ESA other projects

BEPICOLOMBO - Mercury

Artist’s view of BepiColombo at Mercury

Status: Being built and tested

Objective:
One of ESA’s cornerstone missions, it will study and understand the composition, geophysics, atmosphere, magnetosphere and history of Mercury, the least explored planet in the inner Solar System.

Mission:
BepiColombo will provide the best understanding of Mercury to date. It consists of two individual orbiters: the Mercury Planetary Orbiter (MPO) to map the planet, and the Mercury Magnetospheric Orbiter (MMO) to investigate its magnetosphere.

What’s special?

Most of ESA's previous interplanetary missions have been to relatively cold parts of the Solar System. BepiColombo will be the Agency's first experience of sending a planetary probe close to the Sun.

BepiColombo’s mission is especially challenging because Mercury's orbit is so close to our star. The planet is hard to observe from a distance, because the Sun is so bright. Furthermore, it is difficult to reach because a spacecraft must lose a lot of energy to ‘fall’ towards the planet from the Earth. The Sun’s enormous gravity presents a challenge in placing a spacecraft into a stable orbit around Mercury.

Only NASA's Mariner 10 and Messenger have visited Mercury so far. Mariner 10 provided the first-ever close-up images of the planet when it flew past three times in 1974-1975. En route to its final destination in orbit around Mercury in 18 March 2011, Messenger flew past the planet 3 times (14 January 2008, 6 October 2008, and 29 September 2009), providing new data and images. Once BepiColombo arrives in 2022, it will help reveal information on the composition and history of Mercury. It should discover more about the formation and the history of the inner planets in general, including Earth.

Spacecraft

The BepiColombo mission is based on two spacecraft:

• a Mercury Planetary Orbiter (MPO); and
• a Mercury Magnetospheric Orbiter (MMO)

Among several investigations, BepiColombo will make a complete map of Mercury at different wavelengths. It will chart the planet's mineralogy and elemental composition, determine whether the interior of the planet is molten or not, and investigate the extent and origin of Mercury’s magnetic field.

Journey

Several launch methods have been extensively studied. In the selected scenario, BepiColombo will use the gravity of the Earth, Venus and Mercury in combination with the thrust provided by solar-electric propulsion (SEP). During the voyage to Mercury, the two orbiters and a transfer module, consisting of electric propulsion and traditional chemical rocket units, will form one single composite spacecraft.

When approaching Mercury in 2022, the transfer module will be separated and the composite spacecraft will use rocket engines and a technique called 'weak stability boundary capture’ to bring it into polar orbit around the planet. When the MMO orbit is reached, the MPO will separate and lower its altitude to its own operational orbit. Observations from orbit will be taken for at least one Earth year with the possibility of an extension.

History

As the nearest planet to the Sun, Mercury has an important role in showing us how planets form. Mercury, Venus, Earth and Mars make up the family of terrestrial planets; each one carrying essential information to trace the history of the whole group.

The knowledge of how they originated and evolved is key to understanding how conditions supporting life arose in the Solar System, and possibly elsewhere. As long as Earth-like planets orbiting other stars remain inaccessible to astronomers, the Solar System is the only laboratory where scientists can test models applicable to other planetary systems.

Exploring Mercury is therefore fundamental to answering important astrophysical and philosophical questions such as 'Are Earth-like planets common in the Galaxy?'

A European mission to Mercury was first proposed in May 1993. Although an assessment showed it to be too costly for a medium-size mission, ESA made a Mercury orbiter one of its three new cornerstone missions when the Horizon 2000 science programme was extended in 1994. Gaia competed with BepiColombo for the fifth cornerstone mission. In October 2000, ESA approved a package of missions for 2008–2013 and both BepiColombo and Gaia were approved.

In February 2007, the mission was approved as part of the Cosmic Vision programme. Following an unavoidable increase in the mission’s mass during 2008, the launch vehicle was changed from Soyuz-Fregat to Ariane 5. Final approval for the redesigned mission was given by ESA’s Science Programme Committee in November 2009.

BepiColombo represents the first time ESA and JAXA have joined forces for the implementation of a major space science mission.

Partnerships

BepiColombo is a joint mission between ESA and the Japanese Aerospace Exploration Agency (JAXA), executed under ESA leadership.

