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Why the sun is a poor dumping ground for nuclear waste (2010) (csicop.org)
207 points by gus_massa on Apr 13, 2015 | hide | past | web | favorite | 171 comments

> 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 velocity is by far not the optimal method to reach the Sun.

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)

> Solar escape velocity is about 16.5km/s

No, it's about 42 km/s, i.e., sqrt(2) times the Earth's orbital velocity around the Sun, which is 30 km/s. New Horizons was launched to take as much advantage of the Earth's orbital velocity as it could, so that the rocket didn't need to provide all of the 42 km/s of delta-v needed for solar escape.

(You could use the same trick for your scheme, of course. The main issue I see with your scheme is that it greatly lengthens the time that the waste is out in space.)

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

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.

Solar energy is simply a nuclear power system with a sensible waste disposal strategy.

But it also has not been approved by any authority. It is just like sending waste to some shady dude few blocks away "to take care of it"

The sun isn't the shadiest dude in the solar system.

I think leni536 is just addressing the kind of interesting problem of what it takes to shoot anything into the Sun.

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 described in the article etc).

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 solar radii (ignoring minor factors that make this case slightly different to the wikipedia example).

edit: to make it clear, I'm talking about a heliocentric bi-elliptic transfer after Earth escape, where the initial orbit is equivalent to Earth's orbit, and the final inner orbit can be imagined as one scraping the surface of the sun, but since the sun would destroy the craft, the final circularising burn is not required (in sloppy terms: hitting the sun on the edge would be easier than hitting it straight on).

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.


thats not how this manoeuvre works.

the burn to fall into the sun happens way before any possible return to earth if that orbit were not altered... all that happens is that you start near the earth - thats unavoidable because the rocket comes form the earth.

it will of course cross the earth's orbit on the way into the sun, but, with the exception of very small ranges of orbits the chance of hitting the earth on return is tiny, and easily avoided with some timing.

I'm aware of how a bielliptic transfer orbit works. See the long gap between burns 1 and 2 on the Wikipedia diagram? That interval is necessarily going to be more than half a year long, and potentially much, much longer. Spacecraft are pretty reliable once they're in space, but that's still a lot of time for something to malfunction. And if burn 2 doesn't happen, now you have tons of nuclear waste on an elliptical orbit that re-visits Earth's path every so often. At any given perihelion, the earth has only a small chance of being in the right part of its orbit, but eventually...

I'm not saying it's a big risk; the chance of a catastrophic launch malfunction is probably a lot greater. But it's definitely a long-term potential hazard that needs to be accounted for.

unless burn 1 has a very specific effect that thing is not going to return to earth, despite crossing the orbit. hitting a resonance by accident is pretty unlikely... one could say astronomically so :P

its hard enough to hit things when we want to

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.

No, he's right

A bi-elliptic transfer is used for transferring between two orbits around the same body. In some situations, this is more efficient than a straightforward Hohmann transfer, at the cost of taking much, much longer.

For a Hohmann transfer, you reduce the ship's orbital velocity relative to the sun, reducing the orbit's perihelion to somewhere inside the sun. That requires cancelling out almost all of the Earth's orbital velocity.

For a bi-elliptic transfer, you first increase the ship's orbital velocity relative to the sun, increasing the orbit's aphelion to somewhere in the outer solar system. That's your first Hohmann transfer, going apparently the wrong direction, but requires less than 40% as much energy as dropping it into the sun did. Then, at aphelion, when the ship's orbital velocity is lowest, you reduce the ship's orbital velocity to drop it's perihelion inside the sun. From that far out, and at such an eccentric orbit, that requires only a fraction of the energy it did from Earth's orbit.

The entire manuever, potentially, could be far more efficient than a direct transfer. It just takes far longer, and if the ship fails to make the second maneuver, it'll be left in an orbit that crosses Earth's orbit.

you don't understand the link yourself... there are no bodies mentioned.

its about transferring from one orbit to another with a large elliptical orbit inbetween, its very well established. (and e.g. something i am familiar with before googling it or looking at a wikipedia page)

I believe they're referring to a Solar radius orbit as the destination given by the article. Doesn't sound wrong to me.

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?

i think you are right based on a similar feeling from that game, but be careful with that intuition. how much delta-v do you spend lifting the orbit so that lowering the periapse is cheap?

For large orbital changes, substantially less than the niave transfer.

I always thought the biggest reason was that if a rocket carrying nuclear waste exploded in our atmosphere, it would be catastrophic. It's a lot less risky to just bury it underground and pray it never leaks.

Also cheaper.

The author acknowledges the existence of that argument, but then insists that the "real objection" is difficulties in orbital trajectories. I'll believe that's the real objection if we start considering sending nuclear waste on a comparably simple orbital journey into outer space.

