AERO2705- optus - Notes PDF

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AERO2705 – Optus Lecture Series: Structures and Mechanisms Structures - Sized to support the desired mission - Usually bespoke to a point Mechanisms - Mission mechanisms - Deployment mechanisms TCR and CDH subsystem -

Antennas Command receivers Telemetry trasnmitters Decoders Encoders Processors Microcontrollers Data buses FPGA ASIC’s

Power Subsystem - Solar panels - Shunt regulation Batteries - Discharge controllers - Charge controllers Voltage regulators

Thermal Subsystem - Radiators - Heaters - Blankets - Heap pipes Payload subsystem - Antennas - Reflectors - Filters - Low noise amplifiers

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Travelling wave tubes Imagers

ADCS Subsystem - Sun sensors - Star tracker - Momentum wheels - Thrusters - Control loops - Control electronics Propulsion and station keeping subsystem - Thrusters - Fuel tanks - Regulators - Filters - Valves Structure - Primary role is to support the mission and all on board equipment - Provide sufficient surface area to mount all equipment - Sized to meet the mission requirements. Mechanisms - Deployments - Provided for any aspect of the spacecraft that may require mechanical adjustment on orbit - Designed to meet the mission actuation requirements. - Occasional stepping or constant adjustment. LECTURE 2: Telemetry, command, and range TC&R: Telemetry - Information about the spacecraft Command - Directing the spacecraft to perform a task or series of tasks. Range - Accurately estimate where the spacecraft is in orbit Commanding - Command receivers are designed to receive an RF signal, amplify, demodulate and: - Output command data to decoders

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Pass through ranging tones

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Design to provide a minimum level of redundancy and connectivity.

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Typically a low data rate for reliability

Typical Command types: - Relay commands - Pulse commands - Serial commands - Data commands -

Commands received are decoded error checked.

Telemetry - A fundamental requirement for the successful operation of a spacecraft - “normal” and “dwell” stream - Typically a low data rate Telemetry Data Acqusition - Across a spacecraft, there are many different types of sensors - Voltage - Current - Temperature - Pressure - Mechanism angles What makes up telemetry - The process of recording and transmitting readings of an instrument - Needs to be measured in a realisable and practical matter Sample Rates: - Communication relates to how often telemetry is included in frames - Sub, super - Some telemetry is sub-commutated - Some telemetry is super-commutated Frames and communication: - A common standard in the industry is to have 1 major frame of telemetry that contains 32 minor frames - Each minor frame will repeat certain parameters Ranging - No point flying a spacecraft if we cant tell where it is flying

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Ranging involves transmitting a number of tones to a spacecraft and retransmitting them to the ground. We measure the phase delay for each of the different tones.

Antenna coverage - Always want to be able to command, range and receive telemetry. - Two or three types of coverage - Omnidirectional - Wide coverage - High gain DATA HANDLING - Spacecraft avionics - Brains and nervous system of a modern spacecraft. - Managed tasks include - Execution of flight software - Implementation of received commands - Collection and packaging of telemetry What makes up a data handling system

Flight computer/software - Takes on the central processing of almost every aspect of the spacecraft - Sized to meet the mission requirements Mil 1553

FPGA vs. ASIC

Fault Protection - An important routine or ensemble of routines always running to protect against and, recover from anomalous situations - Often happens faster than ground operators can interpret or intercept SPACE ENGINEERING 1 PAYLOAD SYSTEMS Payload Types - A spacecraft payload can be many things: - Military - Exploration - Environmental - Scientific

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Communications Regenerative/switching Non regenerative/amplification

Military - Applications still a dominant driver in satellite design - Often willing to push technology to get an edge on perceived threats - Staggering amounts of money often available. Unmanned Science - Scientific spaceflight has grown in leaps and bounds - Headline missions - Voyager - Viking - Cassini - Galileo and Juno - Sprit, opportunity, curiosity - Perseverance en-route to mars - Earth science Imaging and Sensing - Use of multispectral imaging - Different wavelengths are captured and combined based on the intelligence need - Each band will yield something different about the target. -

Geostationary Multispectral

Imaging and sensing: - E.g. sentinel - Multi spectral imager - Made up of two satellites 180 degrees apart Navigation - Fundamental to modern navigation - Region NAV systems Communications payloads - Adjusted to the technology available and the demand required - Broadcast - VSAT Bands What makes up a communications payload? - Antennas/horns - Filters

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Low noise amplifiers Down converters High power amplifiers

More complex - Digital processors - A/D, D/A converters - Active arrays - Heat pumps OPTUS-11 - Fully software definable and digitally beamformed payload - Receive analogue signals - A to D convert - Process - Digitally manipulate - D to A convert - Transmit analogue signals - Multi band payload A simple payload Polarisation of Electromagnetic waves - Electromagnetic waves are made up of an E-field and an H-field which are orthogonal to each other. - Waves are created when a current is forced to move rapidly back and forth - Generation of an electromagnetic wave that propagates away from the conductor at the speed of light. - The speed of travel isn’t affected by the atmosphere, however, the signal power is. Polarisation -

Refers to the alignment of the E field in a propagating electromagnetic wave. Broken into a number of subcategories Circular polarisation Elliptical polarisation  the E field has a component in both Axis plus vector rotation.

