5 ms·

> -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 li

> -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.

hermitcrab 3y ago
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?
tiborsaas 3y ago
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've found direct fusion drive as a concept a company is working on: https://en.wikipedia.org/wiki/Direct_Fusion_Drive https://en.wikipedia.org/wiki/Direct_Fusion_Drive
- throwup238 3y ago
  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).
- euroderf 3y ago
  > Probably only space based antimatter production makes sense And definitely not too close to Earth. Maybe a Lagrange point.
lucianbr 3y ago
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.
- throwup238 3y ago
  > 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] [1] https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
- deleted 3y ago
  [deleted]
woopsn 3y ago
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.
- hermitcrab 3y ago
  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.
  - woopsn 3y ago
    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.
WithinReason 3y ago
Fun fact, the technology needed to accelerate a spacecraft to 10% of the speed of light already existed in the 60s: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

hermitcrab 3y ago

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?

tiborsaas 3y ago

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've found direct fusion drive as a concept a company is working on: https://en.wikipedia.org/wiki/Direct_Fusion_Drive https://en.wikipedia.org/wiki/Direct_Fusion_Drive

throwup238 3y ago
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).
euroderf 3y ago
> Probably only space based antimatter production makes sense And definitely not too close to Earth. Maybe a Lagrange point.

lucianbr 3y ago

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.

throwup238 3y ago
> 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] [1] https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
deleted 3y ago
[deleted]

woopsn 3y ago

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.

hermitcrab 3y ago
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.
- woopsn 3y ago
  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.

WithinReason 3y ago

Fun fact, the technology needed to accelerate a spacecraft to 10% of the speed of light already existed in the 60s: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...