Assignment 3 Final Report Optus NBN Satellite Mission Executive Summary

Chris Blundell | z5014763

AERO9610 – The Space Segment T1 2020 Due: Monday 4th May 2020

Assignment 3 Final Report Optus NBN Satellite Mission

Executive Summary This report investigates technical and operational details pertaining to the NBN satellite mission, from inception and design through to the projected future mission goals and end-of-life behaviour. The report uses data gathered from press releases, shareholder information, industry reporters and news sources to develop a holistic picture of the satellites and their mission. It is determined that the NBN satellite mission is a critical piece of technological infrastructure that should satisfy the requirements of its users, however there is considerable scope for the mission to be modified to further improve the services it provides, the number of users it can handle, and the capability of the services provided. While the current satellites are providing the required service, the uptake has been higher than expected, and with a growing need for technology even in remote communities, it is expected that the system will reach capacity within the operating life of the satellites. It is therefore recommended that further investment in the program be made for additional capacity either in the way of new satellites or additional bandwidth from other satellites. Alternatively, working with other communication satellite providers may yield increased speeds and network capability, so it is recommended that investigations into the likes of SpaceX’s Starlink program be undertaken. This report is limited in the access to potentially sensitive data surrounding space- going equipment. While there are vast resources on the various satellites in orbit, it is rare to find such a collection of the entire technical details of a satellite and its mission, so to the best of its ability this report acknowledges and attempts to overcome the lack of transparency.

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Table of Contents

Executive Summary 1 Introduction 4 Mission Objective 4 Mission Requirements 4 Speed 4 Coverage 5 Reliability 5 Completion 5 Mission Constraints 5 Cost 5 Politics 6 Technological 6 Users 6 Mission Operations 6 Past operations 6 Current operations 7 Future operations 7 Satellite Payload 8 Satellite Bus Subsystems 9 Structure 9 Thermal 10 Power 10 Solar Panels 10 Batteries 11 Bus Power 11 Attitude Determination and Control 11 Sensors 12 Actuators 12 Control Strategy 12 Propulsion 12 Communication 14 Command and Data Handling 14 Mission Command and Control 14 Ground Stations 14 Customer Hardware 15 Out Door Unit 15 Modem 15 Transmit/Receive Integrated Assembly 15 Launch 15 Launch Details 15 Launch Facility 16 Launch Vehicle 16 Manufacture Details 18 Integration and Assembly 19 Temperature 19

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Humidity 19 Cleanliness and Contamination 19 Electromagnetic Environment 20 Mass Properties 20 Modal Properties 20 Design Loads 20 Electrical Interface 21 Test Details 21 Pre-launch testing24 22 Thermal Testing 22 Static Testing 22 Outgassing 22 Vibration Testing 23 Acoustic Testing 23 Shock Testing 24 Antenna Testing 24 Safety Factors 24 Interface Fit Check 25 In-orbit Testing 25 Conclusion 26 Bibliography 27

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Introduction* The National Broadband Network (NBN) is a large-scale technological infrastructure project established by the Australian Government to deliver high-speed broadband communications services to the entirety of Australia1. It is operated by NBN Co Ltd, a Government Business Enterprise that acts according to the strategic direction out- lined by the Australian Government in their Statement of Expectations1. This document, amongst other constraints and affordances, gives NBN Co the flexibility and discretion of design decisions, including those regarding the technological imple- mentation and network design. It is to this effect that NBN Co commissioned the construction and launch of two satellites, named Sky Muster I and II, to provide coverage to rural, remote and isolated communities in Australia and some surrounding islands2. Satellite link technology allows broad areas of land to be connected to the service with minimal ground based infrastructure at the point of operation, which is beneficial for those communities often neglected in larger infrastructure upgrades2. Instead, centralised ground services can monitor, control and broadcast to the satellites from better- supported locations3.

Mission Objective The mission objective of the NBN satellite project is to quickly and effectively connect remote Australians to a high-speed broadband network, in doing so promoting economic and social benefits to the regions it covers1. The satellite mission is designed to be a cost-effective method of achieving the desired network coverage and data speeds1, with potential capacity for additional services made available upon ful- filling the NBN Co mission.

Mission Requirements The primary requirement of the NBN satellite mission is to deliver broadband internet services to customers who would otherwise require prohibitively expensive ground internet connections. The NBN satellite mission stipulates requirements of broadband capacity and operating speeds1. These expectations are the foundations of the mission requirements, and drive the decisions in all aspects of the design process and mission operation.

Speed The statement of expectations and the NBN Co mission statement both make a commitment to delivering “peak wholesale download data rates of at least 25 Mbps

* This introduction is reproduced with the inclusion of extracts from previously submitted documents pertaining to the same subject. Other sections in this report are similarly reproduced from previously submitted work of this author with editing for clarity, accuracy or brevity. 4

Chris Blundell | z5014763 to premises”1. This includes the satellite-serviced areas, which account for 7,000,000 km2 of regional, rural and remote Australia and its offshore territories and islands4.

Coverage The coverage requirements of the NBN satellite mission are not directly stipulated, but rather implied by omission. The satellite service is to cover regional, rural and remote Australia, including external territories such as Norfolk Island, Cocos Island, Macquarie Island and Christmas Island. This widespread geographic demand requires broad service coverage, however it is not rigidly stated in the public documentation exactly what extent the satellite service will address the areas of need, and which areas will be serviced by other technologies in the Multi-Technology Mix (MTM) approach taken by the government1.

Reliability There are no requirements listed in the statement of expectations to address the service reliability required of the NBN satellite mission1. However, in current use, advocate groups that speak on behalf of regional, rural and remote Australians have identified that reliability is already an ongoing issue5. Given this is not expressed as a requirement from the outset of the mission, it is unsurprising that customers and users have identified issues with the service they are receiving.

Completion NBN Co set the completion goal for 30 June 2020, with the caveat of extending ongoing activity to “complex connections”. The advertised scheduling of the NBN rollout lists the NBN Satellite service as a caveat to the nationwide ready-to-connect status goals, and as such the timeline for the satellite program exists independently of the ground based service delivery. Both satellites are in operation as expected, however much of the ground infrastructure for both fixed services and satellite services remain to be completed in the coming months6.