Polarisation orthogonality - Orthogonality is important as it enables us to isolate one polarisation from another. A simple payload: - Aim to create a payload with the sole purpose of receiving and retransmitting a signal - Receive - Amplify - Transmit A HTS payload - HTS works on a principle of frequency re-use and special isolation

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Beams are typically allocated only the bandwidth they need. Adjacent beams don’t use the same frequencies on the same polarisation.

Antennas -

Designed to provide a Gain in a particular direction May be designed to maximise gain in a single direction Vary in size depending on the mission and the link budgets trying to be met.

Down conversion - Uplinked signals are at one frequency and the downlink frequency is at another. - Frequency difference is called “translation frequency”. Linearised travelling wave tube amplifier - Made up of a number of components - Channel amplifier - Lineariser - TWTA - EPC

TWT – travelling wave tube - Main source of amplification - Electron gun - Life limiting device - Long lead times for manufacture A basic link - Aim to create a payload with the sole purpose of receiving and retransmitting a signal to meet a Bit Error Rate at the output. Isotropic antenna - Isotropic antenna is a point radiator providing equal radiation in all directions. - Not physically realisable - As a reference for expressing directive properties of antennas. Antenna Gain - Expressed as dBi and is a ratio of the gain in a particular direction over the isotropic gain which we know is equal to unity. - Antenna gain is the result of concentrating isotropic RF flux EIRP -

Effective Isotropic Radiated Power EIRP is the total power delivered by an isotropic antenna necessary to achieve the same PFD as a given antenna at distance D.

Path Loss

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The relationship between antenna gain G, effective area A, and wavelength is:

Atmospheric loss - Rain - Humidity - Polarisation angle - Scintillation - Dependant on frequency -

Dependent on frequency

Rain Attenuation

Bit Error rate

POWER AND THERMAL SYSTEMS Power subsystems - Generates power - Regulates and controls power - Distributes that power to loads on a bus - Store power and distributes when needed - Recharges the battery

Solar Arrays -

Made up of the electrical elements: Solar cells Connected to parallel to make “circuits” that provide the required current.

- solar array is blue line - Earth is at the top - The sun goes clockwise around the spacecraft once per day - SLT = spacecraft local time - 15 degrees = 1 hour Output of the solar array - Tilt of the earth - Distance to the sun - Solar radiation - Shadowing Shadowing of the array is an issue - Reflectors are the main culprit - Spacecraft body can also cause shadows - The yoke minimises shadowing by moving the array away from the body - Shadowing is factored into the power budget. BUS REGULATION -

The bus loads determine what the shunt circuits do with the current High loads: more current to the bus

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Lower loads: less current to the bus

Batteries -

Must be very reliable, cannot be replaced by a spare battery. Factored into the power budget.

Load shed: - In an emergency you need to protect the battery - Do not let it go flat - Reduce the load on the battery if state-of-charge is getting too low Eclipses - Are unavoidable for GEO spacecraft - Twice a year - Lasts for 45 days - 90 discharges a year - Battery supports the bus

Moon Shadows: - At random times throughout the year, the sun can go behind the moon. - Can be predicted for the life of a spacecraft at a specific longitude - Can last over 2 hours

Power Budget - Is prepared by the spacecraft manufacturer long before any hardware is built. It is a paper design which shows that the power subsystem will work for the entire mission. - Starts with how big the spacecraft load should be. -

THERMAL SUBSYSTEM - Radiators to get rid of heat - Multi-layer blankets to reduce temperature variations - Heaters to stop units getting too cold - Heat pipes to spread the heat away from hottest units. Hoe to get rid of heat? - The hottest units are the TWTs (travelling wave tube amplifiers). - They are usually installed on the north and south communication panels. - Embedded heat pipes spread the heat across the panels. - The outside of the comms panels are covered in Optical Solar Reflectors (OSRs) to radiate the heat into space. - Spacecrafts get hotter over life period. - Solar absorptance factor

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Emissivity factor

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Temperature varies throughout the day

Thermal Vacuum testing - Units tested beyond their predicted thermal extremes - Then the entire spacecraft is thermal-vacuum tested

ATTITUDE CONTROL Attitude Control System - Actuators - Sensors - Flight software Linear vs Angular Dynamics

Spacecraft coordinates - Be aware of the coordinate/reference frame. - Body frame - Local vertical local horizontal - Earth-centred inertial. - Sun fixed Momentum - Roll - Yaw - Pitch ACS hardware Thrusters - Bi-propellant - Mono-propellant

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Plasma/ionic

Momentum Wheels - A single wheel can transfer momentum to or from the body in a single axis. - Combination of wheels achieves 3-axis control. Sun Sensors - Sunlight passes through a gap or slit in the mask, illuminating a portion of the detector. - Aperture geometry and detector resolution will determine sensor accuracy. Gyroscopes - Detect angular accelerations. Disturbance Torques - Solar radiation pressure - Overturing torque - ‘windmill’ torque - Radio frequency torque - Outgassing - Micro-meteorites - Thermal shock - Propellant/pressure leaks LECTURE – GROUND SYSTEMS Satellite Control Responsibilities Ground: - Maintain the following: - Constant telemetry processing - Constant command capability - Ongoing ranging operations Spacecraft

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Monitor spacecraft health and respond in real time to contingencies. First level responses are time critical and recovery actions are commenced by Satellite Controllers. We then work with spacecraft engineering support to resolve the issue.

