Assuming it costs $10mil per mg in a highly efficient production scenario and you need 10^9 grams for “fast” interstellar travel means this probably isn’t doable.
I guess there’s just no getting around fact that an antimatter reaction that creates 9x10^10 MJ/kg requires more robust electrical generation capabilities than we currently have (I.e fusion)
Aluminium was once more costly than gold or platinum, and bars of aluminium were exhibited alongside the French crown jewels at the Exposition Universelle of 1855.
The fact that something is ludicrously expensive today when manufactured in ultra-small quantities says nothing about the cost if humanity goes all in on mass producing it.
A different process for extracting metal from ore is hardly a new idea, it just took implementing the technology for bauxite. Producing antimatter without spending a ton of energy doing it is much more baked into the fundamental nature of the physics we understand today, and which has been very well tested. We already know what produces antimatter, and in ultra-lay terms it's "Pack so much energy into such a small space that pair production occurs."
The only really conceivable shortcut for antimatter would be the discovery of large quantities of it somewhere close enough for us to essentially mine it. We've looked for the gamma signature of matter-antimatter annihilation in space, and we don't see it anywhere.
So it isn't IMPOSSIBLE for antimatter to become affordable, but it's extraordinarily unlikely. If we want some sort of superior rocket, it's probably going to have to involve either some unforeseen tech, or our ability to spend planetary energy budgets on rocket fuel.
How many orders of magnitude has the price of aluminimum come down? 3? 4?
It says that a Rand study says they might be able to bring down the cost to "$6.4x10^10 per gram" with a dedicated factory. That is still so many orders of magnitude from anything financially feasible.
I don’t disagree. But the point I’m making is that antimatter is essentially an energy store. If you can’t find enough antimatter, you have to make it.
And assuming the laws of energy conservation holds up, you need to find a better way to generate the electricity that is being used for antimatter production.
There are no streaks of gamma radiation (or any sort) going across the Milky Way connecting the stars.
The second issue is less obvious - the Milky Way is some 13 billion years old, has hundreds of millions of stars, but is only 100,000 light years across. Fact - the technological limitations of "today" (this century, this mya), are with empirical certainty not relevant.
Interstellar voyage is not amenable to the time preferences and capabilities of the great ape. The only stuff that could transport life across the galaxy does so slowly and without propulsion.
Well, think about it. In fusion and fission, you're only converting a tiny tiny fraction of the atoms' masses to energy. And then to make antimatter, you want to reconstitute this tiny fraction as entire particles.
IANAP (I Am Not A Physicist) but it seems like the only "realistic" way to create lightspeed-propulsion quantities of antimatter might be to convert entire planetoids and planets to iron.
This is absolutely fascinating, though this isn't my field. Are any of the concepts presented feasible? Is mass-production of antiprotons on Earth realistic?
In the sense that we can currently produce and store some millions of antiprotons at a time, using a proton accelerator "merely" around 200m in diameter. Not in the sense that it would be anywhere near feasible to produce and store even a microgram worth of antimatter.
Some particles, such as protons and electrons, have an 'anti' version. When a particle meets its anti-version they annihilate, releasing energy in accordance to their mass (with the famous E=mc^2 formula).
It's still a bit of a mystery why there was more matter than antimatter when the universe began.
Yes - you can measure the mass and electrical effect of a positron just like you can measure the mass and electrical effects of an electron (a positron is perfectly equivalent to an electron in all known ways except that it has positive charge instead of negative charge, so it would be repelled away by an atomic nucleus, and it would be attracted by an electron).
The anti positron is literally the common electron. If you want to learn more about the subject I would recommend wikipedia, it has a lot of information about quantum mechanics.
Each charged particle in the standard model has a corresponding anti-particle that is (as far as we know) identical to it in all ways except the sign of the charge. The electron has the anti-electron, also called the positron. Each kind of quark has a corresponding anti-quark, and these can form an anti-Proton. There are muons and anti-muons, tau and anti-tau, the plus and minus W bosons are each other's anti-particle.
There is nothing mysterious about anti-particles, they have all been observed directly, and they simply have the opposite electrical charge. The one thing we don't understand is why there seems to be so little antimatter in the universe, despite antimatter behaving identically to matter as long as the two don't meet. This could just be a fluke of the matter distribution in the early universe, but it could also indicate that there is a difference we don't know about.
