Definitions: "realistic", "near-term", station vs ship, generations

The thread title, "Realistic, near-term, rotating space station", produced recurring definitional fights. This page records the working definitions that people actually used.

Key results

"Near-term"

There was never a consensus, and the proposed horizons span a factor of ten.

Proposer Definition
Roy_H (2014) up to 10–20 years Roy_H, 2014-02-24
daveklingler (2015) under 20 years; "realistic" and "near-term" are mutually exclusive without a billionaire daveklingler, 2015-02-23
Coastal Ron (2019) what could be launched on existing launchers with existing or 5-year technology Coastal Ron, 2019-01-08
Coastal Ron (2022/23) operational within 10 years of funding for Mars g; ~20 years for Earth g Coastal Ron, 2022-12-08; later 5–20 years, starting once Starship is operational Coastal Ron, 2023-01-18
Greg Hullender (2022) at most 2–3 Starship launches, about 10 years Greg Hullender, 2022-10-10
edzieba (2022) 5–10 years, on a CLD-class budget (hundreds of millions to single-digit billions) edzieba, 2022-10-11
mikelepage (2022) under 15,000 t, under $1.5B launch cost, under 2.5 years of assembly (about a Virginia-class submarine) mikelepage, 2022-10-14
JohnFornaro 20–40 years JohnFornaro, 2023-01-08, later "a century" JohnFornaro, 2023-01-09
Paul451 (2026) "realistic" = known physics; "near-term" = known technology Paul451, 2026-09-18

JohnFornaro later distinguished "nearer-term" (a Starship dumbbell) from "near-term" (a large ring) JohnFornaro, 2022-12-29. mikelepage proposed dropping "near-term" from any successor thread's title, since it had "caused no end of drama" mikelepage, 2023-01-03.

Station vs spaceship vs testbed

  • Station: stays in one orbit and uses propellant only for station-keeping. Ship: carries significant Δv mikelepage, 2019-04-11. A station is massive enough that it is not designed for large Δv and is rarely or never stopped mikelepage, 2022-10-15.
  • Coastal Ron: a testbed is temporary and gathers data. A station is lived on continuously and keeps rotating Coastal Ron, 2023-05-16. On this basis he called Vast's Haven-1 a testbed Coastal Ron, 2023-05-16. Paul451 replied that the distinction exists "nowhere outside of your imagination" Paul451, 2023-05-16.
  • Paul451's 2019 "open letter" ended the station-vs-ship fight. Every inhabitable rotating structure faces the same six problems: (1) stability, including crew and cargo movement; (2) power; (3) thermal control; (4) resupply and crew transfer; (5) health and psychological effects of rotation; (6) purpose, customers and funding Paul451, 2019-05-14.

Generations and classes

  • Coastal Ron's generations (by material source):
  • 1st: 100% Earth-built.
  • 2nd: a minority of materials from off Earth.
  • 3rd: a majority from off Earth Coastal Ron, 2023-02-07.
  • Earlier he framed them as: 1st generation = sealed 8 m modules, bolted, no welding Coastal Ron, 2022-10-13. Generation One = a "minimum viable dwelling" that proves rotation speed, minimum g, radiation and self-sufficiency Coastal Ron, 2018-11-02.
  • Twark_Main's classes (by number of docking ports), by analogy with Salyut 1–5, Salyut 6–7 and Mir/ISS:
  • Class 0: no port.
  • Class 1: one port (intermittent use).
  • Class 2: two ports (resupply).
  • Class 3: three or more ports (needs de-spun docking; transit hub).
  • He expected Classes 0–2 to be mostly barbells Twark_Main, 2023-02-07.
  • Inspired by the Howe KISS presentation Twark_Main, 2023-02-08.
  • Paul451 accepted that port count correlates with utility but saw no need for the scheme yet Paul451, 2023-02-09.
  • Alternative schemes:
  • Rate by carrying capacity and name classes after built stations ("Aurora-class") mikelepage, 2023-02-08.
  • Label by gravity level (a "0.38 G station") Coastal Ron, 2023-02-08.
  • "3-port station", like "18-wheeler" Coastal Ron, 2023-02-09.
  • Tonnage and passengers, like cruise ships LarryCanuck, 2023-02-08.

Terminology that stuck

  • Spin gravity (SG) is preferred by some over "artificial gravity" mikelepage, 2018-07-14.
  • Tumbling pigeon: end-over-end spin of a single long vehicle Paul451, 2016-01-13. Baton / stick / bola / dumbbell / barbell: see the architectures pages.
  • Rotating frame terms (Paul451):
  • "Non-rotating" = the hub that counter-rotates relative to the station.
  • "Rotating" = fixed to the station.
  • "Counter-rotating" = two opposing habs Paul451, 2022-12-09.
  • Stability terms (after much confusion):
  • Intermediate-axis (Dzhanibekov) instability: rotation about the intermediate axis.
  • Long-axis instability: spin about the minor axis drifts to end-over-end through energy dissipation.
  • Wobble: loosely, nutation or precession.
  • Proposed usage: ΔL = 0 → "IA reorientation / Dzhanibekov motion"; ΔL ≠ 0 → "wobble" 1, 2025-04-22; Paul451, 2025-04-22. See stability.
  • SSPO, "Sun Synchronous Precessional Orbit": JohnFornaro's name for a station whose spin axis tracks the Sun JohnFornaro, 2025-04-28. Twark_Main suggested "Sun-pointing" to avoid confusion with sun-synchronous orbits Twark_Main, 2025-04-28.

