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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 The number of lines is proportional to redundancy Very high survivability

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Dynamics control tether
Dynamics & Control - Tether

Critical Design Review

Anne DeLion

27 February 2001


Tether type multiline
Tether Type - Multiline

  • Multi-line Tether

    • Weight is comparable to a single line tether

    • High redundancy

      • The number of lines is proportional to redundancy

    • Very high survivability

    • Hoytether structure is less likely to tangle on deployment

Survival probability of a failsafe multiline tether

versus an equal-mass single line tether

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)

Tether Specifications


Hab tether cable specifications

Tether Material: Spectra 2000

Cable: 2210 kg/km

Safety Factor: 5 (minimum)

Hab Tether/Cable Specifications



Hab deployment spin up
Hab Deployment & Spin-up

  • Three-Step Deployment Method

    • Thrust to spin up the connected vehicle system to the desired initial spin rate

    • Stop thrust, release vehicles, and conservation of angular momentum will deploy the tether

    • 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 Deployment & Spin-up Numbers

Hab Thrust = ~660 N

NTR Thrust = ~250 N

  • If the tether is cut during the 2rpm spin:

    Imparted DV = 17.8 m/s


Hab tether deployment
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
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 Deployment & Spin-up Numbers

ERV Thrust = ~660 N

MLV Thrust = ~250 N

  • 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




Tether cost risk
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]




Tether cost risk1
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 = ??


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