For the most obvious difference, if you apply two waves to the same chord with the same phase but opposite frequency, the result is a chord which doesn't move (destructive interference). If you collide an electron and a positron, the result is an explosion with the maximum possible energy for their mass (mc²).
Also, you can actually do the phase cancelation experiment with two electrons, as they can behave as waves, and you will get the same cancelation as you do with audio waves - except the net electrical field will be 0 instead of the string not moving.
What do you mean the electron was never directly observed or measured? It is perhaps the single most accurately measured object in the world. We know all measurable properties of an electron to a much better degree of accuracy than, say, the size of a chair. We can predict with much much much more accuracy what will happen if you fire a beam of electrons at something than if you fire a tennis ball cannon.
Antimatter moves mass not space. Its a no-go because of all of the issues--time dilation? You need to move space, but we still haven't found a way to fully create negative energy.
I believe they’re saying that antimatter functions, essentially, as a normal fuel (although an amazingly dense one, far surpassing the energy density of anything else we’ve ever used as a fuel). But it, ultimately, has all the drawbacks that are inherent to “normal” fuels.
But there have been proposals for other ways of traveling through space, that involve manipulating space itself, so the distance between point A and point B are smaller. Think of wormholes, or similar. One such proposal is the Alcubierre drive, which warps space around it to cause the total distance traveled to get from point A to point B to be much smaller.
But such exotic drives require exotic forms of matter that we have no evidence of
Time dilation is not necessarily a problem, it can even be a boon - depending on exactly what you want to obtain. In particular, time dilation means that you can have a crew that actually lives for the duration of a journey that takes hundreds or even thousands of years from our point of view (e.g. in an accelerated space-ship).
If we had ham, we could have ham and eggs, if we had eggs. Another classic "this will be easy as long as we have unobtanium" concept.
I've been baffled, though, by the insistence on this kind of antimatter production. Antimatter production is inherently expensive because we are fighting conservation of baryon number, conservation of lepton number, et al.
Physics does have one theoretical method around this, which never seems to be addressed for these proposals, and that's the baffling issue of black holes having no hair. You throw whatever past the event horizon, all that is conserved is mass, angular momentum, and charge. Baryon number, lepton number, strangeness ... all lost. Re-emission as Hawking radiation, it is thought, would simply be this sort of thing, redistributed without regard to what went in, so long as mass, angular momentum, and charge are accounted for. You would conceivably get out as much antimatter as matter.
Now, that's worth looking at. And not from a "we JUST need to capture an itty black hole" (the word "just" does an enormous amount of lifting here) perspective. Rather, passage through the event horizon somehow strips off (we think, some think it might be preserved in some fashion) all of the variables which account for matter versus antimatter. And yet the event horizon isn't a hunk of matter, it's a ... membrane, a boundary, generated by matter at some distance (as a function of our usual three variables). Somehow, this warpage of spacetime operates on matter, shaving it so it has no hair.
That's what fascinates me, in the sense of the theoretical having some extremely juicy practical results.
> Baryon number, lepton number, strangeness ... all lost.
Even for classical black holes I don't think that's the consensus among physicists. The general assumption seems to be that quantum numbers are still conserved when you throw stuff into black holes, just like electrical charge.
Now, as for Hawking radiation, it's worth pointing out that Hawking's calculation only works for large black holes (low curvature near the event horizon). Once a large BH has shrunken down to a tiny BH (-> high curvature at the event horizon), the calculation no longer works and it is unclear what will happen. Some people say the BH will evaporate completely, some say there will be a remnant – who knows. (Both solutions have their issues.)
All in all, I'm skeptical of the "shaving" you describe.
It's right there in the Wikipedia article on the No Hair Theorem:
"Suppose two black holes have the same masses, electrical charges, and angular momenta, but the first black hole was made by collapsing ordinary matter whereas the second was made out of antimatter; nevertheless, then the conjecture states they will be completely indistinguishable to an observer outside the event horizon. None of the special particle physics pseudo-charges (i.e., the global charges baryonic number, leptonic number, etc., all of which would be different for the originating masses of matter that created the black holes) are conserved in the black hole, or if they are conserved somehow then their values would be unobservable from the outside"
Now, this is all still hypothetical, as we haven't a black hole on hand, but this has been the mainstream view on black holes for decades.
Wasn't LHC supposed to create the occasional microscopic black hole? What are the logistics on capturing one of those, keeping it fed, and making some definitive observations?
> Wasn't LHC supposed to create the occasional microscopic black hole?
That was discussed but AFAIR nobody really believed this was actually going to happen.
