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Institut für Astronomie und Astrophysik

Abteilung Astronomie

Sand 1, D-72076 Tübingen, Germany
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ORFEUS-SPAS in Detail

Echelle spectrometerstar trackerIMAPSBerkeley spectrometerteleskop coverTübingen electronics boxIMAPS electronicsDARA logoNASA logoDASA logoIMAX film cameraShuttle robot armTV camera at shuttle robot armantennaIMAX TV cameratelescope, lower halfsupportsupportsupporttelescope, upper halfEchelle electronicstelescope cover driverobot arm hookBerkeley electronicsBerkeley telemetryASTRO-SPASreflectionHimmel

This is a clickable image map (56KB) of ORFEUS-SPAS! Please load the image first!
Click onto that part of the image about which you want to learn more!


ASTRO-SPAS

The ASTRO-SPAS is a reusable science satellite, which is brought into space by the Shuttle. It is flying free during the mission, captured at the end of the mission and brought back to earth again. It can be equipped with different science payloads, which is in this case the ORFEUS telescope. The mission is therefore called ORFEUS-SPAS. ASTRO-SPAS was developed and built by Deutsche Aerospace AG (DASA, later Daimler-Benz Aerospace AG, then Dornier Satellitensysteme GmbH at DaimlerChrysler Aerospace AG, now EADS-Astrium).

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Telescope Cover

The cover of the telescope serves several purposes:

In closed position the cover prevents the optics from dust or even from falling objects. In space the closed cover also prevents the optics from possible contamination by evaporations from the Space Shuttle.

In opened position during measurements the telescope will be oriented so that the cover tends towards the sun. Thus the cover prevents sunlight from falling into the telescope, which would otherwise produce disturbing straylight.

This image shows the cover during opening. This was to test the cover drive before releasing the ASTRO-SPAS. If for some reason the cover could not be opened, the astronauts would be able to open the cover manually.

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Telescope Cover Drive

Here a part of the cover drive is visible. As the cover has to be closed prior to capturing of the ASTRO-SPAS, the drive is constructed in such a way, that the cover is held open actively. By switching off the power the cover will close automatically by a spring mechanism. The cover has to be closed for landing, as otherwise the cargo bay doors of the Space Shuttle could not be closed.

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Upper Half of Telescope

The upper half of the telescope carries the two spectrometers: The Echelle spectrometer, which is mounted at one side of the telescope, and the Berkeley spectrometer, which is mounted in the centre of the telescope. The two spectrometers use the same entrance diaphragm with a diameter of 20" (arcseconds). A moveable mirror directs the starlight either into the Echelle spectrometer or the light falls directly into the Berkeley spectrometer if the mirror is moved out of the beam.

The telescope has a height of 4 m and a diameter of 1.1 m. It was built by Kayser-Threde.

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Lower Half of Telescope

The lower half ogf the telescope contains the main mirror, which has a diameter of 1 m and a focal length of 2.4 m. The telescope has a height of 4 m and a diameter of 1.1 m. It was built by Kayser-Threde.

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Echelle Spectrometer

The Echelle spectrometer covers the far ultraviolet (FUV) wavelength range from about 90 nm to 140 nm. The spectral resolution is 104, i.e. at a wavelength of 100 nm it is possible to resolve spectral features of 0.01 nm width.

The spectrometer contains an Echelle grating with 316 lines per mm, which is used with spectral orders from 40 to 61, and a cross disperser grating with 1200 lines per mm, which is used to separate the different diffraction orders of the Echelle grating. The detector has a sensitive area of 40mm x 40mm, which records the spectrum as image. Within this image the individual Echelle orders are seen as bright nearly horizontal stripes. For extraction of the spectra the intensity is recorded along each of these stripes belonging to one Echelle order. Each position on the detector image is assigned a certain wavelength, which was calibrated preflight by test spectra and which is also theoretically quite well known. The result are the final spectra: the intensity along the wavelength scale.

The Echelle spectrometer was built by Kayser-Threde together with the telescope. The Echelle detector however was developed and built in our institute.

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Berkeley Spectrometer

The Berkeley spectrometer is mounted in the centre of the telescope. It was built by the Space Science Laboratory (SSL) of the University of California in Berkley. The spectrometer has two speparate wavelength ranges: the Extreme Ultraviolet (EUV, 40 nm to 90 nm) and the Far Ultraviolet range (FUV, 90 nm to 115 nm). It has a spectral resolution of about 3000, i.e. at a wavelength of 100 nm it is possible to resolve spectral features of 0.03 nm width.

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Data Aquisition Eclectronics of the Berkeley Spectrometer

This box contains the electronics for the data aqusition unit of the Berkeley spectrometer.

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Telemetry Electronics of the Berkeley Spectrometer

This box contains the electronics for telemetry of the Berkeley spectrometer. It receives commands from ground and prepares the data to be sent to ground or to the ASTRO-SPAS on board magnetic tape.

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IMAPS

The Interstellar Matter Absorption Profile Spectrograph (IMAPS) is an istrument that is operated indepently from ORFEUS. It was built by Princeton University and was originally designed as a sounding rocket experiment. It was modified for the ORFEUS-SPAS mission and is so the third spectrometer onboard ASTRO-SPAS. IMAPS operates in wavelength region from 95 nm to 115 nm an has a very high spectral resolution of 105, i.e. at a wavelength of 100 nm it is possible to resolve spectral features of 0.001 nm width.

