The European Space Agency plans to take the lead in space science, with the imminent launch of six satellites.
Tim Furniss/PARIS
Six European Space Agency (ESA) spacecraft are being prepared for launch in 1995, which is described as Europe's "year of glory" by Roger Bonnet, director of ESA's science programme.
The glory is, however, being threatened, particularly by ESA member states Germany and the UK, which are demanding up to 25% off ESA's $460 million annual science budget to be decided at the Council of Ministers meeting, in Toulouse, in October. Some bureaucratic and procedural fat could be trimmed, but ESA's long-term plans for the 21st century could be badly hurt by substantial cuts.
Meanwhile, however, ESA's "super science" marches on. The Infrared Space Observatory (ISO), the Solar and Heliospheric Observatory (SOHO), and four Cluster satellites place "Europe at the forefront of scientific exploration," says Bonnet. The satellites include 9t of hardware and 60 science experiments.
The ISO has arrived at Kourou, French Guiana for its Ariane 4 launch in September. It will be used to study objects, from nearby planets to the farthest galaxies, with unparallelled sensitivity through invisible, cold light infra-red radiation sensors.
The SOHO, the first spacecraft to be used for the continuous observation of the Sun in detail, from a unique stationary position between the Earth and the Sun, will be launched in October from Cape Canaveral, Florida, aboard an Atlas 2AS.
The satellite will work in conjunction with the four Clusters, which were originally planned for launch on the first Ariane 5 on 29 November. The maiden launch will now be pushed into 1996. The Clusters will study the Earth's magnetosphere and the solar storms which occur within it, which disrupt radio communications and electrical supplies on the Earth.
Another spacecraft, the Ulysses, meanwhile, is beginning its flight over the north pole of the Sun, providing an unprecedented bird's-eye view. "These missions show that Europe is now taking the lead in in situ exploration of the Universe," says Bonnet.
The Ulysses, ISO, SOHO and the Clusters are parts of ESA's Horizon 2000 project. This also includes the launch of the Huygens spacecraft to Titan, the moon of Saturn, in 1997; the X-Ray Multi-Mirror telescope, in 1999; the integral gamma ray observatory, in 2001; and the Rosetta, in 2003, which will rendezvous with a comet. The Cluster/SOHO, XMM and Rosetta are called Cornerstone missions C1, 2 and 3, while the Huygens and Integral are dubbed Medium-Size missions M1 and 2
The Horizon 2000 project has included ESA's role in the operation of five spacecraft - the International Ultraviolet Explorer, the Hubble Space Telescope, Ulysses, Hipparcos and the Giotto extended mission to a second comet after its triumph at Halley's Comet in 1986.
Three planned Horizon 2000 projects are outstanding and include the fourth Cornerstone mission, the Far Infrared and Submillimetre Space Telescope (FIRST), to be launched in about 2005. Two medium-size missions, the M3 and 4, are outstanding, and are placed in a new ESA venture, Horizon 2000 Plus, to take European space science into the 21st century.
Five of seven candidate missions for the M3 have been selected for Phase A studies. These are Intermarsnet, a network of Mars landers; MORO, a Moon orbiting telescope; Satellite Test of the Equivalence Principle, STEP; COBRAS/SAMBA, a mission to observe cosmic microwaves; and STARS, a stella observatory. A final decision on the chosen project will be made in 1996, with the likelihood that Mars and solar-physics missions will be selected.
Horizon 2000 Plus will include participation in the International Space Station; four new M missions, for X-ray, ultraviolet, infra-red and physics observatories; six small science missions; three new Cornerstone missions (a Mercury mission, gravitational waves observatory; and an interferometry mission); and two new X-ray and infra-red observatories.
As a long-term programme, the Horizon 2000 will depend on stable funding, and that is not certain at this stage. There may be some casualties among the newly planned projects if the budget-cutters have their way.
Solar observers
The SOHO and Clusters are parts of an Inter Agency Solar Terrestrial Science Programme (IASTP) to address unsolved problems of solar, heliospheric and space plasma physics in two combined missions. The IASTP was to be a 14-spacecraft programme, involving NASA, ESA, Japan and Russia. Two Russian Regatta satellites were cancelled through budget cuts, but four Interball spacecraft are still planned. Japan's Geotail was launched in 1992. NASA has launched the Wind, but its Polar satellite is still awaiting launch.
The SOHO will investigate the Sun's internal structure and dynamics, its corona - the tenuous outer atmosphere - and its expansion into solar wind, the stream of highly ionised gas which blow through the solar system. The Clusters will make three-dimensional studies of the solar-wind plasma trapped in the Earth's magnetosphere.
