Tethered Satellite PropulsionTethered Satellite Propulsion

Icarus Student Satellite

ProSEDS

TopicsTopics

What is Tethered PropulsionWhy do we need Tethered PropulsionHow do we implement the model for

Tethered Propulsion

WhyWhy

Normal Satellite Missions– Launch rocket/space shuttle– Shuttle deploys payload (usually satellite)– Satellite performs function, and then eventually

loses enough momentum to fall out of orbit– If Satellite needs more time in space, fuel must

be shipped up to the satellite– Bottom Line: needs fuel

WhyWhy

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/renewable resources not yet a viable solution for propulsion in space

We need a propellant-less propulsion model

HowHow

Earth has magnetic field Earth has electric field Basic law of Physics :

F = B x I If we could utilize the Earth’s

electric and magnetic fields by driving current in the right direction, then we can generate an electromotive force sufficient for use in orbit

HowHow

Keep it simple:– Generate current along a straight line

Use a taut conducting wire (Tether) to channel the current

– Tether needs to be kept taut and oriented properly in the magnetic field

– Another basic rule of physics: if two masses connected by a tether are in orbit, the masses will align themselves along the local vertical regardless of the starting orientation.

Potential UsesPotential Uses

WhatWhat

ProSEDS – Propellant-less Small Expendable Deployer System – Drives current through the tether– Deploys endmass (Icarus)

Icarus (ProSEDS Endmass)– Dead weight (~20 kg +/- 0.4 kg)– Used to study tether physics– Possible backup in case of ProSEDS failure

Icarus Student SatelliteIcarus Student Satellite

First (real) student built, designed, and tested satellite

Part of the tethered satellite propulsion model Scheduled to be launched March/May 2001 Advantageous since it is an instrumented endmass

as opposed to a passive dead weight Helps prove NASA’s “cheaper/faster/better”

solution model

WhatWhat

Payload– GPS, Magnetometer – provide location

information GPS unit uses the GPS satellite network Magnetometer compares the magnetic readings at

present location against the current model of the Earth’s magnetic field

Together, both units provide a complete measurement of the physics of the Endmass

WhatWhat

Control and Data Handling Subsystems– Octagon systems 386 board assimilates the

information, sends it to the transmitterPower: 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

WhatWhat

Control and Data Handling Subsystems– Custom C&DH Board performs tasks required

specifically by the Endmass

• Analog MUX used to multiplex A/D channels – provides 23 total channels

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

WhatWhat

Power and Electrical Subsystems– Power Distribution System– Solar Cells

Used to provide main power to the Endmass in day-side of the orbit (8 W) and to charge the batteries

Total power provided ~16 W

– Batteries (Ni-Cd) Used to provide main power to the Endmass in

Eclipse (~8 W)

WhatWhat

CDH

GSE(J1) Mag(J3)

Tx(J4)

PE(J2)

Octagon(J6)

GPS(J7)

Therm(J5)PE

CDH(J4)Battery(J3)

PAA GSE(J2)

Solar Cells(J1)

Mag

Tx

Octagon

33 wires, ~6”

GPS 14 wires~9.5”

4 wires~6.5”

7 wires, ~18”

2 wires ea~7,17,17,32”

GSE (50pin)PAA (15pin)

2+, 1- each stringnegatives connected on each panel,Tail,Top,PAA: 16.25”, Outboard 26.25”,Nose: 22.5”, Bottom: 24.3”

8 wires~20.5” 12 wires

~38”

25 wires~25.5”

Batt

8 wire~7”

2 wire

Keepalive batteryconnected to CDHboard via jumpersat GSE connector.

16 wires~12”, 15”8 go to 9 pinconnector on PE,8 go to floating connector.

All wire is 24 guage, from the lab downstairs. (Flight qualified.)

24 wires

8 wires

8 wires

PEPAA

PEGSE

4 wires~30” PAAGSE

PECDH1

CDHGSE

PEBattery

PECDH2

CDHMag

CDHBatt

PESolar

CDHTxCDHGPS

37pin

37pin

25pin 9pin,9pin

9pinmale

37pin15pin15pin

9pin

9pin

9pin

25pin

Female on Icarus side, Male from GSE boxFemale on inside, maleon outsidefrom PAAswitches

2 Jumper wires go straight to Octagon board instead of throughC&DH board.

Custom TransmitterConnector (REM- notoxic metals)

Male connector on Mag .,so cable has female connectoron this end.

Male connector on GPS,so cable has female connectoron this end.

Bulkhead MountedBulkhead Mounted

4.1,4.2

WhatWhat

Transmitter– Outputs assimilated data from the Octagon

board @ ~2.247 GHz– Ground stations at various locations around the

world are set up to receive the data from this transmitter

– The data is then relayed back to the Icarus team for analysis and conclusions

SchematicSchematic

Transmitter

GPS

Magnetometer

Octagon 386

Health System

Sampled 1/ 2 secConnection: RS-232

A/D

3 Analog ValuesSampled 1/sec

Digital bit streamConnection: TTL

Thermistors, Currents, VoltagesSampled 1/min Serial Port

Ground Support Equipment

Development and TestingConnection: RS-232

MUX

on/off

data

Serial Port

Dig I/O

MEM

on/off

C&DH System

Payload

GPS Receiver Magnetometer

8 bits

C&DH

Chip 25 MHz

RAM 2 MB

ROM 512 kB

Transmitter (2.2475 GHz)

TelemetryBattery

Power Distribution

Solar Cells

PA

A Separation Switches

ProSEDS

tether

2

Tether attachment point

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 orbit timer

21 day timer

System Level DiagramSystem Level Diagram

T=+60 min Power-up,

Release

T=~3 hoursTether

Deployment

T=?Instrument

MeasurementsT=+1 day

ETDDeployment

T=21+ daysReentry

T=0March/May 2001Delta-II Launch!

Mission PlanMission Plan

The Big PictureThe Big Picture