European Space Agency

In Brief

HST Faint-Object Camera Unmasks 'Cosmic Gamma-Ray Machine'

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The European Space Agency's Faint Object Camera on the Hubble Space Telescope has identified a neutron star, the smallest and densest type of star that exists, lying approximately 3000 light- years away in the southern sky. It is 100 million times dimmer than faint stars seen with the naked eye. Thus the Faint Object Camera is living up to its name by revealing objects in the Universe close to the limit of visibility.

The new-found neutron star is the visible counterpart of a pulsating radio source, Pulsar 1055-52. It is a mere 20 km wide. Although the neutron star is very hot, about a million degrees centigrade, very little of its radiant energy takes the form of visible light. It emits mainly gamma-rays, an extremely energetic form of radiation. By examining it at visible wavelengths, astronomers hope to figure out why Pulsar 1055-52 is the most efficient generator of gamma-rays known so far, anywhere in the Universe.

The Faint Object Camera found Pulsar 1055-52 in near- ultraviolet light at 3400 angstroms, a little shorter in wavelength than the violet light at the extreme of the human visual range. Roberto Mignani, Patrizia Caraveo and Giovanni Bignami of the Istituto di Fisica Cosmica in Milan, Italy, report its optical identification in the 1 January 1997 issue of Astrophysical Journal Letters. The object's formal name is 'PSR 1055-52'.

Evading the glare of an adjacent star
The Italian team had tried since 1988 to spot Pulsar 1055-52 with two of the most powerful ground-based optical telescopes in the Southern Hemisphere: the 3.6 m Telescope and the 3.5 m New Technology Telescope at the European Southern Observatory in La Silla, Chile. Unfortunately, an ordinary star 100 000 times brighter lay in almost the same direction in the sky, separated from the neutron star by only a thousandth of a degree. The Earth's atmosphere defocused the star's light sufficiently to mask the glimmer from Pulsar 1055-52. The astronomers therefore needed an instrument in space and the Faint Object Camera offered the best precision and sensitivity to continue the hunt.

Devised by European astronomers to complement the American wide-field camera on the Hubble Space Telescope, the Faint Object Camera has a relatively narrow field of view. It intensifies the image of a faint object by repeatedly accelerating electrons from photo-electric films, so as to produce brighter flashes when the electrons hit a phosphor screen. Since Hubble's launch in 1990, the Faint Object Camera has examined many different kinds of cosmic objects, from the moons of Jupiter to remote galaxies and quasars. When the Space Telescope's optics were corrected at the end of 1993, the Faint Object Camera immediately celebrated the event with the discovery of primeval helium in intergalactic gas.

In their search for Pulsar 1055-52, the astronomers chose a near-ultraviolet filter to sharpen the Faint Object Camera's vision and reduce the adjacent star's huge advantage in intensity. In May 1996, the Hubble Space Telescope operators aimed at the spot which radio astronomers had indicated as the source of the radio pulsations of Pulsar 1055-52. The neutron star appeared precisely in the centre of the field of view, and it was clearly separated from the glare of the adjacent star. At magnitude 24.9, Pulsar 1055-52 was comfortably within the power of the Faint Object Camera, which can see stars 20 times fainter still.

'The Faint Object Camera is the instrument of choice for looking for neutron stars', says Giovanni Bignami, speaking on behalf of the Italian team. 'Whenever it points to a judiciously selected neutron star it detects the corresponding visible or ultraviolet light. The Faint Object Camera has now identified three neutron stars in that way, including Pulsar 1055-52, and it has examined a few that were first detected by other instruments'.

Mysteries of the neutron stars
The importance of the new result can be gauged by the tally of only eight neutron stars seen so far at optical wavelengths, compared with about 760 known from their radio pulsations, and about 21 seen emitting X-rays. Since the first pulsar was detected by radio astronomers in Cambridge, England, nearly 30 years ago, theorists have come to recognise neutron stars as fantastic objects. They are veritable cosmic laboratories in which nature reveals the behaviour of matter under extreme stress, just one step short of a black hole.

A neutron star is created by the force of a supernova explosion in a large star, which crushes the star's core to an unimaginable density. A mass greater than the Sun's is squeezed into a ball no wider than a city. The gravity and magnetic fields are billions of times stronger than the Earth's. The neutron star revolves rapidly, which causes it to wink like a cosmic lighthouse as it swivels its magnetic poles towards and away from the Earth. Pulsar 1055-52 spins at five revolutions per second.

