Conference 7.286::space

919.0. "Infrared Space Observatory (ISO)" by MTWAIN::KLAES (No Guts, No Galaxy) Thu Sep 08 1994 14:11

From:	US1RMC::"[email protected]" "Andrew Yee, Science North"  
        4-SEP-1994 02:11:13.89
To:	[email protected]
CC:	
Subj:	Europe's Infrared Space Observatory ready for delivery

European Space Agency
Press Information Note No. 11-94
Paris, France					30 May 1994

EUROPE'S INFRARED SPACE OBERVATORY READY FOR DELIVERY

The Infrared Space Observatory (ISO), ESA's next scientific satellite, is 
nearing a very important milestone in its development programme: the 
delivery of its Payload Module, which lies at the heart of the satellite's 
technical sophistication.  Development of the Payload Module has 
recently been completed by the Satellite Division of DASA, Deutsche 
Aerospace AG, DASA/Munich.

The ISO Payload Module is a major technical accomplishment in that it is 
designed to maintain the satellite's highly sensitive scientific instruments 
at an extremely low temperature -- 270 degrees C below zero -- near to 
the lowest temperatures that can be physically achieved.  This represents 
a technological first for a European scientific satellite.

The Payload Module will be delivered to ESA's technology centre 
(ESTEC) in Noordwijk, The Netherlands, by the end of June, where it will 
be mated with the Service Module to form the complete ISO Flight Model 
Satellite.  The satellite will then undergo thorough testing at ESTEC, 
which will last until early next year.  It will subsequently be transported to 
the ESA launch base in Kourou in French Guiana for launch in 
September next year into a highly elliptical operating orbit (perigee 1000 
km, apogee 70000 km, period 24 h) by an Ariane-4.

ISO will be the only infrared scientific observatory satellite in orbit for at 
least the next decade.  It will be used by a large community of several 
thousand astronomers, not only in the ESA Member States but also, through 
agreements currently being negotiated, in the USA and in Japan.

ISO Mission

The ISO satellite will be the world's first true astronomical observatory in 
space operating at infrared wavelengths, providing unique scientific 
capabilities.  Astronomers will be able to point ISO towards specific 
targets in the sky for up to 10 hours at a time and make observations with 
versatile instruments of unprecedented sensitivity.  During its one and a 
half year lifetime, ISO will be used to observe all classes of astronomical 
objects, ranging from planets and comets in our own Solar System, right 
out to the most distant galaxies.  It will be used to study: very weak heat 
sources in the Universe, such as the gas and dust clouds in which stars 
are being born; the formation of planetary systems like our own; and 
evolution of galaxies.

The results from the ISO's infrared measurements will give astronomers 
new insight into the history of the Universe.  The infrared region of the 
spectrum is of great scientific interest not only because it is here that cool 
objects (15 - 300 degrees K) radiate the bulk of their energy, but also 
because of its rich variety of diagnostic atomic, ionic, molecular and 
solid-state spectral features.  Measurements at these wavelengths will 
permit us to determine many of the physical parameters of astronomical 
sources, including energy balances, temperatures, abundances, 
densities and velocities.

For maximum sensitivity and wavelength coverage, it is necessary to cool 
ISO's telescope and its instruments to reduce their own thermal radiation, 
and to operate them in space, as infrared radiation is mostly absorbed by 
the Earth's atmosphere.  The first major step in this direction was taken 
with the highly successful Infrared Astronomical Satellite (IRAS), which 
surveyed over 250000 sources (IRAS was launched in 1983 and was a 
joint British, Dutch and American project).  ISO will build on the results of 
IRAS by making detailed observations of selected sources.  ISO will also 
have longer operational lifetime, wider wavelength coverage, better 
angular resolution, more sophisticated instruments and, by a 
combination of detector improvements and longer integration times, 
several thousand times greater sensitivity.

The Satellite and Scientific Instruments

ISO is 5.3 m high, 2.3 m wide and will weigh approximately 2500 kg at 
launch.  It consists of a Payload Module, a Sun shield covered with solar 
cells to generate electrical power, and a Service Module, which provides 
all the traditional spacecraft services such as power, data handling and 
attitude control.

ISO carries four scientific instruments, which have been developed in 
Europe by four consortia of institute and industries, each led by a 
Principal Investigator.  These instruments are: a camera (ISOCAM), a 
photopolarimeter (ISOPHOT), a long-wavelength spectrometer (LWS) 
and a short-wavelength spectrometer (SWS).  Each of these very 
sophisticated instruments will provide unprecedented performance.

The ISO satellite is being built by an industrial consortium of some 35 
European companies, led by the Satellite Prime Contractor, 
Aerospatiale, based in Cannes (France).

The Payload Module

The Payload Module is a large 'cryostat' 2.3 m in diameter and weighing 
1.5 tons.  This is effectively a very large thermos flask filled with some 
2400 litres of liquid helium, which 'boils' very slowly at a temperature 
below -270 degrees C.  The scientific instruments are mounted on a 60 
cm-aperature telescope installed inside the cryostat.  The latter is 
enclosed in thermal blankets and is shaded from direct sunlight by the 
sunshield mounted on its side.

The development of the cyrostat and the telescope has constituted a 
major technical challenge as there was previously little knowledge or 
experience available on the bahaviour of material at such extremely low 
temperatures.  ISO's telescope has to be very precise and stable at all 
temperatures.

Another major challenge was to design the cyrostat so that its interior will 
be darker than the darkest part of the Universe, to avoid it distributing the 
measurements that will be made.  Special facilities had to built to test 
both telescope and cyrostat.

Crticial technology developments started nearly ten years ago have 
culminated in the delivery of a unique flight-model Payload Module for 
ISO by European industry.  DASA has been responsible for the Payload 
Module's development, Linde AG (Germany) for the cyrogenic 
subsystem, and Aerospatiale (France) for the telescope.