Propulsion Subsystem

Propulsion Subsystem: 

Propulsion Subsystem

Course Outline: 

Course Outline Introduction Rocket Science Design Approach Technology Risk Assessment

Acknowledgements: 

Acknowledgements This lecture is based on material used in internal courses at Telesat Canada

Introduction: 

Introduction • In Conjunction with The Attitude Control Subsystem The propulsion subsystem Provides for control of:  Orbit Insertion  Orbit Maintenance  Orbit Attitude Control Typical Transfer orbit Functions

Functional Description: 

Functional Description 1) Orbit Insertion functions consist of: a) Satellite Attitude, stability and orbit adjust during transfer orbit. b) Reorientation, spin rate, orbit dispersion, East and West drift, eccentricity and inclination corrections during drift orbit and station acquisition. 2) Orbit Maintenance & Attitude Control consists of : Orbit inclination, longitudinal position, drift,eccentricity, angular momentum and Roll and Yaw attitude corrections on Station

Rocket Science - 1: 

Rocket Science - 1 • The basic rocket theory is based on Newton’s Third Law “ Every action has an equal an opposite Reaction” • The two major Rocket Performance Parameters are the Thrust (F) and The Specific Impulse (Isp) . • The Thrust is the amount of Force applied to the rocket F  m.Ve [N] m = Mass flow rate of the propellant [kg/sec] Ve = Propellant Exhaust velocity [m/sec] • The Specific Impulse is the ratio of the Thrust to the Weight flow rate of the propellant: Isp  F/m.g [sec] g = 9.807 [m/sec2]

Rocket Science - 2: 

Rocket Science - 2 • Since thrust is proportional to fuel flow Thrust = dm/dt Isp g • and since F=ma mdv/dt =dm/dt Isp g Which can be expressed as: m(initial) = m(final) eDV/(Isp g) This is the rocket equation which gives the relation between propellant mass consumed and the Isp of the thruster

Typical Propellant Budget for a Communication Satellite: 

Typical Propellant Budget for a Communication Satellite

Design Parameters & Process: 

Design Parameters & Process

Typical Propulsion subsystem: 

Typical Propulsion subsystem ACE Propulsion System (PRIMEX)

Typical Bipropellant System: 

Typical Bipropellant System

Schematic: 

Schematic • Fuel, Oxidizer and pressurant are loaded individually • Fuel and Oxidizer are hypergolic ( burn when mixed) • Cannot launch with system pressurized because of tank design.

Monopropellant Vs Bipropellant Systems: 

Monopropellant Vs Bipropellant Systems Typical Bipropellant System Typical Monopropellant System

Pressurant systems: 

Pressurant systems Liquid Apogee Motor operate in a regulated constant pressure mode to maintain high efficiency On-orbit chemical thrusters operate in a blow-down mode.

Technology Overview: 

Technology Overview

Electro-Magnetic Thrusters: 

Electro-Magnetic Thrusters Hall Current Thruster (PRIMEX) Isp 1500-1800 seconds

How Does It Work?: 

How Does It Work?

Electro-Static Thrusters: 

Electro-Static Thrusters NSTAR Ion Engine Deep Space-1 30 centimeters Isp 3100 seconds 20-92 mN Thrust 8 kg (17.6 lbs)

How Does It Work?: 

How Does It Work?

Xenon Ion Engine: 

Xenon Ion Engine HS 601HP Ion Engine 13 centimeters Isp 2568 seconds 18 mN Thrust HS 702 Ion Engine 25 centimeters Isp 3800 seconds 165 mN Thrust

Chemical Thrusters: 

Chemical Thrusters Chemical Spacecraft Thrusters could be either mono propellant or bi-propellant Bipropellant thrusters provide higher Isp than mono-propellant thrusters Orbital Adjust Module Athena LV (PRIMEX)

Electro-Thermal Thrusters: 

Electro-Thermal Thrusters Arcjet System (PRIMEX) A2100 PPU Isp 500-700 seconds EHT System (PRIMEX) Isp 300 seconds

Risk Areas, Impact & Mitigation Plans: 

Risk Areas, Impact & Mitigation Plans Rupture of fuel systems Impact: Catastrophic failure Mitigation Plans : Rigorous qualification & Test Plan Liquid apogee motor under performance Pyro valve failures Latch valve leakage Thruster valve failures Thruster failures For the last five risk areas Impact: Degraded mission Mitigation Plans : Rigorous qualification & Test Plan and stringent workmanship processes.

General Subsystem Requirements: 

General Subsystem Requirements Thrust levels, torque levels, and linear impulse levels are required as a function of mission phase Total impulse required by all maneuvers Layout envelopes or constraints, centre of mass profile throughout the mission Allowable weight, mass properties, power and TT&C channel budgets as a function of mission phase Environments which will be imposed on the subsystem components Reliability and redundancy requirements Cost and schedule constraints Subsystem safety – proof and burst to operating pressure Accessibility – for aligning thrusters and loading propellants at launch site Cleanliness – both internal and external Life

General Subsystem Interfaces: 

General Subsystem Interfaces Propellant Tanks are located for s/c mass properties reasons, not RCS convenience Thrusters must be located to avoid or minimize plume impingement effects (forces, thermal, contamination) on solar arrays, antennas and other appendages. Additionally they must be located so that needed thrusters are not covered by these appendages when stowed. Locate thrusters to point through s/c centre of mass or to have equal moment arms, and to have alignment capability. Thermal interfaces are generally quite complicated, thrust chambers reach high temperatures (1500°C) and must be isolated from their valves and s/c surfaces. Also since thrusters protrude through s/c exterior surfaces, they form heat leaks which must be insulated. Also, many propellants have a more narrow acceptable temperature range than most s/c hardware and require special precautions. The power subsystem may be called upon to provide high power and pulsed loads. Transient suppression is required to protect the s/c against EMI which could affect switch states and logic circuitry.

Propellant Tank Sizing: 

Propellant Tank Sizing Tanks are qualified over a temperature range from -30°C to 65°C Tanks should be sized with a 4 to 1 margin in stress The stress (s) in thin walled pressure vessels is given by the following relations: a) spherical vessels s =pr/2t where t = wall thickness, r = internal radius and p = gauge pressure b) cylindrical vessels s1 = pr/t, s2 = pr/2t where s1 = hoop stress and s2 = longitudinal stress Titanium alloy ultimate 896 Mpa, yield 827 Mpa Aluminum alloy ultimate 538 Mpa, yield 476 Mpa