CLUSTER :

Artist's impression of the four Cluster spacecraft

Cluster is a constellation of four spacecraft flying in formation around Earth. They relay the most detailed information ever about how the solar wind affects our planet in three dimensions. The solar wind (the perpetual stream of subatomic particles given out by the Sun) can damage communications satellites and power stations on Earth. The original operation life-time of the Cluster mission ran from February 2001 to December 2005. However, in February 2005, ESA approved a mission extension from December 2005 to December 2009.

The four Cluster spacecraft have spent several years passing in and out of our planet's magnetic field. Their mission will be to complete the most detailed investigation ever made into the ways in which the Sun and Earth interact.

What's special?

The Sun emits the solar wind, which is a thin, hot, ionised gas that carries particles and magnetic fields outward from the Sun.

The Earth is shielded from the full blast by its magnetosphere, the region around our planet controlled by its magnetic field. Some solar wind descends into Earth's upper atmosphere through the polar cusps, funnel-like openings in the magnetosphere at the poles. These energetic particles excite atoms and molecules in the upper atmosphere to create the Northern and Southern Lights (the auroras). The part of a planetary magnetosphere that is pushed in the direction of the solar wind is known as the magnetotail.

Cluster will determine the physical processes involved in the interaction between the solar wind and the magnetosphere by visiting key regions like the polar cusps and the magnetotail. The four Cluster spacecraft map the plasma structures contained in these regions in three dimensions. The simultaneous four-point measurements also allow close studies of plasma quantities in both space and time.

During periods of high solar activity (which cycles every 11 years), the solar wind can be particularly energetic. This can have a dramatic effect on human activities, disrupting electrical power and telecommunications or causing serious problems in the operation of satellites, especially those in geostationary orbit. Subtle changes to the weather on Earth also occur during these times. Watching the effects of this increased activity during these periods is one of the main tasks of Cluster.

Understanding the interaction between the solar wind and the magnetosphere and how the plasma levels of the magnetosphere are affected is important. Cluster will help us to prepare for the effects of sudden bursts of solar energy here on Earth.

Spacecraft

The Cluster spacecraft resemble giant 'Lego' sets, assembled from thousands of individual blocks. Each one is shaped like a giant disc, 1.3 metres high and 2.9 metres wide, with a cylinder in the centre.

Six spherical fuel tanks are attached to the outside of this central cylinder. The fuel they carry accounts for more than half the launch weight of each spacecraft. Most of the fuel is consumed soon after launch and in complex manoeuvres to reach their operational orbits. Each spacecraft also carries eight thrusters for smaller changes of orbit.

Around the central cylinder is the main equipment platform. Electrical power comes from six curved solar panels attached around the outside of the platform. Five batteries are used for power supply during the four-hour-long eclipses when the spacecraft enter Earth's shadow.

Rod-shaped booms open out once Cluster reaches orbit. There are two antennae for communications, two sensors, and four wire booms that operate when the spacecraft begins to spin. These measure changing electrical and magnetic fields around each spacecraft.

Journey

At each launch, two Cluster satellites were placed in an elliptical orbit whose height varied from 200 to 18 000 kilometres above Earth. The two satellites of each launch were then released, one after the other and used their own on-board propulsion systems to reach the final operational orbit (19 000 to 119 000 kilometres from the planet).

The first pair of Cluster satellites lifted off on 16 July 2000, the second pair one month later. This gap allowed fewer people to be used for mission control in the European Space Operations Centre (ESOC) in Darmstadt (Germany).

Once the booster reached the correct altitude, after liftoff, the Fregat payload assist module and its two Cluster spacecraft were released. The Fregat main engine fired almost immediately to achieve a circular orbit of approximately 200 kilometres high. About an hour later, the Fregat engine fired again to inject the spacecraft into an elliptical orbit.

The two satellites were released, one after the other. Each Cluster spacecraft main engine performed six major manoeuvres, using the large amount of on-board fuel (about half of each satellite's launch mass).

History

The Cluster mission was first proposed in November 1982. The idea was developed into a proposal to study the 'cusp' and the ‘magnetotail’ regions of the Earth's magnetosphere with a polar orbiting mission. The Cluster idea developed into a proposal and then a mission. In 1996, Cluster was ready for launch.

Cluster was expected to benefit from a 'free' launch on the first test flight of the newly developed Ariane-5 booster. After several minor delays, Ariane-501 lifted off from Kourou, French Guiana on 4 June 1996, carrying its payload of four Cluster satellites. Unfortunately, intense aerodynamic loads resulted in its break-up and initiation of the automatic destruct system.

