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Disposal of radioactive materials

Posted by: slycker - Thu Dec 02, 2004 10:33 pm
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Disposal of radioactive materials 
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Post Disposal of radioactive materials   Posted on: Thu Dec 02, 2004 10:33 pm
Hmm, it seems odd to propose this...
Disposal of radioactive materials is one of the main problems currently, with few viable and realistic ideas for a long-term solution. I have heard the idea of nuclear power being used for propulsion in long-distance space travel, and shy away from any suggestion that the depleted elements merely be ejected when used.

Anyway, here's my question:
If there is no such thing as cohesive nuclei in the sun's plasma state, rendering proton/neutron/electron/positron/etc content of an element irrelevant, would this massive fission reactor not be a perfect disposal site for radioactive materials? I know this may be a stupid idea... and no-one would want to play with the source of life for our galaxy, but I can't think of a single problem that could result from this. Yes, transportation is a significant cost and the vessel used would need to avoid obstacles on the way.

Are there any problems with disposing radioactive materials in the sun, or is the main concern merely the transport of said materials from their starting site (earth, wherever, moving huge masses of materials out of the earth's gravitational field) the main obstacle?


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Post    Posted on: Fri Dec 03, 2004 8:00 am
I doubt that that bit of extra radiation would harm anything up there. The universe is fileld with radiation, so as long as you dont do it too concentrated, it wouldnt be any problem imo (unless you can somehow cause a solarflame ;) ).


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Post    Posted on: Fri Dec 03, 2004 10:32 am
I think that the fear would be that in transporting the nuclear waste out of the earth's atmosphere, the vehicle may, like any other craft, have a failure which leads to the craft's loss, which could lead to radioactive material being spread all across the earth's atmosphere, with catastrophic consequences.

Mankind tends to prefer to put stuff out of sight, so even if we got it out of the atmosphere, we'd probably just place it on the nearest uninhabited place, e.g. the moon, or a passing large body/

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Post    Posted on: Fri Dec 03, 2004 12:06 pm
dolby_uk wrote:
Mankind tends to prefer to put stuff out of sight, so even if we got it out of the atmosphere, we'd probably just place it on the nearest uninhabited place, e.g. the moon, or a passing large body/

If time is not an issue* ... is it easier to send something to the moon or is it easier to send it to the sun?

DKH

*(aware that if time really was no issue, eventually the sun would grow large in its old age and swallow the earth, obviating the need to send anything anywhere at all)

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Post    Posted on: Fri Dec 03, 2004 2:22 pm
You are right that nothing we could put in the sun would effect it in any important way. The sun could swallow the entire Earth without a problem. However this idea will not work for other reasons.

Protesters oppose sending nuclear material even a few miles by truck. Huge protests were directed at the Cassini mission because a few pounds of plutonium were in the space craft.

Getting to the sun takes more energy than getting to another star, if you don’t care how long the trip takes. A proposed mission to fly very close to the sun involves using a Jupiter gravity assist maneuver.

The amount of material that would have to be transported would make the ISS project seem cheap by comparison.

The reason some people propose mining the asteroids is to avoid the high cost of getting tons of low value material off the Earth. You are proposing sending many tons of negative value material off the Earth’s surface to the hardest to get to place in the solar system. It makes no economic sense.


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Post    Posted on: Fri Dec 03, 2004 2:39 pm
campbelp2002 wrote:
Protesters oppose sending nuclear material even a few miles by truck. Huge protests were directed at the Cassini mission because a few pounds of plutonium were in the space craft.

feh ... why doesn't anyone protest the transport of bullets (which kill far more people than nuclear radiation)? I think all these protesters have little knowledge of what "real and present danger" actually means.

camper wrote:
Getting to the sun takes more energy than getting to another star, if you don’t care how long the trip takes. A proposed mission to fly very close to the sun involves using a Jupiter gravity assist maneuver.

Another star? I said "moon" (that's M-O-O-N, like in your avatar/icon thingy) in my question. The jupiter thing is interesting though, I wonder what the reason for doing that was?

campy wrote:
You are proposing sending many tons of negative value material off the Earth’s surface to the hardest to get to place in the solar system. It makes no economic sense.

Yeah but the original poster in his first post explicitly said he wasn't interested in ideas which took that into consideration. Which was, all in all, a smart thing to do in this thread.