IMAPS cannot be operated simultanously with the ORFEUS telescope. The reason is, that the ASTRO-SPAS is not able to receive data from both instruments at the same time, and also, that IMAPS and ORFEUS do not exactly look at the same point of the sky. The optical axis of the two instruments had to be aligned to within 10" (arcseconds) to look at the same star, which would be achievable only with very high technical effort. On the other hand there is no reason to look at the same star with ORFEUS and IMAPS simultaneously, as IMAPS is much less sensitive due to its high spectral resolution than both of the ORFEUS spectrometers. Therefore it has to observe rather bright stars which would be in general too bright for the ORFEUS detectors.

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IMAPS Electronics

This nearly squared tent of multilayer insulating foil hides the electronics of the IMAPS instrument.

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Star Tracker

The star tracker determines the direction of view of the ASTRO-SPAS and thus of the telesope. As it is not possible in space to keep an object absolutely fixed, it is necessary to permanently check the orientation of the telescope in space and to correct the orientation, if a deviation from the desired dirction is found.

The star tracker is a small telescope which registers a part of the sky with an electronic camera. Within the registered images a computer estimates the brightness and positions of the stars and compares these with those of a stored star catalogue. Thus the computer can identify the stars in this image and determine the exact orientation of the telescope.

For correction of small deviations from the desired orientation the nozzles of the ASTRO-SPAS are activated to turn the telescope exactly into the desired direction. By this method it is achieved to kepp the deviation from the desired pointing direction less than 5" (arcsec).

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DARA Logo

Logo of the German Space Agency: Deutsche Agentur für Raumfahrtangelegenheiten, today Deutsches Zentrum für Luft- und Raumfahrt (DLR).

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NASA Logo

Logo of National Aeronautics and Space Administration.

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DASA Logo

Logo of the former Deutsche Aerospace AG, now Astrium.

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IMAX Movie Camera

This large movie camera was used to take movies of the free flying space shuttle. Parts of the sequences taken during this mission are visible in the film "Destiny in Space".
IMAX films are shown only in special IMAX film theaters. They have an extremely lage panorama sized format.

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IMAX View Finder Television Camera

This TV camera was used as view finder for the IMAX movie camera. The actual view of the movie camera could be seen live during shooting the film.

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Robot Arm of the Space Shuttle

This robot arm was used to move the ASTRO-SPAS out of the cargo bay of the space shuttle, to retrieve the satellite after the mission and to move it back into the cargo bay.

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TV Camera at the Robot Arm

This TV camera is used to observe the grapple at the ASTRO-SPAS during capturing of the satellite.

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Grapple for Docking the Robot Arm

This grapple is used for docking of the robot arm when moving the ASTRO-SPAS out of the cargo bay or back into the cargo bay.

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Antenna

This antenna is used for radio communication between ASTRO-SPAS and space shuttle. All telemetry data of the satellite are sent over this antenna to the shuttle and from there via communication satellites to Houston. An other satellite connection is used to transmit the data to the Kennedy Space Center where the ground station of the ASTRO-SPAS and all experiments were located.

Only a small fraction of all scientific data could be sent directly to the ground station as the data rate of the telemtry connection was too low to send all data to ground. Therefore all data were stored on magnetic tapes aboard the satellite and could be retrieved only after the mission. Also an uninterrupted connection could not be guaranteed, so that the ASTRO-SPAS was designed to operate up to 8 hours autonomously.

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Mounting

This is one of the three visible mountings of the ASTRO-SPAS which are used to fix the satellite in the cargo bay of the shuttle. A fourth mounting is located at the bottom side of ASTRO-SPAS.

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Reflection at the Window

This foto was taken from the shuttle cabin through a window. The blue area is a reflection at teh window glas.

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Sky

In space the sky is dark, even at the day side of the earth. On earth the sky is blue because the sunlight is scattered in the earths atmosphere. In space there is nearly no atmosphere and consequently there is no blue sky. The detectors of the ORFEUS spectrometers however are so sensitive that they can detect the very faint scattered light of the extremely rare atmosphere (air glow). Very faint stars are therefore observed from the night side of the orbit.

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Electronics of Telescope and Echelle Spectrometer

Below this tent of multilayer insulating foil the electronics of the telescope and the Echelle spectrometer is located: the control system of the telescope, the high voltage supply of the Echelle detector and the data aquisition unit and onboard processor (with black cover) of the Echelle detector.

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The Tübingen Echelle Electronics Box

The Echelle electronics box includes the data aquisition unit and the onboard processor for the Echelle detector. The box has a black cover which has a direct view into space through a recess clearance in the multilayer insulating foil. Thus the box is cooled very effective by radiating the heat into space.

The electronics in this box was developed and built at our institute, as was the Echelle detector, too. The processor consists of a Motorola 68000 chip, it has to fulfil the following tasks:

Main task is the data aquisition of the Echelle detector. The necessary electronics is integrated in the box. The processor produces an image from the detector signals within its memory. Also all detector signals are written onto magnetc tape aboard ASTRO-SPAS. Additionally some house keeping data are recorded and are sent to the ground station together with a small fraction of the detector data. These housekeeping data are temperatures of the telescope and the electronics, photon count rates of the detector, and status indicators of the processor.

A further important task of the Echelle onboard processor is the reception and execution of telecommands which are sent from the ground station to the Echelle electronics. There are a series of commands for the following functions:

Definition of the measuring mode, switching of the detector high voltage supply, sending compressed images to the ground station, etc. Some special commands allow to change the values of program variables and even to load a completely new software into the onboard processor. Additionally the detector can be switched into a special test mode, which allows a very fast test of the electronics and the imaging quality of the detector.

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Jürgen Barnstedt | Impressum
Last modified 07 Feb 2005
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