SS3011 Space Technology and Applications

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SS3011 Space Technology and Applications
Space System Design and Architecture
Week 9 Sellers, Chapter 12 and Chapter 13, pp
401 - 509
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Orbitology
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Elements of a Space Mission

• Mission
• Orbits
• Launch
• Spacecraft
• Communications
• Operations
• Relevance

Distribution A Authorized for Public Release
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Satellite DesignPrinciple Requirements and
Constraints

• Mission
• Payload
• Orbit
• Environment
• Launch
• Ground-System Interface

P
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Mission

• Operations Concept
• Spacecraft Life and Reliability
• Comm Architecture
• Security
• Programmatic Constraints

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Spacecraft Design According to
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The Design Process
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Spacecraft building blocks

• Payload
• Launch and Propulsion System
• Attitude Determination Control
• System (ADCS)
• Reaction Control System (RCS)
• Electrical Power System (EPS)
• Thermal Control System (TCS)
• Structure
• Telemetry, Tracking Command
• System (TTC)

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Payload

• Single most significant driver
• Physical Parameters
• Operations
• Pointing
• Slewing
• Environment

This Part is the PIs Responsibility (defined
by the mission)
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Types of Payloads

• Communications (UHF, SHF, EHF)
• Navigation
• Earth Observation (Visual, IR, Microwave, Radar)
• Weather
• Warning
• Intelligence Missions
• SIGINT/IMINT/MASINT

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Orbit Environment

• Defining Parameters
• Eclipses
• Lighting Conditions
• Maneuvers
• Radiation Exposure
• Particles and Meteoroids
• Space Debris
• Hostile Environment

Been there Done That!
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Launch and Propulsion

• Launch Strategy
• Boosted Weight
• Propellant Mass Budget
• Envelope
• Environments
• Interfaces
• Launch Sites

Been there Done That!
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Attitude Determination Control System (ADCS)

• It is necessary to establish and maintain
  satellite stability
• Mission requirements payload pointing and
  slewing
• Solar array pointing and tracking
• Directional antennas
• Orientation of satellite for thrust maneuvers
• Thermal Maneuvers
• Station keeping
• Roll, Pitch and Yaw Control

OK . Lets Start Here
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Why Does the Spacecraft Attitude Change?
Remember
Right?
Well not exactly !.
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ADCS (cont.)

• Disturbing Torques
• Atmospheric drag
• Solar wind
• Radiation pressure
• Magnetic fields
• Non-uniform Gravitational fields
• Micrometeorite impact

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Spacecraft Attitude
x
p
r
Y
f
y
y
q
x
z
q
z
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Angular Momentum, Velocity, and Acceleration
Analogous to The Angular Acceleration
Equation is
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What is Torque
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How Does Torque Change Attitude
damping term i.e. friction
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What if We Dont Control Attitude
Assume No Damping, Constant Inertia, and
Constant Torque Vector
Our Initial Attitude Degrades in a Hurry
(Spacecraft Tumble)
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What is the Inertial Tensor Resistance to
Rotation in Three Axes
Diagonal Components of the Inertia Tensor are
commonly referred to as the Moments of Inertia
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Inertial Tensor (contd)
Off-Diagonal Components of the Inertia Tensor
are commonly referred to as the
Cross-Products (or cross-moments) of Inertia
Typically, Diagonal Components gtgt Off-Diagonal
Components
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Multiplying by r (density) and t (thickness of
the element) Gives the Mass-moment of Inertia
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Cross-Products of Inertial
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The Angular Acceleration Equation
Complex Three-Dimensional Dynamics and
Control Problem
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ADCS (cont.)

• Principle stabilization techniques
• Gravity Gradient, Spin, Rate Damping, 3-Axis
• Reaction Control System
• Sensors
• Star, Sun, Earth, Gyros, Magnetometers, GPS
• Actuation Devices
• Reaction Wheels, Gyros, Thrusters, Magnetic
  Torquers
• Control Systems

