US space shuttle returns to Earth 美发现号返回地球

Nasa's space shuttle Discovery has landed at the Edwards air force base in California.

美国航空航天局的发现号航天飞机降落到加利福尼亚州的爱德华兹空军基地。

Plans to land at the Kennedy Space Center in Florida were postponed¹ due to bad weather.

The shuttle missed two landing slots on Thursday, before landing at 1753 PDT on Friday (0053GMT Saturday).

The shuttle had been on a supply mission to the International Space Station (ISS) with seven astronauts on board.

"We're very happy to be back on land here in California," mission commander Rick Sturckow said. "It was a great mission."

Nasa tries to avoid landings in California, because the shuttle must then be transported back to Florida, which takes more than a week and costs $1.7m.

Three spacewalks

Discovery took a furnace（炉子，熔炉） and freezer up to the station for use in science experiments.

It also delivered a new sleeping compartment², an air purification system and a treadmill³（踏车，跑步机） to help maintain astronauts' health.

In addition, Discovery dropped off US astronaut Nicole Stott for a three-month stay on the platform, picking up colleague Tim Kopra for the ride home. Kopra has been living on the ISS for the past 44 days.

Three spacewalks were conducted during the mission. The exterior⁴ work included the replacement⁵ of an exhausted⁶ ammonia（氨水） tank. Ammonia is used in the station's cooling system.

Cabling was also laid in readiness for the arrival early next year of another module⁷. This new "room" will have a large window attached to it. The Cupola, as it is known, is expected to give crewmembers the perfect vantage point from which to control future robotic operations on the outside of the ISS.

The US space agency plans six further shuttle flights to the ISS before retiring its re-useable spaceship fleet at the end of next year or early in 2011.

Atlantis is the next orbiter to launch. Its mission, set for November, will deliver important spares.