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Comment by gataca | Hacker News Reader

Will this ever be safe enough to use as a hazardous waste disposal system? Can we just send the worst of the worst into the sun without too much risk of just spreading it out through the atmosphere in case of an explosion.

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Fun counter-intuitive space fact, it actually takes much less energy to send a space probe out of the solar system than it does to send one into the Sun. To fling something into the Sun you basically have to get rid of all the kinetic energy that was given to us from the Earth's orbit.

Even stranger still is the fact that you have more efficiency if you send the probe into the outer solar system first and then try to slow down. The Ulysses probe did this: https://en.wikipedia.org/wiki/Ulysses_(spacecraft)

Edit:

> "To fall into the sun a spacecraft would first have to escape the earth's gravity, and then after that slow down almost completely from the earth's orbital speed of about 30 km/s (~70,000 mph) around the sun. A four-stage, 3,000 ton rocket (about Saturn-V size) could only launch about 150 lbs into the sun on a direct trajectory, and it would probably cost a little more than $1 billion."

> "To escape the solar system and fly off into interstellar space, a spacecraft only needs to speed up from earth's orbital velocity by about 40% (instead of reducing it by almost 100% to fall into the sun). The required delta-v would be about 17-18 km/s."

From a simple HTML page with content written by a college professor, my favorite kind of webpage! https://van.physics.illinois.edu/qa/listing.php?id=43694&t=l...

No no no - I think we are all missing the point here - if I learned anything from the Superman documentary series then we should be flinging the toxic waste at a trajectory that makes it go around the sun in REVERSE which will also mean it of course will travel backwards in time. And then for sure we can say that is going to end up as someone else's problem.

If we send it back in time we can reverse the half-life too, think of the possibilities!

Half-Life 3 confirmed

How about crashing it into Jupiter?

That's certainly do-able and given that any spacecraft meant to leave the solar system would almost certainly use a Jupiter gravity assist it wouldn't be any more difficult to steer it into the planet itself.

However, if we were truly determined to get radioactive waste off of Earth and into space we could put it into an Earth escape trajectory and leave it in an orbit high enough so that it doesn't encounter the Earth again. That would save a ton of fuel.

We also have the option of impacting it into the Lunar surface. Radioactive waste is primarily a problem for us here on Earth because we have an atmosphere and a water cycle that causes particles to spread all around the ecosystem. But any waste left on the moon will stay put for billions of years because there's nothing to disturb it.

I did some back of the napkin math, USA generates about 2000 tons of nuclear waste a year[1] and it costs DOE half a billion dollars to store it[2].

Instead as you said we could yeet it all into space with like 20 starship launches, taking the $100/kg price tag it would cost us 2 million dollars to send it to space. Starship electronics should be radiation hardened so the unique payload shouldn't affect it much. The only risk is starship blowing up during launch. That would be a bummer.

There's already a paper discussing this[3].

I love the last line in the paper

'Both the technology and the need exist. What does not yet exist is the will and support of the engineering and political communities'

Mind you this came out in 1992, we have far better technology now.

[1]https://www.scientificamerican.com/article/nuclear-waste-let.... [2]https://earth.stanford.edu/news/steep-costs-nuclear-waste-us... [3]https://space.nss.org/wp-content/uploads/Space-Manufacturing...

Your math seems off, 1 ton is 1000kg, but your point still stands at $200 million plus the overhead of containment and transport to starship. This is far more economical that I expected.

But also this is the price to orbit. As the escape velocity is 1.5x higher we can probably assume the same or a greater increase in cost. Maybe you could just justify a really high orbit? It would take a long time for it to build up.

The main risk is taking off, you'd want something well protected and capable of surviving starship blowing up at any point during ascent, including returning safely to earth and impacting. You'd probably want to (unusually) launch over land - perhaps Alaska/Canada, to make retrieval easier should it fail before reaching orbit.

Once it's in a low orbit, the extra shielding isn't needed as much as it's not going to fall back to earth quickly, so boosting from there to a high orbit would reduce the mass needed to be transported.

In theory you could maybe do it for say $4b/yr all in.

How many orbital solar collectors could you use to concentrate energy and beam the equivalent energy currently produced by nuclear plants to a desert based collector?

Yeah, I didn't even consider this. But at what point does orbital solar energy start to make sense?

I wonder what the $/kg before we can just send up solar panels that last 100+ years and provide continuous microwave beams of clean energy to ground stations.

I imagine the risk of the rocket blowing up right after launch and scattering radioactive waste all over Texas would make this a non-starter.

Could we not put it in a thick lead box which is designed to survive explosions?

Thicker box = more weight = $$$. Plus is anything really resistant to thousands of tons of rocket fuel?

Sure, more weight but at the bargain price of $100/kg

Could it be resilient enough? I have no idea. I'm a programmer.

We already make containers that can tolerate being pummeled head on by freight trains without leaking, so I imagine that we could definitely engineer something similar for space travel.

Why don't they just make the whole plane out of the same material as the black box?

Isn't Uranium as sturdy as any material you'd pick to encase it in?