The Atlas 2AS will place the SOHO in a unique "halo orbit", around what is called the L1 Langrane point -a position between the Earth and the Sun, 1.5 million kilometres from the Earth, where the gravitational pull of the Earth balances out that of the Sun. From this vantage point, unlike previous satellites, the SOHO will have an uninterrupted view of the Sun.
The SOHO will study the Sun's structure using a technique called helioseismology, which measures subtle oscillations on the solar surface. These oscillations travel through the Sun as sound waves, which are influenced by the density, composition and internal motions within the Sun. Like waves connected with earthquakes, these internal solar waves yield insights into the structure of the Sun's interior.
The physical processes which form and heat the Sun's corona and give rise to its acceleration and expansion into solar wind, will be studied through advanced spectroscopic diagnostics of the outer regions of the Sun's plasma and by in situ measurements of the particles which make up the solar wind.
The SOHO is a joint ESA/NASA mission. It was built in Europe and the launch and mission operations will be NASA's responsibility. Nine of the principal investigators are European and three are American. Mission life could be as long as four years. The 1,850kg, 3.6m-high spacecraft is built by prime contractor Matra Marconi Space with Alenia, CASA, Saab Ericsson and main subcontractors. Its 11 instruments are provided by the USA, Germany, the UK, France, Finland and Switzerland.
The Clusters will observe the result of the solar wind's interaction with the Earth's magnetosphere. They will be placed into geostationary-transfer orbit by the first Ariane 5 booster and will eventually travel into separate elliptical polar orbits, using on-board thrusters.
The Earth's magnetic field acts as a shield against bombardment by highly energised solar wind, but sometimes some of the particles become trapped in the magnetic field and release part of their energy as radiation. A spectacular manifestation of this energy release is the aurora borealis, or northern lights.
By increasing knowledge of these complex interactions between the magnetic field and the trapped particles stored in it, as well as those coming from the Sun, scientists can better understand that delicate balance between the Sun and the planet Earth and may also be able to warn of disturbances which may affect operators of communications satellites and power grids after sudden energy releases from the Sun.
Each Cluster will carry the same eleven instruments, which will monitor the interactions between the plasma and the magnetic field. These are housed in the cylindrical bodies from which extend six booms, four 50m-long and two 5m-long. On their tips are the experiments' sensors to measure the plasma and magnetic fields. The Cluster's orbits are chosen so that they travel both inside and outside the magnetic field and cross various interesting parts of the magnetosphere during their two-year mission.
The Clusters are built by prime contractor DASA. Main subcontractors are Matra Marconi Space, Contraves, Fokker, Laben and Saab Ericsson. The craft are 2.9m diameter, 1.3m cylinders, weighing 1,200kg each. The 11 instruments are provided by France, Sweden, UK, Germany, the USA, and Austria.
The Infra-red Space Observatory will have an impact on "virtually every field of astronomy", says ESA. During its 18-month life, the ISO's infra-red telescope - cryogenically cooled by liquid helium to a temperature of minus 270¡C - will be used to observe all classes of astronomical objects, from planets to distant galaxies, investigating very weak sources of heat in the Universe, such as gas and clouds, in which stars are being born.
ISO's wide impact
The infra-red region - in the 15o-300oK temperature range - is of great interest to astronomers because it is rich in a variety of atomic, ionic, molecular and solid-state features. ISO's instruments - a camera, an imaging photopolarimeter and two spectrometers - will be up to 1,000 times more sensitive than any other infra-red astronomical instruments, mainly because the spacecraft will be operating outside the Earth's atmosphere, which absorbs most infra-red radiation. The ISO will build upon the results from the joint NASA/Netherlands/UK Infra-red Astronomical satellites, which was launched in 1983. It will launched by an Ariane 44P booster and placed into an elliptical, 5¡-inclination Earth orbit, with a 24h period, with a 1,000km (620 miles) low point, or perigee, and 70,000km high point, or apogee. The ISO will spend 16h outside the Earth's radiation belt and a network of three ground stations will enable operations for 16h a day. The main ground station is in Villafranca, Spain and the others are in the USA and Japan.
The 5.3m-high, 2,400kg spacecraft was built by prime contractor Aerospatiale, with Daimler-Benz Aerospace and Fokker as main subcontractors. The four main instruments in the Ritchey-Chretien optical system are provided by France, Germany, the Netherlands and the UK.
Source: Flight International
