ESA's Cosmic Vision: Europe is narrowing the choices for the next round of space science missions.

Following a mid-October meeting of the European Space Agency's Space Science Advisory Committee (SSAC), candidate missions for ESA's Cosmic Vision 2015-2025 plan have been selected for further assessment and consideration for launch in 2017/2018. The selected candidate missions include four astrophysics missions--a dark energy mission (Dune or Space), a planet-finder mission (Plato), a space infrared telescope (Spica) and an X-ray space observatory Xeus). Also under consideration are four solar system exploration missions to study satellites of Jupiter and Saturn (Laplace and Tandem), space plasmas (Cross-Scale) and a near-Earth object (Marco Polo). These new candidate missions are joined by the Laser Interferometer Space Antenna (Lisa) mission, which was moved into the Cosmic Vision 2015-2025 plan in May 2007.

The new missions are scheduled to follow on from those being developed under the current phase of the Cosmic Vision programme--Herschel and Planck (due to be launched in July 2008), the Gala astronomy satellite (2009), the BepiColombo probe to Mercury (2013), participation in the James Webb Space Telescope (2013) and the Solar Orbiter probe (2015).

At the end of the selection process, the Agency will pick one Medium mission (350 million [euro]) for a launch in 2017 and one Large mission (600 million [euro]), to be launched in 2018. The total cost should be compared with the total ESA science budget of around 400 million [euro] per year. The candidate Large missions are Xeus, Laplace, Tandem, and Lisa; all the others are considered Medium missions, with the exception of Spica, which is classified as an "Opportunity" mission in view of its low budget (less than l00 million [euro]).

Two proposals have been received for the study of dark matter and dark energy--the Dark UNiverse Explorer (DUNE) and the SPectroscopic All-sky Cosmic Explorer (SPACE). While they propose to use different techniques (DUNE is proposed as a wide-field imager, while SPACE is proposed as a near-infrared all-sky surveyor), they address the same basic science goal. In the follow-up study phase a trade-off will be performed leading to the definition in the spring of next year of a proposal for a European dark energy mission to go forward in competition.

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DUNE mission

The purpose of the DUNE mission is to shed light on the dark components of the Universe with a wide field imager in space. To study the dark Universe, DUNE will make use of the weak gravitational lensing effect which provides a direct measure of the distribution of dark matter in the Universe. This is done by measuring the weak distortions induced by intervening large-scale structures on the images of distant galaxies. This can be used to measure cosmological parameters, and, in particular, the dark energy equation-of-state parameter which affects the growth of cosmic structures. The wide-field imager of DUNE will circumvent atmospheric effects, which limit ground based surveys, and provide both high statistics (i.e. more resolved galaxies) and low systematics (thanks to a small and stable PSF) for weak lensing. Another method which will be used to probe dark energy is provided by Supernovae Ia, a homogeneous class of objects which have been shown to provide excellent distance indicators. With its panoramic wide field surveys, DUNE will also provide a wealth of astrophysical insights into the formation of galaxies, the study of galaxy clusters, type II supernovae, baryonic acoustic oscillations, and allow fundamental tests of the theory of gravity on large scales.

Reduced risk and costs

The baseline concept developed during the CNES phase 0 consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from red-shift 0 to 1.

The proposed next-generation planet finder--PLAnetary Transits and Oscillations of stars (Plato) is a photometry mission that will detect and characterise transiting exoplanets as well as measure the seismic oscillations of their parent stars. It will be capable of observing rocky exoplanets around brighter and better characterized stars than its predecessors. Observations of the mission will be complemented by ground- and space-based follow-up observations to derive the planet's masses and study their atmospheres.

Plato will detect and characterize exoplanets by means of their transit signature in front of a very large sample of bright stars, and measure the seismic oscillations of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems. Plato is the next-generation planet finder, building on the accomplishments of CoRoT and Kepler. Features compared with earlier missions include: observation of significantly more stars; stars will be three magnitudes brighter (hence the precision of the measurements will be correspondingly greater as will be those of post- detection investigations, e.g. spectroscopy, asteroseismology, and eventually imaging); capability to observe significantly smaller exoplanets with significantly longer orbital periods. The space- based observations will be complemented by ground- and space-based follow-up observations; for instance spectroscopic measurements of radial velocities of the detected exoplanetary systems will be obtained to derive the planet masses; differential visible and infrared spectroscopy during and outside secondary transit will also be performed, in particular with JWST, in order to derive information on the exoplanet atmospheres.

