The goal of the project is to construct space
observatory operating in millimeter, sub-millimeter and infrared
wavelength ranges using 12-m cryogenic telescope in a
single-dish mode and as an interferometer with the space-ground
and space-space baselines (the later after the launch of the
second identical space telescope). The observatory will provide
possibility to conduct astronomical observations with super high
sensitivity (down to nanoJansky level) in a single dish mode,
and observations with super high angular resolution in an
It is well known that the spectrum of the
sky in the wavelength range of 0.4-20 mm is dominated by the
cosmic microwave background radiation (CMB), which follows
Planck law with the temperature of 2.73 K. This is an absolute
minimum of the brightness temperature over the whole spectrum of
the background radiation.
Fig.1. The spectrum of a electromagnetic
cosmic background for high galactic latitudes (R.C. Henry,
Ap.J., 516, L49-L52, 1999).
At the wavelength of 250 – 500mm there
is a deep minimum both for spectral intensity Inand
total intensity I~n
the background radiation(emission) at the frequency n.
This minimum separates the region with the CMB domination from
the region where the emission of interstellar and interplanetary
dust dominates. If one adopts that the flux sensitivity of the
telescope is restricted only by background radiation, the
estimates show that the sensitivity of the 12 meter space
telescope at the wavelength 300m is
equal to the sensitivity of 1 kilometer ground radio telescope
at the wavelength 2 cm. Two or more such telescopes operating as
interferometer with space baselines (SBLI), will provide angular
resolution by thousands times better than ground VLBI network.
The millimeter and submillimeter wavelength
ranges are now under intensive development. Utilization of these
wavelength ranges has already brought very important information
for cosmology and extragalactic astronomy as well as for the
investigations of our Galaxy and the objects in the Solar
system. Ultra high angular resolution and high sensitivity
possible in these wavelength ranges will enable to investigate
many stars with planetary systems. Negligible effects of
scattering waves on clouds of the interstellar plasma in these
wavelength ranges will facilitate imaging of super compact
objects and will enable high accuracy measurements of
coordinates and motions of such objects. Both continuum and
spectral line (atoms and molecules) investigation will be
possible, as well as polarimetric observations and observations
of variable sources.
Millimetron Project is included into the
Space Research Program of Russian Federation for the term till
the 2015 year. The launch date for the first spacecraft is
planned for 2016 year.
parameters and scientific objectives of the Mission
Preliminary analysis has demonstrated the
possibilities to achieve the following parameters.
Fig.2. The ultimate flux density sensitivity
of the 12-m dish limited by the sky background and by the
quantum noise. 1) space telescope with the bolometer (quantum
counter), or Space-to-Space interferometer in signal
transmission mode without amplification (Mikelson
interferometer), Dn=n, Dt=1
s; 2) the same for Dn=10 GHz, Dt=300
s; 3) the same for Dn=10 GHz, Dt=1
day; 4) the same Dn=n, Dt=1
day; 5) Space-to-Space VLBI mode with the account of zero
quantum noize of the amplifier, Dn=10 GHz, Dt=1
day; 6) Space-to-Space intensity interferometer, Dn=n, Dt=1
day. The vertical line designates high frequency border of the
optimum frequency range (1.5 THz).
The guaranteed operation
life time of the mission will be three years with the
ultimate sensitivity provided by the both active and passive
cooling system of the whole dish and science payload (total
power consumption is about 3.5 kWt)
Subsequent years (up to
7-10 years) the telescope will operate with the passive
12-m dish of the telescope will provide obtaining images in
the wavelength ranges down to 250 mm with the quality
limited by the diffraction.
main and the secondary dishes of the telescope will be cooled
down to 4 K by the cryogenic cooling system, providing the
inherent radiation of the telescope to be below the background
radiation. The passive cooling system only will keep the dish at
the temperature about 50 K.
The design of the
telescope utilizes three-mirror configuration: the deep main
mirror (which simultaneously will act as a heat screen),
the 60-cm diameter Cassegrain mirror, and the flat mirror
used for switching between different wavelength ranges and
for fine pointing to the source (0.3 arc seconds RMS).
Surface accuracy of the main dish after its deployment is
expected to be better than 10 mm, and surface accuracy of
its separate elements as well as the accuracy of the
Cassegrain mirror and the flat mirror will be better than 3
The accuracy of pointing
of the main reflector will be equal to 1 arc second.
The telescope will be
equipped with bolometers (and/or photon counters),
radiometers, spectrometers, and polarimeters in the
wavelength range 10 mm – 3 mm (single or multiple beam
operation with detectors cooled down to 0.1 K or even
The range 0.3-20 mm will
be used for interferometry “Ground-to-Space and
Space-to-Space with the second space telescope”.
