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MAGIC Tether Trade Study

MAGIC Tether Trade Study. Anthony Lowrey Ryan Olds Andrew Mohler November 10, 2003. Background. Purpose of trade study To assess the feasibility of the MAGIC Tether system Concern about design was raised at the PDR Thought of as high risk for DINO

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MAGIC Tether Trade Study

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  1. MAGIC Tether Trade Study Anthony Lowrey Ryan Olds Andrew Mohler November 10, 2003

  2. Background • Purpose of trade study • To assess the feasibility of the MAGIC Tether system • Concern about design was raised at the PDR • Thought of as high risk for DINO • To investigate possible alternatives to the tether • Requirements from DINO • Spacecraft must be nadir pointing Colorado Space Grant Consortium

  3. Introduction to Tethers in Space • Gravity Gradient Stabilization • Lower mass has more gravitational than centrifugal force • Upper mass has more centrifugal than gravitational force • Lower mass slower • Upper mass faster Colorado Space Grant Consortium

  4. Introduction to Tethers in Space • Important issues • Tether length and tension • The longer the tether length, the more tension • Tether material properties • Coefficient of Thermal Expansion (CTE) • Shape Memory • Debris/Micrometeorite resistance • Tether deployment • Recoil • Tip-off rate Colorado Space Grant Consortium

  5. Brief History of Tethers • Tethered Satellite System 1 (TSS-1) • 1992 NASA shuttle tether • 550 kg satellite, 20 km electrically conductive tether • Deployment failed after 256 m from mechanical failure • Small Expendable Deployment System (SEDS) • 1993 NASA project • 25 kg satellite, 20 km tether deployed from a Delta 2nd stage • Successful mission: longest structure ever deployed to that time Colorado Space Grant Consortium

  6. Brief History of Tethers (Cont.) • SEDS-II • Launched in 1994 by NASA • Successful deployment • Tether was cut after only 3.7 days • TSS-1R • 1996 NASA reflight of TSS-1 • Spark severed tether just before deployment end • Tether Physics and Survivability Experiment (TiPS) • Built by Naval Research Lab. Launched in 1997 • 4 km tether survived about 3 years • Success lead to the ATEx project Colorado Space Grant Consortium

  7. Advanced Tether Experiment (ATEx) • Purpose • Demonstrate tether stability and control • Fly a long term, survivable tether • 6 km tether experiment was to last 61 days • Deployment • Deployed at steady 2 cm/s using a stepper motor • Deployment was to take 3.5 days • Sensors • Local angle sensor – 16 LED/detector pairs in a plane • Turns counter to measure length of deployed tether Colorado Space Grant Consortium

  8. ATEx Deployment Colorado Space Grant Consortium

  9. ATEx Failure • Launched atop STEX on 8/3/98 • Experiment began in 1/99 • Deployed 22 meters before being jettisoned by STEX • Tether blocked out-of-bounds LAS due to “excessive slack tether” • Determined reason for failure • Tether thermal expansion • From eclipse to sun, tether expanded 6 inches Colorado Space Grant Consortium

  10. ATEx Lessons Learned • Tethers can’t be fully tested on Earth • Good math models required in design • Provide large margins for error in design • Deployability of tether needed more consideration • Shape memory and CTE proved downfall • Experiment should be focus of mission Colorado Space Grant Consortium

  11. Post-DeploymentTether Dynamics

  12. Deployed Tether Geometry Tip Mass (5kg) Velocity 20m Libration Angle Nadir Zenith • Oscillating Frequencies: • Roll Oscillating Frequency = 0.000368 Hz • Pitch Oscillating Frequency = 0.000316 Hz • Yaw Oscillating Frequency = 0.000177 Hz Main Structure (25kg) Colorado Space Grant Consortium

  13. Current Issues • Tension and Libration • Pendulum Motion Requires Accurate Deployment • Tether Tape Material Properties Colorado Space Grant Consortium

  14. Tension Analysis • For a 20m tether, Tension will be approximately 0.3mN. • Tension this low could fail to provide adequate control in the pitch and roll axes of DINO. • At low tension, tip mass and main structure would rotate freely until tension builds up. Colorado Space Grant Consortium

  15. Pendulum Motion • Pendulum motion of DINO in the pitch and roll axes might not damp out over time. • Accuracy of the deployment would define the pointing accuracy of DINO. • ±10º off of nadir would be possible. Colorado Space Grant Consortium

  16. Material Properties • Thermal Expansion (20x10-6mm/mm/K) 13.7cm expansion in sun • Thermal Snap-Contraction (100x10-6/mm/mm/K) 68.6cm contraction in shade • Stress vs. Strain of Tether • Effective Modulus could differ from specs. Colorado Space Grant Consortium

  17. Conclusion • Issues/Risks • Lack of Tension • Pendulum Motion will not damp out • Tether expands and contracts in and out of sunlight • Possible solutions • A boom would be more rigid and could provide more predictable control. • Build a emergency release mechanism for the tether if it is used and provide a backup such as a momentum wheel. Colorado Space Grant Consortium

