Evaluating generalised calibration / Fay-Herriot model in CAPEX
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Transcript of National Research Council Canada Conseil national de recherches Canada Observing Efficiency and...
National ResearchCouncil Canada
Conseil nationalde recherches Canada
Observing Efficiency and Reliability of Gemini South MCAO
Glen Herriot
Herzberg Institute of Astrophysics
National Research Council Canada
Observing Losses for MCAO
Weather
Satellites
Failures
Other Observatories
Airplanes
Purpose
• This analysis estimates the overall observing efficiency of MCAO, which is NOT specified in the requirements documents.
Top Level Requirements
• Lose no more than 10% of scheduled time to failures
• CoDR book assumed that half the nights in a year will be scheduled for MCAO, (180 x 10 hr).
• But this is a classical scheduled spec. We have taken it to mean 1800 hours per year, queue-scheduled.
• Maximum object setup time (excluding telescope slew and acquire PWFS stars) < 120 seconds
• Telescope Slew and PWFS2 acquisition < 120 seconds.
Lasers Must Not Interfere With Satellites
Fraction of Time Laser Must Be Shut Down.
Lost time due to Satellite Interference
0123456789
0.1 0.2 0.3 0.4 0.5 0.6 >0.7
No. of stars vs. fraction of time lost
Worst Case Laser Duty CycleLaser Clearing House Permitted Laser Operation SAO65711 from Lick site
0
1
2
0 1 2 3 4 5
Time (hours)
Lase
r O
n =
1 or
Off
= 0
Slightly Better Than Typical Case
Laser Clearing House Permitted Laser Operation RA14:28 Dec 43:24 Lick site
0
1
2
0 1 2 3 4
Time (hours)
Lase
r O
n =
1 or
Off
= 0
Good Case
Laser Clearing House Permitted Laser Operation for Star 231 from the MMT
0
1
2
0 1 2 3 4 5 6
Time (hours)
Lase
r O
n =
1 or
Off
= 0
Typical: 28 ‘On’ events, 41% Off time; 20 minute max. On ; 1 minute median Off
Typical Permitted Laser Operation (Star 46158 from Lick)
0
1
2
0 1 2 3 4 5
Time (hours)
Lase
r O
n =
1 or
Off
= 0
Histogram of Permissible Time Durations “Laser On”
Distribution of Laser On-Time
020406080
100120140160180200
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.0
011
.00
12.0
013
.00
14.0
015
.00
>15
MIN
Time Minutes
Probability of “Laser On” vs. Duration > T, ( Avoid Satellites)
1 cum( )slot
m
0 20 40 60 80 100 1201 10
4
1 103
0.01
0.1
1Probability vs. Length of time on
Time T -minutes
P(t
>T
)
exp(-T/)
exp(-T/ +bT2-ct3)
Minutes0 20 40 60 80 100
10%
1%
0.1%
0.01%
100%
Queue Scheduling Increases Odds of Finding a Time Slot.
e TcTbTTt
32
)Pr(
))Pr(1ln(
))Pr(1ln(
Tt
sucN
NTtsuc ))Pr(1(1)Pr(
Probability of 1 slot of length t>T
Probability of success with more targets in queue.
Solve for Queue length needed:
Queue Length - vs. Integration Time >T1 Event Probability of success
Int Time P(t>T ) 0.5 0.6 0.7 0.8 0.9 0.95 0.995 37.9% 1.5 1.9 2.5 3.4 4.8 6.3 9.7
10 16.5% 4 5 7 9 13 17 2615 8.1% 8 11 14 19 27 35 5520 4.4% 15 20 27 35 51 66 10125 2.7% 26 34 44 59 85 110 17030 1.8% 39 52 68 91 130 170 26135 1.2% 56 74 98 130 187 243 37340 0.9% 76 100 132 176 252 328 50545 0.7% 99 130 171 229 327 426 65550 0.6% 124 164 216 289 413 537 82655 0.4% 154 204 268 359 513 667 102660 0.36% 192 253 333 445 637 828 1273
Thin Cirrus Clouds - Blind LGS• Multiple CW LGS
suffer from “fratricide” unless sky is photometric.
• Pulsed laser may tolerate ~20% loss on both upward and downward path.
