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| CLUSTER II project in Oulu
spaceweb@oulu.fi - Last update August 28, 2001 |
Suomenkielinen sivu - Finnish page
Contents:
Introduction - About Cluster Objectives -
The Oulu Space Physics Group in Cluster-project -
Cluster Orbit - Cluster Instruments -
Cluster Science Operations -
First Results -
Pictures and links
Introduction
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The Clusters were carried to
orbit by two Russian Soyuz launchers
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Cluster II is an European Space Agency (ESA) project comprising of four identical satellites flying
in formation orbiting the Earth. Their orbit is placed so that they can study Earth's magnetosphere.
Each satellite carries an identical set of 11 scientific instruments that investigate the phenomena in
the magnetosphere. The launch was made in pairs by two Russian Soyuz launchers on July 15.
and August 9., 2000. The individual spacecrafts have been named Rumba (Cluster 1), Salsa
(Cluster 2), Samba (Cluster 3) and Tango (Cluster 4), to describe how the four spacecraft are
entwined in their weightless dance.
The first four Cluster satellites were destroyed when the Ariane 5 spacecraft exploded
right after launch in June 1996. Later it was decided to build new Cluster crafts,
Cluster II.
The Cluster satellites are a part of an international programme
for finding out more about the Sun-Earth -connection. In this effort they will join many previously launched
satellites already studying the near-Earth space. The Cluster satellites will be able to make the most
detailed exploration yet of the phenomena taking place nearby our planet. They will be spending two years passing
in and out of Earth's
magnetic field.
(See the picture below.)
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Earth's magnetic field and key regions.
Click to enlarge image
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About Cluster Objectives
The Cluster satellites are the first to be able to make detailed, three-dimensional study of
the changes and processes taking place in near-Earth space. In the beginning of the
mission the satellites are only a few hundred kilometers apart, so they will be able to
study small-scale features in the surrounding space. Later they may be separated as
much as 20 000 km and thus get a broader view of the events happening in larger scale.
The satellites' distance will vary between 19 000 and 119 000 km from Earth. As they move
in and out of Earth's magnetic shield they will be able to investigate the magnetic
boundary areas of
near-Earth space, and outside of Earth's magnetic shield they will also be fully exposed to
supersonic
solar wind. They will be able to study the interaction between the Earth's magnetic
field and the solar wind, especially in such areas as the polar cusps, where the solar wind
particles get through. Another interesting phenomenon is the acceleration
of plasma particles during magnetic
substorms in the magnetotail. The four Cluster satellites will be able to study the physical
processes involved in these and other phenomena by visiting these key regions. The four-point
measurements will allow differential plasma quantities to be
derived from the results for the first time. The key regions the Cluster satellites will
explore are solar wind and bowshock, magnetopause, polar cusps, magnetotail and
auroral zone (pictured above). This
mpeg movie pictures how the satellites
move about in the magnetospehere.
Related links:
The Oulu Space Physics Group in Cluster-project
In the Oulu Space Physics Group one strong field of investigation has been the magnetospheric waves,
for example in the area of solar wind and bow shock, and the Cluster
satellites will be able to provide better information than ever on this subject. Also there is a possibility
for simultaneous investigation from the ground with the
EISCAT radar system. The group has been involved with
two of the instruments, the EFW and the RAPID:
EFW
RAPID
For the RAPID (picture on the right) the Oulu people have been involved in testing and making testing software.
The PI institute of this instrument is
Max-Planck-Institut für Aeronomie (MPAe, Germany), which upkeeps a special
RAPID
page. |
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Related links:
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Cluster orbits on Feb 18-21, 2001.
Click to
enlarge image. (Plot from
CSDS, more detailed
description here)
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In orbit the satellites spin axis will have approximately 90° angle with the sun, which will help to get the
optimum performance from the spacecraft's solar-power generator and thermal-control subsystem.
During the mission there will be several eclipses, times the spacecraft are in Earth's shadow and out of
contact with the Earth base, but none of them will be longer than about 240 minutes.
The picture above shows how the Cluster orbit relates to the magnetic areas in the near-Earth
space. Around midwinter the satellites will be fully exposed to solar wind, and at
midsummer time
they will be able to explore the magnetic tail. As the direction changes during the year, we can see
that the satellites can reach all significant boundary areas as well.
On the left there is a plot of Cluster orbits from February 18, 2001 to February 21. The orientation of the
spacecraft is also seen. More plots of orbits and from scientific data can be drawn in the CSDS webpages at the
latest data -section.
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Related links:
Cluster Instruments
There are 11 scientific instruments onboard each Cluster satellite, each satellite carrying an identical set.
