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Dark energy, alien planets are focus of decadal survey

Posted: August 15, 2010

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NASA's top new astrophysics mission should be a multipurpose infrared space telescope to study planets beyond our solar system and seek out dark energy, the driving force of the universe, according to an independent science panel.

Charged with recommending an astronomy and astrophysics science program for federal agencies in the next decade, a National Research Council committee reported projects should focus on the birth and early evolution of the universe, habitable worlds beyond our solar system, and the fundamental physics of the cosmos.

"Three of the most highly-ranked science programs involving dark energy, exoplanet statistics and surveys of our and nearby galaxies required a rather similar type of space telescope," said Roger Blandford, chair of the council's astrophysics decadal survey.

The board identified a leading mission named the Wide Field Infrared Survey Telescope that should be ready to launch by 2020.

Artist's concept of a proposed design for the Joint Dark Energy Mission. Credit: NASA/Department of Energy
WFIRST addresses all three science priorities, so the panel recommended it be the centerpiece of NASA's next decade of astrophysics research.

The WFIRST observatory would have an estimated cost of $1.6 billion.

NASA follows the guidance of decadal surveys in formulating its mission portfolio, and top-ranked recommendations are almost always implemented in some form.

The National Research Council called upon leading astronomers and physicists to review approximately 100 project proposals and determine which missions offered the best science value. The decadal survey panel was on the job for about two years.

"Because of the clarity and the prioritization and the solidity of (this) consensus, science agencies have been empowered to implement the recommendations," said Ralph Cicerone, president of the National Academy of Sciences.

For the first time, the astrophysics and astronomy decadal survey hired the Aerospace Corp. to conduct an independent analysis of the probable cost and schedule risks for the prioritized missions.

The panel requested the risk study to give a more accurate depiction of the cost and schedule for cutting edge space missions, which have been prone to inaccurate cost estimates and slipping schedules.

The James Webb Space Telescope, the top priority in the last decadal survey, has fallen victim to delays and cost overruns. In the 2001 report, the observatory was projected to cost $1 billion, but that figure is now $5 billion and launch is still at least four years away.

Committee members say the missions in this year's decadal survey should fare better.

"This may be the first decade where we have some hope that the targets estimated will be reached, whereas in previous decades there was a lot of dreaming about wouldn't it be great if," said Neil deGrasse Tyson, director of the Hayden Planetarium in New York City. "It remains to be demonstrated, but I just want to make it clear that we learned from previous decadal surveys how we needed to adjust how we approach the reality check."

In addition to schedule and cost concerns, the board considered international cooperation as a keystone of its recommended set of missions.

"One of the changes in this survey was to try to view this with international eyes," said Michael Turner, an astrophysicist from the University of Chicago.

WFIRST has a counterpart project in the European Space Agency named Euclid, a candidate for one of two medium-class launch opportunities in 2017 and 2018. ESA plans to select two of the three would-be probes for implementation by late 2011.

The panelists said NASA should welcome collaboration from ESA on WFIRST, but the United States should take a leading role in the mission.

The WFIRST concept builds upon the Joint Dark Energy Mission, a joint project proposed by NASA and the U.S. Department of Energy. The 4.9-foot telescope has a low-to-medium technical risk and should formally start development in 2013, according to the report.

The decadal survey's second priorty for large-scale space-based research is an augmentation of NASA's Explorer program, a series of small and medium-class satellites.

"The committee feels so strongly that launching more Explorers will lead to such a large science return in the outlay that it became its second recommendation," Blandford said.

According to Blandford, the Explorer program has been "chronically underfunded" but shows great promise. NASA should increase funding for astrophysics Explorer probes from $40 million to $100 million annually by 2015, the survey said.

If implemented, the higher budget would support two new mid-scale and two small Explorer missions in the coming decade. NASA could also afford up to four less expensive missions of opportunity.

Artist's concept of the LISA mission. Credit: ESA
The National Research Council's other two top priorities for NASA are a gravitational wave detector named LISA and the International X-ray Observatory, a follow-up to the Chandra mission.

Both missions aren't likely to launch until the 2020s.

The decadal survey forecasts LISA's total cost will be approximately $2.4 billion, assuming ESA selects the mission in an ongoing competition for a single flight opportunity.

LISA would consist of three spacecraft in an Earth-trailing solar orbit with telescopes and lasers to observe gravitational waves from sources ranging from nearby stars to distant black holes that formed just after the birth of the universe.

Blandford said NASA may only be able to afford technology development work this decade on the $5 billion IXO telescope, a cooperative project between the United States, ESA and Japan.

"If it turns out that our first three recommendations...are adopted, there will only be funds for technology development this decade of IXO," Blandford said. "But the funds should be sufficient to prepare a strong proposal well in time for the next decadal survey."

IXO would follow up on discoveries by the Chandra X-ray Observatory, focusing in on super-hot interstellar gas, black hole accretion disks and neutron stars, the ultra-dense carcass of a large exploded star.

NASA should spend up to $400 million this decade on two technical programs to develop methods for detecting habitable extrasolar planets and studying the period of inflation, when the universe rapidly expanded a fraction of a second after the Big Bang.

"We recognized several activities that needed technology development this decade, and our strong recommendation is support that technology development level where it can do the job to provide a very strong proposal for the next decadal survey," Blandford said.

The decadal survey also concluded NASA should participate as a minor partner in the Japanese-led SPICA infrared space telescope.

Turner said the panel considered multiple budget scenarios and offered alternative implementation strategies for optimistic and realistic funding levels.

Under the survey's expected scenario, which would grow NASA's budget at the same rate as inflation, the agency should afford building and launching WFIRST, augmenting the Explorer program, starting the LISA project, and advancing technologies for IXO, extrasolar planet and inflation programs.

If NASA's budget stays constant in real-year dollars, an effective decline in funding, the nation's top overall priority should be launching WFIRST, bolstering the Explorer missions and partnering on the SPICA telescope, according to Blandford.

The next decadal survey for planetary probes is due out next spring. It will rank the scientific merit of a proposed Mars sample return mission and a flagship orbiter to study Jupiter's icy moon Europa.