Mission Constraints

Cost This is constrained by the government budget, which requires the satellite service to act only as a low cost alternative to more ground-based internet technologies7. A cost benefit analysis and various other trade analyses would have been completed and presented to the NBN Co to drive the decision of implementing a satellite branch of operations. Evidently, the satellite service was deemed a lower cost alternative, so it holds to reason that the limitation of the satellite program cost would be the compa- rable cost of a fixed wireless or wired ground connection network.

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Politics The political climate has had an impact on the satellite service delivery due to a lack of bipartisan support. However, with the commencement of work beginning under the previous government, the current government is able to support the plan without political backlash, effectively granting the program free-reign to continue as planned4.

Technological The technological capabilities of the satellite sector allow for an effective service, but it is not without its technological limitations. Bandwidth on-board the spacecraft is finite, so the service is limited in the maximum throughput achievable on any given constellation of satellites8. Similarly, the orbital placement constrains the minimum speeds due to the signal latency in radio transmissions to and from geosynchronous orbit8.

Users The NBN Satellite network is used primarily by Australian homes and businesses in rural, remote and isolated communities such as in Central Australia2. There is also bandwidth allocated to coastal islands and external territories such as Norfolk Island, Cocos Island, Macquarie Island and Christmas Island2. In practical terms, the broad- er Australian public are the designated users of this system as their taxpaying dollars are the foundation for the government’s investment in the project, and their voting preferences influence the government’s mandate to carry out such an infrastructure project7. The Government is therefore considered the primary customer of the service. The intention of the NBN Co is to remain a wholesale seller of the service5, and as such, other Internet Service Providers (ISPs) such as Optus, Telstra and others, are effectively the secondary customers of the system as they directly interact with the satellite service and on-sell that service to the end-users (Australian homes and businesses) in the form of retail and commercial plans or packages5,7. Tertiary customers include intermediary companies such as Qantas who provide satellite internet services as a part of their existing service models9,10. Their passengers therefore become users of the service.

Mission Operations

Past operations While SSL were constructing and preparing the Sky Muster I and II satellites, the interim solution for remote satellite broadband access was provided by the Interim Satellite Service (ISS), a partnership between NBN co and Optus/IPStar11. The 300 million AUD partnership allowed for the use of additional bandwidth from Optus existing satellite fleet for users in particularly remote areas with no alternative wired or wireless broadband access provisions4. The ISS partnership continued until 28 Febru-

Chris Blundell | z5014763 ary 2017, when users were required to make the switch to the Sky Muster service as Sky Muster II reached its operational phase12.

Current operations Both Sky Muster I and II are currently in geostationary orbit where they are fully operational, delivering satellite communications to the users. Their orbital distance is approximately 36,000 km above the surface of Earth. Sky Muster I is positioned above the equator at 140 degrees East13, and Sky Muster II is at 145 degrees East14. Geostationary orbit is chosen for a number of reasons, and is a critical consideration of the mission plan. There are two primary factors that govern the decision for a GEO insertion: signal latency and coverage. GEO is considerably further away from earth, and even with speed-of-light radio transmissions, the vast distance introduces a latency of 480 ms, compared to 120 ms for middle-earth-orbit or a sprightly 12 ms for low-earth-orbit8. This is problematic given the average human reaction time is 279 ms, and almost all humans would notice a delay longer than 320 ms8. However, GEO allows for satellites to cover vast regions with their transmission spot beams. A cost/benefit analysis is needed to determine the most suitable option between many high speed LEO satellites in constellation (and additional satellites orbiting around earth to get back to a transmission position) and two GEO locked satellites providing steady coverage at a reduced speed. When the launch and fuel costs, along with the added buses for each satellite and the additional network complexity are all considered, it is evident that such an undertaking would be unnecessarily complex and expensive to service a region with comparatively few users. By comparison, SpaceX’s Starlink mission would achieve the same coverage for millions of users, making the investment much more attractive.

Future operations A number of proposed future possibilities arise due to the adoption of the Sky Muster satellite program. Given the success and high adoption rate of the Sky Muster NBN service, the increased load on these two satellites could call for the inclusion of an additional satellite in the constellation. This could be implemented via commissioning a third satellite and launching it privately as has been the case for the current fleet, or could mean buying into additional bandwidth capacity of other satellite communications providers5,15. This may not prove to be necessary, but remains an active potential scenario. Perhaps alternatively, underutilised bandwidth could be designated for other satellite communications services such as portable satellite connectivity. Qantas has begun the process of rolling out an in-flight wi-fi package using satellite connections on some of their flights9,15. Further use of similar technology could see this implemented in other commercial airlines, potentially leading to the widespread adoption of satellite internet services on all forms of transport. This same technology could be implemented on a smaller scale for civilian satellite communication, although the current technology adoption has seen to this application remaining prohibitively expensive15. A notable example of this technology being

Chris Blundell | z5014763 implemented is the Road Muster Truck program, a fleet of satellite internet equipped vehicles that can provide a mobile satellite internet connection point for displaced persons in the event of a crisis. These Road Muster Trucks were deployed in the wake of the recent bushfire catastrophe, allowing bushfire victims to access the internet for information and communication despite the destruction of ground based internet infrastructure6. In the latest corporate plan, NBN Co also revealed their proposed Business Satellite Services, which provides bandwidth for non-addressable locations, supporting the adoption of connected machine services by way of the Internet of Things (IoT). The service provides a committed 2 Mbps of upload and download speed for remote, au- tonomous monitoring and machine to machine communication16. The announcement also includes a new Virtual Internet Service Provider (VISP) that is designed for remote operating companies such as those in the mining, oil and gas sector. This service will provide an uncommitted speed of up to 13 Mbps up and down, and pro- vision of 1,000 GB of data quotas16. There are potential concerns for future operations of the NBN satellite program as well, notably the occasional but regular impact of solar transits on regular communications signals. Due to the positioning of the satellites in geostationary orbit, there are times every year that a solar transit will likely cause some transmission issues as the solar radiation coupled with the signal overloads the ground transceivers. The effects are momentary even at their worst, but consideration may be needed to pro- tect the hardware from damage, and other transmission methods may be needed in order to maintain the signal17. Furthermore, the rain fade experienced on Ka-band transmissions is significantly higher than on Ku- or C-band18. This could provide motive for investment in diversi- fied transmission bands to provided redundancy and backup during peak periods or during increased rainfall5. An additional consideration is that the current rollout plan does not involve decom- missioning copper connections to customers migrating to Sky Muster, meaning that providers that may have hoped to reallocate, sell off or decommission remote ex- changes are contractually obliged to maintain the connection indefinitely15. This is undoubtedly a frustration for providers, but is unlikely to become a major problem for the satellite program.

