Section 17.0

Propulsion Subsystem

Michael S. RheePropulsion Lead

5Space Technology

“Tomorrow’s Technology Today”GSFC

ST5 PDR June 19-20, 2001

ST5 PDR June 19-20, 2001

GSFC

17 - 2

Agenda

• Requirements

• Documentation

• Subsystem Design

• Electrical Interface Block Diagram

• Delta-V Budget

• Mass and Power Budget

• Test and Analysis

• Future Test and Analysis Plan

• Propulsion Hardware Components

ST5 PDR June 19-20, 2001

GSFC

17 - 3

Key Level II Requirements

• The propulsion subsystem shall include a cold gas micro-thruster system. (MRD10302010)

– The ST5 propulsion subsystem is a GN2 cold gas system based on the Marotta cold gas micro-thruster.

• Estimates of supply pressure shall be provided by direct pressure telemetry and/or a combination of indirect temperature telemetry and thruster on-time tracking. (MRD10302030)

– The ST5 propulsion subsystem includes a miniature pressure transducer by GP:50 to allow direct pressure telemetry.

– Tank pressure can be calculated from tank temperature and thruster on-time data.

• The thruster shall provide telemetry indicating the previous actuation activity of the thruster valve. (MRD10101040)

– The thruster control electronics (TCE) includes an indicator to monitor current pulses going to the solenoids.

ST5 PDR June 19-20, 2001

GSFC

17 - 4

Key Level II Requirements

• The thruster shall operate in continuous mode, or pulsed mode. (MRD10302011)

– The cold gas micro-thruster is capable of operating from 0.05 sec. minimum pulse width to continuous firing.

• The propulsion subsystem shall provide a maximum delta-V of 7.6 m/s. (MRD10302020)

– The 15cm (6” OD) tank pressurized to 13.8 Mpa (2000 psia) at BOL gives the system delta-V capability of 7.6 m/s.

• The thruster control circuitry shall have sufficient protections to preclude inadvertent thruster firings due to either hardware or software malfuctions. (MRD10302040)

– The TCE incorporates multiple safety features to prevent accidental thruster actuation that can lead to loss of propellant.

ST5 PDR June 19-20, 2001

GSFC

17 - 5

Key Level II Requirements

• The propulsion system shall be designed such that the pre-welded propulsion system can be installed as one complete and tested assembly to the spacecraft. (MRD10302050)

– Small size and simplified layout of the ST5 propulsion subsystem allows “assembly line” integration approach.

– Each propulsion subsystem is integrated on a duplicate bottom deck plate, which serves as an assembly jig.

– Each completed assembly is leak checked and tested for mechanical and electrical functions.

– Each completed assembly is integrated on to the spacecraft structure.

– The subsystem undergoes environmental test at the spacecraft level.

ST5 PDR June 19-20, 2001

GSFC

17 - 6

Key Level III Requirements

• Operational pressure range: 2000 psia BOL to 100 psia EOL

– Thrust range: 2.1 N (2000 psia) to 0.1 N (100 psia)

