East Meets West to Solve Space Storm Mystery

The exploration of near-Earth space will enter a new phase on 26 July when a
spacecraft called Tan Ce 2 (Explorer 2) lifts off from Taiyuan spaceport,
west of Beijing, on a Chinese Long March 2C rocket. The launch is currently
scheduled to take place at 08:23 BST (07:23 GMT).

Tan Ce 2 is the second spacecraft to be built for the Double Star programme,
a unique collaboration between Chinese and European scientists. Its
predecessor, Tan Ce 1 (Explorer 1), was successfully launched on a similar
rocket from a
launch site in Xichang on 29 December 2003 and is now returning a rich
stream of data.

Eagerly awaited by UK scientists, who have played a major role in the Double
Star missions, Tan Ce 2 will complete a six spacecraft Sino-European
constellation designed to solve a 30 year-old space mystery: what happens
when magnetic storms are generated above the Earth?

MYSTERIOUS STORMS AND EARTH’S MAGNETIC SHIELD

Double Star is the first Chinese programme dedicated to space science, and
the first international space mission involving China. It has been designed
to operate alongside the European Space Agency’s groundbreaking Cluster
mission, in which a mini-flotilla of spacecraft flies in formation around
the Earth.

This joint enterprise involving East and West will revolutionise our
knowledge of the Earth’s magnetosphere — the huge, tadpole-shaped region
of space dominated by our planet’s magnetic field — and its struggle
to protect our
planet from the supersonic particles that stream towards us from the Sun.

The four Cluster spacecraft have been orbiting together since 2000, flying
over Earth’s magnetic poles and revealing for the first time processes
which were only hinted at by earlier missions involving single spacecraft.
Together with Cluster, the two Tan Ce spacecraft will be used to study the
link between the solar wind and geomagnetic activity, and to provide the
most detailed, multi-dimensional view of the complex magnetosphere ever
obtained.

The most exciting investigation is the search for the cause of explosive
magnetospheric substorms, which has been eluding space scientists since
their discovery, more than 30 years ago. These storms can cause havoc with
compasses and power systems on the ground.

During August and September, the four Cluster spacecraft will be spending
much of their time travelling on the nightside of the Earth, in a region
known as
the magnetotail. Careful orbit design has arranged that the two Double Star
spacecraft will periodically join them in this region. Flying closer to the
Earth, they will complete the chain of six spacecraft located at different
distances from our planet.

Scientists hope that this arrangement will enable them to tie down the
location of the onset of a substorm, when large amounts of energy are
explosively
released from the Earth’s magnetic field by a process known as magnetic
reconnection. This energy accelerates charged particles in the magnetotail
and drives powerful electrical currents down into the ionosphere, a region
of the upper atmosphere. The most obvious manifestations of these particle
streams are spectacular auroral displays and disruptions to the magnetic
field.

As yet, no one knows exactly where the energy release process begins, so it
is not possible to choose between several theories of the origin of these
substorms. Mission scientists hope that accurate measurements by the Cluster/
Double Star sextet will answer this problem, and in doing so beat a
dedicated five
spacecraft mission being developed by NASA (named THEMIS, due for launch in
autumn 2006) to solving the mystery!

“On its own, Double Star is scientifically important because it provides new
measurements in key regions of magnetosphere,” said Andrew Fazakerley
(MSSL-UCL), one of the Principal Scientific Investigators (PIs) from the
UK. “For example, it will provide important new information on the
Earth’s ever-changing radiation belts.”

“However, the really exciting part is that the orbits of the two spacecraft
are explicitly designed for co-ordinated measurements with Cluster,” he
added. “So, when Cluster is in the distant magnetic tail and Double Star
is in the near tail, we shall be able to see simultaneously for the first
time what happens in both of these key regions when the huge amounts of
energy that drive the substorms are released.”

UK EXPERIMENTS

UK teams play major roles in both Double Star and Cluster, both through
provision of instruments and involvement in science operations.

Seven of the eight European instruments on the pair of Double Star
spacecraft (including five led by the UK) are copies of instruments on
Cluster.

The Plasma Electron and Current Experiment (PEACE) on TC-1 and TC-2 was
provided by the Cluster team at Mullard Space Science Laboratory, led by
Andrew Fazakerley. This measures the speed, direction and population of
electrons around the spacecraft.

Principal Investigator for the Fluxgate Magnetometer (FGM) experiments on
TC-1 and lead Co-Investigator for the TC-2 FGM is Chris Carr from the
Cluster team at Imperial College London. These instruments can measure
a magnetic field in space 1,000 times weaker than the field at the
Earth’s surface.

An experiment on TC-1 that measures waves (rapid variations in the magnetic
field) includes the Digital Wave Processor (DWP) instrument, developed
by the Cluster team at the University of Sheffield, under the leadership
of Hugo Alleyne.

In addition, Double Star will draw on science operations expertise at the
Rutherford Appleton Laboratory (RAL). RAL has been running the Cluster
Joint Science Operations Centre (JSOC) since the beginning of 2001 and
has adapted this to provide a similar service for Double Star. This
European Payload Operations Service (EPOS) works with the European
instrument teams on Double Star to co-ordinate the commanding of their
instruments and delivers the finalised commanding to the Double Star
Science Application System in Beijing.

