The other ISO legacy: a pioneering infrared space telescope passes on its expertise to its successors
19 February 2001Although 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...).
Tel: +34 91 8131100
ISO Project Scientist
Tel: +34 91 8131253
ESA Science Communication Service
+31 71 565 3223