Leo Metcalfe, Chairman

Tel: +34 91 8131100

Martin Kessler, ISO Project Scientist

Tel: +34 91 8131253

ESA Science Communication Service

+31 71 565 3223

Although a space telescope will, and should, be remembered mainly for its
discoveries, its technology and the way it was operated also provide
invaluable information for the future. Last week, scientists met to discuss
and analyse in detail this other less obvious legacy left by ESA’s Infrared
Space Observatory, ISO, a pioneer in infrared space astronomy. Future missions
will certainly learn from both the successes and the ‘could-have-done-better’
aspects, said the representatives from the next ESA, NASA and Japanese infrared
space telescopes at a workshop in Spain. Thanks to ISO, there are now more
than a hundred new well-understood infrared sources for calibration, including
asteroids and planets.

ISO’s operational life ended in May 1998, but the flow of discoveries from its
observations continues unabated: 650 refereed scientific articles have been
published in the last four years and the number continues to increase by about
150 papers per year. These papers demonstrate clearly that the mission was a
major success. But surely there were things that could have been done better?
The hundred astronomers gathered at the workshop “The ISO Calibration Legacy”,
held at ESA’s station in Villafranca (Madrid, Spain), spent a full week
reviewing scientific aspects of the mission’s technology and operations with
open and constructive criticism.

“In this case we use the same principle as you journalists: good news is no
news”, said, ironically, ESA astronomer Leo Metcalfe, chairman of the workshop.
“Instead of looking at the many things that went well, we have focused on the
much smaller number that could have been done better, because they help us to
learn more”.

ISO was the world’s first true spaceborne infrared observatory — accepting
observing proposals from the whole astronomical community. The US/Dutch/UK
IRAS mission, launched in 1983, had mapped the sky at infrared wavelengths
and acted as a pathfinder for ISO. At the time of ISO’s launch, in 1995,
relatively few astronomers were used to working with these types of infrared
instruments at these wavelengths.

More testing on the ground

The self-examination had to do mostly with how to organise a large
international team; how to explain to the astronomical community the use of
a complex facility; and what is the best way to check the performance of the
instruments. It was concluded that more ground-based tests need to be done
in order to have the best possible understanding of how the system works.

Asteroids to calibrate

Other aspects, on the contrary, turned out to be more successful than expected.
That is the case with the search for more calibration sources in the infrared,
a long-standing need for infrared astronomers — because infrared astronomy
is a relatively young field, only a limited number of sources are known well
enough to use them to check the accuracy of infrared instruments. Two programs,
in the US and Europe, used ISO’s time to observe in detail more than a hundred
sources, which are now available as ‘calibrators’ for the next missions. Many
of these new sources are asteroids, which can now be used also because ISO
scientists developed a model to simulate how the asteroid luminosity changes
according to its rotation and surface irregularities.

Also, the information of how the spacecraft interacted with the environment
was considered to be very useful. ISO spent most of the time outside the
Earth’s radiation belts, but it could not avoid the impact of cosmic highly
energetic particles which caused glitches in the data. That experience is
being used now by researchers studying how to protect spacecraft from bad
‘space weather’ (magnetic storms, cosmic particles …).


* ISO home page

* The Calibration Legacy of the ISO Mission


“The Calibration Legacy of the ISO Mission” poster. 5-9 February 2001, ISO Data
Centre, ESA-VILSPA, Spain.