Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

csicop.org

Post reply on HN
Print view View original

81–90 of 176 posts

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

#81

Post by jsprogrammer »

teraflop wrote: post #70
benjoffe wrote: post #67

Earlier quoted context omitted.

That "trick" would indeed work and is a well known orbital manoeuvre: http://en.wikipedia.org/wiki/Bi-elliptic_transfer (without the final circularising burn). This manoeuvre would be preferable to the article's alternative (a Hohmann transfer reducing periapsis to the sun's radius without the final circularising burn) in all cases where the initial semi-major axis (relative to the sun) is roughly greater than 11.94…

The downside, of course, is that your nuclear waste spends an awfully long time in an orbit that crosses, or at least passes very close to, Earth's. Better not lose control of your rocket, or you'll have a politically inconvenient situation on your hands.

More important than politically inconvenient: a technically inconvenient situation, as that waste could be on a trajectory back to earth.

https://youtu.be/YIqXql6LLz0?t=6m50s

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

#82

Post by kllrnohj »

johngalt wrote: post #17

I'm not rocket scientist, but it seems like the author is calculating a decreasing spiral into the sun rather than an impact. Why not slingshot around a planet and barrel into the sun with all of the orbital velocity still intact.

Because if the orbital velocity is intact you will perputally miss hitting the sun. The only way you can hit a thing you are orbiting is to remove all the orbital velocity (well, remove enough of the orbital velocity such that your orbit drops low enough to scrape the surface anyway).

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

#83

Post by InclinedPlane »

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…

To what end? To spend literally decades, perhaps centuries, with nuclear waste floating around the solar system? Why not just leave it in deep space to start with? Why bother sending it into space in the first place?

Meanwhile, if you succeed in sending nuclear waste into the Sun what do you think happens to it? It doesn't go away, it just gets vaporized and then scattered into the solar wind.

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

#84

Post by acadien »

maxerickson wrote: post #53
tesseract wrote: post #44

Earlier quoted context omitted.

If you read "delta-v" for "acceleration" throughout the article, the whole thing makes more sense.

The author always says "an acceleration", which is the same thing as delta-v. I have no idea how particular it is to phrase it that way, but it isn't confused.

The author says multiple times: "an acceleration of [X] km/s is required", maybe they meant to imply that the magnitude of the change of the velocity?

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

#85

Post by kllrnohj »

3JPLW wrote: post #30
Crito wrote: 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...

> Why remove it when you can just deflect the rocket by the gravity of Venus and redirect the rocket directly towards the sun?

The fundamental thing you are missing is that to point the rocket directly at the sun required removing all of the orbital velocity. If you were to just point a rocket directly at the sun ignoring its relative motion and burn you would never actually hit the sun. You would just burn forever and never make any progress.

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

#86

Post by joe_the_user »

benjoffe wrote: post #67
joe_the_user wrote: post #61

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…

That "trick" would indeed work and is a well known orbital manoeuvre: http://en.wikipedia.org/wiki/Bi-elliptic_transfer (without the final circularising burn). This manoeuvre would be preferable to the article's alternative (a Hohmann transfer reducing periapsis to the sun's radius without the final circularising burn) in all cases where the initial semi-major axis (relative to the sun) is roughly greater than 11.94…

Sorry, your link doesn't mean what you think it means.

What you're missing is that both waste and the earth are already in orbit around the sun whereas the maneuver your link describes involves switching between orbits around different smaller bodies.

Edit: Which is to say as the other have mentioned, this doesn't send the waste into the sun (as the parent post implied) but merely on some orbit similar to the earth as the article described.

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

#88

Post by benjoffe »

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.

Where did you get the "0.5-1%" figure from? That may be true in some cases, but not in this extreme case, here it's closer to half the delta-v (which, due to the rocket equation is enormously less difficult to achieve).

Solar escape velocity is about 16.5km/s* , and since ~99% of this manoeuvre's delta-v budget is used at launch the entire delta-v cost is asymptotically this value.

*http://en.wikipedia.org/wiki/New_Horizons#Launch (see paragraph 4)

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

#89

Post by rosser »

rrss1122 wrote: post #33

We can make it to Mercury. In fact, putting a spacecraft in orbit around Mercury is made more difficult because of the need to decelerate against the Sun's gravity. If you look at the Wikipedia page for the MESSENGER mission, you'll see they tackled that problem by using gravity assists from Earth, Venus, and Mercury to reduce MESSENGER's relative velocity with Mercury and allow it to go into orbit. These gravity ass…

I'm not sure how much I like the idea of using the Earth for a gravity assist on a nuclear waste payload. Getting that one wrong (anyone remember the meters vs. feet debacle with a Mars probe?) wouldn't end well...

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

#90

Post by Terr_ »

kllrnohj wrote: post #82
johngalt wrote: post #17

I'm not rocket scientist, but it seems like the author is calculating a decreasing spiral into the sun rather than an impact. Why not slingshot around a planet and barrel into the sun with all of the orbital velocity still intact.

Because if the orbital velocity is intact you will perputally miss hitting the sun. The only way you can hit a thing you are orbiting is to remove all the orbital velocity (well, remove enough of the orbital velocity such that your orbit drops low enough to scrape the surface anyway).

The sun's pretty big... And if you're worried about overshooting, you could probably lose a lot of velocity just braking against the solar wind.
Post reply on HN