tokyo

Officials at Japan's National Space Development Agency (NASDA) were both surprised and disappointed last week when the agency's US$1.2-billion environmental monitoring satellite ADEOS — the Advanced Earth Observation Satellite — ran out of power and stopped working.

The satellite, launched less than a year ago, carried sensors not only from Japan but also from the United States and Europe for monitoring changes in the global environment. It is the first of a series of such large satellites planned by the agency.

ADEOS stopped sending signals during the morning of Monday, 30 June. It was subsequently discovered that the satellite's solar panel had ceased to function, and that ADEOS had switched to a low-energy-consumption mode. No immediate cause for the breakdown could be identified, and after several failed attempts to reactivate the satellite, NASDA made the breakdown public.

At a meeting of the Space Advisory Committee the following day, several explanations for the failure of the satellite's power system were suggested, including collision with meteorites or ‘space junk’. But there is increasing evidence that the failure was due to a design flaw in the tension-adjustment mechanism of the satellite's solar panel.

According to Tasuku Tanaka, director of NASDA's Earth Observation Research Center, the value of the data gathered during ADEOS's short mission is not yet clear. But he admits that the seven and a half months of actual observation time — less than a quarter of the scheduled 33 months — may be insufficient to answer the global issues ADEOS was supposed to address.

As one success of ADEOS, Tanaka cites results on Arctic ozone depletion, gathered by a total ozone mapping spectrometer developed by the US National Aeronautics and Space Administration (NASA), which point to a phenomenon similar to the Antarctic ‘ozone hole’.

These results appear to have been confirmed by data from the Improved Limb Atmospheric Spectrometer (ILAS) on ADEOS, developed by the Japanese Environmental Agency, which measured the vertical distribution of ozone and various greenhouse gases in the atmosphere. But researchers at the National Institute for Environmental Studies say that the data obtained will now have to be supplemented by ground-based measurements.

Other equipment on board ADEOS included a sensor for measuring the Earth's radiation budget, developed by the French space agency CNES. NASDA officials say they are “surprised” by the accident. But they are confident the loss will not affect the overall development of remote sensing and environmental monitoring capabilities at the agency.

As the first in a series of international environmental monitoring satellites scheduled for launch over the next few years, ADEOS is the cornerstone of an ambitious strategy at NASDA to develop indigenous capabilities in remote sensing. Two more environmental monitoring satellites — the Tropical Rainfall Measuring Mission and a successor to ADEOS — are scheduled for launch by 2000.

NASDA's environmental monitoring programme, which consumes almost 25 per cent of Japan's total space budget, is the cornerstone of research on global change in Japan. While universities spend only about ¥1.3 billion (US$11 million) annually on global environmental research, NASDA's remote-sensing programme consumes almost ¥40 billion. As a consequence, any changes in NASDA's remote-sensing programme would badly affect the state of global-change research in the country, says Akimasa Sumi, a professor of climatology at the University of Tokyo.

Mike Mann, a deputy associate administrator of NASA, described the loss of ADEOS as “a real blow to NASA's science programme”. Mann said in a statement that, fortunately, much of the data from ozone monitoring instruments aboard ADEOS could be replaced by those from instruments on other spacecraft. “But the sea-surface wind data provided by the NASA Scatterometer will be harder to replace, and were opening essentially new opportunities for research and operational users worldwide.”