMT to ensure AO performance Hugh Thompson and Doug MacMartin
TMT.SEN.PRE.13.040.REL01 Development and validation of
vibration source requirements for TMT to ensure AO performance Hugh
Thompson and Doug MacMartin AO4ELT3 Conference, Florence, Italy
26-31 May 2013
Slide 2
TMT.SEN.PRE.13.040.REL01 Presentation Outline
Slide 3
TMT.SEN.PRE.13.040.REL01 3 Rough scale of the problem Many
current AO systems are limited by vibration ALTAIR on Gemini sees
vibration of ~10 mas rms after correction Survey of similar
problems at several telescopes: Caroline Kulcsr ; Gaetano Sivo ;
Henri-Franois Raynaud ; Benot Neichel ; Fran ois Rigaut, et al.
"Vibrations in AO control: a short analysis of on-sky data around
the world", Proc. SPIE 8447, Adaptive Optics Systems III, 84471C
(September 13, 2012) For TMT the entire on-axis NFIRAOS budgeted
wavefront error of 187 nm corresponds to only ~ 5 mas of
tip/tilt
Slide 4
TMT.SEN.PRE.13.040.REL01 On Axis WFE Delivered wavefront187
First order turbulence compensation 117 LGS control loop 117 DM
fitting error 75 DM projection error 46 LGS WFS aliasing error 42
Tomography error 30 Servo lag 4 LGS WFS non-linearity 19 LGS WFS
noise 46 TMT pupil function 27 Opto-mechanical implementation 71
Telescope pupil misregistration 12 Telescope and observatory OPD 37
M1 static shape 26 M2 & M3 static shape 11 Segment dynamic
mis-alignment 14 Dome seeing 16 Mirror seing 14 Field dependent
astigmatism 0 NFIRAOS 51 Residual instrument 30 AO compomnents
errors & higher order effects 66 DM effects 49 LGS WFS & Na
layer 39 Control algorithm 21 Simulation undersampling 48 NGS Mode
WFE at 50% sky coverage 58 Residual tip/tilt jitter due to
windshake 16 Residual telescope vibration 10 Residual telescope
tracking jitter 17 Residual tip/tilt jitter due to turbulence 32
Residual plate scale mode due to turbulence 35 Residual plate scale
mode due to windshake 5 Field dependent wavefront error 20
Contingency 80 How do we flow AO requirements down? Segment dynamic
displacement (due to vibration) 10nm Telescope image jitter (due to
vibration) 10nm equivalent to 0.275 mas Pump impeller Balance Grade
6.3 ?
Slide 5
TMT.SEN.PRE.13.040.REL01 5 The questions in more detail What is
the sensitivity of image quality to vibration? How does this vary
with amplitude, frequency and location? What are the worst expected
sources of vibration with respect to these sensitivities? What can
be done to mitigate them? Do we need to increase AO error budget
allocation to vibration? What standards/requirements do we
have/will we develop to maintain acceptable vibration levels? How
will we assess and verify vibration performance against
predictions?
Slide 6
TMT.SEN.PRE.13.040.REL01 6 Finite Element Model FEM of
telescope structure includes nodes for each M1 segment, M2, M3 and
each instrument Optical sensitivity combined with nodal motions
from FEM determines performance effects due to: image jitter M1
segment motion
Slide 7
TMT.SEN.PRE.13.040.REL01 Additional model details AO rejection
curves included (median conditions) 15 Hz Type II controller for
tip/tilt 63 Hz DM bandwidth No additional narrowband rejection
Frequency-resolved calculations are smoothed Reasonable estimate of
rms performance, not worst case Using simple ground transmission
estimates (no soil and pier model) No direct transmission path
measurements for comparison (either soil or on telescopes)
Instruments modeled as lumped masses wrong above ~12 Hz 7
Slide 8
TMT.SEN.PRE.13.040.REL01 Modelling Goals Determine allowable
vibration source amplitudes Assess: Relative influence of location
of sources Main contributors to image jitter (M1, M2, M3, focal
plane) Sensitivity to source input frequency 8
Slide 9
TMT.SEN.PRE.13.040.REL01 Modelled Sources Unit forces are input
at 6 locations Pier Also covers sources in facility building with
an additional factor to account for attenuation through soil
Instruments (NFIRAOS, MIRES) on Nasmyth platforms Laser Service
Enclosure (LSE) Cable wraps (Az and El) 9
Slide 10
TMT.SEN.PRE.13.040.REL01 After smoothing, after AO rejection
Results combining M1 and image motion 10 Pier forcingNFIRAOS
forcing In both cases image motion is dominant above 10 Hz
Slide 11
TMT.SEN.PRE.13.025.DRF01 Check spatial correctability on M1 11
M1 response at 30 Hz AO spatial correctability is good; correction
is dominated by temporal bandwidth nm/N
Slide 12
TMT.SEN.PRE.13.025.DRF01 Combined M1 and image motion for all
sources 12 AO rejection Mass effect Telescope Pier 10x
Slide 13
TMT.SEN.PRE.13.040.REL01 Model Results Summary All modeled