• GN2 Propellant tank size

– 1730 cc (106 ci) useable internal volume

– 15 cm (6 “ ) maximum outer diameter

• Total propellant load: 0.27 kg of GN2 at 20 degrees C

• Minimum vacuum specific impulse: 60 seconds

• Minimum pulse width: 50 ms

ST5 PDR June 19-20, 2001

GSFC

17 - 7

Key Level III Requirements

• ~1/3 Hz actuation frequency mode

– For attitude control (spin axis precession) at 20 rpm

– 50 ms to 2.95 s pulse widths in 50 ms increments

• 2 Hz actuation frequency mode

– For orbit adjustment at 20 rpm

– 50 ms to 450 ms pulse widths in 50 ms increments

• Capable of continuous firing

• Temperature range

– -20 to 40 degrees C operating

– -40 to 55 degrees C survival

• 1x10-4 scc/s He Maximum allowable system leakage rate

ST5 PDR June 19-20, 2001

GSFC

17 - 8

Documentation Status

• Propulsion Subsystem Specification ST5-495-019

– Preliminary

• Propulsion Subsystem Interface Control Document ST5-495-015

– Preliminary

• Cold Gas Micro Thruster SOW ST5-495-001

– Under Project Configuration Management

• Cold Gas Micro Thruster Specification ST5-495-002

– Under Project Configuration Management

• Other propulsion components SOWs and SPECs are in draft

– Propellant tank

– Pressure transducer

– Propellant filter

– Fill and drain valve

ST5 PDR June 19-20, 2001

GSFC

17 - 9

ST5 Propulsion Subsystem Design

ST5 PDR June 19-20, 2001

GSFC

17 - 10

ST5 Propulsion Subsystem Design

ST5 PDR June 19-20, 2001

GSFC

17 - 11

Electrical Interface Block Diagram

+5VDC

+7.2VDC

GND

GNDTemperature

Pressure

Feedback

Command

PressureTransducer

Thruster ControlElectronics (TCE)

Cold gas micro thruster

Tank Thermistor

TCE Thermistor

Thruster Thermistor

Analog

Analog

Analog

Analog

Analog

Single endeddigital

Single endeddigital

C&DH

ST5 PDR June 19-20, 2001

GSFC

17 - 12

Propulsion Delta-V BudgetS/C CBE Mass (Kg) = 20.96

Moment Arm(cm) = 25Propellent Load (Kg) = 0.274

Thruster ISP (sec) = 60

N-s m/s N-s m/s N-s m/sSun Acquisition

90 Degree Precession 18.1 0.9 18.1 0.9 18.1 0.9Maneuver Sequence #1 & 4

180 deg Precession to Fire Att 36.2 1.7 36.2 1.715 Km Perigee Raise Maneuver 1.6 1.690 deg Precession to Mission Att 18.1 0.9 18.1 0.9

Maneuver Sequence #2180 deg Precession to Fire Att 36.2 1.710 Km Perigee Raise Maneuver 1.190 deg Precession to Mission Att 18.1 0.9

Maneuver Sequence #390 deg Precession to Fire Att 18.1 0.95 Km Apogee Raise Maneuver 0.190 deg Precession to Mission Att 18.1 0.9

Attitude Maintenance~1.0 deg/day Precession 4.5 0.2 4.5 0.2 4.5 0.2

TOTAL 5.3 5.3 6.6

System Capacity

7.6 7.6 7.6Propellent Margin 44% 44% 15%

S/C #1 S/C #2 S/C #3

ST5 PDR June 19-20, 2001

GSFC

17 - 13

Propulsion Mass Budget

• Mass budget

Component Quantity Ea. Unit TotalMicro Thruster 1 0.05 0.05Thruster Control Elec. 1 0.08 0.08Propellant Tank 1 0.56 0.56GN2 Propellant 1 0.274 0.274Fill & Drain Valve 1 0.03 0.03Filter 1 0.065 0.065Pressure Transducer 1 0.06 0.06Tank Mounting Brackets 2 0.15 0.3Tubing & Misc. N/A 0.095 0.095Total 1.364 1.514

Mass (kg)

ST5 PDR June 19-20, 2001

GSFC

17 - 14

Propulsion Power Budget

• Power budget

Component Typical PeakMicro Thruster 0.6 1.5Pressure Transducer 0.2 0.2Total 0.8 1.7

Nominal Mode Power Dissipation (Watts)

ST5 PDR June 19-20, 2001

GSFC

17 - 15

Propulsion Test and Analysis

• Analytical model of the cold gas propulsion system

– Predicts impulse delivered as a function of thruster on-time

– Adiabatic Case: Tank is insulated, dQ/dt = 0

– Isothermal Case: Tank temperature = constant = 20 degrees C

• The actual behavior will fall between these two bounding cases

• The model will be calibrated to match the thrust stand test of the cold gas micro thruster

ItIsp 9.8 Dens V

11

k 1

2

2

k 1

k 1

2 k 1( ) k

DensP 101325

14.7 A Cd t

V

2

k 1

1

Iti 9.8 Isp Dens V exp2

k 1

k 1

2 k 1( )

k P

101325

14.7

Dens A Cd t

V 1

ST5 PDR June 19-20, 2001

GSFC

17 - 16

Propulsion Test and Analysis

• Thrust stand testing of the prototype cold gas micro thruster

– In-House designed and built thrust stand to measure thrust range from 1 to 0.001 N

– Initial testing done in ambient condition; future testing will be done in vacuum.

