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Intro

Accurate Ranging system for Geodetic Observation (ARGO)

ARGO

  • Korean SLR project
  • Accurate ranging system for geodetic observation

Development Period

  • 2008–2016 (nine years)

Final Goal

  • One mobile system (40 cm/10 cm): ARGO-M (2008–2013)
  • One fixed system (100 cm): ARGO-F (2013–2016)

Objectives

  • Space geodesy research and Global Earth Observation System of Systems/Global Geodetic Observing System (GEOSS/GGOS) contribution by laser ranging for satellites with Laser Retroreflector Array
  • Precise orbit determination through laser ranging measurement with millimeter-level accuracy
  • Contribution to international SLR societies and International Laser Ranging Service (ILRS) network participation

History

Development

  • 2004-12 – 2005-11 Research on foundational techniques
  • 2005-07–2006-06 STRM planning research
  • 2007 National R&D agreement with Ministry of Science and Technology
  • 2008 Start of ARGO-M SLR system development

ARGO-M

  • 2008–2012 ARGO-M (movable SLR system) development
  • 2012-09-26 First shot
  • 2012-11-02 Became a member of ILRS (observatory: DAEK)
  • 2013-10-22 Observation data uploaded to ILRS
  • 2014-04-11 Certification as ILRS active station
  • 2015-04 ARGO-M Seojong-Si move & observatory dedication ceremony

ARGO-F

  • 2013-07 KASI-Geochang-Gun memorandum of understanding
  • 2013-12 High-speed TMS design (research commissioned)
  • 2013-08 Purchase of observatory site (4,950 m2)
  • 2014-06 International joint development contract with EOS in Australia
  • 2014-11 Observatory groundbreaking ceremony
  • 2015-10 Completion of observatory construction
  • 2016-04 Observatory dedication ceremony

Facilities

Korea Astronomy and Space Science Institute (KASI) has developed the first SLR system, ARGO-M, which is now in normal operation at KASI headquarters with the station code of DAEK assigned by the ILRS in 2012. Thus, Korea now joins 25 countries that operate SLR systems in support of the international laser tracking network. ARGO-M provides the high-accuracy ranging data that are essential for development and improvement of the International Terrestrial Reference Frame, precision orbit determination, and other space geodesy data products that are essential to understanding global change. ARGO-M will be moved to Sejong city in 2014 to establish the fundamental station for space geodesy research (Beutler et al. 2005).

ARGO-M is designed to enable 2-kHz laser ranging for both daytime and nighttime tracking of satellites at altitudes between 300 and 25,000 km. It has a bistatic optical path employing 40-cm receiving and 10-cm transmitting telescopes. For daylight tracking and 2-kHz laser ranging, ARGO-M adopts an event timer, a special narrow-band-pass filter, and a high-energy laser with 2.5 mJ of energy per pulse at 2 kHz. Fig. 1 shows the appearance of the ARGO-M at the headquarters of KASI, and Fig. 2 shows the firing of the laser from ARGO-M.
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Figure 1. Appearance of ARGO-M

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Figure 2. Laser Tracking in ARGO-M

ARGO-M consists of six subsystems: the optical system, optoelectronic system, laser system, tracking mount, operation system, and dome. In addition, it also has laser hazard radar to monitor airplanes, a ground target to calculate the system delay, and weather sensors to correct for the atmospheric delay and refraction using the Marini–Murray model (Marini 1972). Fig. 3 shows the configuration of ARGO-M, and its major specifications are listed in Table 1.
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Figure3. Configuration of ARGO-M

Major specifications of ARGO-M Information Table
Item Parameter Description/value
Telescope Optical path Bistatic
Rx/Tx telescopes 40/10 cm
Primary mirror F-ratio 1.5
Transmit beam divergence 5–200 arcsec
Max slew rate and acceleration 20 deg/s (AZ), 10 deg/s (EL); >5
deg/s2 (AZ), >2 deg/s2 (EL)
Tracking & pointing accuracy <5 arcsec
Detector Type C-SPAD
Quantum efficiency 20%
Primary mirror F-ratio 100 ps to 2 ns
Laser Wavelength 532 nm
Pulse energy or power 2.5 mJ @ 2 kHz
Pulse width 50 ps
Repetition rate of operation 2 kHz
Beam diameter @ Tx telescope 7.5 cm
Timing system Type Event timer
Single-shot RMS resolution 3.5–4 ps
Aircraft detection Type Radar
Max. detection range 40 km
.