> What are the logistics on capturing one of those, keeping it fed, and making some definitive observations?
Generally speaking, the logistics are that you hope that will never create a black hole. You can't really "capture" a BH: It will fall down (towards Earth) like everything else and then start eating its way to the core…
Unless… you manage to create an electrically charged black hole. Then you might be able to confine it e.g. between two condensator plates, by calibrating the voltage in such a way that electric and gravitational force on the BH cancel out.
Now, one problem would be that we expect small black holes to radiate heavily (Hawking radiation), meaning we would have to keep feeding the BH to prevent it from evaporating. (Unless we believe in black hole remnants, see my other comment.) This whole endeavor would make stabilizing the BH between the condensator plates much more challenging. And we'd also still have to worry about what all that radiation will do to our equipment…
-anti-matter is incredibly difficult to produce (the total produced so far in labs is about enough to boil 1 litre of water)
-anti-matter is incredibly expensive to produce (currently around 1 trillion USD per milligram)
-anti-matter is very difficult to store and manage
-a lot of the energy will be given off as high energy gamma rays, which will be difficult to convert into thrust
-the high energy gamma rays will be very destructive to the spacecraft and crew (biological or robotic) without lots of shielding
-over a ton of anti-matter would be required to get a ton of payload to a nearby star at ~40% the speed of light
So don't start saving up for a ticket on an anti-matter spaceship. Or maybe do start saving, so your ancestors can take advantage of compound interest to buy a ticket in a few millenia, if we ever manage to develop the technology.
1/1 Fuel/Payload to hit 40% C is why it's going to be a trope forever.
In Count to a Trillion, a small group found a way to siphon antimatter off a natural source and effectively ruled the world forever due to the near limitless energy and fast interstellar travel.
I think the issue is more the cost of the anti-matter than the fuel to payload ratio. Chemical rocket people can only dream of 1:1 fuel to payload. Look how much Saturn V + fuel to took to get a tiny payload to the moon and back.
> -over a ton of anti-matter would be required to get a ton of payload to a nearby star at ~40% the speed of light
It all sounds awful until you get to this line. What are the equivalent numbers for fusion? All else being equal, 250 tons of fuel per 1 ton payload? And that payload has to include the reactor and storage and shielding and everything.
Yes, but hydrogen is cheap. Especially compared to anti-matter.
Shielding is also going to be a huge issue for anti-matter drives (even without a human crew). Anyone know how the energy of EM radiation emitted from a fusion reaction compares to that emitted from an matter:anti-matter reaction?
Probably only space based antimatter production makes sense, the risk of blowing up the most expensive and dangerous stuff on Earth is just too big. Fusion sounds like a clear winner as opposed to antimatter.
I assume any future antimatter based propulsion would rely on some sort of metastable particle pair that are made up of matter-antimatter components like protons, except one that can be more easily/efficiently split and recombined. Otherwise the factories will just blow up the first time there's a serious accident or containment failure.
Just as an example: imagine particle A made up of up, bottom, and strange quark and particle B made up of down, charm, and top quarks (I'm ignoring charge) that can be stored without interacting. The engine splits them into quarks that then can annihilate each other (AFAIK that's not how quark plasmas work but you get my drift).
I think hydrogen can be simply found in space, along the way. Not sure about the concentration of deuterium and tritium. I suspect once you get to 1% of c, you can find enough.
If you need to lift all the fuel from Earth, sure, antimatter all the way. Although, they already suggest making it in space for some reasons.
> I think hydrogen can be simply found in space, along the way. Not sure about the concentration of deuterium and tritium. I suspect once you get to 1% of c, you can find enough.
That's called a Bussard ramjet. Long story short:
> A 2021 study found that, while feasible in principle, the practical construction of a useful Bussard ramjet would be beyond even a civilization of Kardashev type II. [1]
The only way to go is to go is slowly and by not sending a ton, ie inject genetic material into a rock that's already on its way, hope for the one in a trillion chance that it takes root somewhere. That we're so alone in the galaxy is proof of this.
I don't think there is any real advantage of matching velocity with a rock and transferring material to it, compared to sending your own spacecraft at that velocity.
A big rock with its own momentum is more likely to come down on the surface (wherever it is) intact enough. But yeah there may be other ways to spread our seed. My point is that it will unpropelled for most of the journey, and a seed not an ape.
I think we have all knowledge we need to produce and store it much more cheaply.
