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Antimatter Engine


Dr. Kerbal

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29 minutes ago, The Doodling Astronaut said:

I do have a question about this. I got the question about this after having a chemistry course on Quantum stuff and alternate universes so I am still wrapping the head around it but.

wouldn't the Matter and Antimatter attract to each other and just explode? Causing no real way of containment? 

It depends on what the matter and antimatter comprise. Matter and antimatter aren't intrinsically attracted to each other by their nature; it all depends on charge. A positron is attracted to an electron, for example, and an antiproton is attracted to a proton. But that attraction is the result of electromagnetic charge, not anything to do with the nature of antimatter. An antineutron is not particularly attracted to a neutron; they both have no net electric charge.

Antihydrogen, which is the atom formed when a positron binds to an antiproton, is electrically neutral and is not electrically attracted to anything. However, it does have spin, which can be used to confine it in carefully-shaped magnetic fields. We were first able to synthesize a significant amount of antihydrogen in 2010, where 38 antihydrogen atoms were trapped in a magnetic trap and persisted for a sixth of a second before annihilating. Within a few months, we were able to trap antihydrogen atoms for several minutes at a time. But that's about as far as we've gotten. We can produce individual antideuterium and antihelium atoms but it's really challenging and long-term confinement remains an open problem.

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Can you please make this easier for me to understand. Think of me as an average Joe. I don’t understand what photons or wired math have to foe worth anything. Sorry, but please simplify so my brain can understand.

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1 hour ago, Dr. Kerbal said:

Can you please make this easier for me to understand. Think of me as an average Joe. I don’t understand what photons or wired math have to foe worth anything. Sorry, but please simplify so my brain can understand.

It's a very complex subject, so explaining simply is hard.

Basically, it's very hard to turn antimatter into useful work because it takes many metres of heavy material to absorb the energy released in the form of gamma radiation (which likes to go straight through things), and that's bad for rockets.

Also the slightest percentage of energy transferred to the vehicle instead of the propellant requires vast radiators to dissipate, and those are heavy and so bad for rockets.

Edited by RCgothic
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4 hours ago, RCgothic said:

It's a very complex subject, so explaining simply is hard.

Basically, it's very hard to turn antimatter into useful work because it takes many metres of heavy material to absorb the energy released in the form of gamma radiation (which likes to go straight through things), and that's bad for rockets.

To simplify even further, perhaps past the point of rigorous accuracy....

Antimatter doesn’t produce thrust; it can only produce heat. If you want thrust then you’ll have to combine that heat with some kind of propellant so that the propellant can explode out the back of your engine and produce thrust.

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This is from NASA.

 

Radioisotope Positron Propulsion

Ryan Weed
Positron Dynamics

Radioisotope Positron Propulsion concept.
Graphic depiction of Radioisotope Positron Propulsion concept.
Credits: R. Weed
 

Current state of the art in-space propulsion systems based on chemical or ion propellants fail to meet requirements of 21st century space missions. Antimatter is a candidate mechanism for a propulsion system that could transport humans and/or robotic systems with drastically reduced transit times, providing quicker scientific results, increasing the payload mass to allow more capable instruments and larger crews, and reducing the overall mission cost. Unfortunately, previous propulsion concepts relied on unrealistic amounts of trapped antimatter - orders of magnitude away from any near-term capability. The goal of this effort is to determine the feasibility of a (TRL 1-2) radioisotope positron catalyzed fusion propulsion concept that does not rely on trapped antimatter. Such a transformative technology inspires and drives further innovation within the aerospace community and can be applied to a relevant mission - the bulk retrieval of an entire asteroid into translunar space - a mission of great scientific and commercial interest (e.g. asteroid mining). The idea of harnessing resources from asteroids goes back more than a century to Tsiolkovsky. Fundamentally, for asteroid mining to become financially viable, the cost of the retrieval spacecraft must be less than the value gained from the asteroid. Therefore, developing technology (e.g. efficient propulsion systems) that decreases the mass and complexity of the retrieval spacecraft must be a priority.

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4 hours ago, sevenperforce said:

To simplify even further, perhaps past the point of rigorous accuracy....

Antimatter doesn’t produce thrust; it can only produce heat. If you want thrust then you’ll have to combine that heat with some kind of propellant so that the propellant can explode out the back of your engine and produce thrust.

 

One day man could convert light to magnetism.

We are already seeing hints it is possible.

Then gamma radiation from an AM bomb would be all you need. For thrust.