DKH

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Post    Posted on: Fri Dec 03, 2004 3:07 pm
You are right, travel to the moon is MUCH easier than the Sun. I was trying to emphasize the huge energy cost of travel to the Sun by pointing out that it actually takes less energy to escape the solar system completely than to fall into the Sun.


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Post    Posted on: Fri Dec 03, 2004 3:30 pm
After a few minutes of searching I found the proposal for a solar mission.
http://sec.gsfc.nasa.gov/solarprobe/sol ... t_1999.pdf
The reason given for the Jupiter gravity assist is to lose its angular momentum about the Sun.


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Post    Posted on: Sun Dec 05, 2004 11:49 pm
After reading the NASA document, I understand the necesity of the jupiter gravity assist. What I can't seem to understand, though, is your assertion of how it would take more energy to reach the sun than another star. The difference in velocity between a LEO and escape velicity is about 2^(-2) (root two), and from that point on it seems to be an aiming issue. With the jupiter gravity assist to lose angular momentum around the sun (and thus save a LOT of time), some more kinetic energy will be lost. I can't understand, though, how this would add up to the order of magnitudes that is being mentioned.

The NASA mission involved two eliptical passes around the sun (requiring greater initial kinetic energy, I think), before the probe drops into the sun just over 3.5 years after launch. So, at maximum, it would take 3.5 years to reach the sun (yes, there's a very big mass difference between the probe being sent and the proposed waste cargo). The mode of propulsion and attitude control would pose a major problem, though, given the large mass of material being transported.

Perhaps it would be better to have the material initially stored on the moon, where the Fg experienced is significantly lower than the earth, and when enough material has accumulated, it may then be sent to the sun.

Regarding activists' concerns regarding the sending of radioactive materials out of the atmosphere, I don't think that I would be comfortable sending any large volume out of the atmosphere until the mode of transportation has a fairly reliable safety record, either.

Anyway, thanks for all the input on this topic!


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Post    Posted on: Mon Dec 06, 2004 9:50 am
slycker wrote:
After reading the NASA document, I understand the necesity of the jupiter gravity assist. What I can't seem to understand, though, is your assertion of how it would take more energy to reach the sun than another star.

I'm sorry? Who made this assertion? It wasn't me. It wasn't anybody. Your imagination continues to work overtime Slyk ... get some sleep.

Thanks for the explanations though, they are interesting and I learned stuff!

DKH

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Post    Posted on: Mon Dec 06, 2004 2:56 pm
slycker wrote:
After reading the NASA document, I understand the necesity of the jupiter gravity assist. What I can't seem to understand, though, is your assertion of how it would take more energy to reach the sun than another star. The difference in velocity between a LEO and escape velicity is about 2^(-2) (root two), and from that point on it seems to be an aiming issue. With the jupiter gravity assist to lose angular momentum around the sun (and thus save a LOT of time), some more kinetic energy will be lost. I can't understand, though, how this would add up to the order of magnitudes that is being mentioned.
!

You are correct that from any circular orbit you need only increase your speed to the square root of 2 times your current speed to escape. So low Earth orbit (LEO) at 17,500 MPH (this old guy still thinks in English units) times 2^(-2) gives the famous 25,000 MPH Moon trip speed. That is a speed change (deltaV) of about 7,500 MPH. Now we assume the deltaV is applied all of a sudden so that you are still at the LEO altitude and going 25,000 MPH, then you "coast uphill" away from the Earth, slowing down all the time. By the time you are about 200,000 miles from the Earth you are down to about 3,000 MPH (I'm not sure about the exact value of this number, but it is in the low thousands). At that point, if you are near the Moon, then you start accelerating toward the Moon, but if you are not near the Moon you continue to slow down relative to the Earth as you move away. But the Earth orbits the sun at 66,000 MPH so you may be nearly at rest as seen from the Earth but you are going 66,000 MPH as seen from the Sun, about which you are now in an approximately circular orbit. From the 66,000 MPH circular orbit you need 2^(-2) times 66,000 MPH to escape the sun. That is about 27,000 MPH deltaV in addition to the 25,000 you needed to escape the Earth's gravity. Now to crash into the Sun, you need to cancel the entire 66,000 MPH solar orbit velocity. So the bottom line is you need 25,000+27,000=52,000 MPH deltaV to go to another star and 25,000+66,000=91,000 MPH to reach the surface of the sun. Of course you slow down from that initial 52,000 MPH as you "coast uphill" away from the sun so it would take thousands or millions of years to get to another star. In that time the radioactive waste would have decayed to stable, non-radioactive elements. So not only are there no worries about "polluting" space, but sending the stuff out of the solar system is actually "cheaper" than dropping it into the sun. Of course dropping it on the Moon is even cheaper.


