Spin-up, propulsion and reboost

Key results

Spin-up and spin-down

• Small stations: RCS is trivial.
• A Starship "tumbling pigeon" at 1 g and 6 rpm has ~15 m/s tangential speed, equal to a ~5 m/s RCS burn Paul451, 2022-10-25.
• Spin-up or spin-down costs 10–40 m/s per Starship (Dragon 2 RCS ~400 m/s) mikelepage, 2019-04-07.
• Pitch-axis RCS spin-up is more efficient than rolling then tumbling (longer moment arm) Twark_Main, 2019-11-05.
• Despin/respin to dock is the cheapest option for a Vast-type baton Paul451, 2022-08-27.
• Calculators. mikelepage's spin-up spreadsheet ("Torque to spin up Rotating spacecraft.xlsx") mikelepage, 2023-01-27. lamontagne's test case: 57 t of propellant, 450 N for ~100 h at Isp 300 s lamontagne, 2023-01-27.
• mikelepage: a full spin-up/down cycle costs less than one tanker load (150 t); 57 t per cycle mikelepage, 2023-01-28.
• Fixed MoI formulas and calculator mikelepage, 2023-01-31; Twark_Main, 2023-01-30.
• Electric spin-up without propellant.
• Counter-rotating segments allow electric spin-up 1, 2018-07-04.
• 2–3 kW motors spin contra-rotating rings from 0 to 1 g in a couple of hours A_M_Swallow, 2015-11-15. A 3 kW motor spins up a 30–60 t vehicle in ~30 min A_M_Swallow, 2015-09-15.
• Solar maglev rails along the hub high road, 2014-02-21. A drive wheel between drums Impaler, 2015-02-17.
• Flywheels: a small super-strong flywheel KelvinZero, 2019-01-07; fast small Kevlar flywheels as a buffer Shevek23, 2019-10-28; see flywheels.
• Starship as anchor: dock Starship radially to the non-rotating centre, and a central motor spins the station while Starship's OMS holds the non-rotating part, so no propellant is transferred mikelepage, 2023-03-31.
• An asteroid as counterbalance, with electric spin-up/down mikelepage, 2024-01-31.
• Lorentz-force spin-up (LMT): a 100 m, 3000 t torus in ELEO at 400 km, spun to Mars g in ~2 months with ~5 cm copper cables along 4 spokes to field emitters; detumble with two magnetorquers LMT, 2023-04-02.
• Large stations. JohnFornaro would spin his ring slowly over 1–5 years; 8 Raptors would do it in 11 h JohnFornaro, 2023-02-04. Coastal Ron: never despin Coastal Ron, 2022-10-25.
• Momentum dumping. Gyros don't cancel constant external torques, so desaturation is needed Paul451, 2022-10-27. Magnetorquers are too weak for docking loads and serve only for CMG desaturation Jim, 2018-07-05. In LEO, magnetorquers can replace CMGs (Kim, Bates & Postlethwaite 2009) LMT, 2018-07-04.

Precession for sun-pointing

• This is the largest recurring propellant cost; see orientation and sun-pointing. Its magnitude is 2π × L per year Twark_Main, 2025-04-29; Twark_Main, 2026-09-19.

Reboost and drag

• ISS scale.
• ATV reboost gave 2.65 m/s in 740 s gbaikie, 2014-02-20.
• Raising ISS (~420 t) with an FH booster gives ~290 m/s per flight for ~$200M cuddihy, 2014-02-18.
• Operational cost is dominated by resupply and reboost gbaikie, 2014-02-17.
• Continuous low thrust is better than weekly boosts Roy_H, 2014-03-17.
• Drag cancellation.
• Electrodynamic tethers and ISEP booms counter drag in VLEO LMT, 2018-07-06; LMT, 2022-11-04; LMT, 2024-03-01.
• Ion station-keeping: a 50%-efficient 3000 s drive with 20% PV gives 2.1 mN per m² of PV, against ≤0.12 mN of drag per m², so it easily beats panel drag Twark_Main, 2024-03-03.
• ASCENT bimodal propellant (Isp ~1500 s in ion mode) LMT, 2023-01-15.
• Water as station-keeping propellant Aussie_Space_Nut, 2014-02-17; water resistojets LMT, 2018-07-16.
• Tiltable thrusters around the rim for station keeping Coastal Ron, 2022-10-25. Thrusters on masts increase the lever arm Twark_Main, 2023-02-04.
• A 3 s burn = 18° of rotation at 1 rpm, so thrust must be pulsed or come from the hub rakaydos, 2019-04-05; Glorky FCY, 2019-04-05.
• Thrust along the spin axis is OK if the acceleration is much less than spin gravity (NTR, fission fragment) KelvinZero, 2019-03-25.
• Formation flying requires matched drag, and station-keeping propellant scales with size, so connect the elements mikelepage, 2024-03-01. CanX-4/5 cm-scale formation flying with cold gas lamontagne, 2024-03-01.

