- Email: [email protected]
7.3. ROSAT and its X-ray eye
region, at 200 pm. Important contributions for the peripherals of this instrument come from the UK, Denmark and Spain. Max-Planck researchers are also working on a second experiment, in spectrometer for short wavelengths (SWS), under the supervision of the Space Research Laboratory in Groningen, the Netherlands. When, in spring 1993, Ariane 44P, assisted by four solid fuel boosters, positions IS0 in its orbit, the satellitic mission will be to detect all astronomical objects which radiate in the infrared range. This includes comets, any planets which may be discovered around distant stars, and especially the ‘cold’ areas shrouded in clouds of gas and matter which are permeable only to infrared, and within which the birth of new stars and perhaps of whole planetary systems takes place. The researchers at the Max-Planck Institute for Astronomy are particularly interested in those galaxies which are apparently on a collision course and subject to interaction, which makes them radiate particularly strongly in the infrared radiation range. In addition, IS0 should enable observations of dust regions and interstellar matter, as well as the solutions of cosmological questions concerning matter that hitherto has been invisible. In their search for ‘extremely cold objects’ (at temperatures down to -26O”C), the researchers concerned are convinced that there will be more than a few surprises. Currently, the so-called phases C and D of this ambitious European venture are being carried out. These comprise the construction of the qualification and flight models of ISO. In 1988, the ‘flight schedule’ for the instrument was also changed. Initially, it was to have had an eccentric orbit of up to 36 000 km. However, now with an orbit of up to 70 000 km, it will spend three quarters of its orbit outside of the Van Allen radiation belt. This will not only make better measurements possible, but will also provide for better protection of the sensitive detectors and electronic devices against radiation damage.
7.3. ROSAT AND ITS X-RAY EYE13’
The result of the work by the high-tech optics specialists at Zeiss can be found in the Guinness Book of Records, i.e. the ‘smoothest mirror in the world, with an average surface roughness of 0.0003 pm. The X-ray telescope in ROSAT, with its aperture diameter of 83 cm contains eight such mirrors. This adds up to a total surface area of about 9.6 square metres, which is equivalent to the ‘light-collecting area’ of an optical reflecting telescope with a diameter of 3.5 m. These X-ray mirrors are shaped and arranged in a complicated manner. X-rays cannot be focused by any system of lenses, but only deflected by means c3)From German
88
Research
Service Special Reports,
Special Issue 2189.
of a so-called ‘glancing’ reflection. In other words, when X-rays strike an extremely smooth surface at a very flat angle, they are reflected as if by a mirror. Accordingly, the ROSAT imaging telescope, which embodies the principle developed by the West German physicist Hans Wolter in 1952, consists of four slightly conical tubes placed inside each other; the wider front end is aimed at the X-ray objects. The front section of this ‘multiple tube’ consists of four concentric parabolic mirrors, and the rear section of four hyperbolic mirrors in the same arrangement; these serve to focus the X-rays on a single focal plane. The supporting material of these mirrors, the glass ceramic Zerodur developed by Schott Glaswerke in Mainz, does not expand or contract when subjected to temperature changes. The reflecting surfaces are vacuum-met~ed gold. The inst~ment is so good that it can take X-ray ‘colour pictures’ in several wavelengths simult~~usly, with a resolution of 30 arc sec., and monochrome images with a resolution of just 3 arc sec. It is thus five times more ‘sharpsighted’ than all other X-ray telescopes used in space to date, such as the one on board the Einstein satellite HEAO-2, which ceased operation in the spring of 1982. The scientific objective of this mission is just as unique as the instrument itself. This telescope will make possible the first complete mapping of the X-ray heavens and is expected to discover, in addition to the 5000 or so X-ray objects already known, about 100 000 more which are estimated to be there. In the second observational phase, selected X-ray sources of particular interest are to be observed, in order to learn more about their energy spectra, time-dependent changes and physical structures. The observations will take us into the highest energy and temperature ranges where excited matter emits X-ray radiation, thereby facilitating study of the final