This would be a cut-price mission using a copy of the spacecraft bus developed for Mars Express. This summer, ESA issued a request for proposals for this mission, and this month it announced three finalists -- one of which will be picked in November, if the money exists for the mission at all.

The first is Venus Express -- a modification of the Mars Express craft to enter an elliptical orbit around Venus, and use copies of most of the Mars Express instruments to make very detailed studies of Venus' atmosphere, as well as getting a surprising amount of new data on its surface geology.

Given the number of Venus missions that have been flown by the US and the Soviet Union, there are a surprising number of big questions remaining about its atmosphere.

These include the exact chemical identity of the substance that makes some of its clouds dark in the UV wavelengths, and the mechanism that drives its "super-rotation" -- the fact that Venus' upper atmosphere all whirls around the planet in the same direction that Venus rotates, but at tremendously higher speeds (up to 360 km/hour in the upper cloud layer, dropping gradually to only 2 km/hr at the surface).

This strange weather, like Earth's weather, is obviously powered by the atmosphere's absorption of solar energy, but nobody is sure quite how. And much is still not known about the structure and trace gases of the lower atmosphere beneath the clouds.

Venus Express would map temperatures, winds and trace gases at various altitudes from the upper fringes of Venus' atmosphere all the way down to the surface, using two Mars Express instruments (PFS and SPICAM), along with a visible and near-IR mapping spectrometer (VIRTIS) copied from the Rosetta comet rendezvous mission and more capable than the similar instrument on Mars Express. It would also use Mars Express' ASPERA instrument to study the way Venus' upper atmosphere interacts with the solar wind.

VIRTIS, in particular, could take pictures in near-IR light to punch through Venus' upper clouds and take pictures of its patchier patterns of lower-altitude clouds, thus studying wind speeds and directions down there more precisely than ever before.

VIRTIS could also obtain a surprising amount of data on Venus' surface geology, thanks to the discovery 20 years ago that there are five "spectral windows" in which near-IR light from the surface can penetrate completely through Venus' cloud layer.

These would allow it to look for temperature peaks and clouds of gases indicating ongoing volcanic eruptions, map the abundance of six or seven important minerals on Venus' surface, and perhaps even detect large local earthquakes by detecting the pressure waves they produce in Venus' very dense lower air.

And another instrument -- the radar sounder from Mars Express -- might also be added to the mission to probe Venus' subsurface down to a depth of 2 or 3 km, measuring the depth of its loose soil and profiling ancient lava flows all over its surface, which could allow a test of the theory that Venus underwent a period of catastrophic eruptions half a billion years ago that resurfaced the entire planet.

Venus Express is a very attractive mission scientifically -- the US has come close to picking Venusian weather satellites for the Discovery program several times, and Japan is seriously considering launching its own Venus weather satellite (VCO) in 2007, although it would be a good deal less capable than Venus Express.

But it's also the most expensive of the three finalists; and if the ESA's Ministers don't provide that extra money this November, it's uncertain whether the savings from the delays in the US-cooperative missions would free up enough money to fund both it and Eddington. So two less expensive 2005 missions using a Mars Express bus are also under consideration.

The first is "Cosmic DUNE", which would be an entirely new type of astronomical satellite -- a "dust telescope". It would consist of an organ-pipe array of tubes with cosmic dust analyzer instruments at their bottoms, which would thus detect and analyze only those dust particles coming from a certain direction. And this would allow it to distinguish those dust particles coming from asteroids and comets in our own Solar System, from the particles of interstellar dust streaming through the Solar System in one particular direction as the Sun hurtles through the Galaxy.

The Stardust comet probe currently on its way to scoop up a sample of the dust around Comet Wild 2 and return it to Earth in 2006 is also using a different part of its dust-collection device to try and collect several hundred grains of interstellar dust for detailed analysis back on Earth, which somewhat lessens the science value of Cosmic DUNE.

But while DUNE's onboard instruments (including copies of the CDA dust analyzer from Cassini, and the CIDA dust-analysis mass spectrometer also carried on the Giotto, Stardust and CONTOUR comet probes) would do a much less precise analysis of the dust's chemical composition, the satellite could analyze samples of both interstellar dust, and dust coming from various directions in the Solar System, which would be much less mixed up together than the dust collected by Stardust's omni-directional collector.

Finally, another proposal to reuse the Mars Express design is "SPORT Express", an astronomy satellite which would continue the attempts to map the faint patchiness in the Cosmic Microwave Background radiation which is an afterglow from the earliest days after the Big Bang.

