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更新时间:2016-6-30 18:47:32 来源:纽约时报中文网 作者:佚名

NASA’s Juno Spacecraft Will Soon Be in Jupiter’s Grip

After traveling for five years and nearly 1.8 billion miles, NASA’s Juno spacecraft will announce its arrival at Jupiter with the simplest of radio signals: a three-second beep.


The long-awaited beep will also mark the end of a 35-minute engine burn to slow the spacecraft down and allow it to be captured by Jupiter’s gravity. NASA expects the beep to arrive at Earth at 11:53 p.m. Eastern time Monday.


“I can tell you when that completes, you’re going to see a lot of celebration,” said Rick Nybakken, Juno’s project manager, “because that means we’ll be in orbit around Jupiter, and that’ll be really cool.”

“我可以告诉你,哔哔声过后,你会看到很多庆祝活动。”朱诺号项目经理瑞克·尼巴肯(Rick Nybakken)说,“因为这意味着我们的探测器进入了木星的轨道,这实在是太酷了。”

Juno’s mission is to explore the enigmas beneath the cloud tops of Jupiter. How far down does the Great Red Spot storm that has swirled for centuries extend? What is inside the solar system’s largest planet?

朱诺号的任务是探索木星表面云层之下的谜团。已经肆虐了好几个世纪的大红斑(Great Red Spot)风暴向下延伸了多少?太阳系最大行星内部都有什么?

“We still have questions, and Juno is poised to begin answering them,” Diane Brown, Juno’s program executive, said during a news conference this month.

“我们仍有很多疑问,而朱诺号做好了着手回答这些问题的准备,”朱诺号项目主管黛安·布朗(Diane Brown)在本月的一场新闻发布会上表示。

Juno will be the first craft to orbit Jupiter in more than a decade. NASA’s earlier robotic explorer, Galileo, spent eight years there and sent back astounding images of the planet and its many moons. It revealed features like a large ocean under the icy crust of the moon Europa, now considered one of the most promising places to look for life elsewhere in the solar system.


This time, the focus will be on Jupiter itself, and in particular what cannot be seen beneath its colorful cloud stripes.


“One of the primary goals of Juno is to learn the recipe for solar systems,” said Scott Bolton, a scientist at the Southwest Research Institute in San Antonio who is the principal investigator for the $1.1 billion mission. “How do you make the solar system? How do you make the planets in our solar system?”

“朱诺号的一个主要目标是研究组成太阳系的基本元素,”耗资11亿美元的朱诺号项目的首席研究员、圣安东尼奥西南研究所(Southwest Research Institute)的科学家斯科特·博尔顿(Scott Bolton)说。“太阳系是由什么组成的?太阳系内的行星又是由什么组成的?”

Jupiter is the titan among planets called the “gas giants,” with more than three times the mass of Saturn, the next largest. But it is far more than a bland ball of hydrogen and helium.


What particularly piques scientists’ interest are the small amounts of heavier elements like lithium, carbon and nitrogen.


“Jupiter is enriched with these elements compared to the sun,” Bolton said. “We don’t know exactly how that happened. But we know it’s really important. And the reason it’s important is the stuff that Jupiter has more of is what we’re all made out of. It’s what the Earth is made out of. It is what life comes from.”


On Monday, as the main engine on the spacecraft fires, in the control room at NASA’s Jet Propulsion Laboratory in Pasadena, California, there will be nothing to control, and all anyone there will be able to do is wait and watch.

下周一,当朱诺号的主发动机启动时,在加州帕萨迪纳市的NASA喷气推进实验室(Jet Propulsion Laboratory)里,将没有什么好控制的,那里的每一个人都只能等待和观望。

If anything goes wrong, there is no way for anyone to intercede. The radio signals take 48 minutes to travel from Jupiter to Earth. By the time engineers receive word the engine firing has begun, the engine should have already switched off, with the spacecraft in orbit.


If the engine shuts off prematurely, Juno might still end up in orbit, albeit in the wrong orbit. If the engine fails, “we don’t end up in a very exciting spot,” Nybakken said.


“We haven’t studied that too much in terms of where we end up, because we’re focused on success and not failure.”


In other words, Juno would zip right past Jupiter and end up in a useless orbit around the sun.


Through Monday evening, mission control will receive only a series of radio “tones” — three-second bursts at different frequencies — telling the sequence of operations the spacecraft is performing. To point the engine in the correct direction, the main antenna will not be pointed at Earth, preventing more detailed telemetry. The spacecraft will also not send back any photographs or data from the instruments, which will be shut down Wednesday, five days before its arrival, and will not be turned back on until a couple of days after its arrival.


Juno is to make a series of 37 highly elliptical orbits passing over Jupiter’s north and south poles over 20 months.


At its farthest, it will be about 2 million miles from Jupiter. For each orbit, it will accelerate inward, passing within 3,100 miles of Jupiter’s cloud tops. The slight fluctuations in Jupiter’s gravitational pull, measured by shifts in the frequency of Juno’s radio signals, will tell the density of the planet’s interior and whether there is a rocky core within, where pressures might reach half a billion pounds per square inch.


“We don’t really know if there is a core in the middle of Jupiter,” Bolton said. “If there is, it tells you sort of when and how and a little bit of where Jupiter must have formed.”


Juno’s science instruments include one to measure Jupiter’s powerful magnetic fields and an infrared camera to observe the glowing auroras around the poles. At depth, increasing pressures transform hydrogen from a gas into a liquid. At even greater depths, the hydrogen is squeezed so tightly that the electrons squirt out, changing it into a metal. It is probably the churning of liquid metallic hydrogen that generates the magnetic fields.


After the first two orbits, during which engineers will check if the spacecraft and instruments are working properly, Juno is to fire its engine again to move into the orbit for making its scientific measurements.


Although the craft are very different in appearance, much of Juno’s electronics and programming are based on the design of Mars Reconnaissance Orbiter, an earlier spacecraft also built by Lockheed Martin. “It’s just configured in a different format,” Guy Beutelschies, the director of interplanetary missions at Lockheed Martin, said in an interview.

尽管在外形上有很大的不同,但“朱诺号”的大量电子器件和程序都是基于火星勘测轨道飞行器(Mars Reconnaissance Orbiter)的设计。后者是早前的一款太空飞行器,同样由洛克希德·马丁公司建造。“只是采用了不同的配置形式,”该公司负责星际任务的总监盖伊·博伊特尔席斯(Guy Beutelschies)接受采访时说。

Instead of developing electronic circuits that could operate in Jupiter’s intense radiation, Lockheed Martin used the same circuitry as Mars Reconnaissance Orbiter but shielded it within the half-inch-thick walls of a 400-pound titanium vault measuring about 1 yard on each side.


Unlike earlier missions to the outer solar system, Juno is powered by sunlight, not plutonium. Three solar panels 30 feet long with a total of 18,698 solar cells gather the dim sunlight to produce about 500 watts.


Even if everything goes better than planned, the mission will not last much beyond the planned 20 months. Despite the titanium armoring, “we know the radiation is going to kill us,” Beutelschies said.


Juno is expected to receive a radiation dose equivalent to more than 100 million dental X-rays.