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DINO: MAGIC Tether April 19, 2023
MAGIC Tether Trade Study
Anthony LowreyRyan Olds
Andrew Mohler
November 10, 2003
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
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mmLT
23
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Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
ATEx Deployment
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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 April 19, 2023
Post-DeploymentTether Dynamics
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
Deployed Tether Geometry
Tip Mass (5kg)
Main Structure (25kg)
ZenithNadir
Libration Angle
20m
Velocity
Oscillating Frequencies:•Roll Oscillating Frequency = 0.000368 Hz•Pitch Oscillating Frequency = 0.000316 Hz•Yaw Oscillating Frequency = 0.000177 Hz
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
Current Issues
• Tension and Libration• Pendulum Motion Requires Accurate
Deployment• Tether Tape Material Properties
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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.
0 100 200 300 400 500 600 700 800 900 10000
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
Tether length [m]
Ten
sion
[N
]
Tether Tension vs. Length
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-1
0
1
Roll
(deg
)
Euler Angles
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-2
0
2
Pitc
h (d
eg)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-2
0
2
time (hrs)
Yaw
(deg
)
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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 April 19, 2023
Tether Deployment
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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 April 19, 2023
Booms
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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 April 19, 2023
Conclusions and Recommendations
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
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
DINO: MAGIC Tether April 19, 2023
Appendix A
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
Appendix B
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-5
0
5x 10
-3
Roll R
ate(
deg/
2)
Euler Rates
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-5
0
5x 10
-3
Pitc
h Ra
te(d
eg/2
)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-2
0
2x 10
-3
time (hrs)
Yaw
Rate
(deg
/2)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-1
0
1x 10
-5
Roll A
ccel(
deg/
s2
Euler Accelerations
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-5
0
5x 10
-6
Pitc
h Ac
cel(d
eg/s
2 )
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-2
0
2x 10
-6
time (hrs)
Yaw
Rate
(deg
/s2 )
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
Appendix C
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-1
0
1x 10
-3
Rol
l tor
que
(N*m
)
Spacecraft Torque
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-1
0
1x 10
-3
Pitc
h to
rque
(N
*m)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6-5
0
5x 10
-7
Time (hrs)
Yaw
tor
que
(N*m
)
Colorado Space Grant Consortium
DINO: MAGIC Tether April 19, 2023
Appendix D
0 100 200 300 400 500 600 700 800 900 10000
0.2
0.4
0.6
0.8
1
1.2x 10
-3
Tether length [m]
Elo
ngat
ion
[m]
Tether Elongation due to Stretching
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