美国发现号航天飞机将退休

The US Space Shuttle Discovery is set to lift off from Florida on November 1 for a mission to the International Space Station. It will be one of the final missions for the shuttle; NASA is ending the program and will retire its remaining fleet of the reusable spacecraft next year. Our correspondent has more on how the US space agency is charting a new course for future human space exploration.

Since the early 1980's, the space shuttle has been carrying astronauts and cargo into space. Four-time shuttle Astronaut Charles Bolden is head of the US space agency.

"It is quite emotional just thinking about coming to the end of the shuttle era however it is absolutely the right thing to do," said Bolden.

NASA is ending its space shuttle program next year and taking the next step in manned space flight. The space agency plans to spend billions of dollars to encourage the development of commercial human spaceflight vehicles. It also wants to invest in advanced space propulsion technology. But so far, efforts to build the new generation of spacecraft and rockets have run into technical problems and substantial cost overruns. Without the shuttle, NASA will have to spend hundreds of millions of dollars to buy transport flights to the International Space Station on Russian Soyuz spacecraft.

President Obama calls the current plan unsustainable and has outlined his own vision for future space flights.

"We will start by sending astronauts to an asteroid for the first time in history," said President Obama. "By the mid 2030's I believe we can send humans to orbit [the planet] Mars and return them safely to earth and a landing on Mars will follow."

In order to achieve the goal of a Mars flight, the Obama administration has proposed funding cuts for plans to send astronauts back to the moon by 2020. It will also scale back other human space programs resulting in job losses for thousands of NASA workers. Bolden says it has been a difficult year.

"To people who are working on these programs this is like a death," he said. "Everybody needs to understand and we need to give them time to grieve and then we need to give them time to recover."

NASA now wants to direct millions of dollars towards private companies like Boeing to develop so called "space taxis" that could take tourists for short space flights by 2015.  NASA Administrator Bolden says helping private companies provide inexpensive transport services is a proper path for the agency to take.

"The commercial space industry will be a very vital part of NASA going forward it means we are going to change the way we acquire services to get us into to space to get humans to space," said Bolden. "If it works well there's a good possibility that people could go to space even if it's just for a few seconds."

"NASA is clearly at a cross road right now," said Mark Lewis. "Big decisions are being made that will affect its future for not only years to come but perhaps for decades to come."

Mark Lewis is an aerospace engineering professor at the University of Maryland. He says NASA's plan to rely entirely on the commercial space industry to transport humans and supplies into orbit could be a setback for the space agency.

"I think it is very important that as we start to look at new opportunities opening up space for new commercial sectors it is also important that we not lose the ability that we have worked so hard to build," he said.

Howard McCurdy, a space analyst at American University, says NASA's funding for commercial rockets and spacecraft will free up the agency to do the kind of technology development needed for deep space exploration.

"The most significant changes we are going to see is that the United States and its international partners for the first time in some 35 years are going to get out of low-earth orbit and get back to the business exploring the inner solar system," said McCurdy.

As NASA charts a new course for future space flight some analysts wonder if its long term goals can be reached. They maintain much depends on who wins the budget battle between the White House and lawmakers over how much to invest in the commercial space industry, versus how much NASA needs to jump-start its missions to explore the far reaches of space.