At its formation in a supernova explosion, a neutron star is endowed with two main forms of energy. One is heat, at temperatures of millions of degrees, which the neutron star radiates mainly as X-rays, with only a small proportion emerging as visible light. The other power supply for the neutron star comes from its high rate of spin and a gradual slowing of the rotation. By a variety of processes involving the magnetic field and accelerated particles in the neutron star's vicinity, the spin energy of the neutron star is converted into radiation at many different wavelengths, from radio waves to gamma-rays.

The exceptional gamma-ray intensity of Pulsar 1055-52 was first appreciated in observations by NASA's Compton Gamma Ray Observatory. The team in Milan recently used the Hubble Space Telescope to find the distance of the peculiar neutron star Geminga, which is not detectable by radio pulses, but is a strong source of gamma-rays. Pulsar 1055-52 is even more powerful in that respect. About 50% of its radiant energy is gamma-rays, compared with 15% from Geminga and 0.1% from the famous Crab Pulsar, the first neutron star seen by visible light. Making the gamma-rays requires the acceleration of electrons through billions of volts. The magnetic environment of Pulsar 1055-52 fashions a natural gamma-ray machine of amazing power. The orientation of the neutron star's magnetic field with respect to the Earth may contribute to its brightness in gamma-rays.

Geminga, Pulsar 1055-52 and another object, Pulsar 0656+14, make a trio that the Milanese astronomers call 'The Three Musketeers'. All have been observed with the Faint Object Camera. They are isolated, elderly neutron stars, some hundreds of thousands of years old, contrasting with the 942 year-old Crab Pulsar, which is still surrounded by dispersing debris of a supernova seen by Chinese astronomers in the 11th Century. The mysteries of the neutron stars will keep astronomers busy for years to come, and the Faint Object Camera on the Hubble Space Telescope will remain the best instrument for spotting their faint visible light.

An image is available of: (i) PSR 1055-52 as seen by ESA's Faint Object Camera on HST, and (ii) the same region of the sky seen by the European Southern Observatory's New Technology Telescope, with the position of PSR 1055-52 indicated. It can be found on the World Wide Web at:

http://ecf.hq.eso.org/stecf-pubrel.html

Czech Republic and ESA Sign Cooperation Agreement

The Minister for Education, Youth and Sports of the Government of the Czech Republic, Mr Ivan Pilip, and ESA's Director General, Mr Jean-Marie Luton, have signed a Cooperation Agreement concerning the exploration and use of outer space for peaceful purposes.

The aim of the Agreement is to establish the framework for cooperation in areas of mutual interest, in particular:

The Czech Republic and ESA plan to interchange information in these areas, largely by facilitating the exchange of scientists, engineers and industry contacts. This could lead to the conclusion of specific arrangements on agreed projects including the possibility for the Czech Republic to participate in ESA programmes.

The Agreement, which was signed on 7 November 1996 in Prague, has a duration of 5 years with a possibility for renewal. In order to execute the obligations set forth, each party is expected to meet its own costs.

SOHO Birthday Greetings

Launched on 2 December 1995, SOHO recently celebrated its first year in space. As the images and other data continue to pour from SOHO at a high rate, a revolution in solar science is in progress.

Among many solar experts who are enthusiastic about SOHO's successes is the leading astrophysicist, Evry Schatzman of the Observatoire de Meudon (France).

'On SOHO's first birthday', Schatzman says, 'I congratulate my European and American colleagues on the most remarkable and successful spacecraft ever devoted to examining the star on which our lives depend. SOHO's astounding ability to probe the Sun's interior by helioseismology gives me hope that we shall at last solve the ancient mystery of the sunspots and the magnetic cycle. The observations of ultraviolet rays and energetic particles give us our best chance of understanding the hot atmosphere and its emissions into the solar system. But to fulfil its high promise, SOHO must continue to operate at least until the maximum of sunspot activity around the year 2000.'

Joining in SOHO's anniversary greetings is Eigil Friis Christensen, a solar-terrestrial physicist at the Danish Meteorological Institute, who has played a prominent role in tracing the effects of solar variations on the terrestrial climate:

'SOHO is now vital for understanding the Earth's environment. I am convinced that long-term changes in the strength and variability of the solar wind alter the climate, but no one knows why those changes occur. In the years ahead, as it follows the dramatic events leading from the sunspot minimum to the sunspot maximum, SOHO should reveal the processes inside the Sun that influence the character of the solar wind. If so, it will open a new chapter in solar-terrestrial climatology.

