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NASA has directed the team developing the Wide-Field Infrared Survey Telescope, a flagship astronomy mission set for launch in the mid-2020s to study dark energy and exoplanets, to reduce the observatory’s scientific capabilities and keep it under a $3.2 billion cost cap.

Fresh off their experience with cost growth on the James Webb Space Telescope, the huge observatory that precedes WFIRST in NASA’s line of flagship-class space telescopes, officials do not want a repeat experience with the infrared surveyor that is just getting under development.

An independent technical, management and cost review panel set up by NASA earlier this year reported its findings last month, concluding that building, testing and launching the mission as currently envisioned will likely cost between $3.9 billion and $4.2 billion.

The head of the agency’s science division directed officials Oct. 18 to look at ways to keep WFIRST’s cost under $3.2 billion.

“The bottom line is the current scope and complexity don’t fit with the ancitipated funds, so obviously something has to give,” said Peter Michelson, chair of the physics department at Stanford University who served as co-chair of WFIRST’s independent review panel. “That was the principle finding of the committee.”

Originally envisioned as an observatory with primary mirror around 3.9 feet (1.2 meters) in diameter, WFIRST is now slated to use optics measuring nearly 7.9 feet (2.4 meters) across, the same size as the Hubble Space Telescope.

The bigger mirror was gifted to NASA in 2012 by the National Reconnaissance Office, the U.S. government’s spy satellite agency. NASA decided to repurpose the optics for WFIRST, which was then projected to cost around $1.6 billion.

The larger telescope will give WFIRST the same sharp vision as Hubble, but with a field-of-view 100 times wider.

Mission planners also added a second instrument to WFIRST, a coronagraph designed to block light originating from nearby stars to detect the faint reflections from their planetary companions. Such an instrument has never flown in space before, but it could give astronomers a powerful new tool to gauge the habitability of exoplanets.

And managers decided to position WFIRST in a halo-type orbit around the L2 Lagrange point nearly a million miles (1.5 million kilometers) from Earth, affording it mostly-interrupted views of the universe. A previously-planned inclined geostationary orbit around 22,000 miles (36,000 kilometers) from Earth would have limited WFIRST’s observing times.

The larger telescope and distant placement of WFIRST led to the requirement for a heavier, more expensive spacecraft, and a bigger rocket to launch it. Instead of launching on a basic, single-booster Atlas 5 or Falcon 9 rocket as initially planned, WFIRST now requires a triple-core Delta 4-Heavy or Falcon Heavy rocket because it will weigh more than 16,000 pounds (7.3 metric tons), plus on-board fuel.

“Normally, the saying goes that with every challenge, there are tremendous opportunities, said Orlando Figueroa, co-chair of the review panel and the former head of NASA’s Mars exploration program. “When someone gives you a telescope of a bigger size, with every opportunity come incredible challenges. This (also) opens the door for significantly greater science.”

WFIRST managers also decided to make the observatory serviceable, incorporating panels that could be opened in space to access internal instruments and avionics.

The high-resolution maps created by WFIRST will require a huge data archive and software to pick out the most promising data. Officials planned to create two science data centers — one in Maryland and one in California — to store the WFIRST archive.

NASA’s internal WFIRST cost estimate stands at $3.6 billion, but reviewers pegged WFIRST’s projected cost at $3.9 billion, a figure which includes additional reserves that could be applied to the mission if it runs into trouble.

The review board also suggested NASA reclassify WFIRST as a “Class A” mission, the agency’s most risk-averse mission classification, which is typically reserved for large-scale, costly strategic programs, such as JWST and the Mars 2020 rover. NASA currently considers WFIRST a “Class B” mission, which means managers would accept higher risks and make more compromises during development.

But Class B missions also give managers more flexibility and decision-making authority, so making WFIRST a Class A mission would add another $250 million to $300 million in cost, ballooning its total budget to around $4.2 billion.

Thomas Zurbuchen, associate administrator for NASA’s science directorate, said he accepted the review panel’s findings.

“The mission, at its core, has grown, and probably more so than we want right now, which is why we did what we did,” Zurbuchen said Oct. 25 at a meeting of the National Academies’ Committee on Astronomy and Astrophysics.

In a memo sent the previous week to the director of the Goddard Space Flight Center, Zurbuchen wrote that he believed “reductions in scope and complexity” are needed on WFIRST to keep it under a preset cost cap of $3.2 billion, a budget ceiling set to ensure the rest of NASA’s astrophysics portfolio does not suffer from WFIRST overruns.