If Starship flies as much and is as safe as SpaceX predicts, they will have enough data to show empirically that Starships launches have an expected risk below 0.1% (i.e., it won't rely on theoretical models). That 0.1% isn't nothing, but it could easily be acceptable if the nuclear waste disposal Starship flight is launched from a sea platform (which is currently a planned Starship capability) in the middle of the Pacific. For instance, it's already been well argued that dilution of radioactive waste in the oceans could also provide a good disposal option, leading to a worldwide increase in background radiation that is much smaller than the baseline levels.

(There are a lot of important details here, including (1) the disputed argument that some isotopes might be preferentially concentrated by some organisms to high levels in any dilution scenario and (2) that an explosion of Starship in the Pacific would not dilute the radioactive waste as uniformly as a dedicated waste dilution program. My comment is just trying to point out that this could plausibly be acceptably safe and more careful analysis would be needed to check.)

But once it's launched it's a lot of potential energy lost for ever, no?

Isn't there part of this spent fuel that could be used as fuel again? I'm thinking MOX on steroids.

Weren't surgenerators supposed to 'recycle' and reduce drastically the amount if 'final waste'? Weren't next-gen fission plants supposed to take in even higher rates of spent fuel?

I believe France has the types of reactors you are talking about in use - from what I remember they still do end up producing some waste though.

I feel like we should probably save the stuff just in case we end up needing it eventually in the future. Could be some aliens out there that love the stuff!

Oh yeah, there'll always be waste but reducing it by orders of magnitude is the best waste management bet I can think of. Less mining in sketchy places too. 'my waste is my energy independence strategy' :-)

Perhaps life on Earth was a long-con destined for us to throw our nuclear fuel out into the stars for easy harvesting

I wonder if lining a spaceship in nuclear waste might actually end up blocking interstellar radiation (assuming the nuclear waste is not also irradiating you). That stuff is pretty dense right?

I imagine that building a breeder reactor could be cheaper per kilogram of nuclear waste it burns, while also generating energy instead of spending it.

> Will this ever be safe enough to use as a hazardous waste disposal system? Can we just send the worst of the worst into the sun without too much risk of just spreading it out through the atmosphere in case of an explosion.

I don't think it is impossible that launch capabilities become safe enough to lower the risk to something some people might consider acceptable. However the physics of it won't change. To even get into earths orbit we have to accelerate anything going up to an average of 7.8 Km/s, where to escape orbit to anywhere else it's 11.8 Km/s.

I think the amount of energy to do that will always be the primary reason why this just isn't practical. Assuming you are advanced enough to be considering this, I would hope that your society is stable enough for long term containment and processing.

A space elevator could fling it out to escape velocity if you can build the containment vessel to survive a fall at terminal velocity (way lower than orbital velocity). Energy wouldn't be a problem for a civilization with the capability of building such an elevator, as there's plenty of solar, and raising 1 ton to GEO uses a trivial amount of energy.

Launching into the sun is a VERY difficult achievement. So far we've launched one solar probe, and dozens of other probes. It launched back in 2018, and still has 3.5 years before it will actually reach the sun.

https://en.wikipedia.org/wiki/Parker_Solar_Probe

We don't actually much care about when trash would hit the sun. But yes, it's a huge delta v compared to just getting to orbit.

Adding a long duration deep space maneuvering system to allow the trash to precisely navigate the necessary gravity assists would also be far from feasibly economical.

Yes, for reference the capability of the Delta IV Heavy [0] (which launched the Parker Solar probe) is ~28,000 kg in to LEO. And the Parker solar probe [1] was only 685 kg. I don't know how close to the limit of the mass this is to get in to this orbit, but it still gives you an idea of the capability to get something to the Sun versus in to LEO.

[0] https://en.wikipedia.org/wiki/Delta_IV_Heavy

[1] https://en.wikipedia.org/wiki/Parker_Solar_Probe

It is, indeed, way cheaper to fling it into space beyond the solar system with the right planetary alignment.

Going to the sun is easy, going there fast is hard. You could put a tiny ion thruster on it and get it there in a million years

Throwing all our radioactive waste into space seems like a shortsighted waste of a non-renewable resource. Once humans pull it out of the ground there isn't a natural process on Earth to create more.

If it was put in a very high Earth orbit or solar orbit, it could be retrieved in the future, if desired.

Spacecraft that use RTGs have to do quite a bit to ensure that the risk of the radioactive contamination is low. It is pretty expensive both technologically and to go through all the regulatory hurdles. So I think getting to a place where this is feasible is still a very long way off.

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

Waste is just a resource we don't know how to use yet. Someday we'd regret throwing all that fuel into the sun.

I know this is beside your point, but launching directly into the sun requires more energy than throwing outside our solar system altogether, as Scott Manley nicely explains here:

https://youtu.be/i5XPFjqPLik

The launch of this material is probably safer than the transportation of that material to the loading/launch facility.

It's not, the probability of a SpaceX rocket spectacularly exploding is somewhere around ~1%. They'd need 860 more problem-free launches to hit ~0.1%.

The probability of a truck spectacularly exploding on its way to the launch facility is way less than 0.1%. In fact, it's astronomically lower than 0.1%.

You can't calculate probabilites that way when the process itself is improving.

> They'd need 860 more problem-free launches to hit ~0.1%

For what it's worth, SpaceX claims that they intend to reach this level of safety by literally performing thousands of launches. Time will tell if they can do that.

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