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Dynamics & Control - Tether Critical Design Review Anne DeLion 27 February 2001 Tether Type - Multiline Multi-line Tether Weight is comparable to a single line tether High redundancy Survival probability of a failsafe multiline tether versus an equal-mass single line tether The number of lines is proportional to redundancy Very high survivability Hoytether structure is less likely to tangle on deployment Hoyt, R. and Forward, R. “The HoytetherTM: A Failsafe Multiline Space Tether Structure.” www.tethers.com Tether Specifications Material: Spectra 2000 Safety Factor: 5 (minimum) HAB ERV Length (m) 324.38 1003.5 Maximum Tension (N) 279600 342400 Diameter (m) 0.0225 0.0249 Mass (kg) 125.32 474.73 Stretch (m) 1.339 4.144 Deployment Reel Mass (kg) ~ 130 ~ 500 Reel Dimensions (m) .5r x 3l .5r x 3l Total Tether/Reel Volume (m^3) 2.49 2.85 Total Tether/Reel Mass (kg) ~255 ~975 Hab Tether/Cable Specifications Tether Material: Spectra 2000 Cable: 2210 kg/km Safety Factor: 5 (minimum) HAB Length (m) 356.8 Maximum Tension (N) 279600 Diameter (m) 0.1 Mass (kg) 2491 Deployment Reel Mass (kg) ~ 2500 Reel Dimensions (m) .5r x 3l Total Tether/Reel Volume (m^3) 5.15 Total Tether/Reel Mass (kg) ~5000 ERV Tether ERV Tether Mass versus g Force Loads [Anne DeLion] 600 Vary Angular Velocity; ERV Distance to CM is constant = 223 m Vary ERV Distance to CM; Angular Velocity is constant = 2rpm Tether Mass (kg) 500 400 300 200 100 0 0.4 0.5 0.6 0.7 0.8 g Force 0.9 1 1.1 Hab Deployment & Spin-up Three-Step Deployment Method 1. Thrust to spin up the connected vehicle system to the desired initial spin rate 2. Stop thrust, release vehicles, and conservation of angular momentum will deploy the tether 3. After tether is completely deployed, thrust to spin the system up to 2 rpm for artificial gravity Note: Thrusting is done on both the Hab and NTR. The thrust is proportional so moments about cm cancel. Also, by doing some thrusting on the NTR less propellent is used. Hab Deployment & Spin-up Numbers Hab Thrust = ~660 N NTR Thrust = ~250 N Initial Spin-up Artificial Gravity Spin-up Burn Time (hh:mm:ss) 00:22:26 08:20:53 Max G Force Generated 1.22g .38g Max Vtangential (m/s) 29.4 17.8 • If the tether is cut during the 2rpm spin: Imparted DV = 17.8 m/s Hab Tether Deployment Tether Deployment Thrust = 0 N Tension is kept on tether by centripetal force Deployment time = 1 hour Is arbitrary and can be set longer/shorter Mechanism to control deployment rate is black-boxed in reel system Final spin rate after deployment = 0.017 rpm ERV Deployment & Spin-up Three-Step Deployment Method Use same method as the Hab One significant difference: ERV will initially spin up to .38g. At some point in the mission, the ERV will spin up .02g additional each day for 31 days to finally create 1g ERV Deployment & Spin-up Numbers ERV Thrust = ~660 N MLV Thrust = ~250 N Initial Spin-up .38g Spin-up .02g Spin-up Total g Spin-up Burn Time (hh:mm:ss) 00:20:17 01:17:49 00:17:51 10:31:13 Max G Force Generated 1g .38g .02g additional 1g Max Vtangential (m/s) 14.0 28.8 - 46.7 • If the tether is cut during .38g phase of spin: Imparted DV = 28.8 m/s • If the tether is cut during 1g phase of spin: Imparted DV = 46.7 m/s ERV 1g Spin-up Total Angular Velocity of ERV System versus g Force Loads [Anne DeLion] 0.21 0.2 Angular Velocity (rad/s) 0.19 0.18 0.17 0.16 0.15 0.14 0.13 0.12 0.3 0.4 0.5 0.6 0.7 g Force 0.8 0.9 1 1.1 ERV 1g Spin-up G Force Loads Over the ERV Spin-up Duration [Anne DeLion] 1 0.9 G Force 0.8 0.7 0.6 0.5 0.4 0.3 0 5 10 15 20 Days 25 30 35 Tether Cost/Risk Manufacturing Cost: $1000/kg Hab Tether: $255 000 ERV Tether: $975 000 Success Probability Hoytether > 95% Avoiding catches in tether winding > 95% Due to greater than 10 N pulling out tether.[Hoyt] ERV 1g Spin-up Total Angular Velocity of ERV System versus Burn Time for Each .02g Burn [Anne DeLion] 0.22 0.21 Angular Velocity (rad/s) 0.2 0.19 0.18 0.17 0.16 0.15 0.14 0.13 75 80 85 90 95 100 105 Burn Time (s) 110 115 120 125 ERV 1g Spin-up Time of Each .02g Incremental Burn versus Total g Force Load [Anne DeLion] 125 120 115 Time (s) 110 105 100 95 90 85 80 75 0.3 0.4 0.5 0.6 0.7 g Force 0.8 0.9 1 1.1 Tether Cost/Risk Manufacturing Cost: $1000/kg Hab Tether: $255 000 ERV Tether: $975 000 Success Probability Hoytether > 95% Avoiding catches in tether winding > 95% Due to greater than 10 N pulling out tether.[Hoyt] Mechanical Risk = ??