A team at Goddard will conduct a study to examine how the WFIRST design could be modified, while still keeping its basic architecture, including the 7.9-foot (2.4-meter) telescope and coronagraph instrument.

Zurbuchen directed the Goddard team to look at reducing the capabilities of WFIRST’s wide field imager and spectrometer, which will survey the cosmos in near-infrared for dark energy research and planet searches. Managers will also treat the coronagraph as primarily a technology demonstration, freeing it from the more stringent requirements normally associated with multibillion-dollar space missions.

Engineers will also consider using more commercial components on the WFIRST spacecraft, which will be assembled in-house at Goddard, and not by an industrial contractor.

“WFIRST remains NASA’s highest priority for a large astrophysics mission following the James Webb Space Telescope,” Zurbuchen wrote. “Making these adjustments to WFIRST in response to the findings in the (independent review) report will ensure its success while preserving a balanced astrophysics program.”

Michelson said the panel reaffirmed the value of WFIRST’s scientific objectives, and found that the mission — as designed — will be capable of meeting goals established by the National Research Council’s decadal survey report released in 2010.

“The wide field instrument has a tremendous scientific capability, and it’s substantially more capable than Euclid (a planned European Space Agency dark energy observatory), and far better than Hubble or JWST, in terms of conducting a faint infrared survey,” he said.

The addition of the coronagraph, while useful to scientists, added layers of complexity to the WFIRST mission.

“There are benefits to coronagraph technologies that are consistent with NASA’s longer-term objectives in the exoplanet program,” Michelson said in an Oct. 25 presentation to the Committee on Astronomy and Astrophysics. “The accommodation of the coronagraph, however, has been a mission system design and programmatic driver through formulation, and it will continue to be a driver. It’s a significant part of this mission, and it carries associated risk, and those have to be recognized and accommodated.”

Astronomers using WFIRST’s wide field-of-view will detect thousands of bright supernovae — a giant explosion at the end of a star’s life — to measure how the rate of the universe’s expansion has changed over time, according to NASA.

Dark energy is a mysterious force accelerating the expansion of the universe.

Scientists expect WFIRST to find up to 20,000 exoplanets orbiting other stars, building on the planet-hunting capabilities of NASA’s Kepler telescope.

NASA has already spent around $300 million on WFIRST during the last few years, officials said.

Figueroa said WFIRST is on track for a launch in late 2025 or early 2026 on the schedule outlined by NASA.

Engineers and scientists at Goddard will propose changes to the WFIRST mission to senior NASA officials in February. If costs are contained near the $3.2 billion target, Zurbuchen said the agency will approve the mission to move into Phase B, the next stage in development.

The trimming of WFIRST’s costs will inevitably sacrifice some of the observatory’s scientific capability, according to Paul Hertz, director of NASA’s astrophysics division.

“You can’t do this without losing some science, so the WFIRST mission that the team brings forward in the February timeframe is going to incorporate reductions from the ones that are baselined right now,” Hertz said. “We accept this because right now the science that we’re baselining is way above the recommendations of the decadal survey.”

Changes that could be in store on WFIRST might include updates that lower the performance of its scientific sensors, accept more off-the-shelf hardware, or reduce the number of detector channels or color filters in the telescope.

Hertz said NASA Headquarters gave WFIRST managers approval to remove equipment from the observatory’s design that would have made it compatible with a future starshade, a separate spacecraft that would fly in formation with WFIRST thousands of miles away.

NASA has no formal plans for a starshade mission, but scientists could propose one for exoplanet research. The technology could allow a large space telescope to take pictures of an Earth-sized planet around another star.

Designers have, so far, assumed WFIRST will carry tracking cameras, navigation gear, and communications hardware to help keep formation with a potential starshade.

Hertz said NASA has decided that “starshade compatibility is no longer a requirement” on WFIRST, allowing managers to remove the capability if needed to reduce costs. But the hardware could still be installed on WFIRST in space on a servicing mission, Hertz said.

If Goddard officials prove unable to get WFIRST’s cost to the $3.2 billion target, Zurbuchen said he will kick off a follow-on study of a smaller observatory closer to the size envisioned before the spy telescopes arrived at NASA’s doorstep.

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