Cables vs trusses vs tensegrity: the load path

How to carry spin loads between masses. Tension members are mass-efficient, but a structure also needs something to resist compression, bending and transients.

Key results

• A rotating station is loaded almost entirely in tension. It is like a suspension or cable-stay bridge without towers. Tension members should be materials good in tension; concrete belongs only in secondary stiffening. Do not bury tension cables in concrete, because inspection matters Barley, 2023-09-29.
• Wire wrap keeps the critical processes in the factory and needs few field joints, while every weld of a plate structure is critical Barley, 2023-09-29.
• Drawn wire is much stronger than sheet ("Bronze Age tech") Barley, 2023-09-28.
• Chain suspension bridges gave way to cables; chains might return early if bolting is the only proven method Barley, 2022-10-13.
• Pure-cable structures need a compression element to avoid coning, resonance and collapse when spin slows JohnFornaro, 2014-03-16; mikelepage, 2015-02-17; mikelepage, 2016-01-13. Solutions proposed:
• Composite truss in compression plus cables in tension (IsoTruss) RanulfC, 2014-03-19.
• A rigid ISS-heritage truss jtrame, 2014-02-20.
• A lattice (a deployable solar-array structure) that damps resonance mikelepage, 2015-02-26.
• A pressurized inflatable tunnel compressed by internal cables, which becomes effectively rigid Paul451, 2022-10-11.
• Tensegrity JohnFornaro, 2014-03-16.
• Telescoping crane-jib trusses (100 m in 9 parts of 12 m) A_M_Swallow, 2015-10-23. JWST-type Telescopic Tubular Masts LMT, 2018-07-16.
• "Lazy tongs" pantographs mikelepage, 2023-12-28.
• Rollable bistable STEM/slit-tube booms (Redwire/Roccor, Opterus) and Altius "sticky boom" jongoff, 2023-12-29; Paul451, 2023-12-28.
• Robotically fabricated trusses: SpiderFab, Archinaut ULISSES, and the MIT bend-forming NIAC (10 m²/kg) Asteroza, 2015-10-22; LMT, 2019-02-27; LMT, 2023-01-10.
• Twark_Main's primary structure. A 3D grid of prefabricated linear tension beams (like a skyscraper frame) from which modular floors, walls and pressure bulkheads hang. Flat tensile floors are vulnerable to gouges; beams are not Twark_Main, 2023-09-30; Twark_Main, 2023-09-30; Twark_Main, 2024-07-16.
• Coastal Ron's primary structure. Build a load-bearing band or "floor" first and hang or attach living modules to it. Living spaces should not be part of the load path, "so a failure of the structure does not guarantee a failure in a module" Coastal Ron, 2023-09-29; Coastal Ron, 2026-08-21. Twark_Main's reply: if the internal structure fails, "it's a collapsing building pancaking into the outer hull", so separation adds no real redundancy Twark_Main, 2023-07-26.
• Island Zero (Jerry Stone, BIS) uses tension rods between modules rather than spokes, which are "not the ideal shape for a tension member". External cabling reduces stress on the ports lamontagne, 2026-07-08; lamontagne, 2026-08-20. Twark_Main suggested beefed-up diagonals as redundant cables Twark_Main, 2026-07-05.
• Cable material cautions.
• Dyneema is high-creep under continuous load above ~20% of breaking strength, even at 35 °C. It is not a structural material; carbon or basalt fibre is better Paul451, 2023-09-19; Paul451, 2023-09-19.
• Coastal Ron counters that cold, shaded, friction-held wraps limit creep Coastal Ron, 2023-09-19.
• Synthetic ropes need UV protection Coastal Ron, 2015-09-03.
• Replaceability. Cables are mass-efficient and replaceable Coastal Ron, 2015-02-14. Rims can be made of parallel standard cables joined at plates Coastal Ron, 2015-09-03. Redundant Hoytethers Roy_H, 2018-06-23.