Satellite Payload The Sky Muster satellites’ primary function is to provide satellite communication services, and as such their payload consists of radio-frequency antennae and transponders. There are 202 standard-equivalent Ka-band transponders on each satellite, which provide the ability to create around 100 spot beams of signal coverage to the earth’s surface. The signal and data processing units that run the transponders are also critical pieces of hardware for mission operation, and form the secondary part of the payload. Together, the hardware in each high-throughput satellite is able to relay 80 gigabits of data per second14.

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The decision to use Ka-band transmission frequencies (26-40 GHz) comes as a result of the increased spot beam density, greater spectrum re-use and spectrum availability and a reduced antenna size requirement for the surface hardware8. The spot beam density is an important consideration for the satellite design, as it can influence the orbital position required for sufficient coverage. By utilising the Ka- band frequencies, the spot beam size is 4 times smaller than Ku-band beams, and 16 times smaller than on the C-band. Consequently, the beams can be packed more efficiently, with a greater ability to re-use frequencies in non-adjacent spot beams19. Additionally, the Ka-band antenna operates at a much higher gain than a compara- ble sized Ku- or C-band antenna – 16,000 W for Ka-band antennae compared to equally sized 4,000 W Ku- or 1,000 W C-band antennae. This means that either higher gain or smaller dish sizes can be used with Ka-band transmissions8. Unfortunately, the Ka-band is plagued by rain fade, where signals are interrupted or lost as a result of atmospheric conditions. As little as 25 mm of rainfall in an hour can result in a 10 dB attenuation of signal for higher Ka-band frequencies8. However, this issue is largely mitigated by the nature of its application – the majority of the satellite service is directed to remote parts of Australia, where rainfall is scarce and consequently rain fade is predominantly a non-issue. Critically, regions of Northern Australia that experience more tropical climates and higher rainfall experience higher rain-attenuation dropouts. In remote areas where flooding can occur, this would amount to a signal loss exactly when communications are most important in the safe and effective organisation of evacuation, rescue and disaster relief5. Additionally, rain attenuation affects both transmission and reception of Ka-band radio frequencies, so when a ground station suffers from rain fade, a large number of end users are simultaneously affected5.

Satellite Bus Subsystems

Structure The main structure of the Sky Muster satellites is the SSL-1300, a modular communications satellite bus designed by Space Systems Loral. The chassis is comprised of composite and aluminium honeycomb panels with a load bearing central cylinder that panels for specific payload configurations can be mated to. This modular approach allows for faster building, testing and verification of designs due to the number of already successful deployments of the platform. There are currently over 100 SSL-1300 satellites in various configurations in orbit20. Other substructures of the spacecraft are also constructed of lightweight composites and alloys to provide strength and stiffness at minimal weight. The deployable appendages that carry the Ka-band antennae are examples of such structures14. The use of advanced materials such as graphite, composites and aluminium honeycomb allows for a light and strong structure with mass properties that can be tailored to the exact specifications of the designers. Standard manufacturing materi-

Chris Blundell | z5014763 als such as billet metal alloys or plastics would not enable such design freedom and control, nor would they be as strong or light in use.

Thermal Thermal management is critical to ensuring componentry on-board the spacecraft can operate efficiently, particularly in relation to sensors, batteries and fuel systems21. The thermal system incorporates both thermal monitoring (via telemetry) and thermal control to measure and manage the temperatures across the satellite. The thermal system of the SSL-1300 is primarily passive, with minimal active control. On the outermost panels, the craft is equipped with Optical Solar Reflectors (OSRs) to reduce the amount of heat absorbed by the satellite. OSRs maintain an absorptivity of 0.08 in the visible spectrum and an emissivity of 0.80 of infrared radiation. Additionally, the body is wrapped in a thermal blanket, which insulates the bus from the space environment. The SSL-1300 also uses a passive dual bore matrix heat pipe system to exchange heat from within communication panels to elsewhere on the satellite20. These heat pipes provide thermal conductivity values orders of magnitude greater than copper, generally in the region of 10,000-100,000 W/mK instead of 400 W/mK for copper21. The use of passive thermal control is generally ideal on satellites due to the reduced fuel and power requirements to otherwise actively manage thermal loads on the craft21. Additionally by both minimising the absorbed heat with reflectors and thermal blanketing and transferring the heat away from sensitive equipment using the heat pipes, the satellite is able to mitigate the potential problems of large heat gradients impacting the function of the payload or bus.

Power Generating adequate power for the spacecraft requires consideration of the power needs of each subsystem, as well as accounting for energy losses. Storage of power is necessary to manage spacecraft operation when the satellite is shaded by the earth, and also allows for management of additional power generation as reserve power. The generation, storage and charging, dissipation and management are all necessary considerations for effective satellite operation.

Solar Panels The Sky Muster satellites are powered by two massive 5-panel Gallium-Arsenide (GaAs) solar arrays spanning approximately 30 m2 20. The panels are folded into a more compact envelope for launch and transit into orbit, at which point they are deployed to power the mission critical subsystems on-board. The 3-axis stabilisation of the spacecraft allows for maximum directivity for the solar arrays, which is necessary for high power applications such as GEO communication. Additionally, the GaAs cells provide approximately 25 W/m2 at 0.9 V, which is a 25% efficiency increase over silicon cells operating at 0.5 V21. The overall operating efficiency of GaAs cells is greater than that of Si panels, with GaAs managing heat fluctuations better, and ex- periencing a lower thermal performance loss across the operational temperature

Chris Blundell | z5014763 range. Consequently, GaAs panels are able to operate at 15.7% efficiency, a large increase over Si cells operating at 7.7% at the same operating temperature (120 °C)21. Solar power is an obvious choice for communications satellites as the solar output in GEO is sufficient to maintain excellent power generation throughout the lifetime of the satellite22. Additionally, there are reduced fuel requirements associated with lev- eraging the solar arrays for ADCS purposes21. Other power sources such as RTGs or nuclear reactors pose risks to transmission interference that would be unacceptable on a communications satellite. Additionally, radioactive materials required for RTGs and nuclear reactors are prohibitively expensive for a low-cost commercial satellite 21 solution . Fuel cells that react O2 and H2 to create heat are efficient for high power output (300-350 W/kg), and their by-product is clean water, however, they require significant fuel storage that would be prohibitive for a 15 year satellite mission22. So- lar panels require sunlight to function, and in GEO there are seasonal eclipses that last up to 1.2 h during vernal and autumnal equinox21. Adequate consideration of the power storage needs to manage these periods must be given so as to not jeopardise the mission.

