Seals, rotary joints and module joints

Key results

Rotary seals and joints (between rotating and non-rotating parts)

Module-to-module joints

  • Modern interfaces use at least two seals between vacuum and atmosphere (the LIDS double O-ring; CBM "Gask-O-Seal") Twark_Main, 2024-01-26; Twark_Main, 2024-01-26. E. H. Davis's CBM design exegeses cover seal design and backup sealing lamontagne, 2024-01-26.
  • Leak rates. The CBM is designed for ~4 g/day of air loss. The ISS actually loses ~300 g/day, and ran at 1.5 kg/day for six months in 2020 before the leak was found Paul451, 2024-01-28. EVAs and docking cycles leak more than modules (Schaezler et al. 2011) LMT, 2024-02-06.
  • Coastal Ron's permanent joints: external bolted load connections, metal-to-metal port contact, internal serviceable seals or tape. Twark_Main: metal-to-metal contacts are not air seals; use speed tape only as a secondary; weld with EBW if the joint is truly permanent Coastal Ron, 2024-01-26; Twark_Main, 2024-02-14; Twark_Main, 2024-01-30.
  • Paul451's internal compression ring overlaps the join with multiple O-rings; air pressure pushes the ring into the seal Paul451, 2024-01-26.
  • Double gasket with vacuum port between them: the reclaimed leak gives ~500× reduction Twark_Main, 2024-02-14.

Berthing and docking standards

Open questions

  • Can a continuous large-diameter vacuum rotary seal be qualified for decades of operation?
  • Are permanent bolted-and-taped joints between modules ever acceptable, or should they be welded or use CBM-style double seals?

Sources

Forum posts

  • cuddihy, 2014-02-17 (reply #12): Canfield joint NASA study. Post.
  • JasonAW3, 2014-03-19 (reply #214): ISS spacesuit rotating joint model. Post.
  • RanulfC, 2014-03-21 (reply #242, 1 like): Paramagnetic LOX bladder seals. Post.
  • A_M_Swallow, 2015-11-13 (reply #769): Slip rings easy; fluids difficult. Post.
  • lamontagne, 2022-09-29 (reply #1818): Large rotary seals exist (Chesterton). Post. Attachments: Station1 (4).png.
  • lamontagne, 2022-10-06 (reply #1884): Microwave power beaming across joint. Post.
  • Asteroza, 2022-10-07 (reply #1885): SARJ metal shavings; arcing. Post.
  • lamontagne, 2022-10-07 (reply #1890): ISS roll rings gold dust (NTRS). Post. Attachments: 19940029729.pdf, 19920014958.pdf, 19940028788.pdf.
  • Twark_Main, 2023-01-16 (reply #2914): Rotating joints inside pressure vessel. Post.
  • lamontagne, 2023-01-19 (reply #2987): Short-term rotating airlock. Post.
  • lamontagne, 2023-01-20 (reply #3007): Short-term rotating berthing port. Post. Attachments: canport.png, can baton.png.
  • Asteroza, 2023-01-23 (reply #3029, 1 like): Temporary sliding seal interface (1 like). Post.
  • lamontagne, 2023-01-24 (reply #3048): Berthing port strength ~100,000 lb. Post. Attachments: IAC-21,D3,IP,4,x64597 Universal Berthing Mechanism Standard.pdf, airlock.jpg.
  • lamontagne, 2023-02-17 (reply #3330): Hydro turbine seals 4 m, 15 bar, 30 m/s. Post.
  • Paul451, 2023-02-17 (reply #3335): Vacuum precludes many materials. Post.
  • JohnFornaro, 2023-02-17 (reply #3338): Outgassing; bearing mass. Post.
  • MickQ, 2023-03-06 (reply #3484): Flanged joint locks when pressurized. Post.
  • DanClemmensen, 2023-04-05 (reply #3584): IDSS 800 mm too small. Post.
  • LMT, 2023-10-31 (reply #4255): Nautilus-X seal tech flown. Post.
  • mikelepage, 2023-12-28 (reply #4376, 1 like): IDSS load limits. Post. Attachments: IDSS mated load limits.png, Dragon SpinG testbed_small.mp4, D2testbed_preview.png.
  • Twark_Main, 2023-12-28 (reply #4378): 100 kN unpressurized. Post.
  • mikelepage, 2024-01-10 (reply #4389, 2 likes): UBM spec (2 likes). Post. Attachments: IAC-21,D3,IP,4,x64597 Universal Berthing Mechanism Standard.pdf.
  • mikelepage, 2024-01-14 (reply #4398): UBM 450 kN capacity limits. Post.
  • Paul451, 2024-01-25 (reply #4405, 2 likes): Separate docking fixtures (2 likes). Post.
  • Paul451, 2024-01-25 (reply #4409): Keep-out zones for fixtures. Post.
  • Coastal Ron, 2024-01-26 (reply #4411): Permanent module joint concept. Post.
  • Twark_Main, 2024-01-26 (reply #4412): Two seals: LIDS O-rings, Gask-O-Seal. Post.
  • lamontagne, 2024-01-26 (reply #4413): E. H. Davis CBM exegesis. Post.
  • Paul451, 2024-01-26 (reply #4418, 1 like): Internal compression ring seal (1 like). Post. Attachments: Berthing port ring seal.png.
  • Twark_Main, 2024-01-26 (reply #4419): Typical multiple seal arrangement. Post.
  • Paul451, 2024-01-28 (reply #4428): CBM 4 g/day; ISS 300 g/day; 1.5 kg/day in 2020. Post.
  • Twark_Main, 2024-01-30 (reply #4436): Speed tape as secondary. Post.
  • LMT, 2024-02-06 (reply #4455): Schaezler 2011: EVAs & docking leak most. Post. Attachments: Schaezler et al. 2011 Table 1.png.
  • Twark_Main, 2024-02-14 (reply #4471): Metal-to-metal not a seal; tape secondary. Post.
  • Twark_Main, 2024-02-14 (reply #4475): Double gasket with vacuum port. Post.
  • Twark_Main, 2025-09-14 (reply #4950): Quadruple-sealed rotating tunnel. Post.
  • Twark_Main, 2025-09-14 (reply #4955): Zero-g core, no sliding vacuum seal. Post.
  • lamontagne, 2026-08-20 (reply #5082, 1 like): Vast large docking adapter standard. Post. Attachments: Image10_002.jpg, Image9_002.jpg, Image10_000.jpg, Image14_001.jpg, Image22.jpg.

External references

  • Nexus Aurora, Universal Berthing Mechanism Standard (IAC-21 D3 IP 4 x64597), nexusaurora.org/projects/ubm/.
  • E. H. Davis, Common Berthing Mechanism core design description, ehdavis.engineering.
  • NTRS 20080003821 (docking seals); NTRS 19940029729, 19920014958, 19940028788 (ISS roll rings).
  • Schaezler, R. et al. (2011). Trending of overboard leakage of ISS cabin atmosphere. ICES 2011-5149.