O3b Satellite Overview
The O3b Satellite Constellation provides telecommunications and data backhaul from remote locations, offering low-latency Internet backhaul to emerging markets and developing countries.
Data speeds of up to 10Gbps are supported by the each satellite with a total capacity of 160Gbps once the constellation has completed deployment. O3b Networks Ltd. is the operator of this new satellite constellation, named after “the Other 3 Billion” – referring to the population of the world that has no access to broadband data services without help. The company is financially backed by a number of industry giants such as Google and SES.
The O3b satellite constellation is planned to consist of eight satellites in its initial phase before the number of active spacecraft is doubled to 16. The fleet of satellites orbits the Earth in a circular, equatorial Medium Earth Orbit at an altitude of 8,062 Kilometers. O3b provides fiber-like trunking capacity to telecom operators and backhaul directly to 3G Cellular and WiMAX towers.
The first four O3B satellites were launched by a Soyuz 2-1B rocket on June 25, 2013 and entered a commissioning and checkout phase before functional checks for their capabilities began. In September 2013, it became clear that transponders installed on the spacecraft were showing an unexpected degradation in their function of providing timing signals required for the downlink of data from the satellites. This prompted the delay of the launch of the second batch of satellites that was pushed from September 2013 into July 2014 to allow the suspect components to be changed.
With the second batch of satellites launched on July 10, 2014, O3b started delivering operational services
The space segment of the O3b constellation is designed and manufactured by Thales Alenia Space utilizing the ELiTeBus satellite platform that has extensive flight heritage on Low Earth Orbit applications such as the GlobalStar communication satellites.
Each O3b Satellite weighs 700 Kilograms at launch with a dry mass of the ELiTeBus of around 450 Kilograms. The satellite bus is trapezoidal in shape, consisting of rigid aluminum honeycomb panels. The spacecraft bus provides all necessary resources to the payload including pointing stability, propulsion capability, a stable power supply and data connections. The platform can accommodate payloads of more than 300 Kilograms that are hosted on an Earth panel that is 3.0 by 1.6 meters in size.
The spacecraft features two deployable three-segment solar arrays for power generation via gallium-arsenide solar cells, avionics are used for power distribution and Li-Ion batteries for power storage. The solar arrays are capable of automatic sun-tracking to increase exposure. Beginning of life power is 2,400 watts and EOL (End Of Life) power is about 1,700 watts with a nominal payload power supply of around 1,000 Watts. A 28-Volt main power bus is used on the satellite.
The satellite platform is three-axis stabilized with precise pointing capability using position data provided by Earth sensors as well as fine sun sensors and an inertial measurement unit. A GPS unit provides orbit position information to allow the calculation of pass geometry over the various ground terminals. Stabilization and attitude actuation is accomplished using a combination of reaction wheels and torque rods for momentum management. Overall, the satellite has a pointing knowledge accuracy of 0.007 degrees. Propulsion for attitude maneuvers and orbit adjustments/maintenance is provided by a Hydrazine monopropellant system containing 141kg of fuel that feeds eight 1-Newton thrusters which can be used for attitude control, momentum dumps and orbital adjustments/maintenance.
The ELiTe bus is equipped with an onboard computer centered around a LEON3 microprocessor which is widely used in space applications. The OBC system provides command and control of all subsystems of the satellite platform and commands payload operations. A 1553B Data Bus is used aboard the satellite, connecting all systems to the computer and also interfacing with the platform’s communication system that operates in S-Band.
Each of the satellites features redundant systems to prevent single-point failures from causing the loss of a spacecraft. The O3b satellites are built for a design life of ten years.
The payload of the spacecraft consists of of a powerful Ka-Band communications system. Twelve fully steerable Ka-Band antenna assemblies are mounted on the Earth-facing deck of the satellite operating at the 4.3GHz frequency. Two beams are for gateway connections and 10 beams are for remotes terminals. Each antenna provides a data throughput of 1.2 GBit/s – 600 MBit/s for up- and downlink resulting in a total capacity of 12 GBit/s per satellite.
Each of the antennas can be moved to any point within the satellite’s range within minutes to allow flexible communication session planning in order to provide comm coverage where it is needed when it is needed.
The Ka-Payload uses repeater technology to allow for straightforward allocation of bandwidth in the satellite footprint that is about 700 Kilometers in diameter per beam. The flexible configuration of the system provides the capability of inter-antenna data transfer making it simple to provide simple trunking solutions between two or more points.
With the constellation orbiting in MEO, data transfer latency is considerably lower when comparing O3b to Geostationary Communication Satellites that feature latencies of ~500 milliseconds. O3b intends to provide voice communications at a one-way latency of 179 milliseconds and an end-to-end latency for data services of 238ms. For maritime services, a connectivity speed of more than 500 Mbps will be provided.
In its initial constellation of 8 satellites that were launched on two Soyuz flights, the O3b spacecraft are flying at an orbital spacing of 45 degrees. Optimal coverage is provided between 45 degrees north and south latitude, for latitudes greater than 62 degrees, there is no service. With four more satellites going up, the orbital spacing will be reduced as part of the expansion of the constellation.