Herschel To Finish Observing Soon

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Herschel to finish observing soon
European Space Agency
05 Mar 2013

ESA's Herschel space observatory is expected to exhaust its supply of
liquid helium coolant in the coming weeks after spending more than three
exciting years studying the cool Universe.

Herschel was launched on 14 May 2009 and, with a main mirror 3.5 m
across, it is the largest, most powerful infrared telescope ever flown
in space.

A pioneering mission, it is the first to cover the entire wavelength
range from the far-infrared to submillimetre, making it possible to
study previously invisible cool regions of gas and dust in the cosmos,
and providing new insights into the origin and evolution of stars and
galaxies.

In order to make such sensitive far-infrared observations, the detectors
of the three science instruments - two cameras/imaging spectrometers and
a very high-resolution spectrometer - must be cooled to a frigid -271°C,
close to absolute zero. They sit on top of a tank filled with superfluid
liquid helium, inside a giant thermos flask known as a cryostat.

The superfluid helium evaporates over time, gradually emptying the tank
and determining Herschel's scientific life. At launch, the cryostat was
filled to the brim with over 2300 litres of liquid helium, weighing 335
kg, for 3.5 years of operations in space.

Indeed, Herschel has made extraordinary discoveries across a wide range
of topics, from starburst galaxies in the distant Universe to newly
forming planetary systems orbiting nearby young stars.

However, all good things must come to an end and engineers believe that
almost all of the liquid helium has now gone.

It is not possible to predict the exact day the helium will finally run
out, but confirmation will come when Herschel begins its next daily
3-hour communication period with ground stations on Earth.

"It is no surprise that this will happen, and when it does we will see
the temperatures of all the instruments rise by several degrees within
just a few hours," says Micha Schmidt, the Herschel Mission Operations
Manager at ESA's European Space Operations Centre in Darmstadt, Germany.

The science observing programme was carefully planned to take full
advantage of the lifetime of the mission, with all of the
highest-priority observations already completed.

In addition, Herschel is performing numerous other interesting
observations specifically chosen to exploit every last drop of helium.

"When observing comes to an end, we expect to have performed over 22
000 hours of science observations, 10% more than we had originally
planned, so the mission has already exceeded expectations," says Leo
Metcalfe, the Herschel Science Operations and Mission Manager at ESA's
European Space Astronomy Centre in Madrid, Spain.

"We will finish observing soon, but Herschel data will enable a vast
amount of exciting science to be done for many years to come," says
Goran Pilbratt, ESA's Herschel Project Scientist at ESA's European Space
Research and Technology Centre in Noordwijk, the Netherlands.

"In fact, the peak of scientific productivity is still ahead of us, and
the task now is to make the treasure trove of Herschel data as valuable
as possible for now and for the future."

Herschel will continue communicating with its ground stations for some
time after the helium is exhausted, allowing a range of technical tests.
Finally, in early May, it will be propelled into its long-term stable
parking orbit around the Sun.

Notes for Editors

An announcement will follow to confirm when the liquid helium coolant
has been exhausted.

Herschel carries three science instruments: HIFI (Heterodyne Instrument
for the Far Infrared), a high-resolution spectrometer; PACS
(Photoconductor Array Camera and Spectrometer); SPIRE (Spectral and
Photometric Imaging REceiver). PACS and SPIRE are both cameras and
imaging spectrometers that together cover the wavelength range 55-672
microns. HIFI covers the two wavelength bands 157-212 microns and
240-625 microns. All three instruments are cooled to -271°C inside a
cryostat filled with liquid superfluid helium.

Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.

For further information, please contact:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus...@esa.int

Micha Schmidt
Herschel Mission Operations Manager
European Space Operations Centre (ESOC), Darmstadt, Germany
Email: micha....@esa.int

Leo Metcalfe
Herschel Science Operations and Mission Manager
European Space Astronomy Centre (ESAC), Madrid, Spain
Email: leo.me...@sciops.esa.int

Goran Pilbratt
ESA Herschel Project Scientist
European Space Research and Technology Centre (ESTEC), Noordwijk, the
Netherlands
Tel: +31 71 565 3621
Email: gpil...@rssd.esa.int