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Tethered Propulsion Tether propulsion requires no fuel, is completely reusable and
environmentally clean, and provides all these features at lowcost.
Space tethers are cables, usually long and very strong, which canbe used for propulsion, stabilization, or maintaining theformation of space systems by determining the trajectory ofspacecraft and payloads. Depending on the mission objectivesand altitude, spaceflight using this form of spacecraft propulsionmay be significantly less expensive than spaceflight using rocketengines.
Three main techniques for employing space tethers are indevelopment
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Types
Electrodynamic tetherThis is a conductive tether that carries a current that can generatethrust or drag from a planetary magnetic field, in much the same wayas an electric motor.
Momentum exchange tetherThis is a rotating tether that would grab a spacecraft and then releaseit at later time. Doing this can transfer momentum and energy fromthe tether to and from the spacecraft with very little loss; this can beused for orbital maneuvering.
Tethered Formation FlyingThis is typically a non-conductive tether that accurately maintains aset distance between space vehicles.
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Consider a Normal Satellite missionLaunch rocket/space shuttleShuttle deploys payload (usually satellite)Satellite performs function, and then eventually loses enoughmomentum to fall out of orbitIf Satellite needs more time in space, fuel must be shipped up to the
satelliteBottom Line: needs fuel
Disadvantages of Fuel:Expensive
Refueling MIR space station costs estimated at about $1 billion.Limited Supply
Earth is already running out of fossil fuels, nuclear/renewableresources not yet a viable solution for propulsion in space
We need a propellant-less propulsion
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Earth has magnetic fieldEarth has electric fieldBasic law of Physics :
F = B x IIf we could utilize theEarths electric and magneticfields by driving current inthe right direction, then wecan generate anelectromotive forcesufficient for use in orbit
Implementation
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HowKeep it simple:
Generate current along a straight lineUse a taut conducting wire (Tether) to channel thecurrent
Tether needs to be kept taut and orientedproperly in the magnetic fieldAnother basic rule of physics: if twomasses connected by a tether are in orbit,the masses will align themselves along thelocal vertical regardless of the starting
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Electrodynamic TetheredElectrodynamic tethers (EDTs) are long conducting wires, suchas one deployed from a tether satellite, which can operate onelectromagnetic principles as generators, by converting their
kinetic energy to electrical energy, or as motors, convertingelectrical energy to kinetic energy. Electric potential isgenerated across a conductive tether by its motion through theEarth's magnetic field. The choice of the metal conductor to beused in an electrodynamic tether is determined by a variety of
factors.Primary factors usually include high electrical conductivity, andlow density.Secondary factors, depending on the application, include cost,
strength, and melting point.
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A space object, i.e. a satellite in Earth orbit, or any other
space object either natural or man made, is physicallyconnected to the tether system.The tether system comprises a deployer from which aconductive tether having a bare segment extends upward
from space object. The positively biased anode end oftether collects electrons from the ionosphere as spaceobject moves in direction across the Earth's magneticfield.These electrons flow through the conductive structure of
the tether to the power system interface, where itsupplies power to an associated load, not shown. Theelectrons then flow to the negatively biased cathode
where electrons are ejected into the space plasma, thus
completing the electric circuit.
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A composite schematic of the complex array of physical effects andcharacteristics observed in the near environment of the TSS satellite.
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Theory and Experiment H.H BritoTwo series of tests were conducted during the period of 1993-1997 byHector Hugo Brito, that under the assumption of Minkowskis Energy-Momentum, tensor being the right one (Abraham-Minkowsckoi ntroversy)the electromagnetic field can modify the inertial properties of the
generating device given suitable charge and current distributions. Thisexperiment consists of mounting the device as a seismic mass top amechanical suspension. By supplying a periodic voltage to the coils at aFrequency close to the fundamental frequency of the seismic suspensionthe expected mechanical effect from inertia variation would cause thefixture to resonate, adding up to the micro seismic noise induced
vibration. Practically in all cases, the results consistently point to amechanical vibration induced by matter-electromagnetic field momentumexchange as predicted by Minkowskis formulation after all other sources ofvibration were taken into account or removed when possible.
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H H. Brito concluded that:Propellantless propulsion, as a mechanism not
requiring reaction mass or beamed power, does notseem to be out of reach, unless from the theoreticalpoint of view. Space-time warping (and the involvedenormous energies) is not necessary, providedinertia manipulation become feasible, within theframework of a mass tensor formalism.
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Momentum exchange tetherThis sub-set represents an entire area of research using a spinning conductive and/ornon-conductive tether to throw spacecraft up or down in orbit (like a sling), therebytransferring (or taking) its momentum.
The act of spinning a long tether end-for-end creates a controlled acceleration on theend-masses of the system and a tension in the tether. This spin is manipulated bycontrol of the angular frequency. From this, momentum exchange can occur if anendbody is released at the right point during the controlled rotation. The transfer inmomentum to the released object will cause the tether system to lose (or gain) orbitalenergy, and lose (or gain) altitude (and may require reboosting) or change orbital
planes; and the opposite to happen to the released mass.
When in a magnetic field, such as in low earth orbit, when using an electrodynamictether it is possible to re-boost without the expenditure of consumables. Other schemesinvolve balancing the momentum flow (such as catching and releasing payloads atalmost the same time), or using conventional rocket propulsion or ion drives.