To recover some of the unique science from the mission, ESA decided to build a fifth Cluster satellite (named `Phoenix'). It would be equipped with flight spares of the experiments and subsystems prepared for the Cluster mission. Phoenix was expected to be fully integrated and tested by mid-1997, opening the way for a launch later that year. However, awareness grew that the scientific objectives of the Cluster mission could not be met by a single spacecraft. There were proposals to rebuild three or four full-size Cluster spacecraft alongside Phoenix.

After a preliminary study, it was decided that a Soyuz rocket could launch a pair of Cluster spacecraft. However, the very eccentric orbit required a new upper stage. Two flights were successfully done at the beginning of 2000 and about six months later, Cluster was launched by a Soyuz-Fregat launcher from Baikonur Cosmodrome, Kazakhstan.

On 10 February 2005, the ESA Science Programme Committee approved unanimously the extension of the Cluster mission, pushing back the end date from December 2005 to December 2009. This extension will allow the first measurements of space plasmas at both small and large scales simultaneously and the sampling of geospace regions never crossed before by four spacecraft flying in close formation.

In October 2009 the mission was extended until end 2012.

Partnerships

Prime contractor for the original (lost) Cluster and replacement Cluster satellites was Dornier Satellitensysteme GmbH (now Astrium), Friedrichshafen, Germany, the leader of an industrial consortium involving 35 major contractors from all of the ESA member countries and the United States.

Each spacecraft carries an identical set of 11 instruments to investigate charged particles, electrical, and magnetic fields. These were built by European and American instrument teams led by Principal Investigators.

The Cluster scientific community includes the ESA Project Scientist, 11 Principal Investigators, and more than 250 Co-Investigators from ESA Member States, the United States, Canada, China, the Czech Republic, Hungary, India, Israel, Japan, and Russia.

SOHO

Artist's impression of the SOHO spacecraft

The Solar and Heliospheric Observatory (SOHO) is stationed 1.5 million kilometres away from Earth. There, it constantly watches the Sun, returning spectacular pictures and data of the storms that rage across its surface. SOHO's studies range from the Sun's hot interior, through its visible surface and stormy atmosphere, and out to distant regions where the wind from the Sun battles with a breeze of atoms coming from among the stars. The SOHO mission is a joint ESA/NASA project.

What's special?

Every day SOHO sends thrilling images from which research scientists learn about the Sun's nature and behaviour. Experts around the world use SOHO images and data to help them predict 'space weather' events affecting our planet.

SOHO moves around the Sun on the sunward side of Earth, where it enjoys an uninterrupted view of the Sun, by slowly orbiting around Lagrange point L1. This a spot in space where the gravitational fields of the Sun and Earth cancel each other and keep SOHO in an orbit locked in line with the two bodies.

Discoveries include complex currents of gas flowing beneath the visible solar surface and rapid changes in the pattern of magnetic fields. In the Sun’s atmosphere, SOHO also sees explosions, remarkable shock waves and tornadoes.

Spacecraft

The total mass of the spacecraft at launch was 1850 kilograms. Its length along the sun-pointing axis is 4.3 metres, and the span of the extended solar panels is 9.5 metres.

The instruments on board SOHO are:

• CDS (Coronal Diagnostic Spectrometer) from Rutherford Appleton Laboratory, United Kingdom.
• CELIAS (Charge, Element, and Isotope Analysis System) from the University of Bern, Switzerland.
• COSTEP (Comprehensive Suprathermal and Energetic Particle Analyser) from the University of Kiel, Germany.
• EIT (Extreme ultraviolet Imaging Telescope) from the Institut d'Astrophysique Spatiale, France.
• ERNE (Energetic and Relativistic Nuclei and Electron experiment) from the University of Turku, Finland.
• GOLF (Global Oscillations at Low Frequencies) from the Institut d'Astrophysique Spatiale, France.
• LASCO (Large Angle and Spectrometric Coronagraph) from the Naval Research Laboratory, United States.
• MDI (Michelson Doppler Imager) from Stanford University, United States.
• SUMER (Solar Ultraviolet Measurements of Emitted Radiation) from the Max-Planck-Institut für Aeronomie, Germany.
• SWAN (Solar Wind Anisotropies) from Service d'Aeronomie, France.
• UVCS (Ultraviolet Coronagraph Spectrometer) from Harvard-Smithsonian Center for Astrophysics, United States.
• VIRGO (Variability of Solar Irradiance and Gravity Oscillations) from PMO/WRC Davos, Switzerland.

