Abstract
An upgraded state of the art servo-control system, to replace the original ContravesTelescope control system for the ASI MLRO telescope, was completed by CybiomsCorporation with support from e-GEOS in March 2016..This system uses state of theart digital electronics, servo-control hardware, and control software to perform SLR(from LEO to GEO) and LLR. The command is performed by the existing MLRO HP-RT machine writing the real-time commands to its IEEE 488 GPIB ports supportingthe AZ and EL axes at a rate of 10Hz and receiving the observed data at the samerate for the GUI needs of station operations. A separate servo-control computerreceives the GPIB commands to drive the new servo-electronics in real-time. Thetracking system currently provides the capability to point, acquire, and track satellitesthat has high orbit accuracy with a laser beam divergence of a few arcseconds, betterthan the previous controller. Data rate is improved above all for Lageos and HEOsatellites. Results are highlighted in the poster.
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MLRO: Scope of Applications
1. Laser ranging of ILRS and other Satellite1. LEO2. Lageos3. HEO4. GEO
2. Lunar laser Ranging1. Apollo 112. Apollo 143. Apollo 15
3. Other Astronomical / Optical /Electro-optical Experiments
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MLRO: Prior Telescope Servo-Configuration
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MLRO: New Configuration
1. Modern state of the art modular servo-controller is incorporated to address the needs ofMLRO; shaded region shows the new controller.
2. The system uses: (1) the MLRO real-time computer and its GPIB, (2) telescope interfacessuch as Limit switches, E-STOP, (3) encoders like the Inductosyn and resolver, as well asthe (4) LAN to complete the seamless integration with the overall system;
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MLRO: Telescope Servo-Controller
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New servo-controller
MLRO: System Upgrade Requirements
1. Implement a switchable servo-configuration from the prior configuration to the new
configuration
2. Ensure that the SW and HW has the capability to handle large range of angular velocities
(0.1-6000 mdeg/sec) encountered in tracking LEO to LLR;
3. Receive real-time commands from the Controller and act upon it every frame of 100ms;
4. Send data back to the real-time controller upon request to support the GUI operations;
these commands are variable and are not repeated every frame.
5. Support handheld operations for any manual activities;
6. Support 1 arcsec laser beam divergence operations;
7. Perform all prior MLRO operations to meet or exceed performance;
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MLRO: HW/SW issues encountered 1. Servo Technology: Manufactured during 1996-98; servo electronics became obsolete;
2. Digital Interface: IEEE 488 migrated to higher versions; absence of product level support
even from a reputed US manufacturer like the National Instruments; GPIB incompatibility
between the old and new implementations;
3. Real-time HP computers (HP-RT): HP dropped support 20 years ago; increasing the scope
of a task is extremely difficult;
4. Insufficient bandwidth: low bandwidth (10Mbps) TCP/IP to interconnect the various
computers;
5. Real-time SW: Customized software uniquely matched the 4 HP-RT machines with the
Contraves servo system and the existing SLR tasks; utilization efficiency of the CPU was
very high (>90%); SW tasks consumed significant CPU time, thus inhibiting the addition of
other features or causing interruptions;
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MLRO: Lessons learned1. Any upgrade strategy, is largely guided by the technical and operational constraints of the
existing system unless it is a very simple part or module; this is particularly true of SW
2. Even in a world of modular SW, the aftershocks of SW changes, in a HW-SW based
configuration, are often felt in many areas for a long time;
3. Even when direct knowledge of a system exists, the issues are often more complex and
intertwined than what is seen from the periphery;
4. Upgrades are often oversimplified.
5. It is always a collaborative team effort with the customer and their support staff to make it
happen;
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MLRO: Tracking Simulation
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0.120
0.140
0.160
0.180
0.200
-5.0E-04-4.5E-04-4.0E-04-3.5E-04-3.0E-04-2.5E-04-2.0E-04-1.5E-04-1.0E-04-5.0E-050.0E+005.0E-051.0E-041.5E-042.0E-042.5E-043.0E-043.5E-044.0E-044.5E-045.0E-04
0 50 100
150
200
250
300
Velo
city
(deg
/dse
c)
O-C
(deg
ree)
Time
1. Each Division is 5E-5 degree 0.18 arcsec;2. 1 sigma for tracking at low angular rates <100 mdeg/sec) is <20 milliarcsecs, limited
primarily by the encoder hardware
MLRO: Real-time tracking issues to overcome
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1. Synchronization issues for AZ and EL real-time commands caused the command to takemore than the expected 100ms update rate or failed to deliver the command until much later(see the secondary axis and the green dots) causing command latencies across the GPIBinterface and perturbing the AZ, EL pointing and losing the track;
2. Code had to be optimized just right for reducing the above latencies.
MLRO: Early issues for Satellite Tracking
Missing data due to real-time command synchronization issues
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0
10
20
30
40
50
60
70
80
90
100
8485
084
890
8493
084
970
8501
085
050
8509
085
130
8517
085
210
8525
085
290
8533
085
370
8541
085
450
8549
085
530
8557
085
610
8565
085
690
8573
085
770
8581
085
850
8589
085
930
8597
086
010
8605
086
090
8613
086
170
8621
086
250
8629
086
330
8637
086
410
8645
0
Lageos2 -s77y2015d176t2334_5986: Tracking efficiency (%) vs. Time of the day (secs)
Lageos2 -s77y2015d176t2334_5986: Trackingefficiency (%) vs.Time of the day(secs)
1. Missing commands manifested as “Gaps” OR reduced RX rates causing loss of data; 2. These problems were solved subsequently to achieve consistent tracking;
MLRO: Improved Tracking Efficiency (%)
1. System tracking capability for Galileo 7201;2. each horizontal division is 10 seconds3. Laser fires at 10Hz and in a 10 second time bin, we have 100 laser fires;4. Number of data points in each RX bin represents the % of tracking efficiency;5. Tracking efficiency >90% achieved for laser BD = 1arcsec on Galileo
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0
10
20
30
40
50
60
70
80
90
100
8484
284
852
8486
284
872
8488
284
892
8490
284
912
8492
284
932
8494
284
952
8496
284
972
8498
284
992
8500
285
012
8502
285
032
8504
285
052
8506
285
072
8508
285
092
8510
285
112
8512
285
132
8514
285
152
8516
285
172
8518
285
192
8520
285
212
8522
285
232
8524
285
252
8526
285
272
8528
285
292
8530
285
312
8532
285
332
8534
285
352
8536
285
372
8538
285
392
8540
2
Tracking Efficiency % (Y-axis): MLRO-Cybioms Controller - Galileo 7201-s77y2015d357t2330_7201.mts
MLRO: Galileo Tracking
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MLRO: Lares Tracking
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MLRO: Glonass Tracking
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MLRO: Tracking Starlette
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Summary
1. Tracking resolution (0.05 arcsec) and RMS jitter (as low as 10-20 milliarcsec)were obtained, which is better than the previous controller;
2. 1 arcsec laser BD was exploited without any loss of data for tracking HEOsatellites, which points to the stable tracking capability of the HW& SW;
3. Lageos tracking was successfully tried with 2 arcsec, even though there is NOlink related need for that orbit for a 1.5 meter system;
4. A quickly switchable (<15 minutes) configuration with the prior controller wasestablished to support dual modes;
5. Minimal OR no changes were made to the existing GUI allowing ease of everyday operations;
6. Secure remote connections from USA to the MLRO network supported most ofthe SW developmental testing and tracking, which helped enormously;
7. The technical and operational support provided by the MLRO team was superband Cybioms extends its gratitude to such a fine team.
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