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Gravity Gradient Stablization
Pico-sat
q
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Spin Stabilization
Spinning mass has angular momentum that is
naturally conserved. This angular
momentum resists the disturbance of perturbing
torques
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Why Does Spin Stabilization Work?
Spin Acts as a Virtual Torque
Spin keeps this small
If we spin counter to the direction of the
expected perturbing torques then we can
counter much of its effects at least in
initially Eventually, the perturbing torques
eat Away at the initial spin and the
spacecraft Spins down and must periodically be
Spun-Up (Reaction Control System)
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Spin Stabilization
Spacecraft Tends Towards Same Inertial
Orientation in Space
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Three-Axis Spin Stabilization
Reaction Wheels Allow More Precise 3-Axis
Control
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Dual-Spun Spacecraft
Single-Spin Spacecraft not very useful for
earth pointing
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Dual-Spin Satellites
Spinning Outer section Provides Stability
Inner Section can be Pointed in Desired
Direction
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Can We Use Damping to KeepAngular Rates Small?
If rate-damping if used to counter perturbing
torques we can keep the angular rates from
growing beyond our RCS-Systems ability to
control the rates As rates build up so do
the effective torques of our rate-damping
system
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Can We Use Damping?
Inner and Outer Hulls have Differing inertias
Perturbing torques cause a local angular
velocity differential Frictional Damping of
Fluid limits max angular velocities
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Reaction Control Systems - Propulsion(RCS)

• The spacecraft propulsion system provides
  controlled impulse for
• Orbit insertion and transfers
• Orbit maintenance (station keeping)
• Attitude Control
• Propulsion Types
• Cold gas, monopropellant, bipropellants, ion

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Reaction Control Systems (RCS)
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RCS (cont.)

• Propulsion system components
• Fuel Tanks
• Thrust engines
• Oxidizer tanks (for bipropellant systems)
• Pressure regulators
• Fill, vent, drain, isolation valves
• Pressure temperature transducers
• Heaters

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RCS Example Cold Jet Thruster
No Combustion Thrust provided by
expansion of gas through Nozzle Low Isp
Simple Mechanism
Gas Storage Tank
Gas Exhaust Nozzle
Pressure Regulator
Actuator Valve for Gas Flow
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Hall Thruster
Hall Thruster
Anode (200 - 1000 V)
Hollow Cathode

• Principle Electromagnetic Acceleration of
  Ions
• Propellant Xe, Kr

Magnets
ION BEAM
Isp 1000-3000 sec ? 30-60 Thrust 5-400
mN Power 50W - 4.5 kW
Gas Inlet
ION BEAM
1. Electrons emitted from the cathode travel
toward the anode. 2. Electrons are impeded in the
discharge channel by a strong radial magnetic
field, causing a strong axial electric field to
concentrate in this region. 4. This electric
field heats the electrons, which subsequently
ionize gaseous propellant (xenon) emitted near
the anode. 6. The ionized gas accelerates axially
through the electric field in the discharge
channel, exiting the device at high speed, thus
producing thrust.
SPT-140 DM3
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RCS Control Maneuvers
Rate Nulling
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RCS Control Maneuvers
0
0
RCS Torque Impulse Counters rates
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Example Yaw Damping
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Example Yaw Damping (contd)
xthrusters
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RCS Thrust Profile
Thrusters Tend to Fire Impulsively
Calibration
Tells Flight Control Computer How Long to Fire
Thrusters
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Fuel Budget for the Burn
From Calibration
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Attitude Controland even More Complex Feed-back
Control Problem
Sensor
Magnetometer
Attitude Determination Loop
Attitude Determination and Control System (ADCS)
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Attitude Controland even More Complex Feed-back
Control Problem
thrusters
Feed-back Control and Actuation Loop
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Electrical Power System(EPS)

• Solar Cells/Batteries, Radioactive Thermal
  Generators (RTG)
• Solar Cells
• Silicon (14 Efficiency) - 190 W/m2
• Gallium Arsenide (18) - 244 W/m2
• Degradation (3-4/yr LEO)
• Temperature (.5 decrease per degree)
• Sun Incidence angle

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Solar Cells
Effect of Temperature On h
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Solar Cell Efficiency
Vmax
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Where is Maximum Power Point
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Max Power Point (contd)
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Effect of Aging
Vmax
Beginning-of-Life Power Must be Large Enough
to Accommodate End-of-Life Power
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Effect of Eclipses
Most Spacecraft Pass into Earths Shadow Once
Each Orbit Effect Causes Cyclic Power
Production
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Cyclic Power Production
Cyclic Power Production Requires Significant
Power Conditioning and Storage capacity
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How Long Will the Eclipse Last
Ignore Effect of Elevation Angle (worst case
scenario)
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Power Distribution and Storage System
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Batteries and Storage Systems
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Batteries and Storage Systems

• Batteries
• Nickel Cadmium, Nickel Hydrogen
• Cycles
• LEO - every orbit (5000/yr)
• GEO - two 45 day periods