Journey

SOHO had such a flawless launch in 1995, that it had to use only very little thruster fuel for course corrections during its journey out to its operating position L1.

SOHO was meant to operate until 1998, but it was so successful that ESA and NASA decided to prolong its life several times and endorsed several mission extensions. In its latest round of mission extensions, ESA approved continued SOHO operations until the end of 2014, subject to mid-term review in 2012.

Three years into its mission, in June 1998, contact was lost with SOHO after a sequence of incorrect commands during what should have been a routine manoeuvre. All attempts to re-establish contact with the spacecraft failed and no one knew where it was for four weeks.

In August 1998, a powerful radar signal from Earth produced a faint echo from the spacecraft. SOHO was still in the right place and angled in such a way that sunlight would begin to fall on its solar cells again during the following months, so enabling it to resume normal operations.

Other difficulties came with the loss of the gyroscopes used to control the spacecraft orientation. Despite these problems, engineers have kept SOHO functioning with all its instruments performing well. SOHO was the first three-axis stabilised spacecraft to be operated without any gyroscopes.

History

SOHO was first proposed 13 years before its actual launch and the roots of SOHO were laid in earlier studies, namely those of GRIST (Grazing Incidence Solar Telescope) and DISCO (Dual Spectral Irradiance and Solar Constant Orbited). It is the combination of the objectives of these two missions that constitutes the core of the SOHO mission.

In June 1976, GRIST had been competing with a 'Solar Probe' as well as other studies involving other disciplines for further study. Solar Probe envisaged a set of instruments on a spacecraft that would get close to the Sun. Although its assessment study cited four scientific disciplines interested in the mission, Solar Probe was not followed up at the time.

The GRIST study, on the other hand, proceeded to a feasibility stage. GRIST was preferred over Solar Probe because the wavelength range accessible through its optics was particularly useful for studying the hot outer solar atmosphere. GRIST was at that time being designed for flights on Spacelab.

Following the 1976 study, GRIST did not make it to project selection either. It was based on a collaboration with NASA which became a victim in 1981 of NASA's cancellation of the US probe in the International Solar Polar Mission (ISPM, the former 'Out-of-Ecliptic Mission', now called Ulysses). GRIST was 'parked', but restricted studies on its main spectrometers were supported by ESA.

In 1980, a group of French and American physicists observed the Sun continuously from Antarctica, studying solar physics with the best conditions available on Earth. These historic observations led to the decision to include the same sort of experiments on board a newly proposed mission called DISCO. DISCO would sit at the L1 Lagrange point between the Sun and Earth, which would be an ideal observing site. A miniaturised version of the South Pole experiment could be used as part of DISCO’s payload, provided its weight could be reduced.

DISCO was conceived as a fairly small and cheap spin-stabilised spacecraft, weighing no more than 520 kilograms. It was intended to prove that ESA could also undertake small and inexpensive missions. A first assessment was made in 1981, when DISCO had remained a relatively inexpensive spinning satellite, very similar to Cluster. ESA's Solar System Working Group preferred DISCO to a competing Mars mission called 'Keller', but DISCO eventually lost out to the Infrared Space Observatory in 1983.

SOHO itself developed as a mission in 1983, combining many of the aspects of the previously planned missions. It became important because it developed momentum, together with the Cluster mission, as part of the International Solar–Terrestrial Physics Programme. In May 1984, ESA identified SOHO as a part of the 'Cornerstone' of its long-term 'Horizon 2000' science programme.

Partnerships

SOHO is part of the first Cornerstone project in ESA's Science programme (the other is Cluster). Both are joint ESA/NASA projects in which ESA is the senior partner. SOHO and Cluster are also contributions to the International Solar-Terrestrial Physics Programme, to which ESA, NASA, Japan, Russia, Sweden and Denmark all contribute satellites monitoring the Sun and solar effects.

Of the spacecraft's 12 instruments, nine come from multinational teams led by European scientists, and three from US-led teams. More than 1500 scientists from around the world have been involved with the SOHO programme.

SOHO was built by industrial companies in 14 European countries, led by Matra-Marconi (now Astrium). The service module, with solar panels, thrusters, attitude control systems, communications, and housekeeping functions, was prepared in Toulouse, France. The payload module carrying the scientific instruments was assembled in Portsmouth, United Kingdom, and mated with the service module in Toulouse, France. NASA launched SOHO and is responsible for tracking, telemetry reception, and commanding.