Cape Canaveral, Florida (CNN) NASA on Thursday evening launched a space probe called OSIRIS-REx to chase down a dark, potentially dangerous asteroid called Bennu . The probe will take a sample of the asteroid and -- in a US space first -- bring the sample back to Earth.

"NASA did it again!" Jim Green, Planetary Science Division director at NASA, said at a post-launch briefing.

"Tonight is a night for celebration," said Ellen Stofan , NASA chief scientist. "We are on our way to an asteroid."

OSIRIS-REx lifted off at 7:05 p.m. ET from Cape Canaveral on top of a United Launch Alliance Atlas V rocket. NASA tweeted, "Our @OSIRISREx spacecraft is on its way, and everything is on the timeline ..."

Our @OSIRISREx spacecraft is on its way, and everything is on the timeline. Keep watching: https://t.co/KX5g7zfYQe pic.twitter.com/89uZ54af0v

Mission managers said the launch was flawless, the spacecraft is in excellent health and that the mission is hitting all its early milestones.

"The OSIRIS-REx spacecraft is happy and healthy," said Rich Kuhns, OSIRIS-REx program manager at Lockheed Martin Space Systems. Lockheed Martin built the spacecraft.

The mission's principal investigator, Dante Lauretta, said the next big moment for him will be seeing Bennu for the first time from OSIRIS-REx.

"Everyone on the team has some image in their mind of what Bennu is going to look like and it's going to be phenomenal to see what it really looks like."

Those images should start arriving in about two years as OSIRIS-REx approaches Bennu.

Life, sort of, imitating art

In this real life story, OSIRIS-REx will study and sample Bennu, a big, roundish space rock that has made it onto NASA's list of Potentially Hazardous Asteroids . That means Bennu is one of the most dangerous space rocks we know of because it could one day collide with Earth.

The probe is scheduled to arrive at Bennu in August 2018. For months it will hang out -- take pictures, make scans of the asteroid's surface and create a map.

Then, in July 2020, OSIRIS-REx will unfurl its 11-foot-long (3.35-meter) robot arm called TAGSAM and make contact with Bennu's surface for about five seconds. During those few seconds, the arm will use a blast of nitrogen gas to kick up rocks and dust and then try to snag a sample of the dust and store it.

"We are basically a space vacuum cleaner," said Lauretta

NASA hopes to get at least 2 ounces (60 grams) and maybe as much as 4.4 pounds (2 kilograms) of asteroid dust and small rocks.

Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth OSIRIS-REx pulled within 12 miles of the diamond-shaped space rock Monday, December 3. Hide Caption 1 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth An artist's concept of what the OSIRIS-REx spacecraft will look like as it orbits asteroid Bennu. Hide Caption 2 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth OSIRIS-REx sits on top of its launch vehicle, a United Launch Alliance Atlas V rocket, after it was rolled to the launch pad at Cape Canaveral on September 7, 2016. Hide Caption 3 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth This drawing shows an artist's concept of what it will look like when the OSIRIS-REx spacecraft briefly touches asteroid Bennu with its robot arm to grab a sample of the asteroid. Hide Caption 4 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth OSIRIS-REx will spend two years mapping and scanning Bennu before taking a sample of the asteroid and flying it back to Earth. Hide Caption 5 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth The OSIRIS-REx spacecraft is sealed inside its protective payload fairing as it sits atop a rocket at Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida on September 2. Hide Caption 6 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth The OSIRIS-REx spacecraft, enclosed in its protective shell, is lifted and examined by workers on August 29 at Cape Canaveral Air Force Station in Florida. Hide Caption 7 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth The OSIRIS-REx spacecraft is sealed inside a two-piece payload fairing on August 24. The fairing will protect it during launch. Hide Caption 8 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth The OSIRIS-REx arrives at Kennedy Space Center on an Air Force C-17 aircraft. The spacecraft was shipped in this huge container from Lockheed Martin's facility near Denver. The spacecraft arrived at Kennedy on May 20. Hide Caption 9 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth The OSIRIS-REx spacecraft was built by Lockheed Martin Space Systems Company in Denver. It is 20.25 feet in length (6.2 meters) with its solar arrays deployed. Its width is 8 feet (2.43 meters) x 8 feet (2.43 meters). Its height is 10.33 feet (3.15 meters). It's powered by two solar panels that generate between 1,226 watts and 3,000 watts. It has five instruments to explore asteroid Bennu and also has a robot arm to touch the asteroid long enough to collect a sample. Hide Caption 10 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth OSIRIS-REx will briefly touch asteroid Bennu to take a sample of the space rock. It will use its 11-foot ( (3.35 meters) robot arm, called the Touch-and-Go Sample Arm Mechanism, or TAGSAM. Above, a worker at Lockheed Martin tests the arm. Hide Caption 11 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth NASA's OSIRIS-REx spacecraft is rotated on a spin table during testing on May 24 at Kennedy Space Center. Hide Caption 12 of 13 Photos: OSIRIS-REx will take a sample of asteroid Bennu and return it to Earth These radar images of asteroid Bennu were obtained by NASA's Deep Space Network antenna in Goldstone, California, on September 23, 1999. Hide Caption 13 of 13

