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15年坎坷路,“新视野号”探访冥王星的故事

更新时间:2015-7-21 10:21:18 来源:纽约时报中文网 作者:佚名

The Long, Strange Trip to Pluto, and How NASA Nearly Missed It
15年坎坷路,“新视野号”探访冥王星的故事

Planetary scientists are coloring in the family portrait of our solar system as close-up photographs and observations stream back from Pluto, a world three billion miles away with towering mountains of ice, vast smooth plains and many mysteries yet to be revealed.

随着特写照片和观测结果从冥王星传输回来,行星科学家们正忙着给我们所在的太阳系的全家福上色。在距离我们30亿英里的冥王星上,有高耸的冰山、广袤的平原和很多尚未揭开的秘密。

The flyby of Pluto last week by NASA’s New Horizons spacecraft is rightly celebrated as a triumph of human ingenuity, the capstone of a mission that unfolded nearly flawlessly.

NASA的“新视野号”(New Horizons)探测器上周飞掠冥王星,理所当然地被誉为人类聪明才智的胜利。这标志着探测任务近乎完美地达成了。

Yet it almost did not happen, which would have left Pluto as just a hazy dot of light.

但这一幕差一点就不能发生了。若是如此,冥王星就只是一个模糊的光点了。

New Horizons overcame skeptical NASA officials, repeated threats to its funding, laboratory troubles that constricted the amount of plutonium available to power the spacecraft and an unforgiving deadline set by the clockwork of the planets. Though none of the obstacles packed the drama of space-exploration crises like the Apollo 13 mission, their number and magnitude seemed unbelievable.

“新视野号”克服的困难包括NASA官员对其持怀疑态度、资金多次受到威胁。此外,由于实验室的问题,可以用来驱动探测器的钚的总量减少了,而且根据行星的运行规律,最后期限也无法更改。尽管这些障碍中没有哪一个具有“阿波罗13号”(Apollo 13)任务等太空探索危机的戏剧性,但它们的数量和程度看上去也颇为惊人。

“If you wrote a novel about it, I don’t think people would buy it,” said S. Alan Stern, New Horizons’ principal investigator.

“如果以此为题材写一本小说,我觉得人们不会买,”该任务的首席研究员S·艾伦·斯特恩(S. Alan Stern)说。

The story of New Horizons, the little spacecraft that could, and did, visit a small planet that is now considered too small to be a planet, started 15 years ago when NASA called it quits on Pluto.

“新视野号”的故事开始于15年前。当时,NASA称其不再进行冥王星的探测了。这个小小的探测器有能力,也的确做到了探访这颗行星。不过现在,人们认为这颗行星太小,不能算作行星。

For a decade, concepts for sending a mission there had been studied but never done. In 2000, the price tag for the latest incarnation, called Pluto-Kuiper Express, appeared to be getting out of control.

在10年时间里,人们研究过向那里发射一个探测器的想法,但从未将其付诸实践。2000年,作为“新视野号”距今最近的前辈,冥王星-柯伊伯快车号(Pluto-Kuiper Express)的成本似乎要失控了。

“When it was canceled,” Dr. Stern said, “the associate administrator at the time, Ed Weiler, held a press conference and said: ‘We’re out of the Pluto business. It’s over. It’s dead. It’s dead. It’s dead.’ He repeated himself three times.”

“任务取消时,”斯特恩说,“当时的副署长埃德·韦勒(Ed Weiler)举行了一场新闻发布会,并在发布会上说:‘我们不再进行冥王星的探测任务了。结束了。不存在了。不存在了。不存在了。’他重复了三次。”

Many planetary scientists and Pluto fans reacted in dismay, especially as it seemed to be a case of then or never.

很多行星科学家和冥王星的粉丝对此感到沮丧,特别是因为在当时看来,那时不去探索,就永远都没有机会探索了。

Pluto had reached the closest point of its orbit to the sun in 1989 and was on the outbound trek, turning colder. Scientists worried that Pluto’s tenuous atmosphere would turn to ice and fall to the ground, making Pluto a much less interesting place to study until it neared the sun again — two centuries later, when they would be long gone.

1989年抵达近日点后,冥王星在向离太阳更远的地方运行的同时,温度降低。科学家担心,冥王星稀薄的大气会变成冰,掉到地面,导致对冥王星的研究兴趣降低,直到它200年后再次靠近太阳,而那时,他们早就不在人世了。

There was a second orbital consideration. The quickest way to Pluto is to take a left turn at Jupiter, using the giant planet’s gravity for acceleration, which cuts the travel time by four years. But a launch after January 2006 would mean Jupiter would be too far out of alignment to provide a boost.

