Europe's scientists have presented the six dream space missions they would like to fly before 2020.
The concepts ranged from a quest to map the "dark" components shaping the cosmos, to a plan to find far-off planets that most resemble Earth.
The European Space Agency (Esa) will probably carry just three or four of the ideas forward for further study.
And it warned some of the concept teams that their likely costs would bust the budget available to carry them out.
The wished-for missions are all competing for just two potential launch opportunities, in 2017 and 2018, under Esa's Cosmic Vision programme, which aims to answer the "big questions" in space science.
The consortia behind the proposed missions presented the details of their preparatory work to peers at the Oceanographic Institute of Paris, France.
The agency intends to allocate the best ventures up to 475 million euros (£430m) (at 2010 prices) each to implement their ideas.
But the early cost estimates indicate four of the competing consortia are already struggling to shape those ideas to the cash available, and two of the missions are projected to have a final price for Esa of 600 million euros (£540m) or more.
Mindful of the recent criticism the agency has received from member states on the issue of cost overruns, Professor David Southwood, Esa's director of science and robotics, told the teams: "Industry and the science community need to get to work on this; it's a collective responsibility."
The six consortia vying for the opportunity to fly a medium-class mission under Esa's Cosmic Vision programme are:
EUCLID - MAPPING THE 'DARK UNIVERSE'
This is a telescope designed to survey the unseen cosmos. It will map the distribution of "dark matter", the matter that cannot be detected directly but which astronomers know is there because of its gravitational effects on the matter we can see. Hubble has done this for a tiny portion of sky measuring two square degrees. will do it across 20,000 square degrees of sky. This should give scientists new insight not just into dark matter, but also into that other great mysterious cosmological phenomenon thought to be driving the expansion of the Universe at an ever increasing rate - so-called "dark energy". "We will get an incredible atlas of the sky out to about 10 billion light-years," said Dr Alexandre Refregier, from CEA Saclay, France. "We will be able to study all the structures and the evolution."
SPICA - TO FILL THE 'INFRARED GAP'
A joint mission with the Japanese space agency (Jaxa) to send the next generation of infrared telescope into orbit. Europe's contribution would include the 3.5m primary mirror and an instrument. would see targets beyond the vision of the current state-of-the art infrared observatories - Esa's new Herschel telescope and Nasa's soon-to-launch James Webb telescope. "Spica will be much more sensitive," explained Professor Bruce Swinyard from the Rutherford Appleton Laboratory, UK. "It means we will be able to go from studying the formation of stars to being able to study the formation of planets. That's a big transition." Jaxa would launch Spica on one of its H-IIb rockets. A Jaxa director, Professor Tadayuki Takahashi, told the Paris meeting: "The European contribution is essential to the realisation of Spica."
PLATO - SEARCHING FOR PLANETS LIKE OURS
A spacecraft incorporating a suite of telescopes to hunt for planets around nearby bright stars. Crucially, these would include many rocky planets in the "habitable zone" - the region around a star where water can keep a liquid state. would find these worlds by monitoring stars for the tiny dips in light that occur when planets move across their faces. "We will end up monitoring half the sky; it's incredible," enthused Dr Don Pollacco, from Queens University, Belfast, UK. "We will study these planets and their stars in intricate detail. And we can eventually use those planets to look for life in their atmospheres." Plato could dramatically increase the numbers of known rocky planets, enabling scientists to really refine their models of how planetary systems form and evolve over time.
CROSS-SCALE - SAMPLING THE SPACE AROUND US
A constellation of spacecraft that would fly around Earth to sample the charged gas, or plasma, that envelops our world. " asks fundamental questions about the nature of the plasma Universe," said Professor Steve Schwartz from Imperial College, London, UK. "Ninety-nine percent of the Universe we see is in a plasma state. It's highly energised, highly charged. Its particles are accelerated up to energies that are far bigger than anything the Large Hadron Collider will ever do. The fundamental physics on all of this currently eludes us." Esa would provide seven spacecraft; Japan and Canada are considering their own mission (Scope) which could bring an additional five satellites. Together they would sample the plasma and detail its behaviour in three dimensions.
MARCO POLO - GRABBING SAMPLES FROM AN ASTEROID
A mission to a near-Earth asteroid to grab a handful of dust and pebbles off its surface to bring back to Earth labs for study. is a spacecraft that would land on the asteroid to try to drill or scoop up what would be perhaps just tens of grams of material. "It's really all about getting back a sample from what we would call a primitive asteroid, something which has been altered as little as possible since the formation of the Solar System," said Dr Simon Green, from the Open University, UK. "It's a time capsule back to 4.5 billion years ago. It tells you what conditions were like when the asteroids formed and the Earth formed." This material might contain organic (carbon-rich) molecules that could inform us about some of the precursor chemistry that eventually started life on our own planet.
SOLAR ORBITER - GETTING UP CLOSE TO THE SUN'S 'ENGINE'
This is one of the most advanced of the concepts in terms of planning. It would be a joint venture with the US. would be a successor, in European terms, to the Soho and Ulysses missions. It would circle the Sun, flying to within 35 million km of our star to make detailed measurements of the activity from the equator to the poles. The multi-instrumented probe would both observe the Sun and take in-situ measurements of its environment. "We want Solar Orbiter to help us understand how magnetic storms happen on the Sun and how they reach Earth, so we can predict them," said Dr Marco Velli of the University of Florence, Italy. "You have to go so close because you need to see the source. If you want to understand a supersonic engine, you have to go to where it is sub-sonic. That's where you can see how things work. You'll never get that information sitting out by the exhaust."
Although the first launch opportunity is in 2017, the current assessment is that none of the teams will be ready to meet this date.
Esa's Space Science Advisory Committee will convene in the New Year and rank the competitors. Their recommendations will then go to the Science Programme Committee who must decide in mid-February which of the projects should go forward for more detailed evaluation. It is expected at least two of the consortia's proposals will be discarded at this stage.
A final decision on the winning missions is not expected before the end of 2011.