Or bury the nuclear waste in oceanic trenches. It is out of the way and future generations won't stumble upon it when humans forget where they buried all this stuff.

This is how you start a war with Atlantis.

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


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

It's not about the actual radiation, that's easy to deal with. It's about the containers cracking or leaking and having that stuff floating around in the ocean, contaminating our food and the environment. Even the strongest container we can make is still susceptible to the corrosive effects of the ocean.

If you're going to bury it in the ocean, your best bet would be to bury it near a subduction zone. But then you have the earth itself possibly being the cause of the container cracks and leaks.

Define "know". Do we have it carved in tablets of stone from on high? No. Are we reasonably confident? Yes. There are already hotter things in the ocean (e.g. black smokers). What kind of effects are you worried about?

Is it a big deal if they break/leak? Are there any theoretical problems that I, as not-an-oceanic non-nuclear-waste expert, am not aware of? Not just over 5 or 10 years, but over hundreds of years? Are we able to monitor them for these problems? How difficult or expensive is it to fix any problems?

I ask because I genuinely don't know. I'd be OK with it if scientific consensus and consultation between the ocean and nuke people said we know enough about them to say there aren't issues. I don't want to just say "lets just dump them in a place I don't personally care about that's really far from me".

And if they do, they'd likely be able to handle it.

Every time the question of nuclear waste disposal comes up, someone is sure to say, “Why not shoot it into the Sun?” It seems so obvious.

Or we could get over our stupid fear of recycling. The stuff's only hazardous because we haven't taken all the energy out of it yet.

Nuclear fuel reprocessing is performed routinely in Europe, Russia and Japan. http://en.wikipedia.org/wiki/Nuclear_reprocessing

In particular, pyroprocessing (http://www.cse.anl.gov/pdfs/pyroprocessing_brochure.pdf), which can separate out all actinides forming the bulk of nuclear waste. The actinides can continue to be used as fuel in an appropriate reactor, leaving just small amounts of short-lived (<1000 years), highly-radioactive "ash" as nuclear waste. Importantly, non-fissile isotopes such as U-238 are continually recycled so that no energy is left unextracted.

This was nearing completion in the form of the Integral Fast Reactor (http://en.wikipedia.org/wiki/Integral_fast_reactor) at the Argonne National Laboratory, until it was cancelled in 1994 at the behest of President Clinton and John Kerry.

The reason for its cancellation? The belief that any nuclear reprocessing is bad for "nuclear proliferation". I cannot even comprehend the mental gymnastics required to justify shutting down vital research which didn't even produce isolated plutonium when the country possessed thousands of nuclear weapons and tonnes of weapons-grade plutonium. How the fuck would this have any affect at all on "nuclear proliferation"?

Note also that civilian reactor "waste" brewed for more than a month has a mix of plutonium isotopes that makes it entirely unsuitable for practical nuclear weapons. Yeah, you can get a bit more than a squib if you're e.g. able to dissipate 100kW of heat (!) from the Pu-238 that's used for deep space probes, but the Pu-240 that made Hanford reactor plutonium unsuitable for the planned "Tall Man" gun assembly bombs strictly limits the potential yield.

This is cargo cult science at best, call it an allergy to anything "nuclear". Sort of like how the government collects a huge tax on reactor "waste", used it to build the Nevada Yucca Mountain repository (temporary construction jobs are always popular, as is "free" money), but just somehow never is going to get around to actually using the place. Well, that might change when Harry Reid retires, we'll see (heh, never considered that he was roughed up so badly he lost the use of his right eye due to eeeevil corporate nuclear power types, instead of his brother or "the mob").

Japan doesn't seem to have a plant online at the moment (http://www.world-nuclear-news.org/WR-Rokkasho-start-up-delay... ).

La Hague apparently has 1/2 of the global light water reprocessing capacity:


That Wikipedia table is interesting, but it is hard to understand who is currently doing what from it. I think Japan is mostly sending their spent fuel to France.

One of the downsides of reprocessing is that it makes plutonium easy to separate out in a form that is good for making nuclear bombs. Therefore it represents a nuclear proliferation risk.

None of the countries that have developed nuclear weapons have gotten their plutonium from nuclear waste because there are much easier ways to get weapons grade plutonium.

