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  • [♪ INTRO]

  • Space travel is likely going to be a big part of our future.

  • But as we send more instruments and people into Earth's orbit and beyond,

  • there's one problem we really need to deal with:

  • There is an invisible shell of radiation surrounding our planet that can wipe out satellites and

  • could endanger future explorers.

  • And we don't have a great solution for it.

  • But scientists are working on combating this radiation, with good old-fashioned radio waves.

  • We've known about this shell of radiation since 1958,

  • when NASA was sending its very first spacecraft into orbit.

  • On the way up, cosmic ray detectors picked up a huge amount of radiation

  • surrounding our planet.

  • In fact, it was so extreme, scientists initially thought they'd detected a Soviet nuclear test.

  • But soon they figured out that it was a natural phenomenon,

  • and that Earth was surrounded by two massive rings of radiation

  • between 650 and 60,000 kilometers above Earth's surface.

  • They're now called the Van Allen Belts, after the physicist James Van Allen, who discovered them.

  • And these donut-shaped rings are full of highly energetic charged particles that come from the Sun,

  • which is constantly releasing a stream of them in what's called the solar wind.

  • Most of these get deflected by our planet's magnetic field,

  • but some of them leak through and get trapped within it.

  • In particular, many of them get trapped in a region centered around Earth's magnetic equator,

  • where magnetic field lines are parallel to the surface,

  • so the particles bounce north and south, but they can't escape.

  • Fortunately, we're pretty safe from all that here on Earth's surface,

  • but this radiation can pose serious problems for our space tech.

  • Our satellites often have to pass through these belts,

  • and some, like GPS satellites, even orbit within them,

  • in the middle of a bunch of electrons traveling close to the speed of light.

  • If satellites were unprotected, these electrons would build up inside their components until they discharged,

  • a lot like a lightning strike, which could fry their electronics.

  • For now, engineers typically use metal casings to shield the sensitive components of satellites,

  • but that's extremely expensive, and it's still not foolproof, they could still get zapped in a solar storm.

  • Or, in a military context, something like a nuclear blast in the atmosphere

  • could make the radiation even stronger and knock out important satellites.

  • Which is another reason scientists are studying all of this.

  • But it's not all about electronics, either.

  • This radiation makes sending people to space complicated, too.

  • It's not much of a problem right now, because our astronauts don't go up that high,

  • but back in the Apollo days, missions had to go through the thinnest parts of the belts

  • to try to limit astronauts' exposure to radiation.

  • And assuming human missions become more common in the future, this radiation will be a major concern.

  • So, to protect us, our future explorers, and our precious space tech,

  • scientists are actively looking for ways to clear these energetic electrons out of the Van Allen Belts,

  • in a process known as radiation belt remediation.

  • And one of the most promising techniques yet uses a fairly low-tech approach: radio waves.

  • Back in 2015, a pair of spacecraft known as the Van Allen Probes

  • showed that human activity has actually helped protect us from the radiation in these belts.

  • See, ever since the 1950s, humans have been producing very low-frequency, or VLF, radio waves,

  • mostly for communication with submarines,

  • since these are the only frequencies that can pass through water.

  • But there's something else that's special about these frequencies:

  • They resonate with the natural vibration of electrons trapped in the belts.

  • So when VLF waves come in contact with them,

  • they can give those electrons a little boost of energy and actually scatter them back into space!

  • That happens primarily during solar storms,

  • when the edge of the inner radiation belt blows closer to Earth's surface.

  • During those times, measurements from the probes revealed that our VLF emissions on Earth

  • create a sort of protective bubble around the planet!

  • So that got scientists wondering if we could deliberately produce VLF waves

  • as a way to reduce the radiation even more.

  • There have even been some early experiments.

  • Like in 2008, a satellite measuring electrons in the inner radiation belt revealed that

  • one powerful radio antenna in Australia produced a measurable change in the belt.

  • But a similar antenna in Hawai'i had no effect.

  • Scientists think that's because the results depend on the local atmosphere and magnetic field,

  • which suggests that a better bet might be to put something in space.

  • So, as a test, a mission called the Demonstration and Science Experiment launched in June 2019.

  • Surprisingly boring name, but It has a massive, 80-meter-wide antenna to generate radio waves,

  • as well as six sensors to measure changes in the radiation field around it, which is not boring.

  • Right now, the spacecraft is in orbit more than 6,000 kilometers above Earth's surface,

  • and is practicing emitting its VLF waves.

  • Scientists are expecting the first results by the end of 2020.

  • And other researchers are looking into a more compact solution,

  • like an electron accelerator that would emit VLF waves and attempt to disperse electrons

  • just like a regular antenna.

  • It is a brand-new technology, since electron accelerators aren't something we normally throw up into space.

  • But scientists plan to launch this experiment in 2021.

  • So, it's likely we'll have to wait a little while longer to find out if these experiments are successful,

  • but either way, the results will help us learn more about the radiation around our planet

  • and how we can protect ourselves from it.

  • Thanks for watching this episode of SciShow Space!

  • And if you liked it, you might like our podcast, called SciShow Tangents!

  • We even have an episode all about the Apollo program, which is the one time in history

  • we've sent humans through these deadly belts of radiation.

  • We also have dozens of other episodes made by some of the same people who make SciShow,

  • including me,

  • and they're full of niche science, fun insights, and some friendly competition.

  • If you want to check it out, you can click on the link below,

  • or search for SciShow Tangents wherever you listen to podcasts.

  • [♪ OUTRO]

[♪ INTRO]

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无线电波如何帮助您清除通往太空的道路(How Radio Waves Could Help Clear the Way to Space)

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    joey joey 發佈於 2021 年 04 月 18 日
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