Recently, there was a http://www.reddit.com/r/space/comments/96iwv/the_year_is_2035_we_have_a_permanent_base_on_the/" on Reddit titled "The year is 2035. We have a permanent base on the moon and have sent multiple teams to Mars and back. What's next for NASA?" There were several interesting responses. I posted http://www.reddit.com/r/space/comme...2035_we_have_a_permanent_base_on_the/c0bliol" myself (not something for NASA per se, but somewhat related to the context). I'll try to describe it more clearly here: It's a few decades in the future, we have a solid presence on the Moon, perhaps we have mastered some self-replicating technologies as well - anyway, it becomes feasible to undertake projects at planetary scale or, at least, at Moon scale. Hence, the idea to build a nice big accelerator girdling the Moon on the equator. First off, it's near vacuum anyway, so the whole thing does not have to be airtight - it can even be an open structure. It does not have to be continuous. It's enough to place segments here and there, each segment appearing above the horizon for both its neighbors. Each segment is, in fact, a linear accelerator (slightly curved maybe), but the whole system, when all segments round the equator are live, becomes one giant circular accelerator, 11 thousand kilometers long. Each segment can be self-contained, it can function based on energy from the Sun (energy requirements? what is the surface of solar cells needed?) I assume the coils are superconductive but do not require powerful cooling. (shade? solar-based heat pumps?) Definitely some sort of local energy storage is needed, which gets slowly charged between pulses. Aiming from an upstream segment to the next segment downstream is going to be tough. These things can be anchored in solid moon rock, but I guess even the Moon vibrates and shakes a little, so some sort of dynamic monitoring and aiming might be required. Advantages? Many. - Something on this scale cannot be accomplished on Earth (there's an atmosphere, too many distractions from tectonics, weather, biosphere, etc.). - The "risk" of popping up a black hole, already tiny anyway, does not matter here - if it does implode the whole thing into a singularity, hey, who cares, it's just the Moon. - An accelerator this big would take us a whole lot closer to Big Bang physics. Problems? - Is the vacuum good enough? - Interactions between the "free range" particle beam and whatever happens to hit it? (cosmic dust, solar wind and photons) - The Moon rotates. Is that going to make things difficult for the segments, each trying to accelerate and shoot the relativistic beam into the next? - Finally, a big accelerator like that will give a new meaning to the expression "hyper-relativistic particle". The segments will have to steer the beam a few seconds of arc or so. I wonder if that will create some problems? (synchrotron radiation, stuff like that) Thoughts? Comments? Would be nice if somebody could do a back of the envelope estimation for the maximum energy such a device could pump into the particles. I don't trust myself enough to attempt it. Would it get close to the highest-energy cosmic rays? The GZK limit? Close to the "oh-my-god particle"? (50 J) Higher than that?