The range of 0.2-3 mm will
be used for Space-to-Space interferometry only.
The frequency band
transmitted in interferometric mode will be 10 GHz and
higher. The possibility of using fiber optics data
transmission is considered as well as the processing the
data on line.
We consider three options
for the orbit of the first spacecraft: the elliptic orbit
with period of about 9-days and with the perigee of 75 000
km and the apogee of 300 000 km (similar to the orbit for
RadioAstron mission); the halo orbit around the Lagrange
point L2 (1.5
from the Earth in the opposite to the Sun direction),
elliptic orbit with the perigee of 75 000 km and the apogee
located near the Lagrange point L2.
The combination of very high sensitivity and
angular resolution in very important for modern astronomy
submillimeter wavelength range offers outstanding possibilities
for all kinds of investigations in continuum, spectral lines,
polarimetry, and monitoring of variability of different types of
objects including measurements with super high angular
resolution. Below is the list of science objectives, which shall
stimulate the discussion on the most perspective studies in
order to rectify the technical specifications for the project.
Molecular content and
physical conditions in the atmosphere of planets and their
Asteroids and comets.
Dust component of the
interplanetary medium, Van Allen and Oort belts.
mapping, rotation and variability of stars of different
kinds (from giants, WR stars, cepheids, dwarfs, neutron and
quark stars, galactic black holes).
Planets and dust envelopes
of stars, detection and investigation of star, planetary
system and even single planets formation & evolution
regions, submillimeter masers, search of life in the
Content, structure and
dynamics of the most cold gas-dust clouds.
Structure and dynamics of
the matter near supermassive black hole in the Galactic
Dynamics of the Galaxy
using radial velocity and proper motion super high precision
Dynamics and masses of
galaxies in the Local Group.
Distribution of Dark
Matter inside our Galaxy and in the Local Group of galaxies.
Structure and dynamics of
gas-dust component in galaxies and quasars, merge of
galaxies, bursts of star formation. Megamasers.
Structure and physical
processes in galactic nuclei, cosmic ray acceleration.
Structure and dynamics of
clusters and superclusters of galaxies, distribution of dark
matter inside these objects.
Extended structure near
radio galaxies: synchrotron emission and scattering of the
Dynamics of galaxies
Early galaxies: detection
of galaxy’s birth event, search of their further evolution,
including evolution of dark matter and gas-dust content.
Gravitational lenses, as
Chemical evolution and
at submillimeter wavelength and cosmology.
Hubble diagram and
Angular dimension –
redshift dependence and cosmology.
Proper motion – redshift
dependence, relic proper motion and cosmology.
Superluminal motion –
redshift dependence and cosmology.
Spatial fluctuations of
CMB at submillimeter wavelength an cosmology.
Physical processes during
the explosion due star’s merging, observing expanding shell
for determination of cosmological parameters.
Search of pre-galactic
objects, investigation of early stage evolution of the
Universe, from the time moment of recombination
(recombination lines) to the beginning of stars and galaxies
formation, search of primordial black holes.
Evolution of matter and
vacuum, dark matter and dark energy state equation,
inflation relics, worm holes, multi element model of the
Universe, additional dimensions of space.
Gravitational emission in
the Galaxy and in the Universe.
in the Galaxy and in the Universe.
Construction of high
precision astronomical coordinate system.
Construction of high
precision model of the Earth’s gravitational field.
Further development of the project suppose a
more detail discussion on each item of this list, it’s possible
extension or reducing of the list, after discussions among high
qualified experts and leading scientists.
3. The content of the Space Observatory
The observatory will include the following
Spacecraft bus of the type
of “SPECTR” module providing all service functions like
power supply, pointing and tracking of the sources, control
and monitoring of science payload, and communication with
Space cryogenic telescope.
Active and passive
(screens) cooling system of the telescope.
Bolometers (or photon
counters), radiometers with the spectrometers, polarimeters,
and additional deep cooling systems.
Frequency standards and
synthesizers to provide high stability frequencies and clock
for interferometric investigations.
Digital data acquisition
system to provide data recording, memorization and
Super broad band coherent
data transmission line providing communication between
Space-to-Space and Space-to-Ground system elements.
On-board system of high
accuracy orbit determination including range and range-rate
measurements, three-axes accelerometer, phase-locked and
laser distance measuring devices.