还有另一个轨道方面的考虑。前往冥王星最快的办法是在木星左转,利用那颗巨行星的重力来加速,这会让飞行时间缩短四年。但如果在2006年1月之后发射,就意味着木星偏离的距离太远,无法起到加速的作用。

Stamatios Krimigis, then the head of the space department at the Johns Hopkins Applied Physics Laboratory in Maryland and a member of a committee that advised NASA on missions to the outer planets, recalled Dr. Weiler’s asking him in the fall of 2000 whether it would be possible to do a low-cost Pluto mission similar to the Near Earth Asteroid Rendezvous spacecraft that the laboratory had built and operated for NASA a few years earlier.

斯塔马蒂奥斯·克里米吉斯(Stamatios Krimigis)当时是马里兰州约翰·霍普金斯大学应用物理实验室(Johns Hopkins Applied Physics Laboratory)太空部主任,也是为NASA的带外行星探测任务提供咨询的一个顾问委员会的成员。他回忆说,2000年秋天,韦勒问他有没有可能开展一次低成本的冥王星探测,就像该实验室在几年前,为NASA建造和操作的“近地小行星交会探测器”(Near Earth Asteroid Rendezvous)那样。

“I said, ‘Well, we can look at that,’ ” Dr. Krimigis said in an interview. He was intrigued but uncertain.

“我说,‘好吧,我们可以考虑考虑’,”克里米吉斯在接受采访时说。他很感兴趣,但并不是很有把握。

Dr. Krimigis pulled together a small group who worked over the Thanksgiving holiday to come up with a cost estimate: $500 million including the rocket. That quick study sketched out a basic design that would turn into New Horizons.

克里米吉斯成立了一个小团队。为了估算成本,团队成员感恩节都在工作。估算结果是:包括火箭在内5亿美元。这项简单的研究介绍了一项基本的设计。该设计后来演变成了“新视野号”。

A few months later, NASA put out a call for proposals, a competition to design a new Pluto mission that would arrive by 2015 and cost less than $500 million.

几个月后,NASA邀请科学家们提交研究计划书。这是一项比赛,内容是设计一个新的冥王星探测器,要在2015年前抵达那里,并且成本要低于5亿美元。

The Johns Hopkins team knew how to build spacecraft, but the science of Pluto was not its expertise. For that, Dr. Krimigis reached out to Dr. Stern, the head of the Southwest Research Institute’s space studies department in Boulder, Colo.

约翰·霍普金斯大学的这个团队知道怎么造探测器,但有关冥王星的专业知识却不是他们的专长。为此,克里米吉斯找到了斯特恩,后者是科罗拉多州博尔德市的西南研究院(Southwest Research Institute)太空研究部主任。

Dr. Stern was a member of the “Pluto Underground,” a dozen planetary scientists who in 1989 met in a Baltimore restaurant and discussed how to push NASA toward a Pluto mission. Over the years, he had worked on various studies for Pluto missions, none of which had paid off.

斯特恩也是“冥王星地下组织”(Pluto Underground)的成员。十几名行星科学家1989年在巴尔的摩一家餐馆聚会,讨论如何推动NASA开展冥王星探测任务,于是成立了这一组织。多年来,他参与过多项有关冥王星探测任务的研究,却无一成功。

But Dr. Stern, who rallied efforts to persuade NASA to again consider a Pluto mission, liked what he heard from Dr. Krimigis.

但极力劝说NASA再次考虑冥王星任务的斯特恩,却喜欢上了从克里米吉斯那里听到的东西。

They discussed, compromised and then agreed.

他们进行了讨论和妥协,最终达成了一致意见。

In November 2001, NASA chose New Horizons. “We busted our butts, and we won it,” Dr. Stern said.

2001年11月,NASA选择了“新视野号”。“我们非常努力,赢得了比赛,”斯特恩说。

That started a four-year, two-month sprint to design, build and test the spacecraft and get it to the launching pad — but almost immediately there was an obstacle. “Two months later, the Bush administration canceled it,” Dr. Stern said, laughing.

探测器的设计、建造和测试由此开始。到将其安放到发射台上,共历时四年零两个月。不过几乎一开始就遇到了障碍。“两个月后,布什政府就取消了该计划,”斯特恩大笑着说。

The president’s budget proposal for 2003 included no money for Pluto, the second year in a row that the administration had tried to kill such a mission. But Congress, persuaded by Senator Barbara A. Mikulski of Maryland, inserted earmarks in the spending bills to keep the Pluto mission on track.

总统2003年的预算案没有包括用于冥王星任务的资金。这是布什政府连续第二年试图扼杀此类任务。但在马里兰州参议员芭芭拉·A·米库尔斯基(Barbara A. Mikulski)的劝说下,国会在开支法案中加入了专项拨款,从而确保冥王星探测任务能继续进行。

“Every year Congress had to keep us on life support,” said Glen Fountain, New Horizons’ project manager.

