NASA managers say the WFIRST mission, the next in the agency’s line of powerful observatories after the Hubble and James Webb telescopes, could cost around $3.2 billion after budgeting for a novel first-of-its-kind instrument to probe the make-up of planets around nearby stars and a bigger-than-expected launch vehicle.

The observatory will be stationed at the L2 Lagrange point, a gravitational balance point about a million miles (1.5 million kilometres) from Earth, to survey the cosmos for dark energy and detect the the faint starlight reflected off of planets in other solar systems, allowing scientists to measure the composition of their atmospheres and surfaces.

WFIRST could help cosmologists and astronomers get closer to answering two fundamental questions: What is driving the expansion of the universe, and where might scientists find an Earth analog around another star?

The space agency formally kicked off development of WFIRST in February 2016, a year ahead of schedule, after several years of technological research and mission concept studies. Congress approved extra money for the project, allowing NASA to press ahead with the mission on a faster schedule than expected.

The Wide Field Infrared Survey Telescope, or WFIRST, is scheduled to be ready for launch by September 2025, employing one of two primary mirrors donated to NASA by the National Reconnaissance Office, the U.S. government’s spy satellite agency.

The NRO no longer needed the mirrors, which were developed for a cancelled surveillance mission that would have carried a downward-looking telescope to capture detailed images of military and strategic targets around the world.

WFIRST’s repurposed primary mirror, made by Harris Corp., did not come with the detectors and instrument needed to make it a functional telescope. Engineers are also making changes to the mirror for WFIRST’s astronomical mission.

After the NRO gifted NASA the two excess mirrors in 2012, the space agency revamped its plans for the WFIRST mission, doubling the size of the mission’s telescope to accommodate the spy assets.

The mirror measures 7.9 feet (2.4 metres) in diameter, the same size as Hubble’s, giving WFIRST the same sensitivity as NASA’s flagship space observatory. But WFIRST will see a swath of the sky 100 times bigger than Hubble’s field-of-view, allowing it to extend Hubble’s deep vision across the cosmos.

NASA officials originally planned for WFIRST to have a telescope half the size of Hubble, and the observatory was to be placed into a geostationary orbit around 22,000 miles (nearly 36,000 kilometres) above Earth.

That would have allowed WFIRST to fit on a rocket like United Launch Alliance’s Atlas 5.

But the bigger spacecraft, coupled with a decision to station WFIRST at the more distant L2 Lagrange point, will mean the observatory must launch aboard a more powerful — and perhaps more expensive — rocket.

NASA is currently looking at ULA’s Delta 4-Heavy or SpaceX’s Falcon Heavy rocket to send WFIRST into space, according to Dominic Benford, the mission’s program scientist at NASA Headquarters.

The James Webb Space Telescope, a partnership between NASA, the European Space Agency and Canada, is set for launch in October 2018 with an even bigger primary mirror — more than 21 feet (6.5 meters) in diameter — comprised of 18 hexagonal segments. But JWST is like Hubble, crafted to peer deep into the universe, not a wide field surveyor like WFIRST.

“WFIRST is like 100 Hubbles, relative to the field-of-view, and it’s going after science that is really compelling,” said Thomas Zurbuchen, associate administrator of NASA’s science mission directorate.

The high-resolution maps created by WFIRST will require a huge data archive and software to pick out the most promising data.

“This is the first astrophysics mission that I would say brings us into the big data era,” said Jeff Kruk, WFIRST’s acting project scientist at NASA’s Goddard Space Flight Center in Maryland. “This is the first NASA mission that’s going to be undertaking large-scale data mining like this.”

Fitted with two science instruments, WFIRST will observe the universe for more than six years. A wide field imager and spectrometer will survey the cosmos in near-infrared for dark energy research and planet searches, and a coronagraph aboard WFIRST is designed to blot out bright starlight to directly image their planetary systems.

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.

While Kepler detects planets that pass between the telescope and a host star, WFIRST will use a technique called microlensing, which is the gravitational effect caused when one star passes in front of another.

When such an event occurs, the light rays coming from the background star are bent by the gravity of the foreground star, called the lens star. Planets around the lens star can also distort the brightness of the background star, allowing astronomers to use microlensing to search for alien worlds.

The coronagraph on WFIRST is an experimental addition to the observatory. Engineers want to check the device’s performance before building a coronagraph for a much larger future telescope that could find another planet like Earth.

“In the long run, for finding Earths, you need a much bigger telescope, but this is proof the technology will actually work in space, and it gives you confidence that when you actually go up to a larger telescope, that it will work,” Kruk said April 13 in a presentation to the NASA Advisory Council’s science committee.

Direct imaging is a key step toward measuring the structure and composition of exoplanets, and in determining whether the worlds are habitable.

The James Webb Space Telescope will be capable imaging giant planets several times the size and mass of Jupiter, hot young worlds that are unlikely to harbor life.

WFIRST will see smaller planets the size of Saturn and Neptune that lie closer to their parent stars, and perhaps even rocky “super-Earths” that are somewhat bigger than our own planet.

Project managers are preparing for WFIRST’s systems requirements review in July, followed by the start of the next phase of development — called Phase B — around Oct. 1.

NASA officials want to keep WFIRST’s total cost around $3.2 billion — in current-year economic conditions — and Bedford said the space agency could “descope” the mission by removing the coronagraph instrument if it looks like it will bust the budget cap.

“The coronagraph is not required for mission success, so we can back off the coronagraph if necessary,” Benford said in the April 13 meeting of the NASA science advisory committee.

Multiple internal and external cost assessments will be completed in the coming months to inform NASA decision-makers on whether WFIRST should remain intact.

An cost assessment by the Aerospace Corp. in 2015 put WFIRST’s project cost between $2 billion and $2.3 billion. A report issued by the National Academy of Sciences last year said the cost of WFIRST had increased by $550 million since the Aerospace Corp. study, and the review panel recommended NASA slash the observatory’s capabilities, such as removing the coronagraph, if costs continued to grow.

NASA does not want to repeat its experience with JWST.

When astronomers first conceived of the once-in-a-generation mission in the late 1990s, they expected it could launch as soon as 2007 and cost around $1 billion. Its launch is now set for late next year, with a cost nearly nine times the initial estimate, carving money out of NASA’s budget that could have gone to other projects.

“Budget is a big concern,” Benford said. “The concern I’m mostly recognising now is the overall mission cost of $3.2 billion. We have to make sure that we make the right choices to keep the science capability while keeping under that cost.

“The problem with mission design is you tend to have a function of science vs. cost that is steep,” Benford said. “You lose more science than you lose cost.”

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