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Post    Posted on: Mon Dec 06, 2004 10:02 pm
DKH,
As usual, you were a bit quick in replying there. You didn't make that assertion, but campbelp2002 did. His reply does a pretty good job in explaining why it takes more energy to crash the materials into the sun than send it out towards other stars to decay. I got some sleep anyway, though, and it was great - thanks for the idea.

campbelp2002,
Your reply was very informative. What, though, of the effect of the jupiter gravity assist in changing the plane of the spacecraft's orbit to one that is perpendicualr to the sun - that is, effectively steering it straight into the sun. Wouldn't that drastically decrease the ammount of decelleration necessary? I'd imagine that it would have to be very precise so as to not 'miss' the sun (which would cause it to enter an orbit around the sun).

(or, perhaps more accurately, what if the JGA was used to sling shot the craft in a direction antiparallel to Jupiter's own orbit around the sun, effectively decreasing it's orbital velocity by a large factor?)


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Post    Posted on: Tue Dec 07, 2004 7:56 am
As far as I remember now the probe Messenger going to Mercury doesn't use any gravity assists outside Earth's orbit around the sun. Messenger needs several years to go to the mercurian orbit but not decades.

So it should be possible to go closer to the sun than the mercurian distance without gravity assists.

Do I remember wrong?

Up to a certain degree it should be possible to avoid to give the craft carrying radioactive materials a significant portion of Earth's orbital velocity by launching it from the orbit around earth backwards from earth - not 180 degree but less, much less to launch it deep into the inner of Earth's orbit.

I don't doubt your explanations campbelp2002 but it seems to be possible that there are additional reasons for the requirement of a gravity assist by Jupiter - unless I remeber wrong and Messenger uses a Jupiter gravity assist.



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Last edited by Ekkehard Augustin on Tue Dec 07, 2004 8:55 am, edited 1 time in total.



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Post    Posted on: Tue Dec 07, 2004 8:53 am
slycker wrote:
DKH,
As usual, you were a bit quick in replying there. You didn't make that assertion, but campbelp2002 did. His reply does a pretty good job in explaining why it takes more energy to crash the materials into the sun than send it out towards other stars to decay. I got some sleep anyway, though, and it was great - thanks for the idea.

Ack ... so he did. Looks like I need some sleep too. :oops:

DKH

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Post    Posted on: Tue Dec 07, 2004 2:54 pm
Ekkehard Augustin wrote:
As far as I remember now the probe Messenger going to Mercury doesn't use any gravity assists outside Earth's orbit around the sun. Messenger needs several years to go to the mercurian orbit but not decades.


Here is a link to the Messenger Trajectory.
http://messenger.jhuapl.edu/the_mission/trajectory.html
Although it does not use Jupiter is does use Venus, Earth and even Mercury itself. This looks like a VERY complicated trajectory to me, but I assume the planners of this mission know what they are doing.

The only other mission to Mercury, Mariner 10, used a Venus assist maneuver but did not enter Mercury orbit because it did not have enough propulsive power to do so. Here is a link to that mission:
http://solarsystem.nasa.gov/missions/pr ... Mariner_10
It seems Mariner 10 was the first flight ever to use gravity assist.

The reason Jupiter is a favorite gravity assist planet it it's huge gravity. I have to admit that when I first learned that the planned solar probe would go all the way out to Jupiter to get to the sun it made me stop and think and investigate. The idea sounded absurd to me at first but sure enough that is the lowest energy way to get to the sun.

And in answer to slyker on the various possible different Jupiter assist maneuvers, I don't know. It MAY be that the only maneuver that would place the space craft at the right distance from the sun required the plane change, but I don't really know. It is POSSIBLE they just wanted to go over the sun's pole for better science return.


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