100 telescopes

Two different mission concepts are being proposed: a "staring" concept and a "spinning" concept. The "staring concept" utilizes 100 telescopes each with its own CCD focal plane, comprised of 24 CCDs with 800 x 1800 pixels, operated in full-frame mode, which monitors the same field for the entire mission, i.e. up to five years. The satellite is three-axis stabilized and uses a Planck-Herschel recurrent platform. The "spinning" concept uses a Gala platform, and three identical 0.72 [m.sup.2] telescopes, pointing 120[degrees] from one another, sweep out a great circle on the sky perpendicular to the spin axis. The payload would also be used half of the time in a fine-pointing mode, during which the spacecraft is three-axis stabilized. The focal plane of each telescope is made up of 32 Gaia-type CCDs operated in TDI mode in the spinning phases and in frame transfer mode in the pointed phases.

The SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a proposed medium- and far-infrared observatory with a large-aperture cryogenic telescope. The mission would address planetary formation, the way the solar system works and the origin of the universe. It would perform wide-field, high-sensitivity photometric mapping at high spatial resolution, spectral analysis as well as coronography of planets and planetary disks. SPICA is proposed in collaboration with the Japanese Aerospace Exploration Agency, JAXA, with ESA providing the telescope and a contribution to the operations.

The X-ray Evolving Universe Spectroscopy (XEUS) is a next-generation X-ray space observatory to study the fundamental laws of the Universe and the origins of the universe. With unprecedented sensitivity to the hot. million-degree universe. XEUS would explore key areas of contemporary astrophysics: growth of supermassive black holes, cosmic feedback and galaxy evolution, evolution of large-scale structures, extreme gravity and matter under extreme conditions, the dynamical evolution of cosmic plasmas and cosmic chemistry. XEUS would be stationed in a halo orbit at L2, the second Lagrange point, with two satellites (one mirror satellite and the other a detector satellite) that would fly in formation.

Various international partners have expressed interest in cooperation in XEUS and discussions will start by the end of the year with the interested agencies to ensure the earliest involvement in study work.

Cross-Scale mission

The candidate Solar System missions include the Cross-Scale mission to investigate multi-scale coupling in space plasmas. Cross-Scale would employ 12 spacecraft to make simultaneous measurements of plasma on different scales at shocks, reconnection sites, and turbulent regions in near-Earth space. It will address fundamental questions such as how shocks accelerate and heat particles or how magnetic reconnection phenomena generate or convert energy. If approved, the mission would be implemented in collaboration with JAXA, the Japanese space and exploration agency. Marco Polo is a near-Earth object (NEO) sample-return mission that would characterise a NEO at multiple scales and return a sample. If approved, the mission would study the origins and evolution of the Solar System, the role of minor bodies in the process, origins and evolution of Earth and of life itself. It would consist of a mother satellite which would carry a lander, sampling devices, reentry capsule as well as instruments. If approved, the mission would be implemented in collaboration with JAXA and possibly combined with the Hayabusa Mark 2 mission

Jovian system

The Laplace mission would explore Europa and the Jupiter System. The Jovian System, with Jupiter and its moons, is a small planetary system in its own right. Unique among the moons, Europa is believed to shelter an ocean between its geodynamically active icy crust and its silicate mantle. The proposed mission would answer questions on habitability of Europa and of the Jovian system in relation to the formation of the Jovian satellites and to the workings of the Jovian system itself. The mission will deploy three orbiting platforms to perform coordinated observations of Europa, the Jovian satellites, Jupiter's magnetosphere and its atmosphere and interior. If approved, the mission would be implemented in collaboration with JAXA and NASA.

The Titan AND Enceladus Mission (TANDEM) has been proposed to explore two of Saturn's satellites (Titan and Enceladus) in-situ and from orbit. Building on questions raised by Cassini, the mission would investigate the Titan and Enceladus systems, their origins, interiors and evolution as well as their astrobiological potential. The mission would comprise two spacecraft--an orbiter and a carrier which will deliver a balloon and three probes onto Titan. If finally approved, the mission would be implemented in collaboration with NASA.

It is expected that an initial down-select between Laplace and TANDEM, i.e. a decision in favour of Jupiter or Saturn exploration, will be made in consultation with foreign partners in the coming years.

The primary scientific goal of the Laser Interferometer Space Antenna (LISA) mission is to detect and observe gravitational waves from astronomical sources such as massive black holes (MBHs) and galactic binaries in a frequency range of 10-4 to 10-1 Hz. LISA consists of three spacecraft that act as an interferometer with an arm length of 5 million kilometres. The plane circumscribed by the three spacecraft constitutes a very large gravitational-wave antenna.

LISA's low-frequency range is inaccessible to ground-based interferometers due to local gravitational noise arising from atmospheric effects and seismic activity. Ground-based interferometers are also physically limited in length to a few kilometres, restricting their coverage to a frequency range that includes events such as supernova core collapses and binary neutron star mergers. In the low-frequency band of LISA, sources are well known and signals are stable over long periods (from several months to thousands of years). LISA will detect signals from numerous astronomical sources with signal-to-noise ratios of 501000 for MBHs, which will allow determination of the internal parameters of their source.

