SAN FRANCISCO — NASA is pushing ahead with plans to use one of the Hubble-sized space telescopes donated by the U.S. National Reconnaissance Office to conduct a $2 billion mission to observe Earth-like planets and explore the nature of dark energy.

While that project would not begin officially until 2017, NASA officials are starting work on mission-related technology as directed by President Barack Obama in the 2015 budget blueprint sent to Congress in early March. Other factors propelling NASA to pursue the mission are congressional appropriations of $66 million for the effort in 2013 and 2014, Obama’s request for $14 million in 2015 funding and the space agency’s plan to provide money for a large-scale astrophysics mission to succeed the James Webb Space Telescope.

“Unless something changes, we are on a path to doing this,” Paul Hertz, NASA Astrophysics Division director, said March 26 during a meeting of the NASA Advisory Council’s astrophysics subcommittee. 

NASA plans to use the partially completed telescope with a 2.4-meter primary mirror given to NASA in 2012 by NRO to conduct an expanded version of the Wide-Field Infrared Survey Telescope (WFIRST) mission, which was identified as a top priority in the 2010 astrophysics decadal survey. NASA is seeking to add a coronagraph to the mission to obtain imagery of exoplanets and debris disks if the instrument’s technology is ready in time.

“We would love to put the coronagraph on it because it expands the science,” Hertz said. However, NASA will drop the coronagraph from the mission if it proves too expensive, time-consuming or technologically risky to develop, he added.

A recent report from the National Research Council (NRC) warned of the risk associated with coupling a technology development program, such as the coronagraph, with a NASA flagship mission. “The coronagraph design is immature and the technology is immature,” said Fiona Harrison, an astronomy professor at the California Institute of Technology and chairwoman of the NRC review panel.

Rather than eliminating the instrument, however, the NRC panel recommended that NASA “move aggressively to mature the coronagraph design and develop a credible cost, schedule, performance and observing program so that its impact on the WFIRST mission can be determined.” Once that work is completed, the space agency should sponsor an external review to assess risks associated with including the coronagraph and determine whether to fly the instrument on WFIRST, according to the March 18 report, “Evaluation of the Implementation of WFIRST Astrophysics Focused Telescope Assets in the Context of New Worlds, New Horizons in Astronomy and Astrophysics.” 

The NRC panel’s overarching message to NASA officials was that the NRO telescope would enhance significantly the scientific potential of the WFIRST mission and that the agency should pursue the project while keeping a close eye on cost to ensure that it does not compromise the astrophysics division’s commitment to research, analysis and frequent flight opportunities for scientific investigations through its Explorers Program. “Our main concern was that NASA recognizes the risks and work as assiduously as possible to retire those risks so the program doesn’t end up overrunning its budget and having to take money from somewhere else,” Harrison said. “If implementing WFIRST Astrophysics Focused Telescope Assets compromises the program balance, then it is inconsistent with the rationale that led to the decadal survey’s high priority ranking for the program.” 

Among the risks associated with using the donated telescope, according to the NRC panel, are greater design complexity, low thermal and mass margins and limited options for descoping the mission if technical or budgetary challenges arise during development.

The NRC panel also noted that the $2.1 billion cost of the proposed mission employing the 2.4-meter telescope without a coronagraph is higher than the $1.6 billion cost projected for the WFIRST mission discussed in the decadal survey, which included the same 1.5-meter telescope studied for the Joint Dark Energy-Omega mission, and the $1.8 billion price tag for a more recent mission design featuring a 1.3-meter telescope. Inclusion of a coronagraph would add roughly $300 million to the latest project design, bringing the total estimated cost to $2.4 billion, according to the NRC report.

NASA science chief John Grunsfeld, who addressed the astrophysics subcommittee to discuss the space agency’s 2015 budget proposal and notional plans for future funding, said the space agency does not expect to receive budget hikes in the foreseeable future. Without increased funding, it is unclear how often the astrophysics community will be able to launch future flagship missions. That is one reason the division is moving forward with plans to include a coronagraph on WFIRST. Putting a coronagraph on WFIRST will not offer the scientific potential of a dedicated exoplanet probe, but “it will do very good, high-priority science much earlier and much cheaper than any standalone mission,” Hertz said.

In case the WFIRST mission proves too costly to complete, the astrophysics division is conducting studies of two exoplanet probes that could be built and operated for $1 billion or less. One proposed mission features an internal coronagraph to detect and study giant planets and circumstellar disks. The other includes a flower-shaped Starshade to block starlight and enable an orbiting telescope to observe distant, Earth-like planets. “Should we not have the budget for a large mission, we have options for a medium class mission,” Hertz said.