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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)

#71

Simple: Just invent a rocket that runs on nuclear waste. Then you have all the fuel you need to get the rocket there. (joking)

If you were to not-quite-spend all the fuel, you could use https://en.wikipedia.org/wiki/Nuclear_thermal_rocket, which coincidentally would be your best chance at getting to the Sun.

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

#72
post #2

Its generally not worth it to give smart answers to dumb questions. I guess its a pet peeve of the author though.

I would argue it's a waste not because it's stupid, but because it's just extraordinarily trite: http://www.reddit.com/search?q=nuclear+waste+sun&restrict_sr... ...variations include "why can't we put garbage in the sun", "why can we put nuclear waste in volcanoes", etc. It's a great question coming from a 6-year-old, but if an adult asks it, he's simply not the kind of person who will spend one second in critical th…

That is a ridiculous and insulting characterization of the audience and the answer.

This is a question that I've actually wondered about on and off over the years, and whatever you think of me for not knowing the answer flat-out, or for never having cared deeply enough about the topic to actually research the answer myself, I did very much appreciate an answer that looked at the actual physics involved, and that led to interesting follow-up questions about orbital slingshots and alternate destinations.

One of the college discussions I remember the most fondly was a night spent scribbling on napkins with physics majors over whether you got more wet if you walked more quickly through the rain, and why.

Not all questions have to be earth-shakingly brilliant to yield interesting and intellectually stimulating discussions.

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

#73
post #5

This is why you'd use gravity braking to do the work for you... You just have to change direction, not slow yourself down, as long as your path intersects the sun you're done... we have sent spacecraft to the sun... it's not beyond our technical capabilities. Basically, it's like flying into a banked curve... as long as you're pointed at the Sun when you exit the curve you're going to hit the sun with out needing to…

> Basically, it's like flying into a banked curve... as long as you're pointed at the Sun when you exit the curve you're going to hit the sun with out needing to bleed 30km/s.

That's not how it works. You're in the planet's reference frame so you inherit its orbital velocity. Exiting a slingshot in the direction of planet's retrograde (not in the direction to the Sun) you can kill off some velocity, but nowhere near enough to just drop yourself into the sun. You do need to bleed out that 30km/s to actually hit the sun.

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

#74
post #41

Use the Jules Verne solution: a cannon. A solar powered mass-driver could sling a steady stream of pellets from Earth orbit into Solar non-orbit using existing technology. That being said, burying it deep near the the start of a plate subduction zone makes at least as much sense.

What does "Solar non-orbit" mean? What would happen, if you managed to make sure all this stuff got escape velocity, is you would wind-up with a bunch of junk (literally) in an orbit around the sun that would inherently pass through Earth's orbit - as long as it doesn't have solar escape velocity, once a thing is moving on pure momentum, it is in orbit and since the orbit fairly closely an ellipse so the object will…

[deleted]

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

#75

Earlier quoted context omitted.

Your "trick" doesn't change any of the conservation of angular momentum considerations in the article. To "get rid of the remaining kinetic energy" would only result in the object getting escape velocity relative to earth. The object would never have "stopped" relative to it's orbit around the sun but even at it's further point would be traveling with fairly close to the same angular velocity as the earth (as describ…

I'm about 80% sure leni536 is right, from playing Kerbal Space Program.

Let me guess: the wonderful experience of putting a satellite orbiting in the precisely opposite direction to the one required by contract, noticing that your orbital velocity at apoapsis is like ~200m/s and realizing that you have enough delta-v to just turn around and reverse the orbit on the spot?

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

#76
post #41

Use the Jules Verne solution: a cannon. A solar powered mass-driver could sling a steady stream of pellets from Earth orbit into Solar non-orbit using existing technology. That being said, burying it deep near the the start of a plate subduction zone makes at least as much sense.

Specifically: Rail gun. Powered by nuclear power :-)

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

#78
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.

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

#79
post #3

Is there any way to use drag to decay the orbit? We don't have to reach the sun quickly . The solar wind is blowing past, is it possible to "sail" against that at an angle and - over time - dump orbital velocity and so end up in the sun?

Yes, using a magnetic sail - which is this case is more of a magnetic parachute:

http://en.wikipedia.org/wiki/Magnetic_sail

The easiest way to use it might be to apply it in the direction perpendicular to the dumptruck - Sun axis. That way, you don't pick up radial speed, but you do lose orbital speed.

Assuming, that is, that i've understood how a magnetic sail works.

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

#80
post #30
post #21

Earlier quoted context omitted.

The ~30km/s figure is what you'd need to drop it straight into the sun, no spiraling involved. Gravitational assists can help, but they can also help you get other places. Getting to the sun would still be ridiculously hard compared to the alternatives.

But that's is expending a whole lot of energy to "remove" earth's orbital velocity[1]. Why remove it when you can just deflect the rocket by the gravity of Venus and redirect the rocket directly towards the sun? Or are we missing something more fundamental? 1. http://www.wolframalpha.com/input/?i=orbital%20velocity%20of...

Gravity assists are helpful but they're not all-powerful. There's a hard constraint: your orbit is deflected more as you make your point of closest approach lower, but you can't make it too low without hitting the atmosphere. (Unless you actually want to crash into Venus instead of the sun; in which case, knock yourself out, but the moon is closer.)

Math time: a Hohmann transfer orbit from Earth to Venus will have 2.7km/sec of excess velocity when it reaches Venus. That means your orbit has a 44000km semi-major axis. With a closest approach of 6100km, that gives you a minimum eccentricity of 1.137; if I'm doing my trigonometry right, the most orbital speed you could lose in a single flyby is 4.2km/sec, or about 11% of your speed relative to the sun.

(See http://en.wikipedia.org/wiki/Hohmann_transfer_orbit and http://en.wikipedia.org/wiki/Hyperbolic_trajectory for details.)

You could do better with multiple carefully-orchestrated flybys, but the point is it's not as simple as just heading for the nearest planet and letting it fling you wherever you want to go.

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