The ABRIXAS Mission
The advantage of an all-sky survey consists of its unbiased view
providing the potential for new discoveries and yielding large samples
of objects for statistical studies.
Ultimately, the unlimited field of view of telecopic sky scans uncovers
extended objects and large-scale structures of the universe.
The Röntgensatellit ROSAT
has demonstrated this advantage very
convincingly in the soft X-ray band between 0.1 keV and 2.4 keV.
The objective of the ABRIXAS mission
(A Broad Band Imaging X-ray All-Sky Survey) will be to perform a sky
survey at higher energies from ~0.5 keV to ~12 keV.
But this mission will not simply complement the
ROSAT All-Sky Survey
to an higher energy range, but give a substantial approvement in spectral
and angular resolution by using a charge coupled device (pn-CCD) detector
camera, built in a complete new technology.
Some ten thousand X-ray sources will be detected with the ABRIXAS mission,
among them at least 10,000 new discoveries, obscured sources,
which are too absorbed to be detected in the ROSAT All-Sky Survey.
Thus, ABRIXAS will have a pathfinder role for the large X-ray missions like
the American AXAF,
the European XMM, and
With its comparatively high spectral and spatial resolution ABRIXAS will
carry out detailed spectroscopy of diffuse large-scale sources which are too
extended for the relatively small field of view of pointed X-ray telescopes.
These investigations will complement our knowledge of nearby supernova
remnants, the diffuse emission region of the galactic ridge, and cluster of
galaxies from the ROSAT survey to study the complex states of hot interstellar
and intergalactic plasmas.
In additon, ABRIXAS will obtain the spatial distribution and high-quality
spectra of the diffuse extragalactic background, which can be studied in detail
after the identification of the thermal galactic contributions through
their line emission.
It will allow to search for fluctuations generated by the large-scale
structure of the universe and for features of the red shifted iron line
expected from superposition of many active galactic nuclei.
After all, since ABRIXAS's compound eye telescope scans the sky in a
regular pattern the time variability of bright X-ray sources can be monitored
in a wide range between seconds and years.
Satellite and Payload
The joint scientific satellite project ABRIXAS of
the Astrophysikalisches Institut Potsdam
the Max-Planck-Institut für extraterrestrische Physik
and the Institut für Astronomie and Astrophysik Tübingen
aims at to survey the whole sky similar like ROSAT by scanning it in
The three-years survey will provide a full sky coverage in the energy band
between 0.4 and 12 keV with an angular resolution of better than 1 arcmin.
Its sensitivity in the energy band
around 1 keV is comparable to that of ROSAT.
The optical system consists of seven identical Wolter I telescopes of
160 cm focal length, each with 27 nested mirror shells of
300 mm lengths and diameters ranging from 163 mm to 76 mm.
All seven focal planes share one common 6 cm × 6 cm
XMM pn-CCD array.
Consequently, their optical axes diverge and their fields of view,
each about 40' in diameter, are ~7° apart of each other
and form a hexagonal pattern on the sky.
The shift of 4' in ecliptic longitude between successive orbits
provides a contiguous coverage of the sky.
The imaging pn-CCD detector used for ABRIXAS including electronics
is identical with the EPIC-Maxi detector
developed by MPE/IAAT for XMM.
However, because ABRIXAS (in contrast to XMM) is circulating the earth in
a low orbit the CCD chip has to be operated at a somewhat higher temperature.
Accordingly, the lowest energy will be between 0.3 keV and 0.5 keV.
Unique features of the detector are its high sensitivity (95% at 10 keV)
and its ~70 ms time resolution in the full frame parallel readout.
This high time resolution (70 ms correspond to a scan path of 17")
is important to avoid source smearing along the scan direction.
ABRIXAS - Technical Data
| telescope system
|| 7 Wolter telescopes, 27 electroformed Ni shells per telescope
|| 6 × 6 cm² XMM pn-CCD, pixel size 150µ, shared FOV
| operating temperature
|| -80°C, ambient cooling
|| 3-axis angular momentum stabilized, continously spinning
| attitude control
|| 1 momentum wheel, 3 magnetic torquers
| attitude sensors
|| 2 sun sensors, 3-axis magnetometer, 1 laser gyro for redundancy
| attitude determination
|| 2 star trackers, global positioning system (GPS)
|| 2.5 × 1.8 × 1.2 m³
|| ~460 kg
|| ~200 W
|| ~580 km circular, inclination 48.5°
|| KOSMOS rocket, April 1999 from Kapustyn Yar, Russia
|| three years
| number of surveys
|| six, 4.000 s average exposure time
The small and low cost satellite with a mass of 460 kg,
which will be launched by a KOSMOS rocket purchased from Polyot,
is devloped and built by Orbital- und Hydrotechnologie Bremen
(OHB) with the
Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation
as the subcontractor for the
attitude measurement and control system.
The X-ray mirrors are manufactured by
Carl Zeiss and tested in MPE's
The imaging CCD detector
is developed and built at the MPI/MPE
Semiconductor Laboratory (HLL)
with parts of the readout electronics being provided by IAAT.
The overall project management is subject to the German Aerospace Center
as the successor of DARA and the ground station will be operated by its
Space Operations Center (DLR/GSOC).
ABRIXAS is expected to be launched with a
in April 1999 from the Russian
located about 150 km east of Volgograd.