Batteries The solar arrays enable the 145-Ah Lithium-Ion battery (18-cell each) to remain powered and provide 16.4 kW of power in its end-of-life configuration20. With a 15- year lifespan, the projected power loss factor of 0.85 over the life of the satellite roughly translates to 19 kW of power generation at solar panel deployment20. The power losses are caused by radiation degradation of the solar array, which is damaged by high-energy protons from solar flares and trapped electrons in the Van Allen belts21. At approximately 33,500 km, the panels are likely to experience a fluence of 2.03x1013 MeV/cm2 22. Battery voltage drops are also necessary considerations over the lifecycle of the satellite, however this is managed according to the power distribution and control systems to mitigate losses through reconditioning cycles and careful charging procedures21.

Bus Power The high power of the satellite subsystems and payload generally lead to higher transmission losses. This suggests that higher voltages in the bus systems would be preferable. Additionally, the large size of the satellites requires longer wiring connections to facilitate power distribution throughout the spacecraft, which also lends itself to utilising higher voltages in the power bus21. The power is managed with a direct energy transfer protocol that sees two regulated power busses – a high voltage 100 V main bus and a low voltage secondary bus that runs at 31 V20.

Attitude Determination and Control The SSL-1300 bus utilises a suite of sensors to garner <60 arc-sec of pointing knowledge and <200 arc-sec of pointing control used in maintaining its 3-axis stabil- ity20. This is the culmination of the input and actions of sensors and actuators that determine and control the spacecraft’s position and direction in space.

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Sensors The sensors include Earth horizon sensing, redundant sun sensors and 2:1 star track- ers20,23. Using a number of independent sensors allows the spacecraft can determine its orientation and position more quickly by polling the fastest sensors independently of others, and refining the result as other sensor data is added to the algorithm22.

Actuators To actuate the craft and counteract the disturbance torques in GEO, the SSL-1300 platform uses 4 reaction wheels (the 4th is aligned on a skewed axis and is for redundancy in case of failure of one of the principle wheels) and 2 Ring Laser Gyros (RLG)20. Additionally, the SSL-1300 bus is specified with a suite of attitude and orbital control thrusters. These are four electrically operated SPT-100 Stationary Plasma Thrusters20. These allow the ADCS system to maintain a 3-axis stabilised Nadir-facing orientation. The SPT-100 thrusters deliver a nominal thrust of 83 mN to torque and translate the craft into its desired orbital position and facing direc- tion23,24. The very high specific impulse provided by these plasma thrusters allows for effective station keeping and manoeuvring with a minimal weight penalty for required fuel. The performance parameters are given in the table below.

SPT-100 Thruster Parameters23 Power 1350 W Thrust 83 mN Specific Impulse 1600 s Voltage 300 V Current 4.5 A Mass 4 kg

Control Strategy By using a 3-axis stabilised control strategy, the satellite is ideally suited to nadir pointing orbital behaviour, with a high pointing accuracy, good manoeuvrability and thrust vector control22. The associated cost of 3-axis stabilisation is higher than other control strategies, but the benefits of pointing accuracy being orders of magnitude higher than others far outweigh the cost for this application21. The ADCS used for the Sky Muster satellites is both very advanced and entirely ap- propriate for the communications satellite functions. Primarily, the spacecraft must demonstrate excellent station keeping and remain pointed in exactly the designated orientation. Using a combination of thrusters and reaction wheels enables very efficient and accurate control over the craft with minimal fuel usage. As such, the expected lifetime of the craft is set at 15 years, but there is considerable likelihood of the satellites continuing to operate effectively after this interval has elapsed.

Propulsion Reaching geostationary orbit (GEO) from the geosynchronous transfer orbit (GTO) requires a large fuel spend, and is accomplished by the primary propulsion system, the R-4D-11 engine23, which is a high-pressure fed liquid fuel system that combines

Chris Blundell | z5014763 two hypergolic propellants (Monomethylhydrazine (MMH)/Nitrogen Tetroxide (NT))20 to produce 490 N of thrust23. The hypergolic bipropellant system does not require an ignition source to produce combustion, however the chemicals involved require special handling considerations21. MMH freezes at around 2 °C, requiring in- sulation and heating to function effectively in space temperatures. Additionally, both MMH and NT are highly toxic, so care must be taken during handling operations such as fuelling and transportation. MMH and NT do not require cryogenic storage, unlike LH2 and LOX, which enables long term storage for increased mission duration. However, the specific impulse of a MMH/NT engine (~300 s) is necessarily lower than a LH2/LOX engine (~450 s) due to the difference in molecular mass. This is demonstrated in the table below21.

Molecular Freezing Boiling Density Propellant Symbol Weight Point °K Point °K at 20 °C

Hydrogen H2 2.02 13.7 20.4 0.071

Oxygen O2 32 54.4 90.0 1.14

MMH CH3N2H3 46.08 220.9 359.9 0.8765 Nitrogen N2O4 92.02 261.9 294.3 1.447 Tetroxide

The craft stores the propellant in 2,272 kg capacity titanium tanks and uses helium as a non-reacting pressurising agent20. These tanks are manufactured by Orbital ATK, and use a Propellant Management Device (PMD) to ensure that fuel delivery is not affected by ullage in the tank as it operates in zero-g conditions. The engine dimensional and performance parameters are given in the table below.

R-4D-11 Engine Parameters20 Length 0.55 m Diameter 0.28 m Dry Mass 3.63 kg Thrust 490 N Specific Impulse 312 s Thrust to Weight Ratio 13.7 Tank Capacity 2272 kg Chamber Pressure 6.9 Bar

The propellant used in the R-4D-11 engine is stored in tanks aligned close to the centre of the satellite to minimise the effect on the centre of mass and moment of inertia as the fuel is expended. This centralisation strategy is additionally beneficial in reducing the static unbalance of the spacecraft in its stowed configuration, as the majority of the vehicle mass is stored in the central tanks21. While the pressures of fuel and the entire fuel system are closely monitored and managed, tanks are still designed with consideration of their failure criterion. In particular, pressure vessels are designed such that defects such as cracks will propa-

Chris Blundell | z5014763 gate through the thickness of the tank and cause a leak, rather than propagating around the tank and causing a bursting failure mode. A leak is much less violent, and can cause a pressure reduction that mitigates the rupture or explosive failure of the vessel. Additionally, leaks can be detected with monitoring equipment, allowing for potential remedy before the situation worsens21.