Open questions

• Is a tension grid or a tension band the better primary structure for a modular torus?
• What damping should be built into long tension members (turnbuckles, power-line-style spacer dampers)? lamontagne, 2018-08-04

Related pages

• Tethered bolas · Hoop stress · Materials · In-space assembly

Sources

Forum posts

• jtrame, 2014-02-20 (reply #100, 1 like): Rigid truss instead of cable. Post.
• JohnFornaro, 2014-03-16 (reply #182): Cable-only coning. Post. Attachments: Tensegrity-Sphere.png.
• RanulfC, 2014-03-19 (reply #208): IsoTruss compression + cables. Post.
• Coastal Ron, 2015-02-14 (reply #275): Cables mass-efficient and replaceable. Post.
• mikelepage, 2015-02-17 (reply #285): Tether = spring. Post.
• mikelepage, 2015-02-26 (reply #424, 2 likes): Lattice/solar array replaces tether. Post.
• Coastal Ron, 2015-09-03 (reply #601): Synthetic cables ~10× less mass, need UV protection. Post.
• Coastal Ron, 2015-09-03 (reply #612): Rim of parallel cables joined at plates. Post.
• Asteroza, 2015-10-22 (reply #717): SpiderFab arms with inflatable tunnel. Post.
• A_M_Swallow, 2015-10-23 (reply #729, 1 like): Telescopic crane-jib truss. Post. Attachments: dreamstime_m_47941409.jpg.
• mikelepage, 2016-01-13 (reply #809): Engineers dislike pure tension; need compression. Post.
• Roy_H, 2018-06-23 (reply #842): Hoytethers. Post. Attachments: MainCutaway.png, AgriculturalModule3.png, StateroomLayout.png.
• LMT, 2018-07-16 (reply #941, 1 like): JWST-type telescopic mast. Post.
• lamontagne, 2018-08-04 (reply #1144): Turnbuckles/shock absorbers on lines. Post. Attachments: Station3c.jpg, Station3d.jpg.
• LMT, 2019-02-27 (reply #1313): Archinaut trusses; GSAL. Post.
• Paul451, 2022-10-11 (reply #1977, 2 likes): Inflatable tunnel + internal cables. Post.
• Barley, 2022-10-13 (reply #2054): Chains vs cables. Post.
• LMT, 2023-01-10 (reply #2846): NIAC 2023 bend-forming trusses. Post. Attachments: cordero_bendforming_2023.png.
• Twark_Main, 2023-07-26 (reply #3903): Interior structure failure punches through hull. Post.
• Paul451, 2023-09-19 (reply #3982): Dyneema creeps. Post.
• Coastal Ron, 2023-09-19 (reply #3984): Cold reduces Dyneema creep. Post.
• Paul451, 2023-09-19 (reply #3985): Dyneema not structural. Post.
• Barley, 2023-09-28 (reply #4048): Drawn wire stronger than sheet. Post.
• Barley, 2023-09-29 (reply #4068, 1 like): No major compression members; bridge analogy; wire wrap (1 like). Post.
• Coastal Ron, 2023-09-29 (reply #4082): Single load path; build band first. Post.
• Twark_Main, 2023-09-30 (reply #4085): 3D grid of tension beams. Post.
• Twark_Main, 2023-09-30 (reply #4088): Grid structure explained. Post.
• mikelepage, 2023-12-28 (reply #4376, 1 like): Pantograph node for two-Dragon testbed. Post. Attachments: IDSS mated load limits.png, Dragon SpinG testbed_small.mp4, D2testbed_preview.png.
• Paul451, 2023-12-28 (reply #4377): Rollable boom types. Post. Attachments: BiSTEM1.png, Boom.PNG, boom spiral.jpg.
• jongoff, 2023-12-29 (reply #4381): STEM booms; jongoff. Post.
• Twark_Main, 2024-07-16 (reply #4649): Grid of prefab tension beams for torus and bolas. Post.
• Twark_Main, 2026-07-05 (reply #5066): Beef up diagonals. Post.
• lamontagne, 2026-07-08 (reply #5072, 1 like): Rods carry support, not spokes. Post. Attachments: Module Assembly_e.jpg, Image15_000.jpg.
• lamontagne, 2026-08-20 (reply #5082, 1 like): External cabling reduces port stress. Post. Attachments: Image10_002.jpg, Image9_002.jpg, Image10_000.jpg, Image14_001.jpg, Image22.jpg.
• Coastal Ron, 2026-08-21 (reply #5083): Living modules shouldn't be structural. Post.

External references

• Tethers Unlimited SpiderFab; Made In Space Archinaut; Cordero (MIT) NIAC 2023 "Bend-Forming of Large Electrostatically Actuated Space Structures".
• NTRS 20190031913 (rollable boom configurations).