A crucial Earth-observing satellite has gone silent,
and its controllers say that the chances of restoring contact are slim.
Replacements will not be launched for more than a year, so earth
scientists face a significant gap in their data collection.
Envisat was launched in 2002 by the European Space Agency (ESA). Since then, its ten instruments have supplied data on environmental factors such as air quality, the extent of Arctic sea ice and oil spills.
But on 8 April, Envisat went quiet – and the ground team has failed to restore contact.
It is not known what happened, but it
is likely that the power to the communications system has failed, says
mission manager Henri Laur of the European Space Research Institute
in Frascati, Italy. The power failure should have caused Envisat to go
into a safe mode, but that may also have gone wrong. His team are
continuing to monitor the satellite to pin down the cause.
Laur is pessimistic about the chances
of restoring contact. Envisat is 10 years old, but designed to operate
for only five. "The chances are low, but as long as we believe there's a
chance we will carry on," he says.
ESA has contingency plans if Envisat
does prove to be irretrievable, but they will only partially make up for
the loss of data. For instance, ESA has an agreement to use imaging
radar from two Canadian satellites, but that will produce far less data
than Envisat. "We will not be able to compensate fully," says Laur.
Satellite observations can sometimes be unreliable, so
it is best to have several instruments that can independently check
each other's results. For instance, four satellites carry altimeters
that track sea level rise. Envisat is the second of the four to
encounter problems after the American-French satellite Jason-1
began experiencing difficulties several months ago. Laur says we may
soon be down to two altimeters, leading to lower-quality data.
Envisat was due to be replaced over the next few years by five new satellites collectively called Sentinel. These are part of a broader programme called Global Monitoring for Environment and Security. Sentinels 1, 3 and 5 will take over the measurements carried out by Envisat.
The Sentinel programme is under threat,
however. Although the satellites are being built, with the first one
expected to be ready by late 2013, "we do not have the funds to operate
them", Laur says.
Even if all these satellites do launch
as planned, there will still be data gaps. That is the result of a
collective failure on the part of the scientific community and
decision-makers, says Laur. Replacements should always be on hand for
ageing satellites, so that data collection can continue uninterrupted,
but they rarely are.
Climate science in particular has long suffered from a lack of satellite data. Last year, Glory, a satellite belonging to US space agency NASA that would have measured the effect of aerosol particles on the climate, was lost at launch: the latest in a string of failures
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