phases in the life of a star, such as supernovae, neutron stars and black holes, as well as explosion areas of entire galaxies, quasars and other mysterious objects. According to current plans, ROSAT is to be launched in February 1990 by an American Delta II rocket and placed in an orbit at 580 km. In all, ROSAT weighs 2.4 tonnes and is 4.3 m long: basically, it is a ‘tube’ for the X-ray telescope. It was constructed within the context of the national space programme of the Federal busts for Research and Technology EMU, under the leadershiop of the German Aerospace Research Estab~shment (DLR) in Cologne, and built by the companies Dornier GmbH of Friedrichshafen as general contractor and Messerschmitt-Btilkow-Blohm (MBB) in OttobruM, near Munich, as subcontractor. Zeiss developed the X-ray telescope itself; the X-ray image receiver was developed and built by researchers at the MaxPlanck-Institute for Extra-terrestrial Physics, at Garching, near Munich. The scientists at the Institute for Extra-terrestrial Physics, led by Professor Joachim Triimper, are also in charge of the scientific aspects of the overall project, and have set up a ROSAT Data Centre in their institute for this purpose. The German Space Operation Centre (GSOC) of the DLR, located in 89
Oberpfaffenhofen, is responsible for operation of the satellite as well as for data transmission. ROSAT is not merely a national project, as NASA has made an X-ray image receiver available, as well as assuming the costs of the rocket launch and the UK Science and Engineering Research Council (SERC) has also made a significant contribution to the mission by providing a telescope which mainly functions in the extreme ultraviolet wavelength range. It is expected that this telescope will provide valuable knowledge, thus enriching the mission. Up to the launch, the BMFT will have contributed approximately 260 million DM toward this satellite, the development of which was based on a proposal prepared by the Max-Planck-Institute for Extra-terrestrial Physics in 1975. The Max-Planck-Gesellschaft has also made significant funds available. It is the crowning achievement of West German X-ray astronomy, which has already been characterized by great successes (not the least of which are due to Professor Triimper). Among these are the X-ray observations made with the ‘Tubingen balloon basket’ in the skies above Texas in 1973, and the related ‘High Energy X-ray Experiments (Hexes)‘. In 1978, a further development of this type of radiation detection device aboard the Soviet MIR Space Station, the so-called ‘MIR-HEXE’, saw for the first time the X-ray radiation of the supernova in the Great Cloud of Magellan. The device has a light-collecting area of 800 square cm, and is the largest detector of its type to date. It can register X-ray radiation with wavelengths between five and 80 billionths of a millimeter. It was developed by the Max-Planck-Institute for Extra-terrestrial Physics in cooperation with astrophysicists of the University of Tiibingen and constructed by MBB in Ottobnmn.
7.4. GAMMA
RAY 0BSERVATORY’4’
The first thorough scanning of the heavens in the gamma ray radiation range begin following the launch of the US Gamma Ray Observatory (GRO) by the Space Shuttle Atlantis in June 1990. This range is even more energy-rich and ‘harder’ than X-rays and therefore bears witness to events in the universe in which large quantities of energy are converted. The German Double-Compton Telescope (COMPTEL) and the Gamma Ray Experiment (EGRET) are expected to make a significant contribution to the success of the project: While scanning the heavens and carrying out the subsequent individual investigations with the GRO, a whole series of objects and processes will be examined, which, with respect to the amount of energy produced, can be called extreme or even exotic. This begins with the powerful paroxysms in the Sun, the c4)From German Research Service Special Science Reports, Special Issue 2/89.
90
7.3. ROSAT AND ITS X-RAY EYE13’
The result of the work by the high-tech optics specialists at Zeiss can be found in the Guinness Book of Records, i.e. the ‘smoothest mirror in the world, with an average surface roughness of 0.0003 pm. The X-ray telescope in ROSAT, with its aperture diameter of 83 cm contains eight such mirrors. This adds up to a total surface area of about 9.6 square metres, which is equivalent to the ‘light-collecting area’ of an optical reflecting telescope with a diameter of 3.5 m. These X-ray mirrors are shaped and arranged in a complicated manner. X-rays cannot be focused by any system of lenses, but only deflected by means c3)From German
88
Research
Service Special Reports,
Special Issue 2189.