Granted, the impulse receiver must still be huge to dissipate any absorbed rays.

 

https://kaw.wallenberg.org/en/research/coupling-light-magnetism-nanoscale

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10 hours ago, WestAir said:

Until you run out of fuel.

If you run out of fuel on a blackhole ship, you have a few months to a few years to either get somewhere or ditch the core. Whether or not you can still use it for propulsion in that time will depend greatly on design, but you can certainly use it for power, so you'll still have life support, etc, and if you have an emergency "parachute" for braking against solar winds in a destination system, it still gives you more chances for getting rescued than any other feasible propulsion system we know of.

But yes, a tiny black hole suitable for power generation is basically a very powerful bomb with a timer once you stopped feeding it matter. It's definitely not something you want to sit in your ship yard without supervision. I didn't say it was perfect. :p

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Hi folks,

Just a note that we've split several posts off into a separate thread.

The discussion is an interesting one (about conservation of momentum)... but has nothing to do with antimatter propulsion per se, and therefore is off topic for this thread.

Please try to stick with the subject at hand (antimatter engines), and if you want to discuss momentum conservation, do it in the other thread.

Thank you for your understanding.

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8 hours ago, Dr. Kerbal said:

So please put this in someplace simple terms. Like how you would explain to a farmer kinda.

"So. Imagine, you're farming bitcoins on your hi-tech lab hardware..."

Edited by kerbiloid
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On 10/23/2020 at 11:08 PM, K^2 said:

tiny black hole suitable for power generation is basically a very powerful bomb

I believe you've talked about black hole propulsion a few times on this forum and I always wondered what the phrase "a very powerful bomb" would mean in this context, since I had a hunch that it's a bit of an understatement. After all, astronomical phenomena tend to be bigger than my puny human intuition. Anyway, I was thinking nuclear bomb big, but it turns out that Mr. Hawking himself has an estimate:

https://www.sjsu.edu/faculty/watkins/blackholes2.htm

"Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs."

Just for comparison, wikipedia article on nukes says that combined yield of all nuclear testing as of 1996 comes up to about 510 Mton, so we are clearly out and well beyond the ballpark of nukes, so I went and looked up some asteroid impact calculators. This one, for input parameters of 2 km diameter iron asteroid impacting at 17 km/s  at 45 ° into sedimentary rock, calculates the following:

4.84 x 1021 Joules = 1.16 x 106 MegaTons TNT

Transient Crater Diameter: 25.2 km ( = 15.6 miles )
Transient Crater Depth: 8.9 km ( = 5.53 miles )

Final Crater Diameter: 38.5 km ( = 23.9 miles )
Final Crater Depth: 888 meters ( = 2910 feet )

That's a big bomb.

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7 hours ago, Dr. Kerbal said:

Okay. So please put this in someplace simple terms. Like how you would explain to a farmer kinda. Please cause. My brain has been blocked but this fascinating topic.

Well, the guys and gals here are trying, but there might be some fundamentals that you haven't learned yet.   Some information that is required to understand the advanced stuff.    With more research and reading, along with the continued explanations here, you'll pick it up. 

It'll help if you'd describe what parts are you having trouble with.  Don't be afraid to ask what seems like a dumb question, if you don't know something, you don't know it, and you'll never learn till you ask. 

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6 hours ago, Shpaget said:

I believe you've talked about black hole propulsion a few times on this forum and I always wondered what the phrase "a very powerful bomb" would mean in this context, since I had a hunch that it's a bit of an understatement. After all, astronomical phenomena tend to be bigger than my puny human intuition. Anyway, I was thinking nuclear bomb big, but it turns out that Mr. Hawking himself has an estimate:

https://www.sjsu.edu/faculty/watkins/blackholes2.htm

"Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs."

Just for comparison, wikipedia article on nukes says that combined yield of all nuclear testing as of 1996 comes up to about 510 Mton, so we are clearly out and well beyond the ballpark of nukes, so I went and looked up some asteroid impact calculators. This one, for input parameters of 2 km diameter iron asteroid impacting at 17 km/s  at 45 ° into sedimentary rock, calculates the following:

4.84 x 1021 Joules = 1.16 x 106 MegaTons TNT

Transient Crater Diameter: 25.2 km ( = 15.6 miles )
Transient Crater Depth: 8.9 km ( = 5.53 miles )

That's a big bomb.

That gives me an idea. 

If you built a really, really big pusher plate.....

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