"We kind of expect a gravel field on the surface of the asteroid," Lauretta said. He said he thinks the rocks will be about half an inch, based on information gathered by NASA's Spitzer Space Telescope

on September 24, 2023, but it won't land. In a bit of Hollywood-style drama, it will fly over Utah and OSIRIS-REx heads home in March 2021 and arrives back at Earthon September 24, 2023, but it won't land. In a bit of Hollywood-style drama, it will fly over Utah and drop off the capsule holding the asteroid sample. A parachute will guide the capsule to the ground at the Utah Test and Training Range in Tooele County.

Will Bennu really hit Earth?

The short answer is maybe. If it does, it's big enough to do some damage.

Bennu has a diameter of 1,614 feet (492 meters). It makes its next approach to Earth in 2135 when it will pass just inside the moon's orbit.

This close approach will change Bennu's orbit, and scientists say that could cause it to impact Earth sometime between 2175 and 2199. The odds are small -- about 1 in 2,500. But NASA wants to get as much warning as possible for anything that threatens Earth.

It's worth pointing out that while Bennu is a known threat, NASA said only about 51% of the near-Earth asteroids of Bennu's size have been found.

Meaning there could be lots of unknown threats out there.

The mission is a first for NASA but ...

This is not the first mission to bring an asteroid sample to Earth. Japan's Hayabusa spacecraft brought back a small sample of asteroid Itokawa dust in 2010.

NASA also has brought back other space rocks and dust:



•

• The

• And NASA has landed on an asteroid before: The • The Apollo astronauts brought back rocks and soil from the moon. NASA's Stardust mission brought back samples of dust from Comet Wild 2.• The GENESIS mission brought back samples of the solar wind, material ejected from the outer portion of the sun, in 2004.• And NASA has landed on an asteroid before: The NEAR-Shoemaker mission touched down on asteroid Eros in 2000. It's still there. But it didn't send back any samples.

What OSIRIS-REx won't do ...

It won't blow up Bennu, and it won't save the Earth from any other menacing space rocks.

Right now, efforts to defend the planet from asteroids and comets are still in their infancy.

"It really takes more than one agency for the kind of capabilities that are needed for this," Lindley Johnson of NASA's new Planetary Defense Coordination Office told CNN.

He said the new office is coordinating with several agencies, the US government and other nations to help develop resources to defend Earth from asteroids of about 330 feet (100 meters) in size or larger. (For smaller asteroids we would just be told to take cover.)

But we would have to know years in advance that a dangerous rock is coming before we could do anything about it.

"We would need probably at least five years warning to 10 years warning to be able to launch an effective space mission to deflect that object," Johnson said.

NASA has a spacecraft called NEOWISE that is hunting potentially threatening asteroids. Ground-based telescopes also are helping watch Pan-STARRS LINEAR (it discovered Bennu in 1999) and the Catalina Sky Survey

Early Monday, the Catalina Sky Survey detected an asteroid close to Earth that had never been seen before. The rock was given the designation 2016 RB1.

"Just right about now, it's on its closest approach to the Earth, passing underneath the Earth at about 21,000 miles (33,796 kilometers)," Johnson said a briefing Wednesday afternoon. "That's closer than communications satellites orbit the Earth."

NASA estimated the asteroid to be between 25 and 50 feet (7 and 16 meters) in diameter and said it was not a hazard to Earth. "If it were to have impacted the Earth, it would have disintegrated in the atmosphere," Johnson said.

Besides trying to identify potentially hazardous asteroids, Johnson's agency is working on plans to deflect them away from Earth. It's collaborating with the European Space Agency on the Asteroid Impact and Deflection Assessment Mission , and it's working with other NASA departments on the Asteroid Redirect Mission

About the spacecraft

The name OSIRIS-REx is an acronym for the spacecraft's mission objectives: Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer. The acronym spells the name of the Egyptian god Osiris.

Minus fuel, OSIRIS-REx weighs 1,940 pounds (880 kilograms). With fuel -- 4,650 pounds (2,110 kilograms).

The sample return capsule weighs about 100 pounds (45.4 kilograms).

The mission costs about $800 million excluding the rocket.

Bennu was named by North Carolina student Michael Puzio during a 2013 international contest. Puzio, who was 9 at the time, thought the spacecraft's robot arm and solar panels looked like the Bennu bird, also from Egyptian mythology. (Before Puzio stepped up, the rock was known in the scientific community as 1999 RQ36.)

And what happens to the spacecraft after it drops off its sample?

OSIRIS-REx will keep flying and will go orbit the sun. NASA said it may be repurposed, but it won't be bringing home any more samples.