It’s just that governments and research institutions don’t have that incentive. Look how fast reusable rockets, and fairing reuse happened once money was on the line. (To use some space examples)
> Or maybe do start saving, so your ancestors can take advantage of compound interest to buy a ticket in a few millenia
My apologies if this is off-topic, but I have recently read and heard a couple cases of "ancestors" being used instead of "descendants", which has sparked my curiosity. Is this a common brain-lapse result?
obviously it's not relevant to our interests for probably hundreds of years still, but it's a very conceptually simple proposition:
1. antimatter is incredibly energy dense, so would be an excellent fuel.
2. there's essentially none of it sitting around, so we need to make it, which takes lots of energy, but that's fine - it's an energy transport system, not an energy production system.
3. just set up square kilometers of solar panels in orbit around the sun or Mercury, use them to power particle accelerators which produce antimatter.
the sun emits enormous amounts of energy - we don't need some magic new energy source, just magic new ways to temporarily bundle up energy in a dense form.
edit: someone did the maths[0]:
> Where will we get the energy to run these magic matter factories? Some of the prototype factories will be built on Earth, but for large scale production we certainly don’t want to power these machines by burning fossil fuels on Earth. There is plenty of energy in space. At the distance of the Earth from the Sun, the Sun delivers over a kilowatt of energy for each square meter of collector, or a gigawatt (1,000,000,000 watts) per square kilometer. A collector array of one hundred kilometers on a side would provide a power input of ten terawatts (10,000,000,000,000), enough to run a number of antimatter factories at full power, producing a gram of antimatter a day.
from TFA:
> Preliminary mission analysis:
> - 10 kg instrument payload could be sent to 250 AU in 10 years using 30 mg of anti-H
> - A similar probe could be sent to Alpha Centauri in 40 years using grams of anti-H
I don't get the placement of some of the technologies on the chart on page 5. How is pulsed fission being beaten out by both thermal fission and chemical rockets in terms of acceleration, considering for all intents and purposes that's propulsion by nuclear detonation? And continuous fusion is all the way on the right despite being the basis of a torchship?? It all just seems so arbitrary
"Your son is correct, that is a typo - it should be 10's of MJ/kg for liquid rocket propellants - thanks for the catch! Thanks too for the heads up re the discussion on antimatter, it is a fascinating topic and great to see there is interest in the community!"
76 comments
[ 1.5 ms ] story [ 129 ms ] threadI guess there’s just no getting around fact that an antimatter reaction that creates 9x10^10 MJ/kg requires more robust electrical generation capabilities than we currently have (I.e fusion)
The fact that something is ludicrously expensive today when manufactured in ultra-small quantities says nothing about the cost if humanity goes all in on mass producing it.
The only really conceivable shortcut for antimatter would be the discovery of large quantities of it somewhere close enough for us to essentially mine it. We've looked for the gamma signature of matter-antimatter annihilation in space, and we don't see it anywhere.
So it isn't IMPOSSIBLE for antimatter to become affordable, but it's extraordinarily unlikely. If we want some sort of superior rocket, it's probably going to have to involve either some unforeseen tech, or our ability to spend planetary energy budgets on rocket fuel.
It says that a Rand study says they might be able to bring down the cost to "$6.4x10^10 per gram" with a dedicated factory. That is still so many orders of magnitude from anything financially feasible.
And assuming the laws of energy conservation holds up, you need to find a better way to generate the electricity that is being used for antimatter production.
The second issue is less obvious - the Milky Way is some 13 billion years old, has hundreds of millions of stars, but is only 100,000 light years across. Fact - the technological limitations of "today" (this century, this mya), are with empirical certainty not relevant.
Interstellar voyage is not amenable to the time preferences and capabilities of the great ape. The only stuff that could transport life across the galaxy does so slowly and without propulsion.
IANAP (I Am Not A Physicist) but it seems like the only "realistic" way to create lightspeed-propulsion quantities of antimatter might be to convert entire planetoids and planets to iron.
I agree, but for scale I want to add that a glass of water has like 1000000000000000000 millions of protons in it.
It's still a bit of a mystery why there was more matter than antimatter when the universe began.
Where do “anti” things exist?
It seems closer to phase cancellation than an anti-thing. Like two sine waves out of phase.
There is nothing mysterious about anti-particles, they have all been observed directly, and they simply have the opposite electrical charge. The one thing we don't understand is why there seems to be so little antimatter in the universe, despite antimatter behaving identically to matter as long as the two don't meet. This could just be a fluke of the matter distribution in the early universe, but it could also indicate that there is a difference we don't know about.
