Dreams and weekdays of the Russian astronomy
In January this year, the radio-astronomers reviewed the results of the 15 years of work: the new RadioAstron telescope was tested in Pushchino. RadioAstron project is an international collaborative mission to launch a free flying satellite carrying a 10-meter radio telescope in elliptical orbit around the Earth.
The aim of the mission is to use the space telescope to conduct VLBI (very-long-baseline interferometry) observations in conjunction with the global ground VLBI network in order to obtain images, coordinates, and evolution of angular structure of different radio emitting objects in the Universe with the extraordinary high angular resolution.
VLBI has the record in resolution, the Earth diameter is a physical limit, therefore space-based radio telescope is needed to improve further the resolution, which is possible, as demonstrated with the Japanese satellite Halca.
The orbit of RadioAstron satellite will have apogee radius in the range of up to 350,000 km. The orbit selection has advantages and disadvantages. A smaller apogee radius would result in better image capability. Space ground VLBI measurements with this orbit will provide morphological and coordinate information on galactic and extragalactic radio sources with fringe size of up to 8 micro arc second at the shortest wavelength 1.35 cm.
The RadioAstron program, initiated by Astro Space Center (ASC) of Lebedev Physical Institute of Russian Academy of Sciences (RAS) in collaboration with other institutions of RAS and Rosaviakosmos, has expanded into a broad international collaboration: scientists from over 20 countries are constructing the instruments, planning the mission profile, and assuring ground radio telescopes support for RadioAstron. Russia will provide the satellite, most of the on-board hardware, interferometer integration and all kinds of the tests. General designer of satellite and SRT is Lavochkin Association (LA) of the Federal Space Agency of Russia.
A number of subsystems, delivered by different countries, passed their guaranteed lifetime with the large delays in the project. Therefore there is concern about the utilization of such equipments, like on-board receivers in the scientific payload.
ESA has contributed to this project by conducting tests of the Radioastron petals in the ESTEC vacuum chamber in 1993 (under leadership of the late main designer at Astro Space Centre: Alexei Gvamichava) A descriptive paper was presented in the Workshop on Large Antennas in Radio Astronomy at ESTEC (WPP-110, Feb 1996). The tests at ESTEC contributed to panel improvements, which have been implemented. In 1998 the panel tests in thermal vacuum have been repeated and showed very good results, as well reported at the 26th RadioAstron meeting in July 2001.
Furthermore, development-tests have been carried out on the unique four-frequency band feed system at ESTEC. The publication of early results in the JINA Antenna Conference in France (1992) was awarded as best paper. Apart from that, it was originally decided to equip RadioAstron with a Prodex hydrogen maser clock developed by the Neuchatel Observatory in Switzerland under an ESA contract.
However, due to the successive delays of RadioAstron launch, the Swiss Space Office decided to support the development of the hydrogen maser clock exclusively for the ACES experiment on board of the International Space Station. Nowadays, Astro Space Centre has approached Vremnia-CH in Nizhniy Novgorod for the procurement of a space qualified maser.
The main scientific goal of the mission is the study of radio galaxies and quasars with unprecedented angular resolution comparable with angular size of magnetosphere and accretion discs near super massive black holes. The resolution achieved with RadioAstron will allow us in principle to study also other phenomena and problems.
Status of the Mission
An engineering model of the main SRT 10-m antenna was assembled and tested at Lavochkin Association. Carbon-fiber elements of this model can be used for the flight model. Antenna reflector was adjusted with RMS accuracy 0.4 mm, integrated with scientific electronics and delivered to for the tests and calibrations (including interferometer modes with the radio telescope RT-22) to Pushchino Radio Observatory. The construction of the special building for tests and calibrations of SRT in Pushchino is completed. Inside the building is ready, and SRT was mounted on appliance to point the radio telescope to astronomical sources.
All electronic equipment (on-board engineering models and ground-base simulators) was tested as zero-baseline interferometer (ZBI) for main operational modes.
Thermo-vacuum and vibro tests of the first model of SPECTR spacecraft with SRT model were completed according to the program. SRT RadioAstronomical tests in Pushchino pavilion (engineering model) were carried out according to the program. The results indicated, that performances at the lowest frequency band could be improved (efficiency of 30%). The efficiency for the 1.6 and 4.8 GHz band was estimated as ~50% and for the highest frequency band a value of 30% was reported from this test. No results about polarization properties were derived. The receiver installed for the highest frequency band during this test was not the one, expected to be realized for the flight model (see below).
The high apogee orbit for RadioAstron was studied in detail and approved as principal.
Upgrade of K-band (18.4 - 25.1 GHz) receiver is under fabrication with new low noise amplifier (LNA). Two NRAO LNA were fabricated (the same as for MAP mission and compatible also with VLA upgraded K-band receiver). This receiver improve sensitivity and provide the frequency tuning in one polarization channel in a band of 18.4-25.1 GHz for multi-frequency synthesis (MFS) of images and for the observation of high red-shift masers on frequencies 21160-21288 and 22136-22232 MHz in both polarizations.
The plan dedicated to RadioAstron mission on upgrade of Radio Observatory of the ASC near Kalyazin was prepared and will be financed by the Russian Academy of Sciences and FSA. It owns a 64 m radio telescope, which will be operating in all RadioAstron bands. The C-band (4.83 GHz) VLBI channel was already installed and a regular observations were started including observations with SRT Halca (VSOP). The operation of the Kaliasin antenna at the highest frequency band is a further goal, but not yet implemented.
The systematic accumulation of the main scientific targets requiring the ultra-high angular resolution is under permanent consideration on the basis of existing observations and astrophysical models and permits to propose an extensive program of prelaunch observations.
General time line and status of the mission correspond to tentative astronomically optimized launch date of March 15, 2006.
The hardware that is to be seen at Lavochkin is impressive: the large 10-m diameter (>1000kg) antenna is poised on the satellite bus that seems a bit too light for it, and the whole structure is mounted on top of the Fregat Upper Stage. The positive sign in the picture is that NPO Lavochkin made an effort to re-consider the general concept and modify the RadioAstron so that it can be launched on the Soyuz, and not on the Proton which, after several delays of the launch date for lack of financial resources, was finally decided to be unrealistic. So, the designers of NPO Lavochkin have made everything possible to make the spacecraft platform lighter.However, by the words of Vladimir Babyshkin, Project Manager of all Spectrum projects at Lavochkin, even in a lighter configuration, RadioAstron will require an additional set of fuel tanks to be added to Fregat to boost up its launch capability.
The fact that it is offered to launch an attractive payload at a well-advanced stage of development on a new satellite bus never flown before and using an Upper Stage in a configuration that was not qualified in flight, makes the whole affair look slightly dubious. However, the fact that, since 2002, RadioAstron has been included into the Federal Space Program and is considered to be the main national space science program, implies some optimism allowing to think that the money flow necessary for further development will be maintained. We are still expecting to receive from NPO Lavochkin more detailed materials on the configuration and performance of the spacecraft platform and the Upper Stage. We’ll keep our reader informed.
A next meeting about the status of the RadioAstron project will be held in Moscow in November 2004.