SOHO Receives Popular Science Award

Esa astronauts
On behalf of SOHO, Mr Vicente Domingo (ESA) accepts the Popular Science 'Best of What's New' award for 1996.

SOHO was recently selected as one of the greatest 100 achievements in science and technology for 1996 by Popular Science Magazine. The award, which is given annually for new technology products or ground-breaking scientific discoveries, bases the selection criteria on one main point: 'each innovation must make a positive difference in our lives'. SOHO is described as the first unblinking observer of our Sun which has already made spectacular finds, '...even though the Sun is now in its quieter state - the lull in the roughly 11-year sunspot cycle - it's still a roiling, violent place subject to fits of exploding fireballs and fantastically twisting magnetic fields'.

Other winners in the same category were 'Life on Mars', 'Discovery of Comet Hyutake' and 'NASA's Near-Earth Asteroid Rendezvous Mission (NEAR)'.

Ariane V92, Successfully Launched

The 92nd Ariane launch took place successfully on Wednesday, 13 November 1996 at 07:40 p.m. Kourou time (11:40 p.m. Paris time).

An Ariane 44L version launcher (equipped with 4 liquid strap- on boosters) placed the Arabian and Malaysian telecommunication satellites ARABSAT IIB and MEASAT 2 into geostationary orbit.

Second European Conference on Space Debris

After the success of the first conference in 1993, the European Space Agency is organising the Second European Conference on Space Debris to be held 17-19 March 1997 at its European Space Operations Centre (ESOC) in Darmstadt, Germany. The British National Space Centre (BNSC) as well as the space agencies from France (CNES), Germany (DARA) and Italy (ASI), and the International Acadamy of Astronautics (IAA), are co- sponsoring this event which will draw over 200 experts from Europe, the United States, Canada, Russia, Japan and China.

Space debris is of growing concern for manned and unmanned spaceflight. The first confirmed hypervelocity collision between an operational spacecraft (CERISE) and a tracked fragment of an upper stage occurred in July 1996.

The purpose of the conference is to provide a forum for the presentation of results from research on space debris; to assist in defining future directions for research; to identify methods of debris control, reduction and protection; and to discuss international implications and policy issues.

At the conference, measurements of space debris and meteoroid population made from the ground and in space will be discussed, along with the results of modelling efforts and supporting ground tests predicting the debris population and its evolution in both the short- and long-term. (See this In Brief, article entitled 'The COBEAM Experiment'.) The conference will also focus on the impact of multi-satellite constellations on the space environment, protection of the International Space Station from debris and meteoroids, and risk assessment in the various orbital regions. Since rules governing space vehicle design and operations with respect to space debris will ultimately be required, policy issues will also be addressed.

A round-table discussion scheduled for 19 March will explore the further steps to be taken in the space debris field.

For further information, please contact:

W. Flury
ESOC
Robert-Bosch-Str. 5
64293 Darmstadt
Germany

Tel: +49 6151 902 270
Fax: +49 6151 902 625
E-mail: wflury esoc.esa.de

The Proceedings of the Conference will be available from ESA Publications Division at the end of April as ESA Special Publication SP-393.

ENVISAT-1 Payload Data Segment Development Contract Signed

Esa astronauts
Signing of the ENVISAT-1 Payload Data Segment Development contract. From left to right seated: ESA's Director General, Mr Jean-Marie Luton; Chairman of Thomson-CSF Services et Systèmes Sol Spatiaux, Mr Alain Delecroix. From left to right standing: Mr F. Roscian (ESRIN), Mr J Louet (ESTEC), Mr J-P Guignard (ESRIN), Mr L Marelli (ESRIN), Mr B Pfeiffer (ESTEC), Mrs E Löffler (ESRIN)

Mr Jean-Marie Luton, ESA's Director General, and Mr Alain Delecroix, Chairman of Thomson-CSF Services et Systèmes Sol Spatiaux, signed the contract for the development of the ENVISAT- 1 Payload Data Segment (PDS) on 9 December 1996 at ESRIN, ESA's Earth Observation Missions Exploitation Centre in Frascati, Italy.

