DINO: MAGIC Tether 11 September 2015 MAGIC Tether Trade Study Anthony Lowrey Ryan Olds Andrew Mohler November 10, 2003

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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 2 nd stage –Successful mission: longest structure ever deployed to that time

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium ATEx Deployment

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Post-Deployment Tether Dynamics

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Deployed Tether Geometry Tip Mass (5kg) Main Structure (25kg) ZenithNadir Libration Angle 20m Velocity Oscillating Frequencies: Roll Oscillating Frequency = Hz Pitch Oscillating Frequency = Hz Yaw Oscillating Frequency = Hz

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Current Issues Tension and Libration Pendulum Motion Requires Accurate Deployment Tether Tape Material Properties

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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.

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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.

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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.

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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.

DINO: MAGIC Tether 11 September 2015 Tether Deployment

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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 Braking System Tether Z-fold Tip Mass Lightband Tether Guides Velocity Tether Wheel (turning) Brake shoe (fixed) Brake

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Booms

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Boom Types There are 5 main boom types to consider: –STEM Boom –Elastic Memory Composite (EMC) Boom –STACER Boom (SSTL) –Coilable Booms –Inflatable Boom

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Student-Designed Boom Citizen Explorer –4 m boom, 2 kg tip mass –Uses three roles of stanley tape measure –Deployed using Starsys’ HOP

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Conclusions and Recommendations

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium 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

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Appendix A

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Appendix B

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Appendix C

DINO: MAGIC Tether 11 September 2015 Colorado Space Grant Consortium Appendix D