Andy wrot:
>> RE: Decaying Orbits.
>>
>> There is no such thing as a decaying orbit!
>
>
>Yeah, yeah, technically. How about "an orbit with orbital
>momentum under escape velocity"
>
>> OK, here's what happens if you try to shoot a rocket into the sun.
><snip>
>
>so it takes a decade to actually hit the sun..not like we need a
>huge thrust then, is it?
No. If you reduce the angular momentum you don't fall into the sun or
spiral into the sun, you simply change your orbit around the sun. You
put yourself into an elliptical orbit with ahelion at Earth's orbit and
perihelion at some lower point. Think about the orbit of Halley's
comet: it goes waaaay out into the outer system, then drops down close
to the sun where part of it vaporizes and makes the coma, then swings
back out into the outer system.
If you simply kill some of your angular momentum, you put your waste
rocket in an elliptical earth-crossing orbit. It won't ever hit the
sun but will keep orbiting the sun forever in an elliptical orbit.
Well, not forever, since as Alberto pointed out there are other
considerations...interactions with the other planets, solar wind, etc.
But typically these are very small components. The probe will fall
towards the sun, but it will always miss!
The other problem is that a rocket, by definition, only has so much
reaction mass. Which means that it can only change its velocity by a
fixed amount, that is determinable at the time the rocket is launched.
Each rocket has a fixed amount of delta-v, which is determined by the
ratio between its mass and the (mass*velocity) of the reaction mass.
Think of it as a canoe full of rocks. You power the canoe by throwing
rocks out the back. Each throw pushes the canoe forward with exactly
the same energy you threw the rock with. So the only way to increase
your delta-v is to throw the rocks harder or to carry more rocks. But
carrying more rocks is a problem, since each rock you carry means that
most of the energy of the rocks is devoted to moving the rocks. Not a
good idea.
The point being that a rocket only has so much thrust, and that thrust
is known beforehand. So, a rocket with enough thrust to hit the sun
may not be possible. I *think* we can't build rockets with that much
efficiency yet. Now, the obvious workaround is to use the
gravitational slingshot.
>> But it would still be much much much much much much cheaper
>>simply to
>> vitrify it in glass bricks and stack it in some old mineshaft or
salt
>> dome.
>
>Until some idiot, 1000 years later dugs it up, yeah. *winces* Or
>when the site gets smashed by an earethquake and groundwater
>gets radiated. Not to mention the politics...
There are plenty of places in the world that are so geologically stable
that they haven't had earthquakes for millions of years. And even if
you had an earthquake, that won't contaminate the aquifer if there is
no aquifer where the stuff is buried. And you can bury it deep enough
that it would take 20th century technology to excavate. And this only
has to be a few sites. What if some idiot digs up an old containment
shell? If we're positing the collapse of civilization here, then the
nuclear plants themselves would be orders of magnitude more dangerous
than a burial site hundreds of meters deep in a remote location.
If we are positing that civilization does NOT collapse, then there is
no problem. Besides the levels of radioactivity will be much much much
smaller within several hundred years. We agree that uranium is
radioactive, right? But it really isn't very radioactive, it's
half-life is very long. The really dangerous radionuclides are
dangerous because they put out a lot of radioactivity, right? Well,
that means that they have a short half-life. A short half-life means
that they will be half as radioactive at the end of that half-life.
Then a quarter, then an eighth, etc. So, really dangerous ones will be
gone quickly. Not so dangerous ones will last a long time, but won't
be so dangerous. Look, there's already tons and tons and tons of
uranium in the earth's crust. Why isn't that considered dangerous?
The danger comes when the uranium is concentrated, which is what they
do to power nuclear power plants. But that doesn't increase the total
amount of radiation on earth, it merely concentrates it in a few
specific spots. If those spots are shielded, and no one goes near
them, then there is no more danger than there was before.
The cheapest way of sheilding them is with dirt. And the simplest way
of putting them where people don't go is to put them deep under a lot
of dirt. Yes, tunnels are expensive. But we tunnel very very deep in
coal mines every day, for very small profit margins.
But you are right, politics is what it is all about. That's why we
don't have safe, cheap and effective nuclear waste disposal. Nobody
wants the stuff in their backyard, and we insist on a zero risk for
nuclear power which we don't insist on for any other technology.
Now, about the safety of nuclear power, and the economic viability of
other power sources. Jeroen complained that people have many times
higher cancer rates near nuclear power plants, but that it was being
kept secret. I highly doubt it. First of all, France and Japan have
the biggest nuclear power programs of any countries. Do they have much
higher cancer rates than other countries? Look, epidemilogic models
are pretty well developed. If cancer rates could be corrolated with
distance to nuclear power plants, then that would be very easy to show.
I think what Jeroen is refering to are so-called "cancer clusters".
Several people in an area are diagnosed with cancer, and some
environmental effect is blamed...power lines, nuclear power plants,
pollution, etc. But, statistically, cancer clusters are to be expected
if cancer distribution is random. If five people who live near a power
plant get cancer that doesn't show that the plant caused the cancer.
What would show that plants cause cancer is to show that cancer risk
increases with distance to a putative carcinogen. For every "cancer
cluster", one should be able to find a "cancer uncluster"...a sample
population with the same exposure that has cancer rates that are below
average. Now, if one *can't* find this, then statistically one will
see that cancer rates are indeed higher the closer you live to a power
plant. But I believe that this has NOT been shown to actually be the
case. Otherwise, we'd already see it.
This has nothing to do with pro-nuclear propaganda vs anti-nuclear
propaganda. There are plenty of people who study cancer that have no
real bias for or against any particular form of power generation,
namely doctors. I am fairly certain that even nuclear workers do not
show higher cancer rates than the average population, perhaps Dan has
some statistics to support this. If nuclear workers have cancer rates
indistinguishable from the background population, I can't believe that
simply living near a nuclear plant could increase your cancer risk.
=====
Darryl
Think Galactically -- Act Terrestrially
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