Real Or Horse Feathers? Would this really work?
Posted 18 July 2012 - 12:53 PM
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Posted 19 July 2012 - 05:30 AM
In my judgement, Richard Obousy’s ideas, featured in Orion Jones’s BigThink article, are scientifically plausible, but optimistically biased (not necessary a bad thing), and decades from feasibility.
This paper has moderately extensive, technical (but not peer reviewed) presentation of Obousy’s VARIES (Vacuum to Antimatter-Rocket Interstellar Explorer) concept. Obousy’s CV shows him to be well educated (2008 PhD in Physics), if not as distinguished as more famous physics PhD’s, and of wide, enthusiastic interests – in short, he sounds like an intensely fun guy, though perhaps a bit overly self-promoting.
The gist of the VARIES idea echos, and adds detail and some twists to, ideas of Robert Forward (whom Obousy cites in his paper, though for his Starwisp, not the paper’s main idea, suggesting still to me that Obousy has read Forward) about the manufacture of antimatter and its use in rockets. In his 1994 book Indistinguishable from Magic, Forward proposed that, by building huge solar-powered “antimatter factories” in space, it would be possible to manufacture (and, importantly, store) large (on the order of 10 kg/year) amounts of antimatter (in the form of frozen antihydrogen). He calculated that, as of 1992, the energy efficiency of manufacturing antihydrogen was about 0.0000017% - that is, for every 60 million units of energy spent, antihydrogen capable of producing 1 unit of energy when annihilating with ordinary matter is produced, and further argued that a purpose-built device might increase that efficiency dramatically, to about 0.01%.
In his paper, Obousy optimistically assumed an antimatter production efficiency of 1%, which may be (though I’m not sure) justified the novel means of manufacturing it he suggests. Rather than Forward, who proposed designing optimizing machines based on existing, particle-accelerator-based ones capable of creating and storing antihydrogen, Obousy proposes a devices base on the Schwinger Mechanism (on which there’s a shortage of non-technical explanations – this companion presentation material for Allor, Cohen and McGady’s 2007 paper The Schwinger mechanism and grapheme is the best I can find).
Obousy’s big twist on the idea of manufacturing antimatter using the energy of a nearby star, then using the antimatter to power a rocket, is that, where Forward assumed the “factory” to be a massive facility in a fixed orbit, Obousy proposes, via the above described increase in efficiency and very light, retractable solar panels, it can be made portable, and included in the rocket ship it fuel. Thus, the ship can travel to a nearby star, “recharge” by deploying its solar panels and running its antimatter factory, then return to Earth’s solar system.
While a nifty idea, I’m still leaning toward Forward’s vision. Given that the mass of antimatter required by the proposed rocket ships is a small fraction of their total mass – 10s of kg of a ship of 50,000,000 or so kg – I can’t see much advantage, for a there-and-back mission like Obousy proposes, to not just manufacture and store twice as much antimatter, allowing the ship to fly the mission without having to haul its antimatter factory around with it.
This is not to say anything against the antimatter factory design Obousy proposes, which promises to be hundreds of times more efficient, and presumably even more times less time and resource expensive to build than the ones Forward imagined. This is to say something against the design idea of hauling one around in an interstellar spacecraft, merely to reduce it its fuel requirements by a factor of 2.