Form the wikipedia page: "Ordinarily (in spent nuclear fuel), plutonium is reactor-grade plutonium. In addition to plutonium-239, which is highly suitable for building nuclear weapons, it contains large amounts of undesirable contaminants: plutonium-240, plutonium-241, and plutonium-238. These isotopes are extremely difficult to separate, and more cost-effective ways of obtaining fissile material exist (e.g. uranium enrichment or dedicated plutonium production reactors)" http://en.wikipedia.org/wiki/Radioactive_waste

As the wikipedia article points out a very good approach to deal with nuclear waste would be burn the waste in pyrometallurgical fast reactors like the proposed Integral Fast Reactor. (For background on the Integral Fast Reactor: http://en.wikipedia.org/wiki/Integral_fast_reactor)

Trying to throw the waste in the sun would be one of the worst possible imaginable ways of dealing with nuclear waste.

> None of the countries that have developed nuclear weapons have gotten their plutonium from nuclear waste

Just because someone hasn't done it before doesn't mean someone won't in the future.

You're also ignoring the larger threat to that plutonium; the issue that someone may not want to separate the contaminants. If they're making a dirty bomb, they don't care if it has contaminants or not.

You're also ignoring the larger threat to that plutonium; the issue that someone may not want to separate the contaminants. If they're making a dirty bomb, they don't care if it has contaminants or not.

So which is worse for that, having a fuck-ton of seriously nasty stuff sitting around forever, or concentrating the nasty stuff to a much more manageable volume and then fairly quickly shipping it off to be destroyed (in a way that just happens to provide useful energy out of the deal).

>Just because someone hasn't done it before doesn't mean someone won't in the future.

It isn't random chance that no one has developed nuclear weapons using nuclear waste from a commercial reactor. It is because it would be far more expensive, a far bigger engineering challenge and far more difficult to hide than any of the other ways to create a nuclear bomb.

>You're also ignoring the larger threat to that plutonium; the issue that someone may not want to separate the contaminants. If they're making a dirty bomb, they don't care if it has contaminants or not.

I didn't talk about dirty bomb because the original statement I was replying too was saying that reprocessing akes plutonium easy to separate out and was a nuclear proliferation risk. It is impolite to criticize me for not bringing up a different issue. In the case of a dirty bomb, it would be many times less dangerous than a nuclear weapon would be and there are many, many potential sources of material for a dirty bomb that would be much easier to obtain and work with than the waste from a commercial nuclear reactor.

As I said before, a very good approach to deal with nuclear waste would be recycle it.

Plutonium makes a rubbish dirty bomb, it's too heavy to disperse.

There's potential (no pun intended) in pyroprocessing to allow extraction of uranium only, leaving behind plutonium with the rest of the HLW that is hazardous to try to steal or be sneaky with.

For clarification, it's traditionally been PUREX (chemical separation) that is considered a proliferation risk.

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 :-)

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 return. As the article mentions, probably not when the earth return to the point. But if you keep throwing stuff "out there", the chances of a return are naturally going to increase.

i think he just means any old trajectory that doesn't come back...

its not a completely rubbish idea.

if you shoot the right way you could end up cancelling enough orbital velocity to intersect the sun before any return to earth.

The biggest problem with the cannon idea is that things traveling at that speed in the atmosphere tend to burn up before getting anywhere. And you get to start in the hardest part of the atmosphere to move in.

Unless you put the cannon on the moon. It's much easier to rocket to the moon than the sun. Now the railgun or whatever launcher doesn't have an atmosphere to deal with. Use the cannon to take away earth orbital velocity from the waste.

Throw in reusable rockets and... it's still really dumb. We have reactors that can make use of "spent" fuel - they're just not legal.

It takes more energy to send something to the moon than to send it escaping the earth.

Space elevator with a railgun at the top of it maybe makes sense.

>> It takes more energy to send something to the moon than to send it escaping the earth.

Sure, but far less than de-orbiting into the sun. Use the rocket to get to the moon-based rail gun where there is no atmosphere.

Given that the past years have "proven" that it's "perfectly safe" to set off hydrogen bombs in the desert; I think it'd be reasonable to assume that it's quite possible to launch a container of junk into space. Not sur why one would care if it hits the sun or not...

Iff one can make a container that can survive the blast/lift-off -- one wouldn't need to worry about the launch vehicle exploding in-atmosphere: there'd be no rocket fuel. Added bonus: find a way to use existing war heads, and combine with nuclear disarmament...

But that would carry the risk of the container filled with nuclear waste colliding with earth at some point in time. And considering there is over 200k tonnes of nuclear wastes, that risk would be a lot larger

Even if it were actually difficult to get to the sun, there are other options that are nearly as effective.

Jupiter would be just as good of a dump or we could just launch on an extra solar trajectory. Hell, we could just put it on a large, non-equatorial orbit around the Earth and it would be effectively gone with the added benefit of being able to recover it should we find a reason to. Space is a big enough place to dump an Earth's worth of trash.

