1. Concept of a Scientific Space Platform (SSP)

We suggest a novel concept of the free flying Scientific Space Platform (SSP) with multiple docking to the International Space Station (ISS). Such a platform can operate at higher orbits and return back to ISS for maintenance, refilling, changing scientific instruments. The SSP can be launched for a long time of operation of the order of 15 years and includes several experiments. This is important difference from other single scientific missions like IRAS, COBE, ISO, SWAS, ODIN, IRIS, SIRTF, FIRST, PLANCK that can operate not more than 2-3 years and do not allow to change instruments, repair, refill, etc. The experience of the Hubble telescope that required change of optics shows strong necessity of maintenance during the flight.

The SSP will be made on the base of a PROGRESS cargo-ship and has allow to arrange in addition to the Submillimetron telescope other observing instruments, for example additional heterodyne instrument for high resolution spectrometry and interferometry with mirror more than 1-2 m. Thus, the SSP offers a space platform for astronomical, aeronomical, physical and other space experiments. The total mass of auxiliary experiments equipment can be about thousand kg, volume about several cubic meters. Power consumption, data transfer and communication, pointing and zero gravitation accuracy possibilities depend on board service systems, which must be installed in accordance with experiment demands. The number of solar panels can be increased if necessary during regular docking to the ISS.

The orbit of the SSP can be made distant enough from ISS to solve problems of contaminations, excessive infrared radiation and shadowing.

The Submillimetron compartment of SSP contains the cryogenic telescope with deployed screens and cooling systems. At present, we propose two versions of telescope: one with a berillium reflector of Cassegrain telescope cooled down to 5 K, and another with 2 m carbon plast reflector with metal coating cooled to 100 K. The focal block is cooled by LHe dewar down to 4 K and bolometer array block is cooled down to 100 mK by adiabatic demagnetization refrigerator (ADR) or to 300 mK by ³He sorption refrigerator. Focal block contains dichroic filters that split the incoming radiation into 7 wavebands from 0.3 mm to 1.5 mm. The readout is based on superconducting quantum interferometer (SQUID) femtoampermeter with resolution below 50 fA/Hz^1/2. The main type of sensor is a normal metal hot electron microbolometer (NHEB) developed at Chalmers and achieved noise equivalent power NEP about 10^-18 W/ Hz^1/2.

The objects of an astronomical study in Submillimeteron project are the "cold" components of the matter in the Universe (3 K radiation relic of Big Bang, extragalactic sources on the stage of star birth burst, dust in the Solar System, in the Galaxy). The primary goal is to conduct a submillimeter wave full sky survey, and to perform studies of the spectra of astronomical sources and their variability, to conduct cosmological studies (study of the anisotropy of the cosmic microwave background radiation and search for Lyman-alpha line at the epoch of recombination and secondary heating). The secondary goal is to provide a test bed to perform the technological experiments needed to develop follow-on projects.

Original and unique task of Submillimetron project - a survey of full sky with sensitivity level of 3-12 mJy in wavelength bands 0.3-1.5 mm with angular resolution 1-10 min of arc can detect about 1 million of astronomical objects. No space, ground-based or balloon instruments planned for this decade can fulfill this important task. Last comparable on the scale experiment was InfraRed Astronomical Satellite (IRAS), which have detected about 100 thousand of astronomical objects in wavelength bans 12-100 m m two decades ago. It was one of the most important works in space astronomy.

Significant part of detected objects will be luminous high redshift galaxies, which emit most
of their light in the submillimeter range. The submillimeter population appears to be a separate set of objects, which could not easily be picked out from other information, received in optical, radio or other observation. Counts of sources and data on their spatial distribution gives invaluable tests of the latest cosmological models of Universe structure and galaxies formation. A study of photometric spectra of unresolved sources and diffused emission will enhance accuracy of measurements of relict Cosmic Microwave Background on angular scale 1-10 min of arc, which is very necessary for understanding of nature of Universe, as was shown in last balloon experiments. Simultaneous and repeatable flux measurements of many sources from infrared to millimeter wavelengths also gives information about spectra and variability, and gives unique tool for determination of nature of different populations of astronomical objects.

The flexible structure of the SSP and large vacant volume allow to perform many different scientific experiments. The close connected to bolometer experiment is a heterodyne detector experiment, for which the mixer block can be easy added to the basic configuration. A promising system is a single-chip superconducting integrated receiver (SIR) designed, fabricated and experimentally studied by joint team from IREE (Russia) and SRON (Netherlands). The SIR consists of a quasioptical quantum-limited mixer and a Josephson-type flux-flow oscillator that allows to achieve noise temperatures of about 50 K at frequencies up to 600 GHz with frequency resolution below 1 MHz. Such lightweight and compact ultra sensitive SIRs are very attractive for both radio-astronomical space applications and remote monitoring of the Earth atmosphere using satellites, where low weight, power consumption and limited volume are vitally required.

Another possibility is to introduce a hot-electron bolometer heterodyne mixer receiver for radio astronomy. Such a receiver can like SIR do spectral analyses of galactic and extra galactic objects, but at much higher frequencies, e. g. between 1 and 3 THz. Recently excellent results have been obtained with a receiver for 1 to 2.5 THz.