Table 1. Major specifications of ARGO-M

ARGO-F (Fixed), Gamak Station

Gamak Station is designed as a two-story building (Fig. 4). It consists of the SLR lab, AO lab, DLT lab , operation room, electrical room, UPS room, and offices. The temperature and humidity of the SLR, AO, and DLT labs are controlled. The station is located at San162 Gwajeong-ri, Sinwon-myeon, Geochang-gun, Gyeongsangnam-do, Korea.
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Figure 4. ARGO-F design

Telescope

The ARGO-F telescope was designed as a confocal paraboloid beam expander (Mersenne) configuration with a primary mirror having a focal ratio of f/1.5 and a Coude path. It can point accurately to an object in the sky to 1 arcsec and can track at 30 degrees per second (AZ) and 20° degrees per second (EL) within 1 arcsec accuracy. It is a common Coude type having the same transmit and receive paths. Its optical tube assembly will be manufactured by EOS Space Systems in Australia, and its tracking mount will be manufactured by Justek in the Republic of Korea.

Laser

The ARGO-F will have two lasers, for laser ranging and for space debris laser ranging. The first is a Nd:YAG crystal solid-state laser with a wavelength of 532 nm. Its pulse width is less than 20 ps, and its repetition rate is 60 Hz. Each pulse has a nominal energy of 15 mJ. The second laser is a high-energy laser with a wavelength of 532 nm that is manufactured by EKSPLA. Each pulse has an energy of less than 2500 mJ. Its pulse width is 4–6 ns, and the repetition rate is 10 Hz.

Major specifications of ARGO-F Information Table"
Type Nd:YAG
Wavelength 532 nm
Pulse width ≤20 ps
Primary mirror F-ratio 1.5
Repetition rate 60 Hz nominal (can support collision band avoidance)
Pulse energy @ 532 nm 15 mJ nominal, 20 mJ maximum (average power ≥1 W)
Beam quality M2 ≤ 1.35

Table 2. Major specifications of ARGO-F

Major specifications of DLT Information Table
Type Site
Wavelength 532 nm
Pulse width ≤4–6 ns
Repetition rate 10 Hz
Pulse energy @ 532 nm 2500 mJ (average power ~25 W)

Table 3. Major specifications of DLT

Transmitting/Receiving (Tx/Rx) Optical System

The Tx/Rx system consists of a T/R disk mirror, C-SPAD, spatial filter, spectral filter, and neutral density filter. The main purpose of the Tx/Rx system is to switch between the transmitting laser and reflected receiving laser using the T/R disk mirror and to detect the laser signal reflected by a satellite. The T/R disk mirror has two through-holes synchronized to the laser firing and is rotated at 30 Hz for a 60 Hz laser repetition rate.

Representative Result

Sejong SLR system joined ILRS network

  • Registration Date: 2015-08-07
  • Code and Monument Number – Sejong (SEJL), 7394
  • DOMES Numbers: 23942601

10kHz ARGO Range Gate Generator and Operating System Development

  • Existing 2-kHz repetition laser tracking stations: fewer than about 10 ILRS stations
  • KASI 10-kHz laser tracking system: the first developed in the world (2015-05)
  • ARGO-M performance upgrade: 2 kHz → 5 kHz (owing to the installed laser specifications)
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ARGG : ARGO Range Gate Generator

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10kHz ARGO Range Gate Generator Test Block Diagram

Data of Stella Screenshot

SLR Raw Data of Stella

Data Processing Result of Stella Screenshot

SLR Data Processing Result of Stella