Communication The Sky Muster satellites are both communications satellites, and naturally have a large proportion of their resources devoted to communications equipment. A small subset of that equipment is designated for communication with the mission control ground station. This consists of an S-band antenna with corresponding transceivers20. This communications avenue allows for the exchange of telemetry and control data with Earth.

Command and Data Handling The SSL-1300 satellite bus is built around a flexible, flight-tested control system comprised of 2 independent RAD-750 central control processors, allowing for complete 2:1 redundancy for central control hardware20. Data processing is through a MIL-STD-1553B serial data bus, which allows for multiplexing and half-duplex command/response protocol action20. Lower level data busses are built around the RS-485 data architecture, as are the routers and Serial Interface Modules (SIMs)20. Data storage for up to 5.6 Tb is available, and the telemetry and command downlink rate is 350 Mbps on the S-band (2-4 GHz)20. Downlink formatting is compatible with both the Consultative Committee for Space Data Systems (CCSDS) and Spacecraft Tracking and Data Acquisition Network (STDN) formats allowing for interoperabil- ity with various ground station protocols20,21. Additionally, both command and telemetry data can be encrypted as per the Advanced Encryption Standard (AES), maintaining security of the satellite from hackers or misdirected command signals20.

Mission Command and Control

Ground Stations The satellite service exists to transmit signals to homes and businesses, but those signals need to be relayed to a ground station in order to provide query and response functionality to the internet experience. There are 10 ground stations built to facilitate this link, with the final station completed by ViaSat in 2015. Across the 10 sites are 24 satellite dishes, with two 13.5 m parabolic dishes per site and an additional two dishes for redundancy, backup, telemetry and tracking at both the Wolumla and Kalgoorlie locations25. The other sites are located in Bourke, Broken Hill, Carnarvon, Ceduna, Geeveston, Geraldton, Roma and Waroona. Each facility is capable of transmitting 10 Gbps. The Wolumna facility is designated as a backup service, remaining on stand-by in case one of the other ground stations is temporarily affected15,25. The required power for such high-energy signals is offset by solar farms, reducing the ongoing environmental cost of the service25. 14

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Customer Hardware

Out Door Unit The other end of the service is the Out Door Unit (ODU), the dish installed on the premise for each of the homes and businesses that are part of the satellite service. There are 3 dish sizes available as part of the service: 80-, 120- and 180 cm. The Ka- band requires a high degree of alignment accuracy due to off-axis signal attenuation. The following table indicates the required accuracy for each dish size15.

Pointing Accuracy Dish Size (cm) (Degrees) 80 1.4 120 1.0 180 0.7

Modem In addition to the dish installed on the premise, premises need to have an NBN Sat- ellite specific modem installed by an NBN contractor26. This modem is manufactured by ViaSat, the company responsible for constructing all of the ground systems for the satellite service. The modem is functionally identical to the RM511x line of Satellite modems, with the addition of an educational port designated for education specific services26. This service segregation is found on a number of NBN service technologies, allowing ISPs to separate and allocate bandwidth preferentially as required.

Transmit/Receive Integrated Assembly The Transmit/Receive Integrated Assembly (TRIA) is a transceiver device that re- ceives and transmits signals from the modem to the satellite via the ODU15. It is available in two variants (3 W and 6 W) depending on the signal strength, predicted rain fade or position relative to spot beam boundaries of the installation location26.

Launch

Launch Details The modular SSL-1300 platform that is used in both Sky Muster I and II is compatible with a number of different launch vehicles, meaning that late stage launch vehicle substitution may be performed20. Despite this, both satellites were launched as planned on-board an Ariane-5ECA3 from the Guiana Space Centre in Kourou, French Guiana27. Sky Muster I was launched alongside another communication satellite designated ARSAT-2. Both the Australian and Argentinian space craft were launched on September 30, 201515. Sky Muster II was also launched alongside another communications satellite, an Indian satellite called GSAT 18. Their launch occurred on October 5, 201615.

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Launch Satellite Launch Site Date Time Vehicle Guiana Space Centre 1730 Local Kourou Sky Muster I Ariane-5ECA27 30/09/201515 0630 Sydney French Guiana 2030 UTC28 South America27 Guiana Space Centre 1730 Local Kourou Sky Muster II Ariane-5ECA27 05/10/201615 0630 Sydney French Guiana 2030 UTC29 South America27

Launch Facility The Guiana Space Centre (CSG) is a European spaceport in French Guiana that has been in operation since 1968. CSG is situated on the coast of South America fronting on to the Atlantic Ocean, and close to the equator (between 2° and 6° North). The coastal location gives CSG serviceable access to the world by land, air and sea. The climate is typical of equatorial regions, with minimal seasonal variation in temperature or humidity.30 CSG is operated the French National Space Agency (CNES) on behalf of the Euro- pean Space Agency (ESA). There are 3 launch facilities (ELA, ELS and SLV) for the three rocket platforms that are launched at CSG, the Ariane 5, Soyuz and Vega. The payloads for any of these rockets are assembled and integrated in the Payload Prepa- ration Complex (ECPU). Mission control is also common to the three sites. The ECPU is the final assembly and preparation facility that processes rockets and flight cargo before launch. It is capable of managing and supporting multiple launch schedules simultaneously, with capacity to share the facility amongst a number of missions at the same time.30 Final preparations and integration between the launch vehicle and the payload are performed at launch vehicle specific sites near the launch site. For the Ariane 5, the launch site, ELA, is near Kourou, approximately 15 km from the CSG main head- quarters and operational command centre.30

Launch Vehicle The Ariane 5 was developed in 1987 as a more powerful heavy launch vehicle than its predecessors. This resulted in a radically different architecture, as the rocket was designed to be highly redundant in order to reach a human-carrying safety rating. The Ariane 5 is significantly more advanced than its predecessors, and achieved this by utilising standardised components and architectures that were elsewhere flight- proven. Designated as a heavy launch vehicle, the Ariane 5 has a spacious nose fairing to accommodate large payloads.30

Payload Fairing Diameter 5.4 m Height 17 m

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The Ariane 5 uses 2 solid rocket boosters (SRBs) to provide 90% of the initial launch thrust, with the rest provided by the core stage – a cryogenic Vulcain 2 engine that continues to provide thrust past the SRB separation and up until the upper stage separation30. Details on both are provided in the following tables30.