A huge amount of information of Submilllimetron sky survey can be source of data for many tasks in addition to astrophysics and cosmology research. One of them is the early warning of asteroid hazard. High sensitivity of the telescope to cold bodies on periphery of Solar system permits to detect dangerous for Earth asteroids at the distance far beyond of Jupiter orbit. Focal instruments for experiment in infrared bands should raise accuracy of such measurements.

The SSP can be a testbed for components of future space missions like cooling systems and heterodyne instruments, a SQUID readout system for imaging array of sensors, on-chip electron cooling and other systems.

The Project Submillimetron of the cryogenic telescope can be developed at really international basis. It can be discussed what parts of this project are reasonable to produce in Russia and what parts can be produced by western countries. The concept of free flying SSP offers new unique opportunity for refilling helium, replacement of the receiver parts, changing experiments and so on.

The volume of free flying spacecraft is estimated as 10 m³. The Submillimetron telescope will occupy around 3 m³. The rest can be used for other experiments.

The bare platform based on PROGFESS cargo spaceship is a robust device that can be quickly fabricated by ENERGIA corporation at the relatively low price. Prices in the tables are only first estimations and can be discussed.

According to the present rate of costs the budget margins of the SSP (without telescope) can be estimated as follows:

Table 1. Scientific Space Platform. Prices are given by Rocket Space Corporation "Energia" (L. Gorshkov)

So, the price of the SSP can be in the range from $ 70 to 100 million.

5.1 The SUBMILLIMETRON telescope consists of the following main systems:

Table 2. Submillimetron Telescope. Prices were given by Astro Space Center of Russian Academy of Scienses (N. Kardashev, V. Gromov, A. Trubnikov) and discussed during the 4^th International Workshop "From Andreev Reflection to the International Space Station", Gothenburg

These estimations bring total budget of SSP with SUBMILLIMETRON in the range of

(For comparison, the FIRST mission budget exceeds $ 675 Million)

Possible new experiments can bring new users with their finance that can greatly decrease the project costs.

The Russian Space Agency (RSA) and Astro Space Center of RAS show active interest to know reaction of the Swedish National Space Board and ESA on this proposal. If SNSB finds interesting this proposal the possible next step could be a letter of Intent to the head of the Russian Space Agency Yu. Koptev and a copy to the President of the Russian Academy of Sciences Yu. Osipov and the Director of the Astro Space Center N. Kardashev. They will contact the Prime Minister M. Kasyanov and the Ministry of Finance.

Any communications and discussions on the concept of SSP and telescope and possible costs can be organized through e-mail or at a meeting of involved participants.

The Proposal to the SNSB and ESA is prepared on the base of proposals of the Astro Space Center of the Russian Academy of Sciences and the Rocket Space corporation Energia, and discussed at the 4^th and 5^th International Workshops "From Andreev Reflection to the International Space Station" in Gothenburg, Octorber 23-25, 2000 and in Björkliden, Kiruna, March 18-24, 2001.

Vladimir Gromov, Astro Space Center, Lebedev Physical Institute of the Russian Academy of Sciences, Profsoyuznaya str. 84/32, Moscow 117810, Russia (gro@asc.rssi.ru)

Leonid Kuzmin, Chalmers University of Technology, Department Physics, 412 96 Gothenburg, Sweden. (kuzmin@fy.chalmers.se)

Michael Tarasov, IREE RAS, Moscow / Chalmers University, Gothenburg, tarasov@fy.chalmers.se

Tord Claeson, Chalmers University of Technology, Gothenburg, (f4atc@fy.chalmers.se)

Nikolay Kardashev, Astro Space Center, Lebedev Physical Institute of the Russian Academy of Sciences, Profsoyuznaya str. 84/32, Moscow 117810, Russia, (nkardash@asc.rssi.ru),

Erik Kollberg, Harald Merkel, Chalmers University

Lennart Nordh, SNSB, Sweden

Roy Booth, Onsala Observatory

Kees van 't Klooster, ESA

A. Trubnikov, V. Slysh, Astro Space Center, Moscow

Leonid Gorshkov, Rocket Space Corporation Energia, Moscow

Igor Markov, Rocket Space Corporation Energia, Moscow

Alexander Andreev, Vice President of the Russian Academy of Science

Peter Sohtell, Torbjörn Hult, Saab Ericsson Space AB, Gothenburg

Paul Wisselius, Valery Kosheletz, SRON, Netherlands

Igor Novikov, Theoretical Astrophysics Center, Denmark

Jukka Pekola, Jyväskulä University, Arttu Luukanen, Metorex, Finland

Mikko Kiviranta, VTT, Finland

Valery Altunin, JPL, Pasadena, USA

Jan-Eric Sundgren, Chalmers University, Rector

Alain Ravex, AIR LIQUIDE, Lionel Duband, CEA, Grenoble

Ecko Valtaoja, Tuorla Observatory, Turku; Juhani Huovelin, Helsinki Observatory, - Antares Consortium

Hans Olofsson, Göran Olofsson, Roland Svensson, Stockholm Observatory

Information about Project Submillimetron can be found on the Web:

http://fy.chalmers.se/~f4agro/Submillimetron/

http://www.asc.rssi.ru/submillimetron/submill.htm

http://fy.chalmers.se/~kuzmin/Submillimetron/Platform.html — this proposal