The only problems are cost and the risk of explosion during launch.

Ehhh, orbit's not a great idea, especially lower-earth orbit. There's already enough space junk in our orbit right now that we're running the risk of an orbital chain-reaction. The chain reaction could take out most of our satellites. I'm sure radioactive waste in our upper atmosphere wouldn't be a good thing, either.


You are vastly underestimating the space of possible orbits and vastly overestimating the size of debris and satellites.

Or possibly you are overestimating the probability of impact beyond which this should be considered too risky.

Hey, Jovian here!

Sling yer 'ook and take your spent matchsticks with you!

It could be much lower than that if you take roundabout trajectories with gravity assists from Earth, Venus and Mercury. Not having to establish orbit is definitely a plus.

Besides, nuclear waste is still mostly unburned fuel which could be reprocessed and burned for power in special reactors.

>Besides, nuclear waste is still mostly unburned fuel which could be reprocessed and burned for power in special reactors.

That was my reaction. Future generations will want to use that stuff for fuel. There's no reason to launch it into space.

Well yes, it could be fuel in the future.

But at current in the US it is stored in holding pools all over the country. None of those are getting any larger, although they are frequently reworked to allow better use of the volume available.

Very little of it is 'weapons grade' and not many people have access to the equipment to weaponize it into a nuclear weapon. But turning any of it into a dirty bomb is trivial if you can steal it.

There is also the problem of accidents, why by definition are unavoidable.

So, you really do want to get rid of the fuel. Launching it into space is impractical. But it should be stored in a difficult to access facility where the chance of it escaping is minimal. The US federal government collected billions for the construction of such a facility, but it was never completed. So as a result, we have fuel scattered all over the US.

Oh, we definitely should open Yucca Mountain. Maybe with Reid out of the Senate it will happen. But we definitely don't want to "get rid" of it.

Yes, but unfortunately logic and reason don't factor into the decision making around nuclear energy policy.

People love to point scream and shout about the dangers of nuclear energy. In conversation I've noticed that people think of nuclear energy as interchangeable with nuclear weapons. Nuclear weapons are incredibly difficult to build compared to a nuclear fission reactor. The experimental data you need to build one either requires numerous tests or stealing it from a government. Nuclear reactors on the other hand, can be very simple. The simplest reactors are just lumps of radioactive material carefully bonded to thermoelectric devices! The biggest risk from a conventional nuclear reactor is a steam explosion and the dispersal of radioactive material. I reckon the second biggest risk is having tons (quite literally) of spent fuel laying around the country for no good reason. The storage ponds aren't 100%, accidents will happen. For most of the ponds if the cooling systems went offline the water would boil away and then the fuel would self-heat till it started to oxidize. At that point you've basically got hundreds of miniature fallout generators going. You better hope the structure above the pond is airtight because no one is going to be entering it again in this century.

The same group of people that scream and shout about nuclear energy being unsafe seem to actively ignore the dangers of conventional energy generation. For example, steam explosions are still a risk to the employees operating the plant. But I guess their lives don't matter? The pollution from coal isn't exactly helping the environment. Then there is this matter of what to do with all of the coal dust after it is burnt. You know, the same coal ash that over 1 billion gallons recently flooded an area of Tennessee. This contaminated a river, people's land, and destroyed their homes.

Even if we ceased 100% of nuclear energy generation today, we still need Yucca Mountain to deal with the spent fuel we already have. It seems that some groups in the US believe that if they scream loudly enough, the problems of the world will simply go away.

Also there is this issue of the fact that the energy consumers and the taxpayers already paid for the fucking thing but aren't getting any of the benefits. At this point it is basically just a boondoggle.

Anybody who's tried doing that in KSP knows how hard it is.

Back in high school I wrote a program that would let you pilot your ship in orbit around the earth and try to dock with things. I discovered just how annoying the physics of spaceflight can be!

Given the magnetic field of the Sun, one wonders if you could use a terminator tether [1] to get the remaining delta-v.

[1] http://arc.aiaa.org/doi/abs/10.2514/2.3565

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 assists greatly reduced the propulsion requirements.

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...

Well, we have done at least one Earth gravity assist with a nuclear payload in the past. There also was some criticism about it back then: http://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens#Plutoni...

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 bleed 30km/s.

The fundamental reason why it doesn't work is because it's really expensive get stuff into space...

If it was difficult to hit things with large gravitational forces we wouldn't see very many comets in the night sky...

Yup! It depends on whether you pass behind of or in front of the planet you're using to gravity assist. http://wiki.kerbalspaceprogram.com/wiki/Tutorial:_Gravity_As...

> 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.