Open questions

  • Should the first facility be judged as a station (permanent habitation) or a testbed (variable-g research)? This affects its requirements, such as docking while spinning and lifeboats.
  • Is any Starship-based configuration a "station"?

Sources

Forum posts

  • Roy_H, 2014-02-24 (reply #136): Near-term = 10–20 years. Post.
  • daveklingler, 2015-02-23 (reply #388, 1 like): Near-term <20 y; needs billionaire; Globus 2014 radiation paper. Post.
  • Paul451, 2016-01-13 (reply #806): Tumbling pigeon coined. Post.
  • mikelepage, 2018-07-14 (reply #923, 1 like): Uses "SG" not AG. Post. Attachments: DeSGAv7animate3b-small.mp4.
  • Coastal Ron, 2018-11-02 (reply #1256): Generation One = minimum viable dwelling. Post.
  • Coastal Ron, 2019-01-08 (reply #1288): Thread aim: existing launchers, near-term tech. Post.
  • mikelepage, 2019-04-11 (reply #1531, 1 like): Definition: station vs ship by Δv. Post.
  • Paul451, 2019-05-14 (reply #1633, 8 likes): Open letter: six problems all rotating structures share (8 likes). Post.
  • Greg Hullender, 2022-10-10 (reply #1967, 1 like): >2–3 Starship launches not near-term. Post.
  • edzieba, 2022-10-11 (reply #2008, 2 likes): Near-term 5–10 yr, CLD-class budget. Post.
  • Coastal Ron, 2022-10-13 (reply #2039): 1st gen = Earth-built bolted modules. Post.
  • mikelepage, 2022-10-14 (reply #2077): Metric: <15,000 t, <$1.5B launch, <2.5 yr assembly. Post.
  • mikelepage, 2022-10-15 (reply #2104, 3 likes): Station = rarely/never stopped. Post.
  • Coastal Ron, 2022-12-08 (reply #2579): Near-term = operational within 10 yr of funding. Post.
  • Paul451, 2022-12-09 (reply #2620, 1 like): Terminology rotating/non-rotating/counter-rotating. Post.
  • JohnFornaro, 2022-12-29 (reply #2721): "Nearer term" concept. Post.
  • mikelepage, 2023-01-03 (reply #2759, 1 like): Proposal to split thread; drop "near-term". Post.
  • JohnFornaro, 2023-01-08 (reply #2812): Near term 20–40 yr. Post.
  • JohnFornaro, 2023-01-09 (reply #2834): Near term = a century. Post.
  • Coastal Ron, 2023-01-18 (reply #2973): Near-term 5–20 years. Post.
  • Twark_Main, 2023-02-07 (reply #3256): Class 0–3 taxonomy by docking ports. Post.
  • Coastal Ron, 2023-02-07 (reply #3257): Generations by material source; lifeboat philosophy. Post.
  • Twark_Main, 2023-02-08 (reply #3259): Howe classification inspiration. Post.
  • mikelepage, 2023-02-08 (reply #3262, 1 like): Rate by carrying capacity; name after stations. Post.
  • Coastal Ron, 2023-02-08 (reply #3263): Classify by gravity level. Post.
  • LarryCanuck, 2023-02-08 (reply #3267): Cruise-ship style metrics. Post.
  • Paul451, 2023-02-09 (reply #3276, 1 like): Port count correlates with utility; classification not needed yet. Post.
  • Coastal Ron, 2023-02-09 (reply #3278, 1 like): Just say "3-port station". Post.
  • Coastal Ron, 2023-05-16 (reply #3714): Haven-1 is a testbed. Post.
  • Paul451, 2023-05-16 (reply #3716): Testbed distinction imaginary. Post.
  • Coastal Ron, 2023-05-16 (reply #3719): Testbed vs station definition. Post.
  • 1, 2025-04-22 (reply #4891, 1 like): Terminology: Dzhanibekov motion vs wobble. Post.
  • Paul451, 2025-04-22 (reply #4897): Long-axis vs intermediate-axis instability distinction. Post.
  • JohnFornaro, 2025-04-28 (reply #4905, 1 like): SSPO defined. Post. Attachments: Ring-SSP0-Animation-10-12-23.mp4.
  • Twark_Main, 2025-04-28 (reply #4906): Call it Sun-pointing. Post.
  • Paul451, 2026-09-18 (reply #5144, 2 likes): Realistic = known physics; near-term = known technology; keep one catch-all thread. Post.

External references

  • M. Howe, Caltech KISS 3D workshop presentation (station classification), kiss.caltech.edu/workshops/3d/presentations/Howe.pdf.