科技英语新闻:High costs, risks, policy shift make U.S. quit space shuttle program

In 2004, former U.S. President George W. Bush made the decision to retire the space shuttles in 2004. Bush wanted astronauts to go back to the moon, and eventually go to the Mars. In order to save money for building a new spaceship to attain that goal, NASA had to stop spending about 4 billion dollars a year on the shuttle program.

President Barack Obama, however, unrolled a fresh project to build a giant rocket to send astronauts to an asteroid, and eventually to the Mars, while transferring to private companies the job of carrying cargo and astronauts to space stations.

During his first-ever Twitter town hall meeting on Wednesday, Obama said NASA needs new technological breakthroughs to revitalize its mission to explore the universe.

Admitting the shuttles' "extraordinary work in low-orbit experiments, the International Space Station," Obama said: "But now what we need is that next technological breakthrough."

He said that the United States should move beyond the space travel models it used in the 1960s for the Apollo program.

"Rather than keep on doing the same thing, let's invest in basic research around new technologies that can get us to places faster, allow human space flight to last longer," Obama said.