> "If it was difficult to hit things with large gravitational forces we wouldn't see very many comets in the night sky..."

The difficulty does not come from the mass of the Sun. It comes from Earth's velocity around it. The waste starts out with that velocity as well. Basically the waste is already in a stable orbit around the sun, and getting it out of that is difficult.

It's not in a stable orbit around the sun...

If it has velocity to escape earth's gravity then it does not match earth and will eventually go somewhere else.

If it does not it will fall back.

Only at a Lagrange point will it not deviate from earth.

Given that it is not heading to earth we simply point it at an appropriate trajectory to intercept the moon and/or another planet using that planet to perform aforementioned "banked curve" which directs it to the sun at increased or decreased velocity.

The primary cost of shipping stuff to the sun is escaping earth, once you do that the additional fuel required to reach the sun is nowhere near the amount of fuel required to slow from 30 km/sec to zero.

Basically all we need to do is reach the moon... from there gravity does the work for us with the correct trajectory and a small amount of fuel to correct the trajectory.

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?

That's not how sailing works. The only reason you can sail upwind in a sailboat on the water is because you have a keel pushing against the water to prevent you from blowing downwind. Essentially, a sailboat sits on the interface between two fluids (air and water) that are moving relative to each other, and abuses that fact to go wherever it wants to. If you couldn't push against the water, or in the extremely unlikely case that the water and wind had identical velocities, you wouldn't be able to sail upwind. (Actually, if the water and wind had identical velocities, you wouldn't be able to sail at all. It would feel like no wind.)

To tie this back to solar sailing, there's obviously no fluid interface in space, so to the extent that solar sailing is possible, solar sailing "upwind" toward the sun is not.

There is a heliospheric current sheet[†], but it's not clear to me if/how it could be practically employed to achieve a sailing effect.

[†] http://en.wikipedia.org/wiki/Heliospheric_current_sheet

Don't use drag use gravity...


Basically you loop in front of a planet, and then it slingshots you back to the Sun.

Voila... done.

From my understanding, solar wind can only push the payload further away from the sun and there is no noticeable drag in space or the earth wouldn't orbit for very long.

You are probably thinking that you can sail upwind on a sail boat but it isn't the same in space. The boat's keel [1] and general shape keep it going straight which is necessary to sail upwind. That doesn't work in space.

Another factor is that a sail works much like an airplane's wing and isn't really 'pushed' by the wind. This allows the force to be perpendicular to the sail in some cases. To my knowledge (take this part with a grain of salt), solar sails works by receiving momentum as the photons hit. This could only push it away from the sun.


The force will be perpendicular to the surface light reflects from, not perpendicular to the light arriving at the surface. Therefore if the sail was mounted at a 45 degree angle to the Sun, there would be a force that reduces angular momentum and puts the object in a spiral towards the Sun.

http://wiki.solarsails.info/index.php/Tacking_Solar_Sails You can tack a solar sail so that it gets closer to the sun, but solar sails need to be very light to work at all... and nuclear waste is heavy.

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


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.

Solar wind won't help you but there are other ways of moving slowly - e.g. an ion drive.

For sub-millimeter particles, there is the Poynting-Robertson effect:


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.

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...

> "Gravitational assists can help, but they can also help you get other places."

Without gravitational assists, you need ~30km/s to drop into the sun, and far less to go other places. With gravitational assists both can be easier, but going to the sun will still be one of the harder places to go.

That aside, if you are going to loop it around Venus, why not just hit Venus? I'm sure Venus wouldn't mind.

Yes, I did read that. But what I didn't understand is why you were disregarding what seems to be a key part of interplanetary travel. The point that johngalt and I are making is that "falling" isn't the only way to get there.

Now, the real point seems to be that the Sun's gravity doesn't help you get there — in fact it works against you! You must rely on very precise calculations and instrumentation to target yourself there. So why not dive straight into another planet instead of using it for a gravity assist. That I can understand.

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.

> 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.

So, getting to the sun is actually really hard, the earth is moving around the sun at ~30km/sec. For comparison, a satelite in low earth orbit is only moving about 8km sec.

30km/sec is a LOT of velocity change, and you'd need to cancel practically all of it to actually fall into the Sun.

Way harder than getting to any of the planets.

Let me put it another way. If it is comparatively cheap to get to any of the other planets. Couldn't we just go to Neptune and stop our orbital velocity from there where it's only 5kms?

How about exiting planetary orbits retrograde? It seems like larger planets would have escape velocities that are larger than their orbital velocity. Why couldn't our space barge leave Jupiter's orbit on a trajectory that would intersect with the sun?

> Couldn't we just go to Neptune and stop our orbital velocity from there where it's only 5kms?

