JMK

Private page for discussing space cable issues. Accessible only to John Knapman and Keith Lofstrom. John, feel free to modify this page, add comments, and create other public pages, or other private pages with the same ACL line at the top.

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I'm now starting to use this page, and I appreciate the trouble you've taken. As promised, I have reexamined the question of dumping excess heat in the original design of the space cable. This is something I worked through several years ago but never published. I have now concluded that, on reasonable assumptions about efficiency, the bearer would not be able to dispose of the heat fast enough. That blows a key assumption. I have added a few comments in AmbitMagnets.


(new!) Look at the new document AmbitMagnets, for reasons for a continuous rotor, and for non-superconducting ambit D magnets.


(old) Comments on "Diverse Configurations of the Space Cable"

Minor edit: Fencepost error: 16 magnets have 15 spaces between them. The length (page 3 column 2 para 1) is 15 meters.

Major issue: Vertical gee forces are enormous. Vehicle release will cause a major perturbation. See DiverseSpaceCable#VerticalGee for more.

Minor issue: MacNab comments (deleted). Thanks for the article.

Major issue: Coil guns are difficult. MassDriver (still in progress) will have more. VelocityTransformer (still in progress) is an idea for transforming rotor/bolt speed into faster (space cable) or slower (launch loop starting acceleration) vehicle-frame magnetic fields.

Major issue: The residual gas inside the tubes will be extremely hot plasma. If there is even a tiny hole in the tube/track, it must be pumped out in the immediate neighborhood, or this will lead to plasma erosion (if dense) or, for a long mean free path, a hyper-velocity spalling cascade Spalling (still in progress) will have more.

General comments

Possible issue: Stability (still in progress). Once a perturbation has grown beyond the size of the bolt/rotor to tube/track spacing, it may be impossible to correct without some source of lateral forces. It is also very difficult to measure curvature, lateral velocity, and other variations from ideal shapes on 100 kilometer scales, especially on a structure bowed by imprecisely predicted winds. I need to reconcile your stability analysis with mine, and bring my 1985 analysis up to date, by including the stiffening effects of a tension-wire truss and the immediate response of local mass actuators.

Possible issue (also for launch loop): The acceleration force on the bolts/rotor goes from strongly upwards to weak downwards right at the end of the ramp. Depending on the bolt/rotor design, the attraction forces must flip very quickly, and this could be a problem.

Regards wind: I am reading a book "The atmosphere and ocean : a physical introduction" by Neil Wells. A good book on the ocean/atmosphere interactions that drive weather, moderately technical but not too difficult. Dr. Wells teaches at University of Southampton http://www.noc.soton.ac.uk/omf/index.php?action=staff_entry&SID=450 and has worked on ENSO ( El Nino Southern Oscillation ), the TOGA ( Tropical Ocean Global Atmosphere ) Array in the western Pacific, and the ARGO data collection system. The right place for launch loop and space cable launchers is just below the equator, in the eastern Pacific off south America, and in a similar place in the Atlantic. Dr. Wells can probably steer us towards a wealth of data and analysis of these regions, and might help us better understand the wind forces we will be seeing. Since he is a few minutes south of you, perhaps you might want to look him up.

JMK (last edited 2011-05-23 14:22:06 by JohnKnapman)