Solid Rocket Boosters (SRB or EAP)30 Fuel State Solid Diameter 3.05 m Height 31.6 m Propellant Mass (each) 240 t Average Thrust 7000 kN Specific Impulse 274.5 s Burn Time 130 s Attitude Control Steerable Nozzle

Main Core Stage (EPC) - Vulcain 2 – 1 chamber30 Fuel State Cryogenic pressurised liquid

Fuel LH2 and LOX

Pressurising Agent GH2 and GHe Diameter 5.4 m Height 23.8 m Dry Mass 14.7 t Tank Material Al alloy Propellant Mass 170 t Thrust (Sea Level) 960 kN Thrust (Vacuum) 1390 kN Specific Impulse (Sea Level) 310 s Specific Impulse (Vacuum) 432 s Burn Time 540 s Pitch and Yaw Gimballed Nozzle Attitude Control Roll 4x GH2 Thrusters

The upper stage is also powered by a cryogenic bipropellant engine, but based on the Ariane 4’s HM7B engine rather than the Vulcain 2 used for the first stage30. The additional rocket stage allows for better nozzle optimisation and increased flight efficiency, since each stage can have their exhaust nozzles optimised for the altitude range covered by flight under the power of that rocket stage21.

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Upper Stage (ESC-A) - HM7B engine – 1 chamber30 Fuel State Cryogenic pressurised liquid

Fuel LH2 and LOX

Pressurising Agent GH2 and GHe Diameter 5.4 m Height 23.8 m Dry Mass 4.54 t Tank Material Al alloy Propellant Mass 14.9 t Thrust 67 kN Specific Impulse 446 s Burn Time 945 s

Attitude Control 4 sets of 3x GH2 Thrusters

The Ariane 5 offers a high degree of orbital injection accuracy, even when multiple satellites are launched together. For a launch inserting the payload into Geostation- ary Transfer Orbit (GTO), the Ariane 5 boasts the following accuracy parameters30.

Symbol Parameter a Semi-major Axis 40 km e Eccentricity 4.5x10-4 m/m i Inclination 0.02 degrees

ωp Argument of Perigee 0.2 degrees Ω Ascending Node 0.2 degrees

Manufacture Details The Sky Muster I and II satellites were both manufactured in California by SSL. The facilities at SSL allow for precise manufacturing processes to exacting specifications required for space hardware. In particular, SSL are recognised as a Centre of Excel- lence in advanced composite technologies, with vast expertise in manufacture, research and development.31 Aside from the manufacturing equipment, the facility itself is designed such that construction, assembly and testing can be performed at certified clean-room standards. Bonding, assembly and testing areas are class 10,000 (ISO7) clean rooms, with class 1,000 settings available for specific missions, and class 100 laminar flow benches also available for particularly sensitive assembly when required.31 In addition to the manufacturing prowess, SSL is equipped with the necessary tools to test, validate and qualify space-going hardware as flight-ready. The in-house testing facilities give SSL the ability to expedite the design and development process, culminating in a viable spacecraft with less time taken in construction.31 Further to this, SSL have made a great number of SSL-1300 satellite bus systems that are currently in operation, so much of the spacecraft hardware is already flight proven. The universal bus design provides off-the-shelf capabilities to clients for a

Chris Blundell | z5014763 number of mission objectives, and further customisation of the platform can be achieved with comparatively low cost when considering the investment in a ground- up build of a new spacecraft.20,31

Integration and Assembly The satellite structure was assembled in California by SSL, but the integration and assembly of the launch vehicle superstructure occurred at the Guiana Space Centre (CSG) in French Guiana. The Sky Muster satellites were both flown from California to CSG in an Antinov An-124, a Russian quad-jet heavy transport aircraft14. Once at CSG, the satellites were tested and fitted to the launch vehicle, an Ariane-5ECA. In order for the launch vehicle to function effectively, the payload must be designed such that it conforms to a strict set of test standards. While much of the ground work for passing these tests was done in the SSL facility, the integration with the launch vehicle is conducted in the CSG facility, with independent pre-flight readiness tests verifying the design and manufacture of the payload were completed according to the necessary requirements.

Temperature The temperature within the CSG facilities is maintained by air-conditioning at a con- trolled and stable 23±2 °C. This provides a comfortable working environment for facility staff, but also minimises the thermal expansion and contraction during assembly. In doing so, greater certainty can be determined in fastener torque specifications, pressure readings and so on. The thermal stability varies slightly when components are transported between facility buildings. In these transiting stages, temperatures are generally in the region of 24±3 °C.30 Once encapsulated in the fairing, the spacecraft payload is cooled by a constant air flush, which results in a minimum temperature of 11 °C. This low minimum temperature is not a concern, however, as the dew point is 6.5 °C, significantly colder than the minimum spacecraft temperature. This means there is no risk of the satellite being contaminated or damaged by condensation.30

Humidity The CSG facilities are air-conditioned in order to provide humidity control, which is critically important in the reduction of static electricity build up. All internal facility buildings maintain a humidity level of 55% (±5%), despite outside humidity generally fluctuating between 60-100%.30 Once encapsulated within the launch vehicle fairing, the spacecraft is subject to low humidity environment of 20% humidity or less. This ensures that there is minimal condensation build up at altitude.30

Cleanliness and Contamination The CSG facilities are also air-conditioned to maintain a clean room status for mission critical assembly and contamination purposes. The satellites arrive at the facility in purpose built payload containers that are kept at class 100,000 (ISO 8) standard

Chris Blundell | z5014763 to ensure that contaminants are not brought into the facility on the payload. The rest of the assembly, integration and testing is then conducted at class 100,000 cleanliness standard. The clean rooms of the facility are monitored for organic contamination and cleaned such that the organic particulate remains less than 0.5 mg/m2/week.30 Launch equipment is similarly cleaned to an organic contamination standard of less than 2 mg/m2.30 The fitting of the satellite to the payload fairing adapter is a particularly critical environment, and the fairing is consequently air-conditioned to class 10,000 standard (ISO 7) after sealing in the payload. 30