Ground Systems -

Need to command a switch onboard the spacecraft to a different position. We sit at the keyboard and send a command (CMD) from the real time operations computer and we confirm via telemetry (TLM) that the switch changed to the correct position.

Realtime Computers - Perform commanding using procs (scripts) or individual commands. - Displays telemetry in various alphanumeric and graphical formats. Ranging Measurement - Tone based ranging systems use a series of relatively low frequencies in a phase delay measurement system to convert phase delay into time delay and time delay into distance. Measurement Loop - To take a measurement, we need to configure the ground/spacecraft system into a loop. Redundancy – example (low noise amplifier)

LECTURE: ORBITS Propulsion System Types

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Chemical propulsion Monopropellant Bipropellant

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Electric propulsion Ion Propulsion

The Rocket Equation:

Transfer Orbits - GTO: Geostationary Transfer Orbit - SSO: Super Synchronous Orbit - Direct Inject GTO: - Perigee altitude = 250 km - Apogee altitude = GEO - Inclination = depends on latitude of the launch site SSO: -

Perigee altitude = 250 km Apogee altitude = 80,000  120,000km Inclination  mostly used by US launchers (27 deg).

Direct Inject - Drops the satellite off as close as possible to GEO Electric Orbit Raising vs Chemical

ORBIT PERTURBATIONS -

Once a satellite achieves geostationary orbit at its final location  not the end of the manoeuvre planning. Luni-solar perturbation of inclination Triaxiality perturbation of drift rate/longitude Solar radiation force of perturbation of eccentricity

Inclination Evolution Luni-solar Perturbations - Orbital radius of the moon is roughly nine times the radius of a geostationary orbit. - Due to the inverse-square law of gravity, the Moon has a greater effect - The sun has a similar effect on the orbit of a satellite with some minor differences. - The sun’s gravity is stronger but its further away and as such the net torque produced by the Sun is slightly smaller. Triaxiality - A perturbation that is caused by asymmetric mass distribution of the Earth. - Tesseral harmonics of the Earth’s gravity field. Solar Radiation Pressure - Satellite is moving towards the Sun and the SRP results in deceleration. - In the evening the satellite is moving away from the Sun and the SRP results in acceleration. - The semi major axis increases Station keeping - Means keeping the satellite at is designated location within set tolerances, typically called a station keeping box. - Regulatory point of view, the satellite can +- 0.5 degrees of its onstation longitude.

Inclined Orbit - As the satellite starts running low on propellant, the operators sometimes take the approach of stopping inclination control manoeuvres to significantly reduce the propellant usage. - The daily latitude motion will increase proportional to the inclination growth. - Will need to have a tracking antenna. Station Changes - Geostationary doesn’t always stay at the same longitude throughout its lifetime. - Assets are sometimes reorganised to better meet changing customer needs. -

To move west  raise orbit above geosynchronous

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To move east  lower orbit below geosynchronous.

Deorbit -

For geostationary satellites, deorbiting means raising the satellite’s orbit above geostationary altitude. Allows the orbital slot to be reused. Companies are offering new spacecraft that can dock with existing satellites and do stationkeeping manoeuvres for them and/or at the end of life  move to a graveyard orbit.

SPACECRAFT PROCUREMENT Procurement overview Blank sheet to RFT - Starts with a business need - Engineers conceptualise a system to meet the need then go to the market. - RFI (request for information) helps align design concept with available technology. - Feeds back to business need until there is sufficient information to Request For Tender (RFT). RFT and BAFO - Tender is released to market with a timeframe to respond. - Tenders will spend hundreds of thousands responding to a bid. - Many bids received. Engineering teams then review and down select against the contract criteria. - Once its down selected to one or two bitters. BAFO are requested. Design reviews - SRR - EQSR - PDR - CDR Initial Integrated System Test - Units are built and tested independently

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Eventually they need to come together as a system System benchmarking prior to environmental testing

Environmental testing - Shake and bake - Thermal vacuum testing exposed most of the integrated spacecraft to vacuum. Acoustic testing - Simulate the acoustic load that will be experienced by the spacecraft. Vibration - Simulate the vibration loads that will be experienced. Pack and Ship - Hold PSR Launch prep - Fuel - Stack - Enclose Orbit raising and IOT - Chemical VS Electric - Deployments - In orbit testing...