“每年都要让国会出面,才能让我们维持下去,”该任务的项目主管格伦·方丹(Glen Fountain)说。

In 2002, the National Academy of Sciences named Pluto a top priority for NASA’s planetary science missions. “At that point, you could feel things change,” Mr. Fountain said.

2002年,国家科学院(National Academy of Sciences)指定,冥王星探测是NASA行星科学任务中的首要任务。“那时,能感觉到情况变了,”方丹说。

Managers of spacecraft missions often talk about the trade-offs between cost, schedule and risk. Too quick and too cheap greatly raise the chance of failure. “We don’t believe in that,” Dr. Krimigis said.

航天任务的管理者经常会谈到成本、时间安排和风险之间权衡。太快、成本太低就会大大增加失败的可能性。“我们却不相信那种说法,”克里米吉斯说。

With just seven instruments, the craft was about the size of a grand piano. Mr. Fountain said the philosophy at the Johns Hopkins laboratory is to stick to proven technologies and keep the design to the essentials, which reduce cost and avoid delays without increasing risk. The one compromise, he said, was a digital radio receiver that would consume less power. The Johns Hopkins laboratory had already started working on the technology in a separate project.

只有七台设备,探测器的体积就达到了大型钢琴的尺寸。方丹说,约翰霍普金斯大学实验室的哲学是,坚持得到验证的技术,把设计限制到最必不可少的东西,这就降低了成本也避免了拖延,同时不会加大风险。他说,唯一的妥协是,数字无线电接收器本来可以少用一些电力。约翰霍普金斯大学的实验室当时已经开始在另外一个项目中研究相应技术了。

“We didn’t think it was a huge risk,” Mr. Fountain said.

“我们没有认为那是很大的风险,”方丹说。

Development continued without any showstoppers, although the cost rose to $722 million.

开发过程继续进行,没有遇到任何阻碍,不过成本提高到了7.22亿美元。

Then, in August 2004, the Department of Energy informed the New Horizons team that it could not provide the plutonium power source. At the far reaches of the solar system, the sun is too dim for a spacecraft to rely on solar panels or batteries. Instead, a chunk of radioactive plutonium generates heat that is converted to electricity.

之后在2004年8月,能源部通知“新视野号”团队,该部无法提供钚能源。在太阳系的边缘,阳光太暗,太空飞行器无法靠太阳能板或电池飞行。替代方法是,用一大块放射性钚产生出热量,之后热量再转变为电能。

Security lapses and safety issues at the Los Alamos National Laboratory in New Mexico had shut down the production of plutonium dioxide pellets for New Horizons’ power generator. Not enough had been made to provide the 220 watts called for in the design.

新墨西哥州的洛斯阿拉莫斯国家实验室(Los Alamos National Laboratory)暴露出了安全漏洞和安保问题,导致“新视野号”的发电机所需的二氧化钚颗粒燃料停产。而已经生产的燃料总量,无法满足设计要求的220瓦电力。

“We said, ‘How much power could you deliver?’ ” Mr. Fountain said. The reply: 180 watts.

方丹说,“我们问,那你们能提供多少电力?”对方回答:180瓦。

Because of design decisions like the digital radio receiver, Mr. Fountain thought the reduced power would be sufficient. In the end, the Department of Energy was able to build a power generator that put out 200 watts during the flyby.

考虑到与数字无线电接收器相关的设计决策,方丹认为,减少后的供电也是充足的。最后,能源部得以制造出一个可以产生出200瓦电力供飞掠时使用的发电机。

New Horizons launched on top of an Atlas 5 rocket on Jan. 19, 2006, making the fastest-ever trip out of Earth’s neighborhood.

“新视野号”是2006年1月19日在一枚Atlas 5火箭上发射升空的,那是脱离地球环境有史以来最快的一次飞行。

Thirteen months later, the craft was at Jupiter already, and the mission team put its instruments to the test. New Horizons captured time lapse pictures of a volcanic eruption on Io, one of Jupiter’s four big moons.

13个月之后,探测器已经抵达了木星,任务团队开始测试探测器上的仪器。“新视野号”拍摄了木星的四大卫星之一,木卫一上火山喷发的延时摄影照片。

Just after the Jupiter flyby, New Horizons suffered its first computer glitch. For spacecraft outside Earth’s protective atmosphere, high-energy cosmic rays occasionally zip through computer memory, causing a crash and restart. Calculations indicated that there would be one such crash during the nine-and-a-half-year trip to Pluto.