RAL is also providing the Double Star Data Management System that will
exchange key data products generated by the instrument teams between
national data centres in Austria, France and the UK, and enable
scientists and the general public to browse and retrieve those products.

Mike Hapgood, lead scientist for both the Cluster JSOC and Double Star
EPOS, says, “This is a great opportunity to advance our understanding
of the large-scale behaviour of the Earth’s magnetosphere.”

NOTES FOR EDITORS

Double Star is the first major collaboration between Europe and China
on a scientific space mission. A major challenge has been to compare
the methods used to develop space missions in Europe and China and to
develop efficient ways of working together.

Each Double Star spacecraft is a spinning cylinder about 2 metres
across and 1 metre high.

Tan Ce 1 (TC-1) is flying in a highly elliptical equatorial orbit of
570 x78,850 km altitude (354 x 48,997 miles), inclined at 28.5 degrees
to the equator. Over a lifetime of at least 18 months, it will sample
key regions on the day and night sides of the Earth where the process
of magnetic reconnection occurs. These reconnection processes dominate
the dynamics of the magnetosphere.

Tan Ce 2 (TC-2) will fly in a highly elliptical polar orbit of
700 x 39,000 km (440 x 24,375 miles). Over a period of at least one
year, it will sample the polar cap and cusp regions. These are the
main regions where energy from the Sun flows into the magnetosphere.
Those energy flows are largely controlled by the reconnection
processes to be studied by TC-1.

European institutes contribute eight of the 16 Double Star scientific
instruments and part of the network of data systems on the ground.
These instruments are almost identical to some of those that have
been flying on the Cluster quartet since the summer of 2000.

The four identical Cluster spacecraft — Rumba, Salsa, Samba and
Tango — pirouette around the Earth in close formation, carrying out
unique multi-scale, 3-D observations of the electrically charged
particles in the solar wind and their battle with the magnetosphere.

In order to allow the combined observations by six spacecraft, the
lifetime of ESA’s Cluster mission has been extended three years until
the end of 2005. If all goes well, the lifetime of all the spacecraft
may be further extended to increase the scientific return of this
unique constellation.

The turbulent interaction between the supersonic solar wind and Earth’s
protective magnetic shield is revealed in various ways. The arrival of
huge clouds of magnetised particles (known as coronal mass ejections)
at the Earth gives rise to the beautiful aurorae — the Northern and
Southern Lights — but it can also produce magnetic storms that may
have serious consequences for human activities, from power cuts to
damaged satellites and communication breakdowns.

CONTACTS:

Chris Carr
PI for the Fluxgate Magnetometer [FGM] (TC-1)
Space and Atmospheric Physics Group
Imperial College
London, SW7 2BZ
Tel: +44 (0)20-7594-7765
Mobile: +44 (0)7714-713377
E-mail: c.m.carr@ic.ac.uk

Dr. Andrew Fazakerley
PI for the Plasma Electron and Current Experiment [PEACE] (TC-1 and TC-2)
Mullard Space Science Laboratory / University College London
Holmbury St. Mary
Dorking
Surrey, RH5 6NT
Tel.: +44 (0)1483-204175
Mobile: +44 (0)7712-760269
E-mail: anf@mssl.ucl.ac.uk

Dr. Christopher J. Owen
Co-I for PEACE (see above)
Mullard Space Science Laboratory / University College London
Tel.: +44 (0)1483-204281
Mobile: +44 (0)7793-671072
E-mail: cjo@mssl.ucl.ac.uk

Dr. Hugo Alleyne
PI for the Digital Wave Processor [DWP] (TC-1)
Space Systems Group
Department of Automatic Control & Systems Engineering
University of Sheffield
Mappin Street
Sheffield, S1 3JD
Tel: +44 (0)114-222-5630
Fax: +44 (0)114-222-5661
Email: h.alleyne@sheffield.ac.uk

Dr. Mike Hapgood
Lead Scientist, Satellite Operations Group
Rutherford Appleton Laboratory
Chilton
Didcot
OXON, OX11 0QX
Tel.: +44 (0)1235-446520
Mobile: +44 (0)789-9908780.
E-mail: M.A.Hapgood@rl.ac.uk or mike@hapgood47.freeserve.co.uk

Trevor Dimbylow
Manager, RAL science operations projects
Rutherford Appleton Laboratory (see above)
Tel.: +44 (0)1235-445827
E-mail: T.G.Dimbylow@rl.ac.uk

FURTHER INFORMATION CAN BE FOUND AT:

Double Star (ESA):
http://sci.esa.int/doublestar

Cluster (ESA):
http://sci.esa.int/cluster

Chinese National Space Administration:
http://www.cnsa.gov.cn/main_e.asp

DWP home page:
https://www.shef.ac.uk/space-systems/cluster_mission.html

FGM home page:
http://www.imperial.ac.uk/research/spat/research/dblstar/index.htm
http://www.iwf.oeaw.ac.at/english/welcome1024_e.html

PEACE homepage:
http://www.mssl.ucl.ac.uk/www_plasma/missions/double_star/

Double Star data and orbit visualisations:
http://edds02.iwf.oeaw.ac.at/dsdsweb/

Rutherford Appleton Laboratory (Cluster / Joint Science Operations Centre):
http://jsoc1.bnsc.rl.ac.uk/pub/DSP_coord/DoubleStar_RAL.html