A U.S. teacher designated to fly on a futurespace shuttle（航天飛機）mission says she accepts the risks despite the death of seven astronauts on the Columbia orbiter in February. She spoke to high school students on Wednesday, the 45th anniversary of the U.S. space agency NASA.

Barbara Morgan, a teacher from the western U.S. state of Idaho, may be the world's most patient person. NASA chose her 18 years ago for a program to send teachers into space. But her dream wasset back（受到阻礙）when NASA canceled the program after teacher Christa McAuliffe and six other astronauts died in the 1986 shuttle Challenger explosion. NASAreinstated（恢復）the program five years ago and began training Ms. Morgan for a mission to the international space station scheduled for next month. But her patience was tested again when the Columbia tragedy delayed all shuttle excursions indefinitely.

NASA hopes to return shuttles to flight by the middle of next year after making a series of technical and organizational improvements recommended by experts who investigated the Columbia accident.

Ms. Morgan continues to train for her mission, but she told Washington area high school students that the two shuttle accidents caused her to consider flight risks seriously. However, she says she dismissed them as less important than the potential gains of the mission, which will expand the space station.

"I can't think of anything more important than you guys, our future and your future, and doing this for education and doing this for the learning and the things that we can do to bring back, not just for our country, but for the whole human race and once you've made that decision, you go forward and you really don'tdwell on（細想）the risk."

The head of NASA, Sean O'Keefe, told the students that the agency intends to carry out all of the investigators' flight safety recommendations before shuttles launch again. He says they will address the technical flaws and the human errors found to be at fault in the disaster.

"So if we concentrate on both of those, we're going to make sure that when Barbara and her colleagues fly on every successive mission, they are going to be in a much safer condition that we have ever been before."

On other issues, Mr. O'Keefe says NASA hopes to overcome two major problems that currently restrict the length and distance of space missions. One is how to limit theravages（創傷）of weightlessness on the body. The other is how to develop newpropulsion systems（推進系統）that would shorten the long journey to Mars and beyond.

Under current methods, he says it would take 15 years to reach the edge of the solar system. "Now, we can't afford that kind of time because most of the American people won't be patient enough and most scientists won't be patient enough for that long a span of time for one mission. So it's something we have to look at of how you evolve that capability to get places sooner in a way that will give us the opportunity to spend time there really exploring."

The NASA chief says the U.S. space agency's Project Prometheus aims to develop a nuclear reactor to propel spaceships at least three times faster than current technology.