< ~1/3 magnitude extinction.
Fraction of Year Lost to Clouds-CTIO 1997-1999
MCAO
CW Pulse Useless for any Science
1997 46% 32% 21%
1998 49% 31% 19%
1999 41% 26% 15%
Average 46% 30% 18%
Useful Science Time Lost to MCAO - Caused by Thin Clouds
Fraction of Science time lost
CW Pulse
Classical 33.3% 13.9%
Queued 18.9% 8.9%
Failures
Mean Time Before Failure (MTBF)
Reliability MTBF HrsAdaptive Optics Module 528Beam Transfer Optics 1107Laser Launch Telescope 25000SALSA ( satellite, aircraft, laser safety system )
5085
Laser ( minimum MTBF for <10% downtime from failures )
>48
Gemini South MCAO MTBF 42
Overall reliability calculated from subsystems’ Mean Time Between Failure.
11
i itotal MTBF
MTBFReciprocal of sum of reciprocals
• Total MTBF is poorer than any individual subsystem’s reliability.
•Total MTBF dominated by “weakest link in a chain.”
Subsystem reliability: e.g., Beam Transfer Optics MTBF
Hours
Shutter & Beam Dump 50000Relay Optics 6249M6, M7 Slow tip/tilt & steering 8333Diagnostics 200005 Fast steering mirrors 2000Rotator 50000Electronics 30000
Overall BTO reliability 1107
Sensitivity Analysis: MTBF & Downtime vs. Laser Reliability
0
50
100
150
200
250
300
350
25 40 48.3 100 200 1000 5000
%
Laser MTBF Hours
hr
Overall MCAO reliability
% Downtime due to failures
Laser MTBF Hours
0
5
10
15
20
25
30
25 40 48.3 100 200 1000 5000
Interference With Other Observatories, Aircraft
• Gemini South neighbours at CTIO and SOAR have right of way for natural guide star observations.
• Estimate ~1 incident per night where MCAO must shut down, costing ~2% lost time.
• Interference problem is Rayleigh “light sabres” clashing, not the 90 km beacon itself.
Observing Scenarios for Satellite Interference Studies.
Scenario
Slew, Acquire PWFS
NGS Astro-metry
Laser Launch, Acquire
Science Integra-
tion
Queue Size
N
Lost Time
%
Full overhead 2.0 2.0 0.47 30 150 12.9
Astrometry + Partial setup
1.3 - 0.47 30 150 11.8
Partial setup, no astrometry
0.3 - 0.47 30 150 9.1
Calib’n. while Laser off
2.0 2.0 0.47 3 x 15 TBD??
8.3
Dwell on same Object
2.0 2.0 n x 0.47 n x 6.6 1 43%
% Time Sky Useful for Astronomy, But MCAO Not Available.
Availability Calculation
Failures from MTBF Calculation 10.0%
Cirrus Losses for pulsed laser 13.9%
Satellite Interference *** 8.3%
Other Observatory Interference 2%
Total Lost time best case 26%
*** Optimistic Case:
Do Sky calibrations, change filters and gratings while laser off. (~38.5% of time)
Availability Calculation:Combining lost-time factors
i
itotal lossloss ))Pr(1(1)Pr(
A. Convert each lost-time factor to a Probability of Success. Multiply together to get overall ‘up-time’ percentage.
B. Subtract ‘up-time’ from 1 to get total percentage of time lost due to all factors
Lost Time: Overhead, Clouds, Satellites, Failures
Satellite Interference ScenarioSatellite Loss
Pulse CW(MCAO)
Full Setup + Astrometry 12.9% 30% 38%
Partial Setup + Astrometry 11.8% 29% 37%
Partial Setup, no Astrometry 9.1% 27% 34.9%
Part Setup- no astr'y. – cal. if laser off 8.3% 26% 34.3%
Dwell on Same Object 43% 54% 59%
Laser Format
Total Down time
PDR Agenda
Friday, 5/25
0800 Laser System
0900 CTIO Sodium Studies
0915 Control System
0945 Break
1000 RTC Electronics
1045 Safety System
1100 Availability analysis
1130 Closed vendor sessions
1200 Lunch
1300 Cost and schedule
1400 Committee session
1700 Committee report
1800 Adjourn