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.

1

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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-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

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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

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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

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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

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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

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092

8510

285

112

8512

285

132

8514

285

152

8516

285

172

8518

285

192

8520

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212

8522

285

232

8524

285

252

8526

285

272

8528

285

292

8530

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312

8532

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332

8534

285

352

8536

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372

8538

285

392

8540

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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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