Least risky

The interest of LISA science was summarized by one of the conclusions of the assessment of NASA's Beyond Einstein programme, recently completed by the National Reasearch Council. The NRC declared: "On purely scientific grounds LISA is the mission that is most promising and least scientifically risky. Even with pessimistic assumptions about event rates, it should provide unambiguous and clean tests of the theory of general relativity in the strong field dynamical regime and be able to make detailed maps of space time near black holes. Thus, the committee gave LISA its highest scientific ranking."

When LISA-related activity started at ESA following its selection as a cornerstone mission of the Horizons 2000 scientific programme in 1995, it was immediately obvious that several technology challenges were going to face the developers. Although all of LISA's technology existed in some form at the beginning of the development effort and no new "inventions" were required, an incremental performance increase and additional functionality from proven technology was required. This applies to the fields of micropropulsion, drag-free sensing and actuation, interferometric measurement systems, phasemeters, high-precision pointing mechanisms. Additionally, the challenge of LISA really comes in tying all these pieces together at the system level, more than in advancing individual technology items. Several Technology Development Activities were put m place, some are still ongoing and some are planned to start in the near future. Between the start of development and now, technology in the above fields has progressed enormously and much of it will be flight-tested on LISA's technology demonstration mission LISA Pathfinder, to be launched in 2010.

International Collaboration

LISA is an ESA/NASA collaborative project. An initial agreement between ESA and NASA on roles and responsibilities for the Mission Formulation phase was finalized in August 2004. It foresees joint ESA and NASA conduction of the Mission Formulation phase in order to achieve a baseline mission architecture that allows requirement specifications to be derived and interfaces to be clearly defined. It also includes a tentative share of responsibility for deliverables and services, to be reviewed prior to entering later project phases, that shows NASA providing the three spacecraft, the launch vehicle, operations, the use of the Deep Space Network and elements of the payload and ESA being responsible for the delivery of the complete payload and the three propulsion modules. An update of the current agreement is planned to start soon to formalize ESA and NASA roles and responsibilities for the Implementation phase.

The technology demonstration mission LISA Pathfinder is an ESA mission that will fly the US Disturbance Reduction System (DRS) package along with the European LISA Technology Package (LTP).

RELATED ARTICLE: Europe ponders manned spaceflight uncertainties.

An ESA/DLR-sponsored international conference on space exploration in early November in Berlin provided the opportunity to take stock of the situation one year ahead of the next ESA ministerial council meeting. In the manned spaceflight domain, the major unresolved question concerns the operation of the International Space Station. The US wants to withdraw from the facility in 2015, while the other partners wish to continue to operate the ISS through 2020.

Other issues include the European contribution to the US Constellation programme. Collaboration with Russia on an alternative transportation system seems to have come to n halt.

Europe's Aurora programme for manned and robotic exploration of the Moon and Mars actually pre-dates the US decision to return to the Moon. The 2001 ESA Ministerial Countil meeting in Edinburgh voted a budget of 14 million [euro] for the period 2002-2006, to which n further 41.5 million [euro] was subsequently added. The following Ministerial Council in Berlin in 2005 adopted n budget of 724 million [euro] for 2006-2009. This funding was used for the ExoMars mission and a research programme including the investigation of a European contribution to the Russian Clipper system.

ExoMars is now scheduled for 2013. A demonstrator mission to the Moon or Mars, Next, is set for 2014-2016 to clear the way for a sample return mission. The Mars sample return mission is envisaged in the 2020 timeframe. Germany has plans to perform its own lunar exploration programme and is looking for 300-350 million [euro] in funding for an initial orbiter mission. France and Italy are more focused on robotic exploration of Mars. In November the Member States approved phase B2 of Exomars. The preferred scenario is a heavy mission launched by Ariane 5, the cost of which has risen from 650 million [euro] to 1 billion [euro]. Next is expected to cost 300 million [euro], while the Mars sample return is budgeted at around 2 billion [euro], if financing can be shared with NASA.

If Europe wishes to pursue its orbital flight activities after 2015, it will have to launch an autonomous orbital laboratory to take over from the ISS. The cost would be on the order of 10 billion [euro]. A further 1 billion [euro] would be required to upgrade the Guiana launch facilities and the Ariane 5 or Soyuz 2 launchers for manned spaceflight from Kourou. To this list must be added the eventual cost of a European contribution to the US-led Constellation programme (elements of the lunar base).

In other related developments, India has announced that it is studying plans to put a man on the Moon, and Korea says it wants to launch a lunar orbiter by 2020 and achieve a lunar landing five years later using a new 300t launch vehicle due to be ready in 2017.

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