Open questions

• Can electrodynamic or Lorentz-force systems scale to 1000+ t stations?
• For large sun-pointing stations, is precession propellant a showstopper compared with an edge-on orientation?

Related pages

• Sun-pointing · Flywheels · Location and orbits

Sources

Forum posts

• gbaikie, 2014-02-17 (reply #17): Resupply/reboost dominate. Post.
• Aussie_Space_Nut, 2014-02-17 (reply #18): Water propellant. Post.
• cuddihy, 2014-02-18 (reply #69): FH ~290 m/s per flight. Post.
• gbaikie, 2014-02-20 (reply #93): ATV reboost. Post.
• high road, 2014-02-21 (reply #104): Solar maglev rails. Post.
• Roy_H, 2014-03-17 (reply #192): Continuous low thrust. Post.
• Impaler, 2015-02-17 (reply #281): Drive wheel between drums. Post.
• A_M_Swallow, 2015-09-15 (reply #643): 3 kW, 30 min. Post.
• A_M_Swallow, 2015-11-15 (reply #776): 2–3 kW motor. Post.
• LMT, 2018-07-04 (reply #864): Magnetorquers vs CMGs. Post.
• 1, 2018-07-04 (reply #868, 1 like): Counter-rotating electric spin-up. Post.
• Jim, 2018-07-05 (reply #879): Magnetorquers too weak. Post.
• LMT, 2018-07-06 (reply #886, 1 like): ISEP boom. Post.
• LMT, 2018-07-16 (reply #941, 1 like): Water resistojets. Post.
• KelvinZero, 2019-01-07 (reply #1266): Small fast flywheel. Post.
• KelvinZero, 2019-03-25 (reply #1398): Axial thrust OK. Post.
• Glorky FCY, 2019-04-05 (reply #1472, 1 like): Hub thrusters. Post.
• rakaydos, 2019-04-05 (reply #1473): Pulsed burns. Post.
• mikelepage, 2019-04-07 (reply #1501, 2 likes): 10–40 m/s per Starship. Post.
• Shevek23, 2019-10-28 (reply #1699): Kevlar flywheel buffer. Post.
• Twark_Main, 2019-11-05 (reply #1706, 1 like): Pitch-axis spin-up. Post.
• Paul451, 2022-08-27 (reply #1730, 1 like): Despin/respin cheapest. Post.
• Paul451, 2022-10-25 (reply #2206): Tumbling pigeon spin-up ~5 m/s. Post.
• Coastal Ron, 2022-10-25 (reply #2207): Never despin. Post.
• Paul451, 2022-10-27 (reply #2227, 2 likes): Gyros need desat. Post.
• LMT, 2022-11-04 (reply #2315): Electrodynamic tethers with PV capacitors. Post. Attachments: Globus_Table6.png.
• LMT, 2023-01-15 (reply #2911): ASCENT bimodal. Post.
• mikelepage, 2023-01-27 (reply #3126, 3 likes): Spin-up spreadsheet (3 likes). Post. Attachments: Calculator screenshot.png, Torque to spin up Rotating spacecraft.xlsx.
• lamontagne, 2023-01-27 (reply #3130): 57 t, 450 N, 100 h. Post.
• mikelepage, 2023-01-28 (reply #3149): Spin cycle < one tanker. Post.
• Twark_Main, 2023-01-30 (reply #3192): Torus MoI formulas. Post.
• mikelepage, 2023-01-31 (reply #3202, 1 like): Fixed calculator. Post. Attachments: Torque to spin up Rotating spacecraft-updated.xlsx.
• Twark_Main, 2023-02-04 (reply #3237): Thrusters on masts. Post.
• JohnFornaro, 2023-02-04 (reply #3238): Slow spin-up. Post.
• mikelepage, 2023-03-31 (reply #3566, 1 like): Starship anchor spin-up (1 like). Post.
• LMT, 2023-04-02 (reply #3571, 1 like): Lorentz spin-up (1 like). Post. Attachments: 400 km geomagnetic field at 0 N 0 E.png.
• mikelepage, 2024-01-31 (reply #4450): Asteroid counterbalance. Post.
• mikelepage, 2024-03-01 (reply #4522): Formation flying costs. Post.
• lamontagne, 2024-03-01 (reply #4523, 1 like): CanX-4/5. Post.
• LMT, 2024-03-01 (reply #4526): Johnson & Herrmann 1998. Post. Attachments: Johnson and Herrmann 1998 Fig4.png.
• Twark_Main, 2024-03-03 (reply #4532, 1 like): Ion beats panel drag. Post.
• Twark_Main, 2025-04-29 (reply #4917, 2 likes): 2π·L per year (2 likes). Post.
• Twark_Main, 2026-09-19 (reply #5153): Correct factor. Post.

External references

• Johnson, L. & Herrmann, M. (1998). International Space Station electrodynamic tether reboost study. NASA.
• Kim, Bates & Postlethwaite (2009), magnetorquer attitude control.