The phone call came like a bolt out of the blue, so to speak, in January 2011. On the other end of the line was someone from the National Reconnaissance Office, which operates the nation’s fleet of spy satellites. They had some spare, unused “hardware” to get rid of. Was NASA interested?


So when John Grunsfeld, the physicist and former astronaut, walked into his office a year later to start his new job as NASA’s associate administrator for space science, he discovered that his potential armada was a bit bigger than he knew.


Sitting in a room in upstate New York were two telescopes the same size as the famed Hubble Space Telescope, but built to point down at the Earth, instead of up at the heavens.


NASA, struggling to get human space exploration moving again, had spent the previous year trying to figure out how good these telescopes were and what, if anything, they could be used for. Working with a small band of astronomers for the past couple of months, Dr. Grunsfeld, famous as the Hubble telescope’s in-orbit repairman, has now come up with a plan, which was presented to the public on Monday at a meeting at the National Academy of Sciences in Washington.


It is to turn one of the telescopes loose on the cosmos, pointing in its rightful direction, outward, to investigate the mysterious dark energy that is speeding up the universe’s expansion.


If the plan succeeds — and Congress, the Office of Management and Budget and the Academy of Sciences have yet to sign on — it could shave hundreds of millions of dollars and several years off a quest that many scientists say is the most fundamental of our time and that NASA had said it could not undertake until 2024 at the earliest.


“This is a total game changer,” said David N. Spergel of Princeton, who is co-chairman of a committee on astronomy and astrophysics for the National Academy of Sciences, which sets priorities for NASA and other agencies. Alan Dressler, of the Carnegie Observatories in Pasadena, Calif., who reported to the Academy committee on the scientific potential of a mission with the NRO-1 telescope, as astronomers are calling it, said he was “really excited.” He told the gathering, “I think this is a tremendous opportunity for this community.”


For now, the two telescopes and some spare parts are still in their clean room at ITT Exelis, in Rochester. Michael Moore, who, as NASA’s acting deputy director for astrophysics, took the original call last year, has been to see the telescopes several times. He called their optics “astounding.”


Dr. Grunsfeld described the telescopes as “bits and pieces” in various stages of assembly, lacking a camera and other accouterments, like solar panels or pointing controls, of a spacecraft. “We can’t say what they were used for,” he said.


A spokeswoman for the National Reconnaissance Office, Loretta Desio, said, “This is not something we’re going to talk about,” adding, “We’re hoping this becomes a NASA story.”


The two telescopes have a 94-inch-diameter primary mirror, just like Hubble, but are shorter in focal length, giving them a wider field of view: “Stubby Hubbles,” in the words of Matt Mountain, director of the Space Telescope Science Institute, adding, “They were clearly designed to look down.”


Dr. Grunsfeld said his first reaction was that the telescopes would be a distraction. “We were getting something very expensive to handle and store,” he said.


This spring he asked a small group of astronomers if one of the telescopes could be used as they were to study dark energy.


The answer, he said, was: “Don’t change a thing. It’s perfect.”


Astronomers have lobbied for a space mission to investigate dark energy ever since observations of the exploding stars known as supernovae indicated that the expansion of the universe was speeding up, the discovery that won three American astronomers the Nobel Prize. The fate of the universe, as well as the nature of physics, scientists say, depends on the nature of this dark energy.


But a decade of wrangling between agencies and astronomers over money and technical specifications had resulted in no consensus on a mission until 2010, when a committee of the National Academy of Sciences that was charged with determining astronomical priorities cobbled together a plan that would do the trick. In its report, “New Worlds, New Horizons,” the committee gave that mission the highest priority in space science for the next decade.