Yes. This is a bi-elliptic transfer, it's a standard technique, and another thread claims it would save about 40% of the required dV.

> How about exiting planetary orbits retrograde? It seems like larger planets would have escape velocities that are larger than their orbital velocity. Why couldn't our space barge leave Jupiter's orbit on a trajectory that would intersect with the sun?

It could. That's a gravity assist, and it's the only practical way to go just about anywhere with current technology (all our interplanetary probes do that).

(There are arguments against using either with nuclear waste, but I don't think the page is seriously talking about that)

If you're interested in this stuff, definitely play Kerbal Space Program.

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.

While the solar wind gets stronger closer to the sun, it's an r-square law that balances the r-squared force of gravity. Fun fact: If a solar sail could be in a fixed position at Mercury orbit then it could also be in fixed position a Neptune orbit.

Quoting from http://en.wikipedia.org/wiki/Solar_sail, the "total force exerted on an 800 by 800 meter solar sail, for example, is about 5 newtons (1.1 lbf) at Earth's distance from the Sun".

The Orion space capsule is ~25 sq meters. I'll round that up to 100 sq meters (I'm being generous), giving a breaking force of 5/64 N on the waste barge.

The capsule mass is 20 tons. Assuming the waste barge were the same mass (I'm being generous) gives a solar gravitational force in Earth orbit of 120 newtons. This far exceeds the push from solar wind, even with wildly optimistic numbers. (Note: there's some 50,000 tons of high-level nuclear waste in the US.)

So no, you couldn't lose a lot of velocity just braking against the solar wind. Not unless you've also developed effective solar sail technology.

Your calculations seem sensible, but you're only talking about radial forces, ie. countering the "downward" force of gravity with "upward" thrust of a solar sail.

But space flight maneuvers typically use tangential or almost tangential thrust. Slowing down or accelerating the orbital motion will cause the altitude to vary, preserving the orbital energy and angular momentum. Placing a solar sail in a 45 degree angle from the sun will change the orbit slowly but surely, as there will be a little tangential and radial thrust.

I still don't think it's viable for throwing anything into the sun, though.

I think it's viable. There are no other forces acting on you. Set up the solar sail at 45 degrees "against" your orbit. You will slowly but inevitably spiral into the sun without burning any fuel.

If you have effective solar sail technology then all my calculations are thrown out the window.

If you don't, then the time to spiral into the sun is large. Figuring 5/64 N on 20 tons and an orbital velocity of 30km/s gives

  t = v / a = 30 km/s / ((5/64) N / 20000 kg)
    = 245 years to cut the orbital velocity
This assumes all of the force could be used to slow the waste hauler. As http://en.wikipedia.org/wiki/Solar_sail points out, the force is cos^2(theta) so the actual time at 45 degrees is

  t = 245 * (sqrt(2)/2)^2 = 490 years.
The actual time will be smaller because you only need to hit the sun, and solar wind will get stronger. So, 350 years? As a wild-ass guess.

That same page points out that sails don't work much inside of 0.25 AU, because the temperature can exceed the material properties of the sail. Though I think if the apogee is inside of 0.20 AU it's good enough.

To make it worse, the solar wind fluctuates, so unless there's active control on the rocket, its orbit will be unpredictable over the centuries. When it's still near Earth orbit, or when it approaches Venus orbit, what are the chances of a gravitational assist leading to an Earth-return?

With 50,000 tons of high-level waste, and 15 tons per rocket => 3,333 rockets in uncertain orbits, the chances become much higher.

its not the only way, its just one way... there are other ways to increase the eccentricity of an orbit - increasing the orbital velocity at the right time, and in a direction that is not radial is less efficient but since the earth's orbit is nearly circular, its not by much.

this is essentially the brute force approach or the bielliptic transfers mentioned in other comments.

he is describing making it fall into the sun directly (if the 'burn' is instantaneous), or if you like, starting to spiral but then just falling in a straight line.

a slingshot changes orbital velocity... thats the whole point. you are right that it is possible to slingshot into an ellipse intersecting the sun... although setting up that manoeuvre itself would be pretty expensive.

This is all assuming that we don't have a space elevator.

tldr; it costs a lot of money to launch mass into space.

Sending 1 pound of water into space costs $50,000. This is more than the price of gold on earth. A space elevator changes the economics dramatically.

No, this is about the speed of the earth relative to the sun. E.g. even if we wanted to shoot, say, the ISS into the sun, it'd be hard. As soon as you point it towards the sun it will go into an elliptical orbit.

A space elevator takes care of a portion of the earth escape velocity, still leaving >20 km/s left once you get to the top.

I wonder.. would the spent rocket fuel generate more power in (an appropriate) power station than the original nuclear material?