ENVISAT-1, ESA's most ambitious and complex satellite, to be launched in mid-1999, will be the successor to the ERS Earth observation satellites. Carrying on from the ERS-1 and ERS-2 missions, it will provide the user community with enhanced observation of the Earth and its environment in the field of atmospheric constituents and Earth-surface features, maintaining the flow of data well into the next century.

This contract covers the development and installation of the data management, data acquisition, data processing, and corresponding user service interfaces at the two ESA sites involved, ESRIN in Italy and the Kiruna/Salmijärvi station in Sweden.

It also includes the development of units to be used by national facilities which will make up the ENVISAT PDS network providing data archiving, off-line processing and distribution of data to users.

The contract, the largest ever signed by ESA with industry for ground segment investments, is worth some 75 million ECU; several European and Canadian companies are also associated with it, in support of Thomson-CSF, the main contractor.

A significant proportion of the development work, and most of the integration activities, are to be performed by Italian companies.

Space Robotics Workshop

Mars terrain
Demonstration of a mobile robot on a mockup of a Mars terrain.

The fourth ESA Workshop on Advanced Space Technologies for Robot Applications 'ASTRA 96' was held on 6 and 7 November 1996 at ESTEC, Noordwijk (NL), and was attended by 112 participants from European industry, research institutes and national space agencies. The objective was to provide a forum for discussion and brainstorming by of the European space Automation and Robotics (A&R) community, covering areas of A&R technology.

The workshop was structured in three main parts: an overview of potential missions and application scenarios; presentations on research and development programmes in space A&R; and a number of parallel sessions on the main technology areas.

The first part included presentations on:

On both days of the workshop, a demonstration and exhibits session took place in the laboratories of the Automation and Ground Facilities Division (including a small Mars and Moon terrain model). Particular highlights were the various contributions, during the presentation sessions and in the lab demonstrations, on mobile robots, which could be of interest for sensor deployment on Moon or Mars missions.

The workshop was rated as very successful, providing an inspiring forum for the European space A&R community to exchange ideas and assess the project application potential of the latest robotic technologies.

ESA and Matra Marconi Sign Contract for ISS Freezer

ISS
Mr J. Feustel-Büechl (left) and Mr C. Guionnet (right) signing the ISS Freezer contract.

After the successful completion of several months of negotiations, the European Space Agency signed a contract with Matra Marconi Space, as the prime contractor representing a consortium including L'Air Liquide, Linde, Damec, Kayser Threde and Etel, for the development of a freezer operating at - 80°C to be used on the International Space Station.

Three freezer units will be delivered to NASA in return for early access to the Space Station by ESA. A further unit will be delivered to Japan's space agency, NASDA, in return for twelve Space Station payload mounting racks.

The contract, amounting to 22.3 MECU, was signed on 14 January 1997 at ESTEC by the Director for Manned Spaceflight and Microgravity, ESA, Mr Jörg Feustel-Büechl and the Director of Space Transportation and Manned Spaceflight, Matra Marconi Space, Mr Claude Guionnet.

ESA Successfully Tests its ATV Rendezvous and Docking Technology on STS-80

The European Space Agency took advantage of NASA's recent Space Shuttle flight, STS-80, which ended on 7 December 1996, to test elements of the automated rendezvous and docking system that it is developing for the International Space Station.

The system will be used when ESA's Automated Transfer Vehicle (ATV), which will ferry supplies to the Station and periodically 'reboost' the Station into higher orbit, performs its rendezvous and docking with the Station. The ATV is one of the main elements that ESA is developing as part of its participation in the International Space Station. It is scheduled to be launched for the first time by Ariane 5 in March 2002.

All of the technologies and concepts used for the ATV - many of them new and leading-edge - must be demonstrated and validated before they are implemented. ESA's precursor project, called the ATV Rendezvous Pre-development (ARP), focusses on the key technologies and equipment used in the rendezvous.

During STS-80, ESA verified its absolute and relative navigation systems which are based on Global Positioning System (GPS) technology. An ESA-developed GPS receiver had been installed on the German ORFEUS SPAS satellite that was deployed by the Shuttle crew at the start of the mission. GPS data was used to determine the satellite's precise location with respect to the Shuttle.

