Space Elevators: An Assessment of the Technological Feasibility and the Way Forward
International Academy of Astronautics
Peter A. Swan, David I. Raitt, Cathy W. Swan, Robert E. Penny, John M. Knapman
Notes for an Index
- p009: 20 MT climbers
- p009: $500 / kg
- p010: 100,000 km tether
- p011: strength-to-weight ratio within 20 years
- p011: positive ROI 10 years after erection is complete
- p013: Nodal layout - marine node
- p013: AC Clarke laughing quote
- p014: liftoffs every day
- p017: Clarke's first law "... elderly scientist ..."
- p017: ref Edwards and Westling 2003
- p018: EW width 1 meter
- p018: EW 20 ton payloads, two week trip, 5 concurrent payloads
- p018: IAC current 7 concurrent payloads, one week trip
- IAC solar-only, 25-30 MY
- p020: Technology readiness levels
- p021-24: Chapter outlines
- p026: 14 tonne cargo
- p027: slingshot interplanetary mention
- p027: Min orbital injection altitude 23390 km
- p028: Megaprojects
p029: EW estimate $6B to >$10B
p032: Tether Characteristics Table 2-III
38 MY, 49.4 GPa, 1300kg/m3 rated
- Operational 35.2 GPa, 27 MY, 1.4 safety factor
- Taper ratio 6
Cross section: GEO 1m x 62.8 μm, Earth 1m x 10.5 μm
- Climber: 6 tonne structure, 14 tonne payload
- 7 climbers, equivalent mass 29 tonnes
- 6300 tonne tether
- 1900 tonne apex anchor
- 100 000 km radius
p033 Table 2-4 Equivalent Weight on Tether Carrier
- 20@6378, 5@12756, 2@19134, 0.8@26600, 0.8@27000, 0.3@34000
- ??? spacing near 26600
p034 Estimated speeds
- 59 m/s, 11.8 MW
- p040 Feasibility Condition
- ... Standard Throughput Unit ... Time to Double ... Fraction Weight of Spare on Orbit ...
- p045 Table 3-1 Relationship Power vs. Strength
- p045 Figure 3-1 Projected CNT Strength
- Yarn at 11 MY in 2011 (Zhang), with projections
"density at 1g/cm3 is assumed" ---> 8.5 MY, actually?
- Yarn at 11 MY in 2011 (Zhang), with projections
- p048 Summary of research on CNT
- p050 CNT length graph, no units given, presumed mm, max 200mm in 2010
p050 CNT growth rate graph, up to 85 μm/second in 2010
- p052 Alternate materials
- p063 Table 4-1, repeat of Table 2-4
- p065 CNT Improvements in spacecraft
- assumes 4x reduction in mass
- is this justified for electrical? EW numbers for CNT conductivity much worse than copper
- not justified at all for ferromagnetic materials
- p067 Table 4-3, Reduction of Mass by CNT Incorporation
- p068 quotes numbers for linear motor drives 518 km/h
- p068 quotes Tsuchida 2009 (in Japanese)
- p074 Fig 4.4 Shelef 2008 glider structure
- "The glider ring is also then charged, so it repels the tether"
- KHL This violates Earnshaw's theorem. Systems of static fields are at best neutrally stable, practically unstable
- KHL REALITY: Must assume active control of circumferential electrodes - stiffness must be provided by power transfer, quicker response == more power. Electric fields are always attractive (energy density proportional to E field squared), though this can appear "repulsive" if the attraction is to an outer container, such as in foil electrometers.
- "The glider ring is also then charged, so it repels the tether"
- p076 Reference to Shelef 2008 solar cell foils
KHL The picture Shelef uses in 2008 as a solar cell foil is actually a solar SAIL, a thin film of metalized plastic foil that reflects sunlight and produces no electrical power, just 9 μN/m2 thrust. Real solar cells are fragile photovoltaic semiconductor materials with conductors on both sides; the front side conductor either transparent or partly shading the photovoltaics. The best space grade photovoltaics are 400 nm thick graded junction indium phosphide layers, with extra material front and back for conductivity, with a thicker front-side Indium Tin Oxide conductor. These devices often have as much as a millimeter of glass in front to absorb some of the particle radiation.
- p076 Deployment spacecraft
- p081 Table 4-7 Mass of Deployment Satellite
- p083 Buildup spacecraft
- KHL: New tether must be deployed and bonded at full tension, to match existing tether. That will require a lot of roller friction and a lot of power.
- p087 Chapter 5 End station Infrastructure
- p088 5.4 Apex anchor
- KHL: Isn't this a good place to store lots of spare tether, and the tools to deploy it? If you lose lower tether, you will need to trim the apex anchor to match
- Later on, we learn that the apex anchor thrusts towards GEO with rocket engines. GEO is where we store more tether.
- KHL: Isn't this a good place to store lots of spare tether, and the tools to deploy it? If you lose lower tether, you will need to trim the apex anchor to match
- p089 5.5 Marine Stage 1
- p091 Q1: Off zero latitude
- shows 50% reduction at 33 N/S, 100% reduction at 48 N/S
- KHL note: The reduction for 8 S is far, far smaller. My numerical estimates show 0.75% reduction, well worth the advantages
- "Yes, Stage One could be located off the equator, but best for carrying capacity if there"
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p191 Wright 2013 - 32uW at 9mA -> 0.4 ohm/meter (Edwards value). * 62.8mm2 -> 2.5E-3 ohm-meter, 1500x copper.