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View Full Version : Density of interstellar space+collecting atoms, combining with antimatter for fuel?



WaxRubiks
2018-Aug-07, 09:57 PM
Is interstellar space peppered with enough atoms to be feasibly collected, as a space ship went along, to be usefully combined with onboard antimatter to use as fuel and reactive mass?

One problem, is that a collection device may be damaged by large particles/rocks etc.

SuperTJ7272
2018-Aug-07, 10:27 PM
Well could you go through the Oort Cloud first, store a load of ice, ammonia and methane and add it then during the flight?

DaveC426913
2018-Aug-07, 10:46 PM
Read up on Bussard Ramjet (https://en.wikipedia.org/wiki/Bussard_ramjet).

The idea was tossed around for a few decades. You needed a magnetic scoop several hundred kilometres in diameter.

Jens
2018-Aug-07, 11:05 PM
Is interstellar space peppered with enough atoms to be feasibly collected, as a space ship went along, to be usefully combined with onboard antimatter to use as fuel and reactive mass?


You’re looking for a solution to a non-problem. The challenge to creating an antimatter drive is producing and storing the antimatter. I suspect that you would be better off just taking the matter with you than adding the mass of a device to scoop up matter.


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WaxRubiks
2018-Aug-07, 11:07 PM
You’re looking for a solution to a non-problem. The challenge to creating an antimatter drive is producing and storing the antimatter. I suspect that you would be better off just taking the matter with you than adding the mass of a device to scoop up matter.


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Yes, but collecting matter, would allow you to take more antimatter, rather than carting a load of ordinary matter with you, allowing you to go faster, and, or, further.

Darrell
2018-Aug-08, 08:04 PM
If I remember correctly the Bussard Ramjet concept was eventually shown to be untenable due to drag. At velocities necessary to achieve fusion drag would exceed thrust.

Noclevername
2018-Aug-09, 12:34 AM
Using a magnetic field as a ramscoop, the vessel would generate more drag than thrust. Updated proposals suggest ionizing the ISM ahead of the craft using a particle beam or a lasers, then attracting it electrostatically.

Jens
2018-Aug-09, 03:48 AM
Using a magnetic field as a ramscoop, the vessel would generate more drag than thrust. Updated proposals suggest ionizing the ISM ahead of the craft using a particle beam or a lasers, then attracting it electrostatically.

The original question was about collecting matter for an antimatter annihilation drive. I don't really understand how the ramjet relates to that, except for the fact that it also has a scooping mechanism. Would it be true for an antimatter drive that it would generate more drag than thrust?

Darrell
2018-Aug-09, 02:02 PM
The original question was about collecting matter for an antimatter annihilation drive. I don't really understand how the ramjet relates to that, except for the fact that it also has a scooping mechanism. Would it be true for an antimatter drive that it would generate more drag than thrust?

Perhaps not, but modeling this is a bit beyond me. There is no threshold you have to get over to achieve thrust as with the original fusion ramscoop concept in which you are relying on relative velocity and the shape of the magnetic scoop (funnel) to generate the pressure and heat necessary to achieve fusion. With the antimatter ramscoop in principle any amount of matter collected will give you some thrust, however tiny. Efficiency might be a problem. How much energy would it take to maintain a scoop large enough to collect enough matter to generate worthwhile thrust? Depends, among other things, on relative velocity and particle density. Where does that energy come from? From the matter-antimatter reaction?

Darrell
2018-Aug-09, 02:03 PM
Accidental double post.

Noclevername
2018-Aug-10, 01:55 AM
The original question was about collecting matter for an antimatter annihilation drive. I don't really understand how the ramjet relates to that, except for the fact that it also has a scooping mechanism. Would it be true for an antimatter drive that it would generate more drag than thrust?

As long as it doesn't have a big honkin' magnetic field acting as a parachute on the interstellar medium, it could be possible to generate more thrust than drag with a M/AM reaction.