(Assuming gravity assist is used)

I've been curious about his last paragraph for a while - send trash out into nowhere - and unless I'm being an idiot, it looks like we'd still be paying (at the author's implied Saturn-V costs) ~48 million USD per short ton of waste.

Compare this to Yucca Mountain's current cost of $9b for ~77k short tons of storage (~$117k/sh tn) and it's still pretty awful.

We do get the ongoing benefit of no upkeep and happy NIMBYs for spacebound waste, but there are always the downsides of making a mess in our space-backyard (what will the aliens think when they come to visit? How embarrassing. Almost as bad, what if it comes back a la Futurama or gets in the way of future endeavors) and losing access to that waste if we figure out a means of making use of waste in the future.

I don't think he is seriously suggesting that we blast nuclear waste out into space, only pointing out that it would be easier to do than throwing it into the sun. This emphasizes why "throw it into the sun" isn't a very good idea.

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.

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?

No, just the opposite. Given any position and velocity relative to the Sun (or the Earth), an object in that position at that velocity is in an "orbit" that will be a conic section of some sort. Most of them are ellipses i.e. stable. The only way to not be in a stable orbit is to go fast enough that it becomes a parabola or hyperbola - a flyby - or slow enough that the ellipse becomes so narrow that it's just a straight line (or rather, narrow enough that it hits the thing you're orbiting).

When you throw a ball it flies in a parabola, right? But actually that parabola is just one end of a very long, narrow ellipse, with the Earth's centre as one of the foci. If you could "turn on noclip"[1] and allow the ball to fall through the Earth, it would already be in a stable orbit.

(If you want to get a better intuition for this kind of thing, play Kerbal Space Program)

[1] And if the Earth were a point mass located at its centre, which it isn't. And ignoring air resistance.

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.

> 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.


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.

Ok, continuing the argument from the article and not discussing practical methods of waste disposal...

Instead of using chemical rockets for the entire dV how about using a rocket to get into orbit and then using an ion engine driven by solar energy to lose the additional 20km/s? It seems the "fuel" weight required would be significantly less.

You could swing by Jupiter and use the pull from that to bend the trajectory back to the Sun. That's what they did in practice for the Ulysses probe:


Offshoot topic but noting how things we launch from earth already have all the energy they need to orbit the sun, why isn't it really easy to get to earth sun Lagrange points? It seems like we could kind of just float over there since we don't need any additional speed to orbit the sun.

You can't just "float over" to another point along your orbit; to move the forward Legrange point you would have to slow down, causing you to drop into a lower orbit which moves around the sun quicker, then speed up to a larger orbit that intersects with the desired Lagrange point and then finally speed up again when you reach that point to stabilize the orbit.

To try this in Kerbal space Program: place two craft into the same equatorial orbit, but with one 1/6th of an orbit ahead of the other. Now make them dock.

It's both counter intuitive and easy once you know how.

Ok, that kind of makes sense. But as an extreme example let's say you moved out to earth sun L4 leaving from earth and moving at 1MPH*.

Once you got there, you're there besides station keeping. So in theory there's no deltaV required? That's what confused me.

Of course moving at 1MPH you'd be expending energy fighting earth's gravity until you got there. But I think that's a separate issue.

If you accelerate by 1MPH you're not in the same orbit anymore. It's not like driving on earth, where you can go faster along the same path by pushing the accelerator down; the speed you're moving at is a component of your orbit.

Could anyone here please explain why every time the rocket will return to Earth’s orbit and,the Earth won’t be there.

Does our solar system is constantly moving? Isn't it stationary with sun at center bending space and time and making planets to revolve around it?

This article just ruined every Star Trek episode for me where they fly a ship into a star.

To be fair, the problem here is that the waste is already in orbit (by virtue of being part of earth). His point is that if you want to hit the sun: don't orbit it. To stop an orbit around the sun is a hell of a job.

But if you're not orbiting in the first place: no problem.

Why does it have to be the sun? Why not just perpendicular to the sun/earth plane?

You'd still be in orbit, and would still cross the plane at regular intervals, so you wouldn't "get rid of it", as with flying out of the solar system or into the sun.

Just leave earth SOI, and the vessel will be orbiting the sun. the orbit will naturally decay in years/centuries/+

just try not to hit mercury too much. but even if this happens, not that big of a problem

Creating all that force ourselves isn't the only option. We could use gravity assists from Venus and/or Mercury to alter velocity directly towards the sun, too.

the article claims that the sun is super inaccessible compared to escape velocity, but they are extremely closely related. as an orbit gets more and more ellipitcal, the delta-v required to get the orbit to cut through the sun drops (for a well timed burn at aphelion), in the limit of escape velocity this delta-v vanishes to zero... the implication is that they are comparable in cost, if you were to use such a method to drop something into the sun.