GPS data was collected at three times: during the deployment of the satellite, during its free flight and again when it was retrieved. All three activity periods were successful and large amounts of valuable data were collected. The measurements will be compared to data gathered simultaneously by NASA's GPS receiver on the Shuttle and the Trajectory Control Sensor (TCS) in order to validate the prototype ATV relative navigation design.

It was the first flight demonstration in a series of three. The second and third will take place during two Shuttle-to-Mir docking missions, STS-84 in May 1977 and STS-86 in September 1997.

Matra Marconi Space (F) holds the overall responsibility for the ARP core activities, while Daimler Benz Aerospace (D) is in charge of the implementation and execution of the ARP flight demonstrations. Laben (I) developed and supplied the GPS receiver.

International Space Station: Scale Model Inaugurated at Noordwijk Space Expo

Esa astronauts
The new 1:10 scale model of the International Space Station attracts many of the young visitors to Noordwijk Space Expo, some of whom might one day find themselves working on the Station or on Station-related projects.

One year before the first element of the International Space Station is scheduled for launch into orbit, a 1:10 scale model of the station has been assembled at Noordwijk Space Expo (NSE) and will remain there on permanent exhibition.

On 21 December 1996, the model was inaugurated by the ESA Director of Manned Spaceflight and Microgravity, Mr. J. Feustel- Büechl, during a small ceremony at NSE hosted by Prof. H. Wittenberg, Chairman of the NSE Foundation, and Mr. B. van Gool, Director of NSE. The inauguration received wide coverage in the Dutch media and the model immediately became one of the major attractions for the visitors to NSE.

Noordwijk Space Expo, ESTEC's Visitor Centre in Noordwijk, The Netherlands, is open to the public six days per week. It not only attracts Dutch visitors, but also the many foreign tourists visiting the seaside resorts and tulip fields nearby.

The COBEAM Experiment

FGAN FGAN

The FGAN Tracking and Imaging Radar dome (left) in Wachtberg-Werthhoven, and the 100-m radio telescope dish at Bad- Münstereifel-Effelsberg, near Bonn.

The space environment surrounding the Earth is becoming increasingly polluted with space debris. Since 1957, more than 3800 space launches have led to a current population of approximately 8000 trackable objects (larger than 10 cm ) in near-Earth space, only 400 to 500 of which are operational spacecraft. The remainder is space debris. It is also believed that there are many more objects in orbit that cannot be tracked operationally (up to 100 000 or more of centimetre size).

In order to describe the spatial distribution of space debis of any size, ESA has developed the MASTER model. With the help of this model, the collision risk for satellites can be calculated. This is especially important for satellites in the most crowded altitude regions, between 750 and 1500 km (e.g. ERS- 1 and ERS-2), but also at an altitude where the International Space Station will be flying (400 to 500 km). MASTER is based on a population of objects which consists of the 8000 known objects and hundreds of thousands of simulated objects which are too small to be trackedregularly and maintained in a catalogue.

How accurately does the MASTER model describe the population of untrackable debris? A complete answer to this question would require a comprehensive and nearly continuous observation of space. However, point checks on the model can be made with radar observations from powerful radar stations available, for instance, at FGAN (Forschungsgesell- schaft für Angewandte Naturwissen- schaften) in Wachtberg-Werthhoven near Bonn. This radar system is so powerful that objects smaller than 2 cm can be detected at a distance of 1000 km. The sensitivity of the measurements increases even further if the FGAN transmitting radar is combined with a large receiving antenna. One such antenna is located only 21 km southwest of FGAN in Bad- Münstereifel-Effelsberg. It is the world's largest steerable radio antenna: the 100 m radio telescope of the Max-Planck- Institute for Radioastronomy (MPIfR). Combined, these two facilities provide a unique opportunity to test the MASTER model.

On 25-26 November 1996, a 24-hour cooperative experiment was performed whereby the FGAN L-band radar transmitted (and received) at 1.33 GHz and the MPIfR radio telescope received the echoes. Objects as small as 0.9 cm could be detected. In total, 150 GBytes of data were collected during the 24 hour period. Detections of 67 objects were made, of which 16 were known and 51 had not previously been identified. Preliminary results from this experiment will be presented at the ESA-organised Second European Conference on Space Debris to be held in Darmstadt on 17-19 March 1997.


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Right Left Up Home ESA Bulletin Nr. 89.
Published February 1997.
Developed by ESA-ESRIN ID/D.