The OSIRIS-REx spacecraft lifts off from the launch pad at Cape Canaveral, Fla., on Thursday evening. (John Raoux/AP)

GODDARD SPACE FLIGHT CENTER, Md. – NASA launched a spacecraft skyward Thursday evening on an ambitious seven-year voyage to intercept an asteroid more than 100 million miles from Earth, scoop up a piece of it and bring the sample home.

Only once before has a spacecraft successfully completed such a mission, and never have astronomers attempted to gather such a large asteroid sample. The material that OSIRIS-REx collects from its target, Bennu, is made of the same substances that were present at the beginning of the solar system. Scientists believe they could help reveal how the planets were made and perhaps even how the ingredients for life arrived on Earth.

The spacecraft blasted off at 7:05 p.m. Eastern from Cape Canaveral, Fla., streaking across a cloudless sunset sky. At Goddard Space Flight Center in Greenbelt, Md., a crowd of scientists and their families burst into applause, then fell into an anxious silence as they watched a livestream of the rocket accelerating upward. At one minute after the clockwork-perfect liftoff, the spacecraft had gone supersonic, surpassing the speed of sound.

The image on the screen shifted to show the back of the rocket, speeding away from the pale blue curve of Earth, and the tension in the room broke. By 8:05 p.m., the spacecraft escaped Earth's gravity and shed the Atlas V rocket that had borne it upward.

"OSIRIS-REx is flying free," came the announcement from mission control. More than a dozen years and a billion dollars after it was first conceived, NASA's first-ever asteroid sample return mission was fully underway.

The destination is a small, dark asteroid roughly as wide as the Empire State Building is tall. Born out of the chaos surrounding the sun's formation, a survivor of the cataclysmic accumulation, bombardment and rearrangement of planets, Bennu is a 4.5-billion-year-old relic.

"It really is a time capsule," said Dante Lauretta, the mission's principal investigator.

But before OSIRIS-REx can attempt to open that capsule, it has to get there. The asteroid is classified as a "near-Earth object" and has a small but non-zero chance of crashing into our planet in the next 200 years, but it is still a long, long distance away. It will take two years of OSIRIS-REx flying through the dark void of space, plus one slingshot-like gravity assist from Earth, for the spacecraft to reach its target.

After rendezvousing with Bennu at a spot more than 100 million miles from where it launched, the craft will do what NASA scientist Lucy McFadden calls a "gravitational dance" with the asteroid. For two years, OSIRIS-REx will scoot alongside the space rock, surveying its surface and conducting research on its behavior.

OSIRIS-REx will be the first U.S. mission to sample an asteroid, retrieve surface material and return it to Earth for study. (Joel Kowsky/NASA)

The mission's name — a convoluted acronym of "Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer" — hints at its main goals. OSIRIS-REx carries three spectrometers, a laser altimeter and a suite of cameras that will map Bennu's surface and analyze its chemical composition.

"Bennu is an unexplored world," Lauretta said at a pre-launch news conference. "We are going out into the unknown."

Preliminary surveys of Bennu have revealed an alien place. Its albedo, or reflectivity, is so low that it is almost indistinguishable from the surrounding space.

But the asteroid's size and life history make it appealing to astronomers: Bennu is large enough to be safely approached — smaller asteroids spin too wildly — and its chemical composition suggests it has persisted mostly unchanged since the solar system's genesis. It is rich with carbon and and could contain amino acids, the building blocks of proteins that are essential for life.

"One of the basic questions that scientists are still asking is, where did the organics come from that allowed life to arise on Earth?" said Ed Beshore, deputy principal investigator for the mission. If scientists find those ingredients on Bennu, that would suggest they were available in the solar system when Earth was first formed.

"On the other hand," Beshore added, "if we don't find them, we'll be asking ourselves, how could it have been delivered another way? Because we know it’s here."

OSIRIS-REx will also be measuring a phenomenon known as the Yarkovsky effect, in which the absorption of solar energy slightly alters the course of an asteroid's orbit. Bennu itself has only a one-in-2,800 chance of striking Earth. But the maneuvers practiced on this mission could inform a future effort to deal with a potentially hazardous asteroid — if one ever threatened.

The true star of the mission is the Touch-And-Go Sample Acquisition Mechanism, or TAGSAM. The 10-foot robotic arm is capable of scooping 60 to 200 grams worth of material from Bennu, about enough to fill a small yogurt container.

NASA has sampled a comet before, and the Japanese space agency JAXA successfully collected dust from an asteroid in 2005. But the fragments gathered by OSIRIS-REx will be the largest sample of extraterrestrial material brought to Earth since the days of the Apollo missions. A quarter of the sample will be made available to current researchers, who will be able to apply for access to a tiny piece of the collection. Yet the bulk will be saved for future use -- set aside in a sterile storage facility at the Johnson Space Center, awaiting the day when it can be analyzed using technologies that haven't been invented yet.

"It's really a sea change in the way we are going about exploring our solar system," Beshore said.

In July 2020, in a maneuver that Beshore likened to a kiss, the TAGSAM arm will extend toward the asteroid, blow a puff of nitrogen gas onto the surface and suck up rocks and dust from the resulting cloud of rubble.

The spacecraft carries enough gas to perform the maneuver three times, but scientists hope that won't be necessary. Every swipe along the asteroid's surface is an opportunity for something to go wrong.

Once its precious payload has been stowed, OSRIS-REx will pack up its instruments and set its sights toward home. The spacecraft won't stop at Earth, just pass through our atmosphere long enough to drop the sample canister somewhere over the desert in Utah.

The capsule is due back on Sept. 24, 2023 — just over seven years after it departed. Beshore, who has been working on the OSIRIS-REx mission for more than a decade, already has the date marked on his calendar.

"I’m going to be sitting there in a lawn chair that morning," he said. "I can't wait to see it streak across the sky and release its parachute and watch it float down to Earth gently. That’s going to be a wonderful moment."

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