And I thought the 11km/sec escaped velocity was intended to shoot rocket without any further fuel supply nor any air-resistant? No?

Just set it down at the south pole.

It draws some doubt that the author lists accelerations in units of km/sec, not km/sec^2.

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?

Accelerating at some rate km/ss for a period of s results in km/s. So the net result of "an acceleration" can be expressed as a velocity.

(what it comes down to is that "an" is an indefinite article and always modifies a noun and km/ss is described by the verb acceleration. Yay English.)

If i go from at rest (0m/s) to walking at 2m/s, I've completed an acceleration of 2m/s.

Delta-v is common in orbital mechanics, which is often referred as "an acceleration".

Superman can do it.

So can Jebediah Kerman.

"Technology solves all problems!" - every YC commenter

This is a crappy comment. It would have been funnier, though, if you had posted something like, "I could solve this with a Perl one-liner."

Why not just send it into deep space?

Sometimes rockets fail. I mean like they blow up on launch.

When the Shuttle was first commissioned, my concern at the time was that America's most reliable rocket was the delta, which failed every thirty launches.

When it's nuclear waste, it's not good enough just to have launch insurance.

> When the Shuttle was first commissioned, my concern at the time was that America's most reliable rocket was the delta, which failed every thirty launches.

You were right to be concerned. The shuttle had "a 40% vehicular failure rate and a flight failure rate of 1.5%", killing more people than any other space vehicle. [1]

[1] http://www.forbes.com/sites/carolpinchefsky/2012/04/18/5-hor...

And the space shuttles carried many more people than other space vehicles except for the current generation of Soyuz.

You don't measure failure rate by number built divided by number crashed. You measure by how much it's used. The more often something is used the more likely it it that it will fail one of those times.

> You don't measure failure rate by number built divided by number crashed.

Sure, you measure by number of launches divided by number crashed - or some similar measure that includes how much utility you get out of it. But the Shuttle does very poorly on any such measure.

The problem with nuclear waste is that you need a 0% failure rate or you might detonate a dirty bomb in the atmosphere. It doesn't matter how often it worked if it fails once.

Also it's a great target for sabotage for radicals.

> you might detonate a dirty bomb in the atmosphere

Which would put less radioactive material up there than coal power plants already do as a matter of course.

But it's a bit hard to say at which altitude the failure would occur. Plenty of rockets have exploded on the launch pad.

Sure, but the 1.5% flight failure rate is completely unacceptable when you're sending up hundreds of flights with humans on board. Surely, with all the safety precautions that NASA is known for, we'd be targeting a flight failure rate of << 1%.

omg....when I was 10 I wrote a story about how humanity takes nuclear waste to the sun. tl;dr results in nuclear apocalypse destroying the entire solar system.

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

That's not true - if your goal is to change minds or address a standpoint, treating the position fairly and giving a smart, reasoned, and respectful response to a charitable interpretation of your opposition's standpoint is the BEST way to proceed forward.

Were this universally the case, creationism would have ceased to have adherents several generations ago. Therefore, I submit that your position is only true for rational positions reached and held by rational people who are willing to be convinced by rational discourse.

"Why can't we launch waste into the sun?" doesn't really signal irrationality. If they prefaced it with "I believe the earth is 6000 years old and I wonder..." then maybe you'd have a point.

Most people don't have such ... strongly-held ... beliefs about rocket science as they do their origin.

I suspect you are correct.

I simply wished to make a point about the generality of parent's point.

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 after the moon is basically noise compared to the amount needed just to leave the surface of the earth (which is HUGE, as the author points out).

It's still probably cost prohibitive, but the delta-V required is a lot less than the author thinks.

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

Not true - sometimes a dumb question exposes confusion which when corrected reveals a smarter answer. Same reason testing works: if you're worried that your implementation (understanding) is wrong, put in malformed data (ask a dumb question) and see what you get out.

I would argue it's a waste not because it's stupid, but because it's just extraordinarily trite:


...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 thought, or in researching anything himself. So, yeah, not worth it.

You're right of course, we're free to determine how to spend our time. And you thought it worth yours to search for reddit discussions to post here to illustrate why you felt this topic not worth your time, perhaps as a lone beacon to guide future generations who might be tempted towards the folly of exploring questions which have answers you already know.

Discussing good explanations for a topic, no matter how common, is not a waste for anyone who is interested, especially any curious people who might currently be lacking the tools to solve it themselves. I don't believe any of us comes fully equipped.

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.

Just wait until parenthood...

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