Electromagnetic Environment Ariane-5ECA telemetry system consists of two transmitters, each with its own antenna. They operate at 8 W on a selection of the five allocated frequencies in the 2200-2290 MHz band (2206.5, 2227, 2254.5, 2267.5 and 2284 MHz). The payload spacecraft must not operate on or overlap these frequencies with a margin of 1 MHz. There are two other sets of two receivers and transponders each on the cryogenic core stage operating in the 440-460 MHz and 5400-5900 MHz bands respectively. The lower frequency pair of receivers is designated for telecommand-destruct reception, and as such its two antennae are omnidirectional and non-polarized. The second system is a radar transponder system that can transmit at 400 W with a minimum pulse of 0.9 μs. The two transponders have a total of four omnidirectional antennae that are polarized in a clockwise circular pattern. Due to the high electromagnetic radiation environment at the launch site, Arianespace recommend that satellites demonstrate an electromagnetic susceptibility of 150 dBμV/m or more in the 1-40 GHz range.30

Mass Properties The Ariane-5ECA mandates that its payload is mounted with a static unbalance of less than 0.046 m for a 3-axis stabilised satellite weighing approximately 6440 kg. There are no specified dynamic unbalance requirements for 3-axis stabilised craft, irrespective of weight. The satellite is however required to have a ratio of centre-or- gravity to separation plane of less than or equal to 2.6. This ensures the separation and jettisoning of the fairing and craft are performed without issue.30

Modal Properties The vibrational modes of the spacecraft are measured well in advance of flight to ensure that the fundamental resonant frequencies in the lateral and longitudinal directions do not correspond to operating vibration loads, as this would likely cause damaging resonance behaviour. To avoid this, it must be ensured that the 1st fundamental lateral frequency is greater than or equal to 8 Hz, and the 1st fundamental longitudinal frequency is greater than or equal to 27 Hz.30

Design Loads The dynamics of flight impart great forces onto spacecraft, and as such, the satellite must be designed to withstand large acceleration loads. The following table repre-

Chris Blundell | z5014763 sents the recommended design loads, represented as Quasi-Static Loads that are demonstrative of both dynamic and static loads encountered during the mission. This table and its contents are reproduced from the Ariane 5 User’s Manual30.

Acceleration (g) Additional Critical Flight Longitudinal Lateral Line Load Events Static + Static Dynamic (N/mm) Dynamic Lift-Off -1.8 ±1.5 ±2 26 Aerodynamic Phase -2.7 ±0.5 ±2 23 Pressure Oscillations/ -4.40 ±1.6 ±1 37 SRB end of flight SRB Jettisoning -0.7 ±3.2 ±0.9 0

Electrical Interface During installation, the satellite and launch vehicle are connected physically and electrically, with specific requirements for the electrical interface between the two. During launch and space flight, the satellite is required to not send, receive or generate control commands so as not to interfere with the electromagnetic radiation environment that the launch vehicle is designed for.30 Otherwise, the spacecraft is connected through umbilical lines to the launch vehicle and back to mission control through the mast gantry on the launch site. Radio frequency link is also facilitated through either a radio-transparent window or a passive repeating unit.30 The launch vehicle can also transmit telemetry data on the spacecraft’s behalf, as well as supplying power and optional dry loop command circuits as required.30

Test Details Testing of spacecraft, components and systems is a critical element in readying a satellite for launch. Testing broadly begins at the manufacturing stage, where only high quality, defect-free material is chosen. This incredibly stringent testing procedure is maintained for the entire development and manufacture of the satellite. However, the critical testing phases are carried out at more complete stages of the build process. By testing entire subsystems, components or indeed the whole satellite, a better understanding of the spacecraft performance can be determined.21,22 There are broadly two types of tests conducted in the mission development: verification tests and readiness tests. Verification involves the correlation between theoretical models, predictions and simulations with the experimental data gathered from real world testing. This process is vital in developing new approaches to spacecraft design. Readiness testing is carried out later in the process, and serves as a screening tool to exclude otherwise unnoticed design flaws, defects or abnormalities30. These must be carried out in a flight-like configuration in order to confirm that no erroneous behaviour is encountered when larger assemblies are created from their constituent components. 21

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Pre-launch testing Pre-launch testing is a vital part of verifying the capabilities of both the satellite and the launch vehicle prior to lift-off. By performing a series of rigorous tests, the designers and engineers can assess the suitability of their computer models, assumptions and predictions for in-flight behaviour. This allows for a greater chance of mission success, and also provides valuable data to add in to future simulations and predictions. It is important to note that pre-launch testing encompasses tests carried out in flight-like configurations long before the final readiness checks that are also know as pre-launch tests. SSL, the Californian based company tasked with the manufacture of Sky Muster I and II, were responsible for the pre-launch testing. This was conducted at SSL’s production and testing facility, where suites of testing apparatus are available.32

Thermal Testing Each satellite undergoes thermal tests to ensure they are able to withstand the ex- tremes of launch and their operational life in space. The thermal testing process is comprised of several different tests to characterise individual performance parameters, as well as combined tests to ensure safe operation in maximally and minimally extreme cases. Thermal cycling simulates both the temperature gradients experienced in orbit, as well as the extreme temperatures associated with launch. The test can cycle between temperatures as low as -160 °C and up to 180 °C. Additionally, the spacecraft is subject to thermal vacuum and thermoelastic distortion testing at temperatures ranging from -170 °C to 150 °C, with a vacuum condition of 1.333x10-9 Bar. This gives engineers an accurate idea of the behaviour of the spacecraft in a space environment, especially with regards to the thermal expansion and contraction of the structure. The tests also allow for the simulated testing of the thermal management system on- board, confirming that the spacecraft will operate as intended in orbit.31

Static Testing The Sky Muster satellites are built to withstand static forces greater than 4.55 g and 0.25 g in the longitudinal and lateral direction respectively. This is a minimum standard required by the Ariane 5ECA launch vehicle, but standard practice indicates that the flight-ready safety factor also adds to the design requirements.30

Outgassing Outgassing is a phenomenon that occurs when materials are subjected to very low- pressure environments such as the vacuum of space. This can result in the release of absorbed gasses and volatiles trapped in the materials or structure of the spacecraft as well as migration of plating materials across thermal gradients. The effect of this is a potential change in material properties such as strength, stiffness, ductility and so on, as well as physical and structural changes such as structural distortion, shifting mass properties and surface contamination. Additionally, outgassing can cause a loss of lubrication in moving parts, leading to seized mechanisms and flight hardware or mission failure. Furthermore, the surface coatings on mating parts can deteriorate

Chris Blundell | z5014763 leading to cold welding, which can again prevent the deployment of spacecraft mechanisms and cause critical systems to fail.21 Given the potential severity of problems caused by outgassing, all spacecraft and flight hardware are tested to ASTM E595 standards, in addition to addressing the launch vehicle criteria for spacecraft materials presented in the following table. These launch vehicle compatibility tests are measured in accordance with the procedure ECSS-Q-70-02A30.