telescope sources are roughly comparable in effect Pier forcing a
factor of 10 less impact Locations in facility building likely
reduce sources by an additional factor of 5-10 relative to pier
Performance most sensitive to forces 5-20 Hz M1 soft actuators
reduce M1 response at 30 Hz by factor of 10 Motion of M2 largest
contributor to image motion above 10 Hz Residual dominated by image
motion, not M1 above 10 Hz Means that feed-forward of M2 motion may
be effective Narrowband rejection of tones may also help Internal
flexibility of instruments not accounted for 13
Slide 14
TMT.SEN.PRE.13.040.REL01 Compare actual sensitivity with fit to
shaping filter for each source Filter W(f): f 1 =5 Hz f 2 =20 Hz
14
Slide 15
TMT.SEN.PRE.13.040.REL01 Vibration Budget Sensitivity (nm per
N) Fraction of budget Allowable force (N) Pier0.4335%20
Instruments3.750%3 LSE1.95%2 Cable wraps1.35% each2.5 each 15
Specification on rms force after filtering by shaping filter
(allows higher vibration at low or high frequency)
Slide 16
TMT.SEN.PRE.13.040.REL01 16 Source example Forces ~1N at 1- 2
Hz Frequency is low but higher harmonics can be problematic Large
numbers required for TMT has led us to turbine expander cooling
with no low- frequency reciprocating motion ESO study of
cryocoolers: Low-vibration high-cooling power 2-stage cryocoolers
for ground-based astronomical instrumentation Gerd Jakob,
Jean-Louis Lizon Proc. SPIE. 7733, Ground-based and Airborne
Telescopes III 77333V (July 16, 2010)
Slide 17
TMT.SEN.PRE.13.040.REL01 17 Source example in the summit
facilities 4-pole induction motors on 60 Hz AC generates ~29 Hz but
newer VFD equipment moves frequencies with system demand Do we want
this? Need tight imbalance requirements and single or multi-stage
isolation Large fluid cooler used to exhaust all TMT waste heat has
8 fans of Balance Quality Grade 1 Results in 10 N of force per
rotor or worst-case in-phase imbalance of all 8 rotors equal to 80
N At 59 Hz even 1 kN should be acceptable but careful tracking of
all equipment is required
Slide 18
TMT.SEN.PRE.13.040.REL01 Pipe vibration Konstantinos Vogiatzis
has made some initial models of turbulent flow in coolant pipes
Forces are low in straight runs, but elbows produce significant
broad-band forces 18 TMT is considering replacing water-glycol with
phase-change refrigerant to reduce coolant mass flow (and forces)
by a factor of 10
Slide 19
TMT.SEN.PRE.13.040.REL01 Impact of increasing the error budget
allocation to vibration An increase from 14 nm to 30 nm would not
dramatically reduce observing efficiency Roughly 3% impact in J
band
Slide 20
TMT.SEN.PRE.13.040.REL01 Things to do 20 On-going work needed
to: Develop the allowable vibration source budget allocated to
subsystems Improve estimate of propagation through soil (for
enclosure and summit facility sources) Improve all source estimates
Hopefully through force measurements made at a telescope near
you!
Slide 21
TMT.SEN.PRE.13.040.REL01 Conclusions 21 Vibration sources on
the telescope must be limited to a few Newtons Vibration sources in
the facility must be limited to a few hundred Newtons Possibly need
to increase AO error budget allocation to vibration Further
mitigation may be possible via M2 feed-forward Narrow-band
rejection algorithms Conventional cryocoolers are not acceptable
for TMT Keep summit facility source frequencies at 60 Hz when
possible Reduced sensitivities Allows effective use of ~ 5 Hz
isolators
Slide 22
TMT.SEN.PRE.13.040.REL01 Acknowledgements 22 The TMT Project
gratefully acknowledges the support of the TMT partner institutions
the Association of Canadian Universities for Research in Astronomy
(ACURA), the California Institute of Technology the University of
California the National Astronomical Observatory of Japan the
National Astronomical Observatories and their consortium partners
And the Department of Science and Technology of India and their
supported institutes. This work was supported as well by the Gordon
and Betty Moore Foundation the Canada Foundation for Innovation the
Ontario Ministry of Research and Innovation the National Research
Council of Canada the Natural Sciences and Engineering Research
Council of Canada the British Columbia Knowledge Development Fund
the Association of Universities for Research in Astronomy (AURA)
and the U.S. National Science Foundation.
Slide 23
TMT.SEN.PRE.13.040.REL01 Mass helps TMT dome = 2300 tons
Brunellescis dome = 37000 tons The Duomo likely doesnt have a
vibration problem! You can build large structures without vibration
problems
