tag:blogger.com,1999:blog-192883022973901942.post262261276011532965..comments2023-10-08T02:46:24.823-07:00Comments on Bootstrapping Space: Lunar circumferential railwayChris Wolfehttp://www.blogger.com/profile/11247630943891521469noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-192883022973901942.post-35154005706121478482016-01-05T11:39:23.243-08:002016-01-05T11:39:23.243-08:00Right. The polar loop allows you to fine-tune your...Right. The polar loop allows you to fine-tune your inclination on departure, while the equatorial loop allows slightly better efficiency. The equatorial loop would produce electricity grossly in excess of the amount required.<br /><br />The basic maglev concept could be done with existing technology and a lot of cash, potentially cheaper with advances in automation and additive manufacturing. I suspect a launch track sized for Lagrange destinations could be done with modest tech advances at nearly the same cost. This probably deserves its own post. More aggressive destinations may require significant advances in maglev technology.<br /><br /> A full-scale launch loop would be a significantly bigger project. Lunar escape speed is 2.38km/s; accelerating at 1 g would take only four minutes and cover 290km of track for a C3=0 launch (Lagrange points). That's only about 2.7% of the full circumference, so you would need a compelling argument for why the entire track should be upgraded for orbital launch. Throughput and the lack of launch windows would be compelling arguments if the system needs to move a large enough mass of cargo.<br /> The peak centripetal acceleration for this launch would be 3.26m/s² minus the 1.62m/s² surface gravity for a net upward acceleration of 1.64m/s². This is very reasonable; a 10-ton payload would generate 16.4kN of force on the upper arch (equal to the resting weight of a 1.7-ton object on Earth). In fact, a properly-designed lower track should easily handle this load without the need to change the upper structure or use a second track at all. This system could be expected to last centuries provided adequate maintenance of the electrical systems, though the open areas for payload release would be at higher risk of damage from meteorites and radiation.<br /><br /> Higher energies require longer tracks and/or higher acceleration. A Jupiter mission direct from the Moon would require C3~80km²/s², or a departure velocity from the Lunar surface of roughly 11.4km/s (2.4km/s to escape plus 9km/s to transfer). A 3 g launch (30m/s²) would take 6 minutes 20 seconds and cover 2,166km of track (about 10.4%). Travel time would be about 2 years 9 months and orbital insertion would require about 5.7km/s (high-thrust).<br /> The peak centripetal acceleration for this launch would be 74.86m/s², or a net acceleration of 73.22m/s². The same 10-ton payload would now be generating 732kN of vertical force. This sort of profile would likely require an upper rail, with release accomplished by simply ending the upper rail at an opening in the arch. (Such a design would use a sled or sabot for the lower track with rods to carry launch force to the payload, while the centripetal force would be resisted entirely by the upper track; the payload module would slide right off the rods with no complex release mechanisms.) The payload itself would experience a peak net acceleration of 80.65m/s² (8.22 g, via pythagorean theorem combining the centripetal acceleration with the launch acceleration). Note that this launch profile is near the limit for eyeballs-in human endurance.<br /><br /> For an unusual twist, consider a mobile habitat that travels full-time on the track at speeds high enough to experience a stable 1 g acceleration. That would be 4.454km/s. The hab would circle the moon about every 41 minutes. Mechanical failure would be promptly fatal, so this is probably too risky to actually do. Still, it would be possible to reach any desired acceleration between 0.165 g and several g.Chris Wolfehttps://www.blogger.com/profile/11247630943891521469noreply@blogger.comtag:blogger.com,1999:blog-192883022973901942.post-85097953677631104202015-12-20T12:16:44.457-08:002015-12-20T12:16:44.457-08:00Since you're talking about maglev this would o...Since you're talking about maglev this would only be the starting point of what you could do with a circumlunar train. Build those arches much beefier and put another track on the bottom. Put a second maglev rig on the top of your train--now it can exceed orbital velocity. The train goes round and round, faster and faster. When it's going as fast as you want it to go a cargo capsule separates and is ejected--on anything from a sungrazer to solar escape orbit trajectory (with human-tolerable accelerations.) Mega engineering but what it will save you in rockets over the years...Loren Pechtelhttps://www.blogger.com/profile/08348494458707790769noreply@blogger.com