The Oulu Space Physics Group is involved in two of the instruments, the EFW and the RAPID (more detailed
description above). The instruments are:
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Cluster plots from one orbit period from five instruments
(CIS,
EFW, FGM, PEACE and STAFF) at 10-minute
resolution. This plot shows basic field, particle
and wave
information. (Plot from
CSDS, more detailed
description
here).Click to enlarge.
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- FGM - Fluxgate Magnetometer
Consists of two magnetometers on a five-metre long boom from the spacecraft to avoid interference.
It measures the magnetic field along the orbit.
- EDI - Electron Drift
Instrument
Measures the strength of electric field by shooting out two weak beams of electrons that return
to the satellite on opposite side. Magnetic field is measured too as a by-product.
- ASPOC - Active Spacecraft
Potential Control experiment
Neutralises the positive charge that is built on the spacecraft and would seriously interefere with
the measurements. It emits indium ions to space through a small needle.
- STAFF
- Spatio-Temporal Analysis of Field Fluctuation experiment
Consists of a magnetometer on the end of a five-meter long boom that looks at waves (rapid
variations in the magnetic field)
- EFW - Electric Field and Wave experiment
Measures electric field to study plasma convection and waves with sensors on four 50 m long
wire booms
- DWP - Digital Wave Processing experiment
Controls the wave experiments and makes calculations for them. Helps the WEC-instruments to make
effective use of spacecraft power resources and telemetry information.
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WHISPER - Waves of High frequency and Sounder for Probing of Electron density by Relaxation
experiment
Measures the density of charged particles that fill near-Earth space with resonance sounding
(radar) technique.
| The satellites being built
(click to
enlarge)
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- WBD - Wide Band Data
instrument
Makes high-resolution measurements of both electric and magnetic fields in selected frequency
bands from radio sounds from particles around Earth's magnetic poles
- PEACE - Plasma Electron And Current
Experiment
Looks at all electrons in space which have low to medium energies, counts them and measures their
direction and speed. One part of the instrument measures faster electrons, another part slower ones.
- CIS - Cluster Ion Spectrometry experiment
Analyses the composition, mass and distribution functions of ions in the nearby space plasma and
in the solar wind during each four-second spin of the spacecraft
- RAPID - Research with
Adaptive Particle Imaging Detectors
Uses two different and independent systems (Imaging Electron Spectrometer and Imaging Mass
Spectrometer) to record the highest energy electrons and ions.
- A combined effort: Wave Experiment Consortium (WEC)
DWP, EFW, STAFF, WBD, and WHISPER, which all measure electric and magnetic fields and waves
in some form, have been grouped together to form WEC in order to maximise resources
Related links:
Cluster Science Operations
The Cluster Ground-Based Data Centre (GBDC)
provides organisational, scientific and planning
data to enable the ground-based community to coordinate campaigns with the Cluster II mission, and make good
use of the data it will provide. There are data/tools to assist with the planning of
co-ordinated campaigns, and in addition there is a substantial database of Ground-based
instruments worldwide.
The GBDC is based at the World Data Centre C1 for Solar-Terrestrial Physics
(WDC-C1 for STP) at Rutherford Appleton Laboratory (RAL).
| The ESOC control room in
Darmstadt, Germany
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The European Space Operations Centre (ESOC) is responsible for
day-to-day operation of the four spacecraft, and also for their launch and control. They also are responsible
for collecting and distributing the raw science data.
The Clusters have already gathered quite a large amount of data now that it's been
about a year since they were launched. The Cluster Science Data System
(CSDS) is responsible
for data exchange and distribution between the different teams for each instrument.
On their quicklook
pages you can for example create plots from
latest results and find
description
of the plots, or play with a
Cluster locator -tool
(requires correct plugin).
The Cluster Joint Science Operations Centre (JSOC)
co-ordinates the science operations. It's primary task is to merge the commads for all 11 instruments
into an overall command schedule. It's also responsible for planning the instrument operations and
keeping track of the performance of the instruments.
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Clusters and the solar wind
(Click to enlarge) |
First Results
First results from the spacecraft have already
been acquired. The Clusters have been able to confirm that waves do exist in the magnetopause, and that the
solar particles cause the magnetosphere to behave like a punching bag under heavy blows. Also it was found that
the bow shock, a shockwave that is formed when the supersonic solar wind particles bump into Earth's
magnetosphere, migrates through space as a result of these punches. In the polar cusp area it was found that
the upper regions of the cusps were moving through space at the speed of 30 km/s. Later on the data from the
Cluster satellites is expected to give even more detailed idea of what's going on in the magnetic key
regions over there outside our planet.
Related links:
More pictures and links
For more images of the Cluster -project and Cluster-related links listed together see
here.
Contents:
Introduction - About Cluster Objectives -
The Oulu Space Physics Group in Cluster-project -
Cluster Orbit - Cluster Instruments -
Cluster Science Operations -
First Results -
Pictures and links
See also:
Images on this page from ESA.
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