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Graphic of the US Naval ResearchLaboratory's TiPS tether satellite
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Momentum-Exchange/Electrodynamic-Reboost (MXER)tether systems can provide propellantless propulsion for a widerange of missions, including: orbital maneuvering andstationkeeping within Low Earth Orbit (LEO); orbital transferof payloads from LEO to GEO, the Moon, and Mars; andeventually even Earth-to-Orbit (ETO) launch assist. By
eliminating the need for propellant for in-space propulsion,MXER tethers can enable payloads to be launched on muchsmaller launch vehicles, resulting in order-of-magnitudereductions in launch costs. In order for MXER tethers to
achieve their potential in real-world application, several keytechnologies must be developed and demonstrated, includingspace-survivable tethers incorporating both high-strength andconducting materials, technologies for rendezvous with andgrappling of payloads, and techniques for predicting andcontrolling tether rotation and dynamics.
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Icarus Student SatelliteFirst (real) student built, designed, and testedsatellitePart of the tethered satellite propulsion modelWas scheduled to be launched March/May2001Advantageous since it is an instrumentedendmass as opposed to a passive dead weightHelps prove NASAs cheaper/faster/better
solution model
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ProSEDS Propellant-less SmallExpendable Deployer System
Drives current through the tetherDeploys endmass (Icarus)
Icarus (ProSEDS Endmass)Dead weight (~20 kg +/- 0.4 kg)Used to study tether physics
Possible backup in case ofProSEDS failure
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PayloadGPS, Magnetometer provide locationinformation
GPS unit uses the GPS satellite
networkMagnetometer compares the magneticreadings at present location against thecurrent model of the Earths magnetic
fieldTogether, both units provide acomplete measurement of the physicsof the Endmass
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Control and Data Handling
SubsystemsOctagon systems 386 board assimilates the information,sends it to the transmitter
Power: 3.0 W
Memory: 2.64 MB total 2 MB DRAM
512 kB FLASHROM
128 kB SRAM (battery backed)
A/D: 8 channels, 12 bit accuracy
Serial Ports: 2 UART 16C550 chips with RS-232 voltage level Digital I/O: 24 channels (TTL)
Operating Temperature: -40 to 85 C
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Custom C&DH Board performs tasks required specificallyby the Endmass
Analog MUX used to multiplex A/D channels provides 23 totalchannels
Platform for Health Data Collection
Power and Data Connections for all Subsystems
2 4-Orbit Timers in Series
2 21-Day Timers in Parallel
GSE Data Connection GPS Hard Reset Switch
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Power and Electrical SubsystemsPower Distribution SystemSolar Cells
Used to provide main power to theEndmass in day-side of the orbit (8 W)
and to charge the batteriesTotal power provided ~16 W
Batteries (Ni-Cd)Used to provide main power to theEndmass in Eclipse (~8 W)
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Schematic
Transmitter
GPS
Magnetometer
Octagon 386
HealthSystem
Sampled 1/ 2 sec
Connection: RS-232
A/D
3 Analog ValuesSampled 1/sec
Digital bit streamConnection: TTL
Thermistors,Currents, VoltagesSampled 1/min Serial
Port
GroundSupportEquipment
Development andTesting
Connection: RS-232
MUX
on/off
data
SerialPort
DigI/O
MEM
on/off
C&DH System
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TransmitterOutputs assimilated data from theOctagon board @ ~2.247 GHzGround stations at various locations
around the world are set up to receivethe data from this transmitterThe data is then relayed back to theIcarus team for analysis andconclusions
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Payloa
dGPS Receiver Magnetometer
8bits
C&DH
Chip 25 MHz
RAM 2 MB
ROM 512 kB
Transmitter(2.2475 GHz)
Telemetry
Battery
PowerDistribution
Solar Cells
PAA Separatio
nSwitches
ProSEDS
tether
2
Tether attachmentpoint
U of M GSE
SRAM 128 kB
GPS Almanac Data
V = 5.0 V DCI = 11 mA
V = 5.0 V DCI = 185 mA
V = 5.0 V DCI = 650 mA
V = 12.0 VDCI = 400 mA
Power Path
Data Path
Control
4 orbittimer
21 daytimer
System Level Diagram
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Structural Layout
GPS antennawire feed through
Battery box
C&DH and Computerboard component stack
Transmitter
Tether attachhole pattern
Transmitter antennawire feed through
Power Distribution and GPSboard component stack
PAAMagnetometer
GSE Connector
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T=+60 minPower-up,Release
T=~3 hoursTether
Deployment
T=?Instrument
Measurements
T=+1 day
ETDDeployment
T=21+ daysReentry
T=0March/May 2001Delta-II Launch!
Mission Plan
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Students in Lab working on Icarus -
Winter, 2000
Icarus at NASA/MSFC for Vibration
Testing - May, 2000
Icarus in Development
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ReferenceU.S. Patent 6,116,544, "Electrodynamic Tether And Method of UseCP458, Space Technology and Applications International ForumWikipedia.orgWikiflight gearFreelibrary.comIcarus journalNasa.govNasaspaceflight.comSciforum.comGitoriou.orgQuantum potentialLongbets.orgYoutube.com
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Thank You!!