  18. Tether Deployment

  19. Brake Tether Tip Mass Wheel (turning) Tether Guides Velocity Brake shoe (fixed) Lightband Braking System Tether Z-fold Design at PDR • Open-Loop Deployment • Lightband will provide kickoff velocity of 2 ft/s • Deployment will take approximately 40 sec • Tether will be “left-behind” by tip mass • Braking system will slow tip-mass near end of travel • Simple compared to a complex motor system Colorado Space Grant Consortium

  20. Deployment Suggested Changes • Spoke with Jeff Slostad of Tethers Unlimited Inc • Longer tether • Having extra tether on board • Liked fast deployment • Liked “leave-behind” method • Feedback control system for braking Colorado Space Grant Consortium

  21. Booms

  22. Introduction to Booms • Provides gravity gradient stabilization on small spacecraft • Accurate to within 5 deg of nadir • Used for “short” deployments (< 6m) • High stiffness compared to tethers • Bigger and heavier than a tether Colorado Space Grant Consortium

  23. Boom Types • There are 5 main boom types to consider: • STEM Boom • Elastic Memory Composite (EMC) Boom • STACER Boom (SSTL) • Coilable Booms • Inflatable Boom Colorado Space Grant Consortium

  24. STEM Boom • STEM: Storable Tubular Extendable Member • One of the oldest and most successful deployable booms • Current stems use either Beryllium Copper or Stainless Steal • Limited in size due to stored energy strains and high density • Reel-stored Extendable Boom • Analysis shows: • Significant reduction of mass • Improved specific stiffness • Reduced stored strain energy Colorado Space Grant Consortium

  25. Elastic Memory Composite (EMC) Boom • CTD’s STEM boom • A coilable Longeron Deployable Boom • Deployment force provided by stain energy • Made of unidirectional S-glass/epoxy • Prototype EMC longerons exhibited • Highly predictable • Repeatable structural response • Packaging performance • Significant reduction in system mass • Reduced stored strain energy Colorado Space Grant Consortium

  26. STACER Boom • SSTL-Weitzmann 6m Deployable boom is • A rigid structure • Contains a prefabricated 1-13kg tip mass and deploying mechanism • Deploys at a rate of 0.3 m/s • Has a mass of 2.2kg (without tip mass) • Requires 5 A for >10 msec. • A history of 25 years, with over 600 Units used Cons: *Has a storage size of 102x115x264 mm *Deploys using Pyro-Cutter actuation Colorado Space Grant Consortium

  27. Coilable Booms • ABLE Coilable Booms • 100% Successful Flight Heritage • Two types • Lanyard Deployed • Most common • Compact mass stowage (2% of deployed length) • Extremely light weight capability (<50g/m) • Stowed strain energy gives positive deployment force • Least expensive • Canister Deployed • Motor driven • Retractable/deployable • Larger stowage volume Colorado Space Grant Consortium

  28. Inflatable Boom • Inflatable boom from ILC Dover • Thermoset composites • Thermally cured • Power requirement of 0.01W/in^2 • Heater performance(survivability) validated • Outgassing negligible outside of MLI • Deployment Component if desired (as shown above) BUT: -Expanded in a inflation gas reaction (gas tank required) -Less stiff of a structure than other boom types Colorado Space Grant Consortium

  29. Student-Designed Boom • Citizen Explorer • 4 m boom, 2 kg tip mass • Uses three roles of stanley tape measure • Deployed using Starsys’ HOP Colorado Space Grant Consortium

  30. Student-Designed Boom (Cont.) • Starsys • Designs many booms for customers • Jeff Harvey and Carlton Devillier offered to help • Both worked on booms at AEC Able for years • Suggested using 1 inch Stanley tape • Poor torsional stiffness, but more than tether • Deployment and damping mechanism still needed • Once deployed, it is sure to work • Said we should design ourselves • They will review our designs • Can provide flight qualified tape • Lightband could still be used Colorado Space Grant Consortium

  31. Conclusions and Recommendations

  32. Tether • Pros • Low mass • Already procured • Design started • Cons • Hard to predict dynamics • Very low tension at current length • Difficult to deploy • Tether material is not ideal Colorado Space Grant Consortium

  33. Ways Tether Could Work • Lengthen tether • Longer tether would mean more tension • Tether Spool • More predictable control of tether • Controlled braking • Prevents recoil • Treat as an “experiment” and provide backup • Focus more attention on subsystem Colorado Space Grant Consortium

  34. Boom • Pros • Structurally rigid • Easier to deploy • More predictable dynamics • A lot of flight experience • Cons • Greater mass and volume than tether • 6 meter (20 ft) maximum length • New design Colorado Space Grant Consortium

  35. Trade Study Conclusion • Tether could work • Boom is better decision for DINO • Less risk than tether • Easier to win flight competition • Direct help from industry • Still a lot of student involvment Colorado Space Grant Consortium

  36. Appendix A Colorado Space Grant Consortium

  37. Appendix B Colorado Space Grant Consortium

  38. Appendix C Colorado Space Grant Consortium

  39. Appendix D Colorado Space Grant Consortium

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