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Why the sun is a poor dumping ground for nuclear waste (2010)

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Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#141

Post by leni536 »

kllrnohj wrote: post #78
leni536 wrote: post #32

> To reach the Sun you need to subtract 100 percent of Earth’s orbital velocity; to reach solar escape velocity you need only add 41 percent to it. You could send the waste with near solar escape velocity to travel on a really long ellipsis trajectory, at the furthest point you can get rid of the remaining kinetic energy with minimal fuel and let the waste fall back straight into the Sun. Subtracting Earth's orbital…

A straight Hohmann transfer requires ~0.5-1% more dV than a bi-elliptic transfer. Calling this "by far" not optimal is by far not correct. So instead of 32 km/s you need 31.68 km/s. This changes nothing.

It's not a full bi-elliptic transfer, it's missing the third "retrograde" burn. In this situation the target orbit would be inside the Sun, the third burn is completely unnecessary. Your rule of thumb comparison of the two strategy doesn't work here.

[1] https://en.wikipedia.org/wiki/Bi-elliptic_transfer

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#142

Post by leni536 »

Houshalter wrote: post #140

It's not that I don't believe the author is correct, but I'm having a hard time picturing why it is true. Imagine a rocket pointed in the exact opposite direction the earth is orbiting. So the rocket starts to orbit the sun slightly slower than the Earth, and so the Sun's gravity would pull it closer and closer every year.

That's not how it works. It would just place the waste on an elliptical orbit around the Sun.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#143

Post by vhffm »

Houshalter wrote: post #140

It's not that I don't believe the author is correct, but I'm having a hard time picturing why it is true. Imagine a rocket pointed in the exact opposite direction the earth is orbiting. So the rocket starts to orbit the sun slightly slower than the Earth, and so the Sun's gravity would pull it closer and closer every year.

It would not.

If you start out with a velocity slightly slower than the Earth's, you end up with an elliptical orbit (instead of Earth's almost circular orbit). Barring some sort of drag (to further loose energy), there's no reason it would decay into the sun.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#144

Post by Houshalter »

leni536 wrote: post #142
Houshalter wrote: post #140

It's not that I don't believe the author is correct, but I'm having a hard time picturing why it is true. Imagine a rocket pointed in the exact opposite direction the earth is orbiting. So the rocket starts to orbit the sun slightly slower than the Earth, and so the Sun's gravity would pull it closer and closer every year.

That's not how it works. It would just place the waste on an elliptical orbit around the Sun.

But aren't the vast majority of possible orbits unstable? If the Earth were travelling just a bit slower wouldn't it slowly spiral into the sun?

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#146

Post by MichaelGG »

throwagravity wrote: post #22
MichaelGG wrote: post #8

Earlier quoted context omitted.

Why is that so? It's not a particularly dumb question for many people that don't know anything about launch costs or the massive amount of energy. I'd bet many people think if you can get it out past the moon's orbit it should start to fall into the sun. And even if it was a flippant question, showing exactly how wrong it is through an in-depth analysis is a great way to refute such positions.

It's a dumb question if you know anything about orbital mechanics, which the author purports to do. > I'd bet many people think if you can get it out past the moon's orbit it should start to fall into the sun. This thought is actually true, to a first-order approximation. If you time it right and use gravity slingshot(s) to bleed off velocity and/or adjust the direction towards the sun. The amount of delta-V needed a…

Funny coincidence. I was putting my daughter to bed and she asked aren't rockets launches in danger of going into the Sun?

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#147

Post by vhffm »

Houshalter wrote: post #144
leni536 wrote: post #142

Earlier quoted context omitted.

That's not how it works. It would just place the waste on an elliptical orbit around the Sun.

But aren't the vast majority of possible orbits unstable? If the Earth were travelling just a bit slower wouldn't it slowly spiral into the sun?

If Earth was travelling a bit slower, it would just be on different orbit. Either more eccentric or just further away from the sun. This is encapsulated in Kepler's laws [1], which describe the motion of a single planet around a single star.

If you have other planets in the system (like our solar system does), things are more complicated. Orbital stability then depends on the arrangement of other planets. You are right in pointing out that the Earth's orbit is (possibly) unstable [2] over a timescale of billions of years.

[1] http://www.physicsclassroom.com/class/circles/Lesson-4/Keple...

[2] Unstable in the sense that Earth's orbit may become eccentric enough to smash into another planet, get ejected from the solar system, or dive into the sun.

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#148

Post by jwmerrill »

Houshalter wrote: post #144
leni536 wrote: post #142

Earlier quoted context omitted.

That's not how it works. It would just place the waste on an elliptical orbit around the Sun.

But aren't the vast majority of possible orbits unstable? If the Earth were travelling just a bit slower wouldn't it slowly spiral into the sun?

> But aren't the vast majority of possible orbits unstable?

No. Ignoring perturbations from other planets, planetary orbits are stable ellipses with the sun at one focus.

http://en.m.wikipedia.org/wiki/Kepler's_laws_of_planetary_mo...

Re: Why the sun is a poor dumping ground for nuclear waste (2010)

#150

Post by bcmit »

mindcruzer wrote: post #95
sbov wrote: post #93

Earlier quoted context omitted.

Do we know enough about our oceans to know that there would be no harm from this?

No

Really? Water is just about the best radiation shield in existence. It would only affect the ~10 feet of ocean immediately around it.
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