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  • Nuclear waste. We've got a lot of it, it'll stay dangerous for tens of thousands of years,

  • and we don't really know what to do with it. So why don't we just send it into space and

  • crash it into the sun?

  • Well, first, it's really dangerous to put nuclear waste on a rocket, since rockets have

  • a tendency to occasionally explode while launching, making any nuclear-waste-filled exploding

  • rocket into a really big dirty bomb.

  • But the bigger reason is that it's actually really really hard to *get* to the sun. It

  • might seem like it should be easy, since the sun's gravity is always pulling us towards

  • it. But we're also orbiting really fast sideways around the sun, so that as we fall towards

  • it, we miss it.

  • In order to crash _into_ the sun, you have to slow down so that you're _not_ going sideways

  • really fast. The earth - and everything on it - is moving around the sun at around 30

  • kilometers per second, so you'd have to accelerate to a speed of 30kilometers per second backwards

  • away from the earth in order to stop moving around the sun and do a sun dive. And you

  • have to slow down all the waywith even a little bit of sideways speed, you'll miss

  • the sun and whip around, not crashing.

  • Ok, so a speed of 30 kilometers per second is really fast, but just how fast? Well, from

  • earths's orbit, you only need to be going _11_ kilometers per second faster than the

  • earth in order to escape from the entire solar system. Which means that it's much, much harder

  • to crash into the sun than to escape it altogether. Let me say that again: it takes less acceleration

  • to get to _other_ stars than it does to get to our own sun. Crazy.

  • But it gets weirder: because the gravity from an object is stronger the closer you are to

  • it, the smaller your orbit is, the faster your orbital speed. For example, Mercury goes

  • around the sun at a speed one and a half times faster than earth, while Pluto goes only a

  • sixth as fast. And that means it's actually way harder to crash into the sun from Mercury

  • than from the earth, even though you're closer, because you'd have to accelerate to a speed

  • of 48 kilometers per second backwards instead of 30. And it's way _easier_ to crash into

  • the sun from Pluto, since you only have to accelerate to a speed of five kilometers per

  • second backwards.

  • In fact, if you're trying to crash into the sun just using rockets, it's far more efficient

  • to first go to the outer solar system where your speed is much lower, then do a second

  • burn to counteract that slow orbital speed and allow you to fall directly into the sun.

  • And that's precisely why early mission trajectories for NASA's spacecraft to study the sun proposed

  • going out to Jupiter firstto make it easier to slow down and get to the sun. Ultimately

  • they decided instead to use repeated flyby's of Venus to slow down the probe and save on

  • rocket fuel getting to the sun.

  • But how gravity assists work is a topic for another day. Speaking of whichhow long

  • would a day be on the sun?

Nuclear waste. We've got a lot of it, it'll stay dangerous for tens of thousands of years,

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B1 sun speed sideways slow earth accelerate

Hitting the Sun is HARD

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    Summer posted on 2021/10/14
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