The 'dark science' and poker of space telescopes
Pick your dream space mission. That's what a panel of US scientists has done.
The Decadal Survey produced by the National Research Council has listed what it believes the big priorities should be in the coming 10 years for American astronomical and astrophysical research.
The document is based on wide consultation within the scientific community, and it puts a concept known as WFIRST at the top of the pile.
The Wide-Field Infrared Survey Telescope is regarded as a must-have because it would help settle some fundamental questions about the nature of "dark energy", the mysterious phenomenon which appears to be driving the Universe apart at an accelerating rate.
The existence of dark energy was established in 1998 and is one of the great discoveries of recent years, but science understands precious little about it.
WFIRST is envisaged as a 1.5m telescope costing about $1.6bn.
It would be despatched to a gravitational "sweetspot" in space known as L2, a location more than a million kilometres from Earth on its night side where the observatory could have an unencumbered view of the sky.
One key objective would be to spy as many stellar explosions, or supernovas, as possible. Scientists will want to see how their light has been stretched by the expansion of space. This will give them greater insight into how dark energy has worked through time and perhaps give them some clues as to how it might operate in the future.
WFIRST would get complementary information by mapping the distribution of some two billion galaxies. The pattern in the great voids that exist between the galaxies can be used as a kind of "yardstick" also to probe the expansion through time.
And a third technique, known as weak lensing, would look at how the light from far-distant galaxies has been subtly shaped by intervening matter, again giving insights into the influence of dark energy through the epochs.
WFIRST wouldn't be just a dark energy mission, though. It would address broader issues, too, including undertaking a survey of exoplanets in the Milky Way to try to put some better statistics on how many Earth-like objects might be out there.
The idea for WFIRST hasn't come out of thin air. Like all mission concepts, it's had a long gestation [50KB PDF]. Previous ideas have been some of this way before, most notably a concept known as the Joint Dark Energy Mission (JDEM).
And from this blog's perspective, there's a European Space Agency mission (Esa) already in study that would do much of what WFIRST aspires to do. It's called Euclid.
Euclid is currently in a competitive selection process with a couple of other Esa space concepts for two launch opportunities, in 2017 and 2018.
Would the US and Europe independently fly their own, very similar missions, or would they seek to merge the two concepts? The latter would seem the logical option, but achieving a happy marriage is by no means a straightforward task.
Europe expects to make a decision on whether to fly Euclid within the next 12 months; the US probably wouldn't make up its mind on whether to go with WFIRST for three or four years for what would be a launch in 2020. So the timelines are different.
Whilst the Decadal Survey indicates it would like to see international cooperation on WFIRST, it is adamant that the US should lead such an important dark energy mission.
European scientists, on the other hand, have stated already that a Euclid-type mission is a top priority for them too, and they (and European industry) would also want to lead any co-operative venture. So, primacy would be a sticking point.
Technically, Europe needs American involvement in Euclid. The European telescope's infrared detectors would have to be sourced from the US because they do not exist on this side of the Atlantic. But then Europe is in the advantageous position of having a far-more advanced design which is now undergoing detailed industrial assessment. It's in a good position to drive a hard bargain.
An important observation to make is that the Decadal Survey is a report from an influential panel; it's not an agency that implements the science. That's Nasa's job. And starting in September, at bilateral talks, Nasa will begin to talk to Esa inearnest about how their dark energy ambitions can both be met.
The poker, the horse-trading - whatever you call it - will start to get serious. How it will turn out is anyone's guess.
Professor Bob Nichol from Portsmouth University, UK, is working on Euclid. He believes the European concept is in a strong position right now:
"Euclid is one of three remaining missions in the M-class Cosmic Vision process with Esa. The decision will be made mid-2011 and two of the three will go forward for construction. So Euclid has a two in three chance of being selected and flying. Esa has an announcement of opportunity out at present to select the team that will complete the definition phase for Euclid by mid-2011, so it is an interesting time and Esa is making good progress in selecting its Cosmic Vision missions.
"It is worth stressing that Euclid already could include upto 20% involvement from Nasa and this is written into all the Euclid documents as an option. US scientists have been involved in parts of the discussions, and Esa certainly continues to talk with Nasa about Euclid involvement."
One aspect that bears down on both agencies, and which is likely to shape the stances they adopt, is the present fiscal environment.
The 2000 Decadal Survey top-rated the James Webb Space Telescope, which is due for launch in 2014/2015. This observatory's cost has spiralled in recent years to something like $5bn (Esa is the "junior partner", providing instrumentation and the launch rocket).
Neither the US nor Europe can afford to repeat the JWST experience.