of a so-called ‘glancing’ reflection. In other words, when X-rays strike an extremely smooth surface at a very flat angle, they are reflected as if by a mirror. Accordingly, the ROSAT imaging telescope, which embodies the principle developed by the West German physicist Hans Wolter in 1952, consists of four slightly conical tubes placed inside each other; the wider front end is aimed at the X-ray objects. The front section of this ‘multiple tube’ consists of four concentric parabolic mirrors, and the rear section of four hyperbolic mirrors in the same arrangement; these serve to focus the X-rays on a single focal plane. The supporting material of these mirrors, the glass ceramic Zerodur developed by Schott Glaswerke in Mainz, does not expand or contract when subjected to temperature changes. The reflecting surfaces are vacuum-met~ed gold. The inst~ment is so good that it can take X-ray ‘colour pictures’ in several wavelengths simult~~usly, with a resolution of 30 arc sec., and monochrome images with a resolution of just 3 arc sec. It is thus five times more ‘sharpsighted’ than all other X-ray telescopes used in space to date, such as the one on board the Einstein satellite HEAO-2, which ceased operation in the spring of 1982. The scientific objective of this mission is just as unique as the instrument itself. This telescope will make possible the first complete mapping of the X-ray heavens and is expected to discover, in addition to the 5000 or so X-ray objects already known, about 100 000 more which are estimated to be there. In the second observational phase, selected X-ray sources of particular interest are to be observed, in order to learn more about their energy spectra, time-dependent changes and physical structures. The observations will take us into the highest energy and temperature ranges where excited matter emits X-ray radiation, thereby facilitating study of the final phases in the life of a star, such as supernovae, neutron stars and black holes, as well as explosion areas of entire galaxies, quasars and other mysterious objects. According to current plans, ROSAT is to be launched in February 1990 by an American Delta II rocket and placed in an orbit at 580 km. In all, ROSAT weighs 2.4 tonnes and is 4.3 m long: basically, it is a ‘tube’ for the X-ray telescope. It was constructed within the context of the national space programme of the Federal busts for Research and Technology EMU, under the leadershiop of the German Aerospace Research Estab~shment (DLR) in Cologne, and built by the companies Dornier GmbH of Friedrichshafen as general contractor and Messerschmitt-Btilkow-Blohm (MBB) in OttobruM, near Munich, as subcontractor. Zeiss developed the X-ray telescope itself; the X-ray image receiver was developed and built by researchers at the MaxPlanck-Institute for Extra-terrestrial Physics, at Garching, near Munich. The scientists at the Institute for Extra-terrestrial Physics, led by Professor Joachim Triimper, are also in charge of the scientific aspects of the overall project, and have set up a ROSAT Data Centre in their institute for this purpose. The German Space Operation Centre (GSOC) of the DLR, located in 89
Oberpfaffenhofen, is responsible for operation of the satellite as well as for data transmission. ROSAT is not merely a national project, as NASA has made an X-ray image receiver available, as well as assuming the costs of the rocket launch and the UK Science and Engineering Research Council (SERC) has also made a significant contribution to the mission by providing a telescope which mainly functions in the extreme ultraviolet wavelength range. It is expected that this telescope will provide valuable knowledge, thus enriching the mission. Up to the launch, the BMFT will have contributed approximately 260 million DM toward this satellite, the development of which was based on a proposal prepared by the Max-Planck-Institute for Extra-terrestrial Physics in 1975. The Max-Planck-Gesellschaft has also made significant funds available. It is the crowning achievement of West German X-ray astronomy, which has already been characterized by great successes (not the least of which are due to Professor Triimper). Among these are the X-ray observations made with the ‘Tubingen balloon basket’ in the skies above Texas in 1973, and the related ‘High Energy X-ray Experiments (Hexes)‘. In 1978, a further development of this type of radiation detection device aboard the Soviet MIR Space Station, the so-called ‘MIR-HEXE’, saw for the first time the X-ray radiation of the supernova in the Great Cloud of Magellan. The device has a light-collecting area of 800 square cm, and is the largest detector of its type to date. It can register X-ray radiation with wavelengths between five and 80 billionths of a millimeter. It was developed by the Max-Planck-Institute for Extra-terrestrial Physics in cooperation with astrophysicists of the University of Tiibingen and constructed by MBB in Ottobnmn.
7.4. GAMMA
RAY 0BSERVATORY’4’
The first thorough scanning of the heavens in the gamma ray radiation range begin following the launch of the US Gamma Ray Observatory (GRO) by the Space Shuttle Atlantis in June 1990. This range is even more energy-rich and ‘harder’ than X-rays and therefore bears witness to events in the universe in which large quantities of energy are converted. The German Double-Compton Telescope (COMPTEL) and the Gamma Ray Experiment (EGRET) are expected to make a significant contribution to the success of the project: While scanning the heavens and carrying out the subsequent individual investigations with the GRO, a whole series of objects and processes will be examined, which, with respect to the amount of energy produced, can be called extreme or even exotic. This begins with the powerful paroxysms in the Sun, the c4)From German Research Service Special Science Reports, Special Issue 2/89.
90