男女羞羞视频在线观看,国产精品黄色免费,麻豆91在线视频,美女被羞羞免费软件下载,国产的一级片,亚洲熟色妇,天天操夜夜摸,一区二区三区在线电影

Science and Health

Comet-hunting spacecraft shuts down after 12 years


Updated: 2011-03-25 22:24
Large Medium Small

DENVER?- NASA ordered its comet-hunting Stardust probe to burn its remaining fuel on Thursday, setting off a sequence that shut down the spacecraft after a 12-year career.

Stardust had finished its main mission in 2006, sending particles from a comet to Earth. It took on another job last month, photographing a crater on an asteroid.

It accomplished one last experiment on Thursday, firing its thrusters until its last hydrazine fuel was gone. The length of that burn, a little under 2 1/2 minutes, will tell engineers exactly how much fuel was left so they can see how accurate their calculations were.

That in turn will help with the design and operation of future probes.

Spacecraft don't carry fuel gauges because they don't work in zero gravity.

It will take a few days to analyze the fuel data, said Jim Neuman, a mission operations manager for Lockheed Martin, which built and operated the probe at its complex south of Denver.

Engineers gave Stardust the order to begin its final burn at 4:41 pm local time. Once the fuel was gone, the probe lost its ability to keep its antennas pointed toward Earth, and the control room lost radio contact at 5:33 p.m. local time.

"Like saying goodbye to a friend," said Allan Cheuvront, the Stardust program manager for Lockheed Martin, who has worked on the probe since 1996, when it was in the detailed design stage.

He paused, fighting back tears.

"It's been an amazing spacecraft. It's done everything we asked, it's done it perfectly."

Since launching in 1999, Stardust has traveled 3.5 billion miles (5.63 billion kilometers). In 2004, it flew through a cloud of dust and gas enveloping the Wild 2 comet, capturing tiny samples. Those were sent back to Earth for study in 2006, via a parachute-equipped canister.

NASA then recycled Stardust, sending it past the Tempel 1 comet last month to photograph a crater left by a projectile launched by another space probe, Deep Impact.

If Stardust executed all of its final orders as expected, it put itself in "safe mode," turning most of its systems off, about 1 1/2 hours after the last command was sent.

With no fuel, Stardust can't keep its solar panels aimed at the sun, and once its batteries are drained it will shut down for good.

Stardust will be left in an orbit around the sun. Engineers project that in the next 100 years, Stardust won't get any closer than 1.7 million miles (2.74 million kilometers) of Earth's orbit or 13 million miles (20.9 million kilometers) of Mars' orbit.

 

分享按鈕
主站蜘蛛池模板: 镇巴县| 张家界市| 彭泽县| 卢湾区| 邵武市| 钟山县| 饶平县| 彰武县| 班玛县| 东安县| 和平区| 惠州市| 七台河市| 盐边县| 宜君县| 阿鲁科尔沁旗| 清河县| 宣城市| 辽宁省| 昆山市| 镇宁| 怀柔区| 筠连县| 巴南区| 新乐市| 仪陇县| 托克托县| 南华县| 夏邑县| 渭源县| 邹城市| 凌海市| 陆河县| 禹州市| 延长县| 兰坪| 潢川县| 兴安县| 濉溪县| 浑源县| 大竹县| 台前县| 张北县| 石渠县| 深州市| 南丰县| 化德县| 潼南县| 大石桥市| 隆昌县| 乐亭县| 扬州市| 十堰市| 平乐县| 启东市| 准格尔旗| 黄大仙区| 南投县| 永平县| 西充县| 嵊州市| 宜兴市| 历史| 徐水县| 温州市| 洪雅县| 兰溪市| 仁化县| 玛纳斯县| 石首市| 清新县| 合山市| 纳雍县| 普定县| 兴海县| 合作市| 额尔古纳市| 舒城县| 辛集市| 邹平县| 安宁市| 东丰县|