For the most obvious difference, if you apply two waves to the same chord with the same phase but opposite frequency, the result is a chord which doesn't move (destructive interference). If you collide an electron and a positron, the result is an explosion with the maximum possible energy for their mass (mc²).
Also, you can actually do the phase cancelation experiment with two electrons, as they can behave as waves, and you will get the same cancelation as you do with audio waves - except the net electrical field will be 0 instead of the string not moving.
Its makeup is inferred. So what is physics? The measurement of consistent imagination?
It exists only by inference.
I have no idea what that means. Care to clarify?
But there have been proposals for other ways of traveling through space, that involve manipulating space itself, so the distance between point A and point B are smaller. Think of wormholes, or similar. One such proposal is the Alcubierre drive, which warps space around it to cause the total distance traveled to get from point A to point B to be much smaller.
But such exotic drives require exotic forms of matter that we have no evidence of
IIRC The Alcubierre drive would require a significant fraction of the mass-energy of the entire universe to work.
We need a Douglas Adams-style infinite improbability drive!
I've been baffled, though, by the insistence on this kind of antimatter production. Antimatter production is inherently expensive because we are fighting conservation of baryon number, conservation of lepton number, et al.
Physics does have one theoretical method around this, which never seems to be addressed for these proposals, and that's the baffling issue of black holes having no hair. You throw whatever past the event horizon, all that is conserved is mass, angular momentum, and charge. Baryon number, lepton number, strangeness ... all lost. Re-emission as Hawking radiation, it is thought, would simply be this sort of thing, redistributed without regard to what went in, so long as mass, angular momentum, and charge are accounted for. You would conceivably get out as much antimatter as matter.
Now, that's worth looking at. And not from a "we JUST need to capture an itty black hole" (the word "just" does an enormous amount of lifting here) perspective. Rather, passage through the event horizon somehow strips off (we think, some think it might be preserved in some fashion) all of the variables which account for matter versus antimatter. And yet the event horizon isn't a hunk of matter, it's a ... membrane, a boundary, generated by matter at some distance (as a function of our usual three variables). Somehow, this warpage of spacetime operates on matter, shaving it so it has no hair.
That's what fascinates me, in the sense of the theoretical having some extremely juicy practical results.
Even for classical black holes I don't think that's the consensus among physicists. The general assumption seems to be that quantum numbers are still conserved when you throw stuff into black holes, just like electrical charge.
Now, as for Hawking radiation, it's worth pointing out that Hawking's calculation only works for large black holes (low curvature near the event horizon). Once a large BH has shrunken down to a tiny BH (-> high curvature at the event horizon), the calculation no longer works and it is unclear what will happen. Some people say the BH will evaporate completely, some say there will be a remnant – who knows. (Both solutions have their issues.)
All in all, I'm skeptical of the "shaving" you describe.
"Suppose two black holes have the same masses, electrical charges, and angular momenta, but the first black hole was made by collapsing ordinary matter whereas the second was made out of antimatter; nevertheless, then the conjecture states they will be completely indistinguishable to an observer outside the event horizon. None of the special particle physics pseudo-charges (i.e., the global charges baryonic number, leptonic number, etc., all of which would be different for the originating masses of matter that created the black holes) are conserved in the black hole, or if they are conserved somehow then their values would be unobservable from the outside"
Now, this is all still hypothetical, as we haven't a black hole on hand, but this has been the mainstream view on black holes for decades.
That was discussed but AFAIR nobody really believed this was actually going to happen.
> What are the logistics on capturing one of those, keeping it fed, and making some definitive observations?
Generally speaking, the logistics are that you hope that will never create a black hole. You can't really "capture" a BH: It will fall down (towards Earth) like everything else and then start eating its way to the core…
Unless… you manage to create an electrically charged black hole. Then you might be able to confine it e.g. between two condensator plates, by calibrating the voltage in such a way that electric and gravitational force on the BH cancel out.
Now, one problem would be that we expect small black holes to radiate heavily (Hawking radiation), meaning we would have to keep feeding the BH to prevent it from evaporating. (Unless we believe in black hole remnants, see my other comment.) This whole endeavor would make stabilizing the BH between the condensator plates much more challenging. And we'd also still have to worry about what all that radiation will do to our equipment…
Long story short: Don't do it!
