article_snippet: Nasa had chosen the ambitious mission that will visit a comet and pluck a boulder from a comet surface to create an orbiting base for astronauts.
article_snippet: The so-called Asteroid Redirect Mission is estimated to cost .
article_snippet: about $1.25 billion not including launch costs and is targeted .
article_snippet: Nasa also considered bagging a smaller asteroid and . relocating the entire body into a high orbit around the moon.
article_snippet: After extensive studies, Nasa opted to collect and move a . boulder, a mission that will cost about $100 million more, but . which better prepares the U.S. space agency for the ultimate goal of .
article_snippet: Nasa plans to study a smaller asteroid for about a year and test .
article_snippet: Before an asteroid is considered a valid candidate for the mission, scientists must first determine the mission characteristics, in addition to size, such as rotation, shape and precise orbit.
article_snippet: As well as this, returning asteroid samples will help Nasa develop  tools and techniques for future space exploration.
highlights_snippet: Astronauts would study an asteroid and collect samples .
  