OGS

Technical data
Configurations
Instrumentation
Configurations
Space debris website

The telescope

Latitude: 28º 18' 03.4N Longitude: 16º 30' 42.6"W Altitude: 2393m

The Optical Ground Station (OGS), installed in the Teide observatory 2400 above the sea level, was built as part of European Space Agency (ESA) long term efforts for research in the field of inter-satellite optical communications. The original purpose of the station, equipped with a telescope (1m aperture), is to perform the in-orbit test of laser telecommunications terminals on board of satellites in Low Earth Orbit and Geostationary Orbit. Since 2001, the ESA survey of Space Debris in the Geostationary Orbit and the Geostationary Transfer Orbit is also being carried out with a devoted wide field camera attached to the Ritchey-Chretien focus. Furthermore, approximately a third of the observing time is used for basic astronomical research from ESA and IAC science teams with dedicated instruments either in the coudé or in the Ritchey-Chretien foci.

The Optical Ground Station was inaugurated in 1995. The Instituto de Astrofísica de Canarias participated in the integration of the station instruments and has since then been in charge of the station operation. Since January 2001, ESA-ESOC has been carrying out periodic survey campaigns of the space debris in GEO and GTO. This is the contribution of ESA to the worldwide common efforts on this task with NASA and NASDA (National Aerospace and Defense Agency of Japan).

Since November 2001, the bidirectional link with GEO satellite ARTEMIS has been established in more than 100 successful sessions. This is in practice the first world stable free optical laser link ground-satellite. The purpose of this programme is the analysis of the effect of atmospheric turbulence on optical communications performance between ground stations and satellites in the geostationary orbit. Additionally, since 2002, a sodium Laser Guide Star has been implemented by th High Spatial Resolution group in the IAC in order to analyse the short/long term variation of the height, width and density of the sodium mesospheric layer. This study is part of the first generation of adaptative optics instruments development.

In September 2003, it was performed the validation test of the LUCE optical terminal, the optical payload of OICETS satellite successful launched in august 24th 2005 by NASDA. In addition, since april 2004 a periodical links programme with SMART-1 satellite, in its trip to the moon in order to characterize turbulence effects in the optical links to the deep space, has been carried out.

Finally, the OGS has actively participated in the Lunar laser Communications Demonstration (LLCD) with the NASA’s spacecraft Lunar Atmospheric and Dust Environmental Explorer (LADEE) for transmission and reception of information through laser rays.

OGS telescope main features:

  • High speed: up to two degrees per second, with highest acceleration 0.5 deg/sec2
  • High pointing accuracy: average error in any orientation better than 10arcsec.
  • High tracking accuracy: average error 2.5 arcsec/hour

Configurations

OGS telescope can work using three different configurations, each of them with its own secondary mirror:

  • Básic Ritchey-Chrétien, 13.3m focal, small field, useful for some science observations.
  • Coudé, 38.95m focal, used for communication tests with Artemis satellite and other satellites using an infrared laser.
  • Ritchey-Chrétien, 4.5m reduced focal and wide field (0.7×0.7 degrees).

The launching optical system of the communications equipment consists of a 25 W Ion Argon laser to pump a titanium-sapphire laser tunable from 760 to 890 nm (6W). The beam is divided into four sub-apertures in the optical bank in order to mitigate the effect of turbulence in the uplink.

The receiving box of the communications system is equipped with a spectrometer, a polarimeter, an avalanche photodiode feeding a Bit Error Rate analyser, and a Pointing, Acquisition and Tracking system in closed loop. The LGS is generated with a dye laser tunable in the sodium D2 line (1.5 W).

Instrumentation

Instrumentation for satellite communication tests

  • Spectrometer. Spectral range between 750 and 900 nm. Resolution better than 0.1 nm.
  • Astrocam CCD camera. Format: 1152×1242 pixels.
  • Tunable laser between 750 and 900 nm, with power up to 5 W.

Spatial Debris Observation Camera

  • CCD of 4096×4096 pixels. The detector consists of a 4 EEV 42-40 chips mosaic, each with 2048×2048 pixels.
  • Pixel size: 13.5×13.5 µm².
  • Spatial scale: 0.62″/pixel.
  • Field of view: 0.709°x 0.709° (diagonal: 1°, surface: 0.5 squared degrees).
  • Cooled to 160 K using liquid nitrogen.
  • Dark current: less than 2 electrons/hour/pixel.
  • Front illuminated devices.
  • Spectral range between 400 and 1050 nm.
  • Quantum efficiency at 700 nm: better than 40%.
  • Pixel to pixel illumination response differences: less than 2%.
  • Number of bad pixels: less than 100 in each chip.
  • Readout time: 12 seconds.
  • Readout rate: adjustable between 6 and 50 µs.
  • Readout noise: less than 8 electrons/pixel.
  • Charge transfer efficiency: better than 0.99999
  • Designed to work in the modified Ritchey-Chrétien configuration with a focal relation of 4.5.

Other features

  • Three different secondary mirrors (one for each optical configuration), that must be exchanged when changing the telescope configuration.
  • Two shutters: the first one is an E100 Iris which allows minimum exposures of 125 milliseconds. The second one is a rotating disk shutter which allows minimum exposures of 5 milliseconds. Exposure time precision when using both shutters: 1 millisecond.
  • Meteorological station to measure the wind (speed and direction), pressure, relative humidity and temperature outside the dome.
  • All the instrumentation can be remotely controlled, including pre-programmed sequences of measurements.

Manuals

Telescope and dome control system for operations at the OGS

A. Starting up the telescope and pointing an object

  1. START voltage control by pushing the button placed in the box on the left of the control PC.

  2. Log in in the control PC: Pressing upper right button on the screen, log in window will appear.

    (user and password can be consulted on the control room manual)

  1. Turn on the dome by pressing ON button on the DOME window.

  2. In order to open shutters, push OPEN button of the corresponding shutter. In case you want to stop it, press STOP. Shutter status will be ‘UNKNOWN’.

  3. To turn on the telescope, press ON on the TELESCOPE window. If the square on the right of the INIT button is not green-coloured the telescope should be initalized. If it is the case, press INIT.

  4. To open the mirror covers, push OPEN button in the DEW-CAP window.

  5. Introduce the coordinates of the object to observe and press SLEW.

  6. Press AUTO from DOME if the dome following the telescope is wanted.

  7. To stop both telescope and dome push STOP on the TELESCOPE window and DOME window respectively.

B.  Stopping the telescope and parking it on the zenith position.

  • Stop the telescope and the dome by pressing STOP button in the TELESCOPE and DOME windows.

  • Press CLOSE button in the DEW-CAP window to close mirror covers.

  • Press POSITS in the TELESCOPE window.

  • A new window will appear (PREDEFINED POSITIONS). Select ZENITH option by pushing POSIT button on the right.

  • In the MECHANICAL COORDINATES window, press SLEW.

  • Close shutters pressing CLOSE button in the appropriate window.

  • Turn off the telescope and the dome by pushing OFF in the TELESCOPE window and also in the DOME window.

  • STOP voltage control by pressing the button on the box placed on the right of the control PC.

  • Log off in the control computer: a window with the logoff option will appear when the upper right button on the screen is pressed.