-anti-matter is incredibly difficult to produce (the total produced so far in labs is about enough to boil 1 litre of water)
-anti-matter is incredibly expensive to produce (currently around 1 trillion USD per milligram)
-anti-matter is very difficult to store and manage
-a lot of the energy will be given off as high energy gamma rays, which will be difficult to convert into thrust
-the high energy gamma rays will be very destructive to the spacecraft and crew (biological or robotic) without lots of shielding
-over a ton of anti-matter would be required to get a ton of payload to a nearby star at ~40% the speed of light
So don't start saving up for a ticket on an anti-matter spaceship. Or maybe do start saving, so your ancestors can take advantage of compound interest to buy a ticket in a few millenia, if we ever manage to develop the technology.
In Count to a Trillion, a small group found a way to siphon antimatter off a natural source and effectively ruled the world forever due to the near limitless energy and fast interstellar travel.
As opposed to more conventional solutions, which require 1e5 / 1, or more, or more magical ones, that make no sense.
It all sounds awful until you get to this line. What are the equivalent numbers for fusion? All else being equal, 250 tons of fuel per 1 ton payload? And that payload has to include the reactor and storage and shielding and everything.
Shielding is also going to be a huge issue for anti-matter drives (even without a human crew). Anyone know how the energy of EM radiation emitted from a fusion reaction compares to that emitted from an matter:anti-matter reaction?
I've found direct fusion drive as a concept a company is working on: https://en.wikipedia.org/wiki/Direct_Fusion_Drive
Just as an example: imagine particle A made up of up, bottom, and strange quark and particle B made up of down, charm, and top quarks (I'm ignoring charge) that can be stored without interacting. The engine splits them into quarks that then can annihilate each other (AFAIK that's not how quark plasmas work but you get my drift).
And definitely not too close to Earth. Maybe a Lagrange point.
If you need to lift all the fuel from Earth, sure, antimatter all the way. Although, they already suggest making it in space for some reasons.
That's called a Bussard ramjet. Long story short:
> A 2021 study found that, while feasible in principle, the practical construction of a useful Bussard ramjet would be beyond even a civilization of Kardashev type II. [1]
[1] https://en.wikipedia.org/wiki/Bussard_ramjet
https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
It’s just that governments and research institutions don’t have that incentive. Look how fast reusable rockets, and fairing reuse happened once money was on the line. (To use some space examples)
My apologies if this is off-topic, but I have recently read and heard a couple cases of "ancestors" being used instead of "descendants", which has sparked my curiosity. Is this a common brain-lapse result?
1. antimatter is incredibly energy dense, so would be an excellent fuel.
2. there's essentially none of it sitting around, so we need to make it, which takes lots of energy, but that's fine - it's an energy transport system, not an energy production system.
3. just set up square kilometers of solar panels in orbit around the sun or Mercury, use them to power particle accelerators which produce antimatter.
the sun emits enormous amounts of energy - we don't need some magic new energy source, just magic new ways to temporarily bundle up energy in a dense form.
edit: someone did the maths[0]:
> Where will we get the energy to run these magic matter factories? Some of the prototype factories will be built on Earth, but for large scale production we certainly don’t want to power these machines by burning fossil fuels on Earth. There is plenty of energy in space. At the distance of the Earth from the Sun, the Sun delivers over a kilowatt of energy for each square meter of collector, or a gigawatt (1,000,000,000 watts) per square kilometer. A collector array of one hundred kilometers on a side would provide a power input of ten terawatts (10,000,000,000,000), enough to run a number of antimatter factories at full power, producing a gram of antimatter a day.
from TFA:
> Preliminary mission analysis:
> - 10 kg instrument payload could be sent to 250 AU in 10 years using 30 mg of anti-H
> - A similar probe could be sent to Alpha Centauri in 40 years using grams of anti-H
[0]: https://worldbuilding.stackexchange.com/questions/240278/how...
"Chemical combustion: ~ a few MJ/kg • Solid Propellants: ~ 5 MJ/kg • Liquid Propellants: ~ 1 MJ/kg"
Which doesn't look right. My son (a rocketry enthusiast) tells me:
"Liquid engines have energy density between 12 and 20MJ/kg. Apparently they just left off the 0 and likely meant to put 10MJ/kg"
"Your son is correct, that is a typo - it should be 10's of MJ/kg for liquid rocket propellants - thanks for the catch! Thanks too for the heads up re the discussion on antimatter, it is a fascinating topic and great to see there is interest in the community!"
Please don't retire for another 10 years (or more).