• Issues
• Depth of Discharge (Deep-Cycle Tolerance)
• Charge/Discharge Time
• Weight
• Power Regulation and Distribution

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Power Distribution and Storage System(example)
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Thermal Control System

• Manages Heat Flow Through Spacecraft to Keep
  Systems within Operating Temperature Ranges
• -- Typical operating ranges (?C)
• 0 to 40 for Electronics
• 5 to 20 for Batteries
• 7 to 35 for Hydrazine
• Propellant
• -100 to 100 for
• Solar Arrays
• -200 to -80 for IR
• payload sensors

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Thermal Control Systems (TCS)

• Spacecraft Heat Sources
• Internal, Direct Solar, Albedo, Earth, Space

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Forms Of Heat Transfer

• Radiation, Conduction

Radiation -- heat transmission through space
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Radiation
Incoming Radiant Energy
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Radiation (contd)
Emitted Radiant Energy -- as object heats
up, it radiates energy back into space
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Example How Fast Does an Insulated Plate Heat Up
Assume Sun angle is q
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Example (contd)
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Change in Internal Energy of the Plate
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Radiation Heating Example (contd)
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Radiation Heating Example (concluded)
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How Do TCS Work

• Radiation, Conduction
• (No Convection -- no air)

Conduction -- heat transmission through a solid
x
k -- thermal conductivity W/ ? k m
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Conduction
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Heat management techniques

• Two basic techniques
• Passive thermal control
• Thermal coatings
• Thermal insulation (MLI)
• Heat Sinks
• Mirrors (OSR)
• Active thermal control
• Heaters/Thermostats
• Louvers/shades
• Heat pipes

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Heat Pipes
Low Boiling Point Liquid Liquid Absorbs Heat
at Hot-end Vaporized Liquid Condenses at Cold
end . Releases heat Capillarity Action
Carries Liquid back to Hot End of Tube
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Structure

• Provides stable support and maintains its
  integrity during all mission phases
• Provide a compatible interface with the launch
  vehicle
• Must meet the functional requirements of all
  subsystems

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Structure (cont.)

• Must withstand
• Launch loads
• Ground qualification and acceptance test loads
• On-orbit loads
• Shock and vibration (separation loads reach 5,000
  to 10,000 Gs)
• Pyro shock

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Example Launch Loads
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Structure (cont.)

• Primary and secondary
• Primary
• Main load bearing element, provides the most
  direct and efficient load path from various
  spacecraft components to the launch vehicle
  interface
• Goal is to achieve high strength and stiffness,
  low weight and high buckling strength
• Secondary
• Includes all other bracketry, solar arrays,
  antennas and appendages
• Structure is typically 5 to 20 of total weight

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Types of Loads
Axial
Shear
Lateral
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Types of Loads (contd)
T
Bending
Torsional
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Stress versus Strain
Stress (force per unit area tensor)
Fz
Fx
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Stress versus Strain
Strain deformation due to load
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Mechanisms

• Electro-mechanical devices employed to carry out
  key functions
• Separation systems
• Antenna deployment and pointing
• Attitude control
• Experiment orientation and control
• One-shot or Continuous

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Mechanisms (cont.)

• 3 Basic Categories
• One Shot
• Solar array deployment
• Antennas
• Booms
• separation ordnance
• Continuous Operation
• Momentum wheels
• solar array drives

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Spacecraft Harness

• The spacecraft harness provides electrical
  connections for both signal and power between all
  subsystems, instruments and payloads. It
  includes
• All interconnecting cables
• Umbilical wiring for ground checkout and launcher
  interface
• Separation switches
• Grounding connectors

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Telemetry, Tracking and Command (TTC)

• Telemetry
• Gathers data from other subsystems
• Processes and formats data
• Transmits data to the ground station
• Tracking
• Determines satellite position
• Command
• Satellite control is established and maintained

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Telemetry, Tracking and Command (TTC)
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Ground System Interface

• Degree of Autonomy
• Ground Stations
• Space Links
• Guidance Navigation
• (Orbit Determination)

Uplink
Data
Facility
Mgmt
Output
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Testing and Flight Qualification

• Static loads
• Alignment verification
• Acceleration tests
• Centrifuge
• Vibration / Acoustic
• Pyro shock
• Spin balance
• Mass properties

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Testing (cont.)

• Appendage deployment
• Antenna patterns
• Magnetic moments
• Thermal vacuum and thermal screening
• Solar simulation
• Electromagnetic compatibility
• Leak / Pressure tests
• Integrated system electrical functional
• Ground station compatibility