Outgassing standards30 Recoverable Mass Loss (RML) ≤ 1 % Collected Volatile Condensable Material (CVCM) ≤ 0.1 %

Vibration Testing The vibrations induced by a rocket launch can cause extreme stresses in spacecraft. SSL use a shaker table capable of generating 18,000 lbf to test the satellites’ ability to withstand such forces31. Ariane 5 rockets require testing to demonstrate the spacecraft can withstand the sine-equivalent dynamic loads presented in the following table30. This accounts for the lower frequencies of random vibration as well, with higher frequency random vibrations tested in the acoustic test following30.

Longitudinal Direction Frequency (Hz) Acceleration Load (g) 2-50 1 50-100 0.8

Lateral Direction Frequency (Hz) Acceleration Load (g) 2-25 0.8 25-100 0.6

Acoustic Testing Acoustic loads generated by the launch vehicle and turbulent flow phenomena are potentially damaging to spacecraft structures, especially if they are not considered in the design stage21. The acoustic test generates a simulated launch-like acoustic environment and allows for the measurement of the response of the satellite to acoustic pressure fluctuations. The following table and contents, reproduced from the Ariane 5 User’s Manual30, indicate the expected acoustic noise spectrum, and the intensity of each octave band.

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Qualification Protoflight Acceptance Level Octave centre Level (dB) Level (dB) (flight) (dB) frequency (Hz) (reference: 0 dB = 2 x 10–5 Pa) 31.5 131 131 128 63 134 134 131 125 139 139 136 250 136 136 133 500 132 132 129 1000 126 126 123 2000 119 119 116 Overall 142.5 142.5 139.5 Level Test Duration 2 1 1 (min)

Shock Testing Shock testing is conducted by performing a drop test on a protoflight or flight model, and measuring the shock levels on the individual model component units and the in- terface30. The measured response is then corrected by two factors: uncertainty and safety. Both corrections add 3 dB to the shock response as a measure of precaution30.

Antenna Testing The primary function of the satellite is to provide radiofrequency communications between ground stations and receiver dishes. As such, testing the antennae of the spacecraft is vital to ensuring the payload is able to perform its function effectively in orbit. SSL can test compact and near field antennae in their facility, on frequencies including the Ka-band. The facility tests both Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC) allowing for a holistic understanding of the electromagnetic signature and response of the spacecraft.31

Safety Factors All design factors are carefully considered in the creation of a spacecraft, however the launch environment and service life in space can generate conditions outside of the expected operation for a given satellite. As such, the minimum viable product is ap- pended by a safety factor to ensure that errors of uncertainty of random variations are not detrimental to the success of the space mission. Below is a table from the Ar- iane 5 User Manual30 of recommended safety factors to be applied to spacecraft components, structures and subsystems at various stages of flight proven status. Where there is no listed safety factor for a given production item or test certification, the recommendation is for a safety factor of 2 or 100% to be applied.

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Qualification Protoflight Acceptance Spacecraft Duration/ Duration/ Duration/ Test Factors Factors Factors Rate Rate Rate Static 1.25 N/A 1.25 N/A N/A N/A Sine 1.25 2 oct/min 1.25 4 oct/min 1.0 4 oct/min Vibrations Acoustics +3dB 120 s +3dB 60 s 1.0 60 s Shock +3dB N/A +3dB N/A N/A N/A

Interface Fit Check Performed at either SSL or Arianespace facilities, the fit check ensures compatibility between the satellite and the launch vehicle componentry, especially the mating sur- faces, electrical connections. Testing this early in the pre-launch preparations allows for adjustments to be made if necessary, and confirms the launch vehicle requirements are met before transport to the launch site. Additionally, the satellite provider can verify the interface does not affect the necessary communication with other launch site equipment. This equipment is responsible for monitoring the satellite at all times during the launch campaign, and as such it must remain in contact with the spacecraft when installed in the launch vehicle hous- ing. At its most basic level, however, the fit check is conducted from the outset of the spacecraft design process, ensuring that the satellite can be stowed in the launch vehicle fairing without damage to mission critical subsystems on board. For this reason, the satellite must use articulated mechanisms for deploying solar panels and antennae, as they would not fit within the launch vehicle in their extended configuration.

In-orbit Testing Once inserted into their geostationary orbit, both Sky Muster I and II spent over 2 months performing in-orbit tests before the activation of the satellite service for customers. This testing is an important part of the mission as it verifies the capability of the satellite to perform its duty in service. The testing was performed by Optus’ satellite division, and focused on telemetry, tracking and command metrics, as well as throughput capacity, response latency and beam forming coverage. Upon the successful completion of this testing period, the NBN satellite service could be activated, and the Sky Muster satellites could commence providing broadband internet services to the hundreds of thousands of users on earth.

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Conclusion The NBN satellite program is a fascinating example of the potential for space technologies to benefit thousands of people in remote areas. The geographical challenges of Australia’s land mass required a novel solution to connect rural, regional and remote Australians to the internet. The utilisation of a satellite network allows for vast distances to be covered with considerably less ground infrastructure than fixed connections, and consequently resulted in the satellite program offering a competitive cost advantage. While the achievements of the NBN satellite service are numerous, there is considerable scope to adapt and improve the service to keep up with growing technological demands, such as internet speeds, bandwidth capacities and reliability demands. It is determined that satellite internet is an effective solution, but in its current form it is not optimised for future growth. The mission critically addresses the requirements set out in the Statement of Expec- tations, although there is concern that the goals of the mission were neither ambitious enough, nor truly representative of the needs of the end users. In this re- gard, it is suggested that the mission be remembered as an example of successful execution of an unsuccessful aim.

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