4. Design and main parameters of the Space
4.1. The main mirror of the telescope
The main 12-meter reflector consists of solid
3-meter diameter central part and 24 petals which will be
automatically deployed in space after launch. The design is
identical to that which used in RadioAstron project, but the
surface accuracy and its stability will be kept within 10 mm
(RMS). All construction will be cooled and shielded from
radiation of the Sun, the Earth, and the Moon by the special
screens. The screens position will be controlled by the special
control system. General view of the telescope with
screens-radiators is shown in Fig. 3.
Schematic diagram of the main components of
the telescope is presented in Fig. 4.
Surface accuracy and its stability is
provided by the high accuracy of fabrication of the elements, by
the design of the unfolding and fixating system and by cryogenic
4.2. Cooling system of the telescope
Complicated cooling system will be used to
achieve the highest sensitivity. The cryogenic system will
include two stage: passive radiation cooling which releases the
heat into space providing the cooling of the telescope down to
50 K, and the cryogenic machine to be used for the deep cooling
of all telescope mirrors (made of solid aluminium or
carbonsilicon) through the capillaries in the segments of its
construction, which will provide cooling down to 4 K. Some
devices of the telescope will be cooled below 0.1 K.
4.3. Complex of the scientific devices
Total spectral range 10 mm
– 2 cm is separated into 10 bands by octave. Switching between
the bands will be possible by the selected command with the turn
of the flat mirror when it necessary. There will be the
following bands: 1) 15-30 GHz (1-2 cm), 2) 30-60 GHz, 3) 60-120
GHz, 4) 120-240 GHz, 5) 240-480 GHz, 6) 480-960 GHz, 7)
0.96-1.92 TGz, 8) 1.92-3.84 TGz, 9) 3.84-7.68 TGz, 10)
7.68-15.36 TGz (9.8-19.5 mm).
To achieve the highest sensitivity in flux
density the scientific complex will be optimized for the range
of 200-400 mm. The
scientific complex will include the following devices:
broad band matrix
bolometer (or photon counter) – deep survey camera (»100
elements, wavelength range 0.2-3 mm),
system of medium resolution (R=l/lD » 103)
for investigation of active galactic nuclei,
system of high resolution (R » 106)
to study sources with low temperatures and maser sources in
the range of 10 mm
– 3 mm,
system of low resolution (R » 5)
with the possibility to cover broader wavelength range
(10-800 mm, with
constant beam size (angular resolution) for wavelengths
shorter than diffraction limit near 200 mm),
Space-to-Ground and Space-to-Space (frequency ranges 0.1,
0.2, 0.4, 0.65, and 0.85 THz) will operate in the ranges of
the best transparency for ground radio telescopes, in
particular for the multi element aperture synthesis system
ALMA in Chili,
Space-to-Space for the whole range of 0.2-1 mm (0.3-1.5 THz)
with the direct signal transmission from one spacecraft to
another (without amplification) and with data processing
on-board (Michelson interferomer with very high sensitivity,
but with limited baseline extension).
Potential parameters of space telescopes for
millimeter and submillimeter wavelength ranges open up
outstanding opportunities for astrophysical investigations. The
research program proposes increase in number of simultaneously
operating satellites, longer operation time, and extension of
their orbits. There may be three modes of operation for such
autonomous operation of
space telescope with the optimization for highest
sensitivity in wavelength range of 0.2-0.4 mm,
Space-to-Ground for observations optimized in wavelength
range 0.35-3 mm in conjunction with large ground telescopes
(for example, ALMA, Attakama desert in Chili, or 70-m radio
telescope, at Suffa plateau in Uzbekistan),
Space-to-Space consisting of two space telescopes optimized
in the same range (this mode anticipates development of
space array in a future).
In a case of Moon-perturbed elliptic orbit
with the apogee up to 300 000 km the interferometer fringe width
will be equal to 0.2 mas.
However, in order to achieve better conditions for cooling the
telescope and the receiver system, galo-orbit or orbit with the
apogee near the Lagrange point L2 may
be selected for space telescope. In this case the interferometer
fringe width will be equal to 0.045 mas
at 350 mm for the
baseline of 1.5x106km.
It may be advisable to place telescopes in
triangle Lagrange points L4 and
achieve even higher angular resolution of the interferometer. In
this case interferometer fringe width will be equal to 0.4
nanoseconds of arc at 300 mm
for the baseline of 1.5x108 km.
Possible scenario of development of the
system of space telescopes is shown in Fig.5. The system begins
with the orbits within the Moon orbit, and it ends with the
array near Lagrange point L2, accompanied with very
distant antennas located in the triangle Lagrange points.
Fig.5. Scenario of development of the system
of space telescopes. The system begins with the orbits within
the Moon orbit, and it ends with the array near Lagrange point L2,
accompanied with distant antennas located in the triangle