ST5 PDR June 19-20, 2001

GSFC

17 - 17

Future Test and Analysis Plan

• In-House thrust stand testing of the cold gas micro thruster as a part of the qualification program

• Refined analytical model of the propulsion system based on thrust stand test results

• Create analytical model for predicting propellant usage based on thruster on time data and tank temperature

• Structural analyses (Swales)

• Thermal analyses (Code 545 or Swales)

ST5 PDR June 19-20, 2001

GSFC

17 - 18

•Propulsion Hardware

• Cold gas micro thruster (NMP Technology)

– Developer: Marotta Scientific Controls, Montville, NJ

– Low power (1 watt), light weight (50 g) design

– Prototype hardware delivered to GSFC in July ’99

– In-House thrust stand testing of the prototype thruster in Dec. ’00

– Contract awarded to Marotta in Sep. ’99 for full development program

– Currently in Phase B/Design stage; Phase C to begin in June ‘01

– Qual unit: proto-flight test levels

– Flight units: acceptance test levels

ST5 PDR June 19-20, 2001

GSFC

17 - 19

Propulsion Hardware

• Thruster Control Electronics (NMP Technology)

– Developer: Marotta Scientific Controls, Montville, NJ

– Prototype TCE delivered to GSFC in July, ’99

– Contract awarded to Marotta in Sep. ’99 for full development program

– Currently in Phase B/Design stage; Phase C to begin in June ’01

– Incorporates multiple safety features for increased reliability

• Telemetry Feedback Signal

• Thruster ON Limit Timer

• Thruser ON Limit Timer Disable

• Disable Valve Open Command when Capacitor Charge is too low

• Automatic Valve Close on Power Loss

– Qual unit: proto-flight test levels (To be performed In-House)

– Flight units: acceptance test levels (To be performed In-House)

ST5 PDR June 19-20, 2001

GSFC

17 - 20

Propulsion Hardware

• Baseline Pressure Transducer

– Vendor: GP:50

– 7.2 VDC, Low power (200 mW), lightweight (60 g) design

– Analog electronics previously flown in STS

– ST5 version will undergo full qualification program based on ST5-495-007, “Component Test Requirements and Guidelines”

– Current status: SOW and Spec completed. Ready to start procurement.

• Miniature Fill and Drain Valve and Propellant Filter

– Vendor: Vacco

– Fully qualified, COTS

– Deliverables: Three flight units with acceptance data packages

– Current Status: SOW and Spec completed. Ready to start procurement.

ST5 PDR June 19-20, 2001

GSFC

17 - 21

Propulsion Hardware

• Propellant Tank

– Vendor: Carlton Technologies Inc.

– Lightweight composite vessel: carbon fiber with aluminum liner

– Proof factor of 1.5x MEOP; Burst factor of 2.0x MEOP

– Full qualification program based on MIL-STD-1522A and ST5-495-007 “Component test requirements and guidelines”

• One qual unit for cycle test (min. 50 cycles) and burst

• Three flight units (leak and proof)

• Environmental testing at the spacecraft level

– Current Status: SOW and Spec completed. Ready to start procurement.

ST5 PDR June 19-20, 2001

GSFC

17 - 22

Risk Mitigation – Delta-V Budget

• Risks to Available Performance– Increase in S/C Mass

• Current propulsion system delta-V capacity based on 20.96 kg spacecraft mass• Any increase in spacecraft mass will reduce the system delta-V capacity

– Thruster Isp is lower than 60 sec.• Current Predictions for Isp Analytically Based• Ambient Measurements of Performance Lower Than Expected• Currently Updating Model and Planning In-Vacuum Testing

• Mitigation– Alter Constellation Design

• Eliminate Apogee Raise Maneuver Sequence• No Impact to Mission Success or Resources

– Change Propellant• Use of Heavier Fuel, at Lower Isp Can Yield Significant Increase in Delta-V at Same

Volume and Pressure• Impact: Increase in Spacecraft Mass

– Increase Tank Volume• Increase in Available Propellant for Same Pressure• Impact: Increase in Both Spacecraft Volume and Mass