就在飞掠木星之后,“新视野号”遭遇了首次电脑故障。地球的大气层有保护性,飞行器在驶出大气层后,高能宇宙射线有时候会穿透电脑的存储器,导致系统死机和重启。最初的计算显示,在飞往冥王星九年半的旅程中,会出现一项这样的故障。

Instead, they occurred almost once a year. But none caused lasting damage, and they proved good learning experiences.

但实际上,这种故障几乎每年都会发生一次。不过,这些故障都没有造成持久性的损害,而且事实证明,这些故障也都提供了很好的学习经验。

“It was just eventful enough to keep us alert,” said Christopher Hersman, the missions systems engineer. “It actually helped.”

“挫折的程度刚好可以让我们保持警惕,”探测任务的系统工程师克里斯托弗·赫斯曼(Christopher Hersman)说。“实际上是有帮助的。”

The rest of the long cruise was mostly uneventful. Flinging a spacecraft to a rendezvous at the edge of the solar system is indeed rocket science, but not groundbreaking rocket science. The equations — the basic laws of Isaac Newton — are the same ones that were used decades ago.

这段长途跋涉里的其他时间,大都风平浪静。让一艘飞行器驶往太阳系的边缘诚然是复杂的科学问题,但不算是具有开创性的尖端科学任务。探测过程中需要的公式都是几十年来一直在用的,比如牛顿的基本法则。

Still, the engineers were careful with their calculations — tiny errors can grow calamitous — and periodic checkups made sure everything was working smoothly on the spacecraft.

然而工程师对于他们的计算工作仍然十分认真——微小的误差都能产生灾难——他们还经常进行检查,确保探测器上所有设备都能顺利运转。

Then, on July 4, 10 days before the Pluto flyby, the spacecraft suddenly fell silent. Alice Bowman, the mission operations manager, said years of experience had given her a sense when a problem might be the fault of the receiving stations and when it might be a problem with a spacecraft.

接着,在7月4日,飞掠冥王星之前10天,探测器突然陷入沉寂。探测任务的运行主管爱丽斯·鲍曼(Alice Bowman)说,由于有着多年的经验,她能判断,问题可能出在接收站身上,还是可能出在飞行器身上。

“I pretty much knew it was something on the spacecraft,” she said.

“我基本上明白问题出在飞行器上面,”她说。

She called Mr. Hersman. “Where are you?” she said, summoning him urgently to the missions operations center.

她给赫斯曼打了个电话,直接说“你在哪儿?”接着急迫地叫他来到飞行任务运行中心。

After an Independence Day barbecue with neighbors, Mr. Hersman was already on the way to the office anyway. “Going in, I was thinking, ‘Remain calm,’ ” Mr. Hersman recalled.

在与邻居们吃完独立日烧烤之后,赫斯曼本来就已经要回到办公室了。“在回办公室的路上,我想,‘要保持冷静’,”赫斯曼回忆道。

Ms. Bowman called Mr. Fountain. He, too, headed in.

鲍曼也给方丹打了电话,后者也来到了办公室。

Thoughts of the worst popped into his mind: “Could we have been so extremely unlucky that we hit something?” Even debris the size of a grain of rice could destroy a delicate craft moving so fast.

最坏的情形闪过了他们的头脑:“我们是不是运气极为糟糕,撞上了什么东西?”即使是一粒米大小的碎屑,也可以摧毁如此高速飞行的精密仪器。

But it turned out the spacecraft’s computer had overloaded trying to do two things at once — receive instructions for the flyby while compressing images in its memory banks. By design, the main computer entered what engineers call “safe” mode to avoid damage to the spacecraft, and the backup computer kicked in.

原来问题在于,飞行器在尝试同时处理两件事情时,电脑过载了。它一面接收飞掠的指令,一面压缩存储库里的图像。按照设计,主电脑为了避免飞行器损坏,进入了工程师所说的“安全”模式,备用电脑启动了。

An hour and a half later, the ground stations detected the signal from the backup computer. “Then I knew we could do it,” Ms. Bowman said. “The question was, could we do it in time?”

一个半小时后,地面站检测到了备用电脑发来的信号。“于是我就知道了,我们可以做到,”鲍曼说。“问题是,我们能按时做到吗?”

A nine-day sequence of commands to guide New Horizons through the flyby was set to begin on July 7. Ms. Bowman spent two nights at the office, taking only short naps. “You would be amazed how much that can do,” she said. “I can’t say I slept.”

一串长达九天的指令会指引新视野号飞掠冥王星,指令从7月7日开始。鲍曼在办公室待了两晚,期间只打了几个小盹。“这些能起到多大作用,足以让你惊讶,”她说。“我不能说我睡觉了。”

With hours to spare, the craft was back in operation. Then the flyby directions kicked in, and New Horizons did everything it was told to do.

时间还富余几个小时,飞行器已经恢复运转。之后,飞掠指令生效,新视野号按指令执行了所有操作。

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