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发帖数: 1 | 1 An asteroid could destroy humanity like it did dinosaurs. A Hopkins team has
a plan to save the world.
Andy Cheng, chief scientist at the Johns Hopkins Applied Physics Laboratory
in Laurel, is co-lead investigator on the Double Asteroid Redirection Test
mission, NASA's first test of a defense mission to deflect an asteroidt by
smashing a spacecraft into it. (Kim Hariston/Baltimore Sun)
By Tim Prudente February 4 at 6:53 PM
A team of scientists, astronomers and engineers meets weekly in a conference
room on a Howard County, Md., research campus and plans to save the world.
“Keep calm and carry DART,” reads a poster on the wall.
DART — the Double Asteroid Redirection Test — is their plan to avert
catastrophe. It’s also NASA’s first mission not to explore space, but to
defend against it.
The research team at the Johns Hopkins University Applied Physics Laboratory
in Laurel plans to launch a spacecraft, speed it up really fast and smash
it into an asteroid.
The impact, they hope, will bump the big space rock off course — actually
more like nudge it slightly. Someday, the thinking goes, this method may
save people from the fate of the dinosaurs.
“Kind of like a big missile,” said Elena Adams, the mission’s lead
engineer. “It’s very exciting. You are actually doing something for the
fate of humanity.”
An estimated 100 tons of space debris falls to Earth every day, according to
scientists with NASA’s Jet Propulsion Laboratory at the California
Institute of Technology. This debris is mostly dust and sand.
Occasionally, space sends something bigger.
In February 2013, a fiery meteor cut across the Siberian sky. It came
streaking down as fast as 40,000 mph. Then came a midair explosion, a flash
and boom.
The shock wave blew out windows across the Russian city of Chelyabinsk. A
factory roof collapsed. More than 1,000 people were hurt, mostly from
shattered glass. Scientists estimate the meteor unleashed a force stronger
than the atomic bomb detonated in Hiroshima.
The rock was about the size of a school bus. That’s a pebble compared to a
meteor believed to have exploded over remote Siberia in 1908, flattening
hundreds of square miles of forests. Researchers estimate that fireball
equaled 185 Hiroshima bombs and heated the air to near 50,000 degrees. If
the Tunguska meteor had arrived, say, three hours later, it could have
obliterated Moscow, said Lindley Johnson, whose title with NASA is planetary
defense officer.
“That probably would have changed the entire history of the 20th century,”
said Johnson, who runs NASA’s asteroid defense programs. “These are
natural disasters that we need to be aware of.”
Some time in a span of several hundred thousand years, scientists say, an
asteroid even larger could strike Earth and wreak global disaster. They
believe a meteor 8 to 10 kilometers in diameter crashed into the Gulf of
Mexico 65 million years ago and killed off the dinosaurs.
“We’ve found all the nearest asteroids that size. We’re safe from that,”
said Paul Chodas, who runs an asteroid search team at the NASA lab in
California.
But smaller asteroids can unleash megatons of energy, too.
“Even down to the 1-kilometer size, if it hits in the right spot, could
cause global devastation,” Chodas said. “It’s the small asteroids that
pose the risk.”
In the 1990s, Congress ordered NASA to locate dangerous asteroids in the
solar system. Researchers today aim to catalogue the orbits of 90 percent of
asteroids 460 feet or bigger.
They predict 25,000 of them hurtle through the solar system. Chodas said
they have found and charted about a third of them. The researchers can
calculate each asteroid’s trajectory decades into the future.
Scientists have long debated what to do if they discover one on a collision
course with Earth.
Hollywood portrayed such events in “Deep Impact” and “Armageddon.” In
both movies, mankind narrowly escapes doom by planting nuclear bombs and
blowing the asteroids to pieces.
It’s not that easy.
NASA has considered nuking an asteroid with warheads, but that risks turning
a single incoming rock into a shower of debris as happened in “Deep Impact
.” Another plan calls for flying a spacecraft beside the asteroid and
gradually drawing it off course like a gravity tractor.
DART offers a third strategy, and will be the first to be given a live test.
“It’s the simplest and most effective,” Chodas said.
Now the team at the Hopkins laboratory in Laurel has begun the final design
and construction of the DART spacecraft. About the size of a Honda Civic, it
’s scheduled for launch in summer 2021.
While it sounds simple, the crash mission involves some tricky engineering.
The target is the tiny moon of an asteroid. The two bodies are collectively
named Didymos, or Greek for “twin.” They orbit the sun between Earth and
the Asteroid Belt. The moon is not much bigger than the Washington Monument
— minuscule in the scale of space.
“This is by far the smallest object anyone has ever flown a spacecraft into
,” said Andy Cheng, the mission’s co-lead and chief scientist in APL’s
space department.
The spacecraft will be powered by solar panels that unfurl like wings. Its
journey will take more than one year, and the researchers mostly will be
flying blind.
“We don’t see the moon of the asteroid until we’re just an hour away,”
said Adams, the engineer. “That last hour is going to be really thrilling.”
They plan for DART to reach speeds as fast as 15,000 miles per hour. The
crash in October 2022 will fling debris from the asteroid moon. A small
satellite will accompany the DART spacecraft to measure the effect.
The team wants to hit the asteroid moon with enough force to bump it, but
not break it apart. The moon orbits the asteroid at a speed of about seven
inches per second. They hope to change the speed by about a centimeter, or .
39 of an inch, per second.
“We’re just going to give it a love tap,” said Andy Rivkin, the mission’
s other co-lead and planetary astronomer at APL.
In theory, taps over time could deflect an asteroid off a course for Earth.
One impact may suffice if scientists have enough warning time. An imminent
asteroid strike, however, would require multiple launches and impacts.
“You could have a constant stream,” Rivkin said. “Each one nudges it a
bit more.”
It’s humanity’s best plan to save Earth, but one the team hopes they never
have to use.
— Baltimore Sun | o**n
发帖数: 2130 | | b*******8
发帖数: 37364 | 3 第一句话就托福不及格
has
Laboratory
★ 发自iPhone App: ChinaWeb 1.1.5
【在 g**********1 的大作中提到】
: An asteroid could destroy humanity like it did dinosaurs. A Hopkins team has
: a plan to save the world.
: Andy Cheng, chief scientist at the Johns Hopkins Applied Physics Laboratory
: in Laurel, is co-lead investigator on the Double Asteroid Redirection Test
: mission, NASA's first test of a defense mission to deflect an asteroidt by
: smashing a spacecraft into it. (Kim Hariston/Baltimore Sun)
: By Tim Prudente February 4 at 6:53 PM
: A team of scientists, astronomers and engineers meets weekly in a conference
: room on a Howard County, Md., research campus and plans to save the world.
: “Keep calm and carry DART,” reads a poster on the wall.
| g**********1
发帖数: 1 | 4 你是说真猫不如假猫叫的像猫？
【在 b*******8 的大作中提到】
: 第一句话就托福不及格
:
: has
: Laboratory
: ★ 发自iPhone App: ChinaWeb 1.1.5
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