SPORT would be designed to try to map the slight differences in polarization of these ancient microwaves coming from different directions -- which is so faint that it's even harder to sense than the incredibly tiny differences in the microwaves' intensity that the COBE, MAP and Planck astronomy satellites have mapped or will map in the future.

This polarization could tell us even more about the lumpiness of the superhot plasma in the Universe's very earliest days than a direct measurement of the microwaves' strength can -- for the latter is influenced by the fact that, as that ancient, distant radiation has traveled billions of light-years to reach us, its path has been somewhat bent by the gravitational fields of the galaxies and other mass concentrations that it's passed.

Its polarization has not been so affected, and might even be able to tell us whether the new "Big Crunch" theory -- that the Universe's formation was triggered when two empty space-time continuums crashed into each other in a bigger multidimensional continuum -- is "correct".

And the polarization could also tell us just when stars began to form in the ancient Universe -- which is currently thought to be about a billion years after the Big Bang, but is very uncertain (and cannot be determined in any other way).

However, it's possible that other instruments -- on ESA's already-scheduled 2007 Planck satellite, or from balloons or even ground observatories -- might be able to map the polarization first. It's also possible that SPORT's microwave detectors could do an equally good job mounted on the Space Station -- which was the form the proposal originally took, and which would be cheaper.

Also, while two other astronomy-satellite proposals that would have reused the Mars Express bus to look for extrasolar planets -- EXOCAM and COAST -- were rejected, the judging committee found their features useful enough that it recommended a study of possible improvements to Eddington's design to incorporate them.

EXOCAM's view-field would have been much wider than Eddington's; and COAST would have used a coronagraph to blot out the light of individual stars and actually try to directly observe the light from large planets circling them -- thus detecting giant planets in other stars' outer solar systems, too far away to be detected by the transit or wobble techniques. If either or both of these features could be added to Eddington, it would be a much more formidable rival to Kepler in the search for planets of other stars.

Finally, if ESA does get that five percent hike in its funds this November, other improvements in its current program are possible. For instance, if the Bepi Colombo Mercury mission is indeed split in two, its first half -- carrying the Mercury lander and the little MMO orbiter -- might be launched in 2008 rather than 2009.

There is some feeling that the larger MPO orbiter, with its surface-mapping cameras and spectrometers, is something of a redundant repeat of the American MESSENGER Mercury orbiter scheduled for launch in 2004 to orbit Mercury in 2009 -- especially since MPO wouldn't reach Mercury until 2012.

However, the US and European teams are working together to try to minimize the scientific duplication. And since MESSENGER is set for a highly elliptical orbit with an apoapsis of fully 15,000 km over Mercury's south polar region, the European MPO -- which will be in a much more near-circular polar Mercury orbit -- can certainly provide much more detailed coverage of Mercury's southern hemisphere.

Finally, the additional money might also allow the launch of ESA's Solar Orbiter to be advanced from 2012 to 2010 -- which, according to a scientific workshop held on the mission last month, would allow it to be much better coordinated with the upcoming series of American "Living With a Star" spacecraft designed to study the way that solar activity interacts with Earth's magnetosphere and produces the so-called "space weather" which can sometimes interfere with the functioning of satellites and the world communications net.

Indeed, the workshop recommended that a new cooperative effort called "International Living With a Star" be launched, which would better coordinate the solar astronomy and magnetospheric missions launched by all nations in the future.

At any rate, it's clear that the form of ESA's space science program in the coming decade is about to change again, and that the decisions its governing council makes in November will be major ones. It's also painfully clear that the Space Station's continuing woes are tentatively starting to move the momentum of space science research from the US to other nations.

Part Two - A Flexi Approach To Science

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SPACE SCIENCE

Space Science Row Exposes NASA Budget Friction
Cameron Park - July 25, 2001
While not all the details are yet available, a significant collision seems to be developing between the US House of Representatives and the Senate on how to modify President Bush's proposed NASA budget for the coming fiscal year of 2002.

Bonnet Calls For More European Investment In Space Science
Paris - April 9, 2001
Greater investment in space science would help nurture Europe's scientific community and consequently build up the knowledge-based society that Europe's heads of state declared they wanted at the European Union summit in Lisbon last year. This was a common message delivered to the General Assembly of the European Geophysical Society in Nice last week by the outgoing and incoming directors of ESA's science programme.

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