VOA标准英语2013--NASA: Humans Could Visit Asteroid in 2021（在线收听）

NASA: Humans Could Visit Asteroid in 2021

These chunks of ancient space rocks hold clues about the formation of the universe, pose threats to our planet, and present new territory for explorers.

NASA's proposed asteroid mission is a logical next leap for the space agency, says associate administrator for human exploration and operations Bill Gerstenmaier.

"It essentially fits right with what we were doing already.  This whole mission activity captures a lot of what we were doing before.  It captures the observation things.  It captures the electric propulsion, and it captures and utilizes our Orion [capsule] and SLS [rocket] just as it was envisioned," said Gerstenmaier.

Astronomers already are identifying and tracking near-Earth asteroids in an attempt to find potential threats, which will help as NASA chooses a target.

And the space agency's engineers are working on propulsion technologies that use sunlight to efficiently produce low thrust, reducing the amount of propellant needed for such a mission.

"We're going to capture and redirect a 7-10 meter, approximately 500-ton near-Earth asteroid to a stable orbit in translunar space, probably a deep retrograde orbit around the moon, and this will enable an astronaut mission to the asteroid as early as 2021," said Gerstenmaier.

A successful mission would show that humans can alter an asteroid's path, and be useful if one is found to be a danger to Earth.  

NASA says there is no threat to our planet if something goes wrong during this capture mission, because an asteroid this size would disintegrate before it struck the planet.  

Gerstenmaier says lunar orbit is stable enough that the asteroid possibly could stay in place for a century.

"So once we get the spacecraft and the object in this orbit, it's there for us to go visit multiple times in the future," he said.

Astronauts could use the Space Launch System and Orion space capsule that are being developed. Space explorers could spend about five days near the asteroid and venture out of the Orion capsule to collect samples that would be returned to Earth.   

Gerstenmaier says this will give astronauts and mission control experience working in deep space, far from Earth and the International Space Station.  

"In this case, we're going to have to make sure we have the right abort scenarios, the right redundancy in place, that we can tolerate being in this situation for up to five days.  So that helps us take a step toward the bigger missions that we want to do going forward," he said.

Bigger missions such as a manned voyage to Mars in the 2030s.