Artist impression of Optus D1, built on the Orbital STAR Bus platform

The STAR-2 Bus is a fully redundant, flight-proven, spacecraft bus designed for geosynchronous missions.

It is a satellite platform manufactured by Orbital Sciences Corporation with an apogee kick motor to place a communications satellite into geostationary orbit, a thruster to provide the satellite with orbital station-keeping for a 15 year mission, and solar arrays to provide the satellite payload with 5 kW of electrical power.[1]


Orbital's GEOStar-2 Bus design is unique within the satellite industry. Orbital’s GEOStar-2 Bus provides an affordable low-to-medium power satellite platform that is ideal for missions of this size. Rather than being a less efficient version of a larger, heavier product, Orbital’s GEOStar-2 Bus is designed specifically for the 1,000 to 5,550 watts payload class. The GEOStar-2 Bus is flight-proven with excellent operational performance among the 29 currently in-orbit. With two more GEOStar-2 satellites now in production or awaiting launch, Orbital has established its class of GEO satellite products as the unquestioned market leader.[2]


The GEOStar-2 Bus satellite is a modular, mass efficient structure, designed for simplified integration to reduce manufacturing cycle times. The structure is supported by a composite thrust cylinder, to which the bus, payload, nadir and base panels are connected. Energy from two multi-panel solar wings and lithium ion batteries is electronically processed to provide 36 volts regulated power to the satellite throughout the mission. All active units aboard the satellite are connected through a 1553 data bus. Commands and telemetry are processed through the flight software resident on the flight processor, which provides robust autonomous control to all GEOStar-2 satellites. The modularity of the structure and the standard 1553 interfaces allow parallel assembly and test of the bus and payload systems, reducing manufacturing schedule risk by minimizing the time spent in serial satellite integration and test flow.[3]

Payload Support

While primary applications are Fixed Satellite Services (FSS) and Broadcast Satellite Services (BSS), the GEOStar-2 Bus can be adapted for MSS, Earth and space science applications, as well as for technology demonstration or risk reduction programs. Depending on mission duration requirements, the GEOStar-2 Bus can accommodate payloads in excess of 500 kilograms, and provide up to 5,550 watts of power. Instrument data can be provided in standard format such as CCSDS or through secured encryption, as approved by the National Security Agency (NSA).[4]

Mission List

SKYM-1 Mission: Ku- and R-band Launch: TBD

Amazonas 4A Mission: Ku-band Launch: 2014

Thaicom-6 Mission: Ku- and C-band Launch: 1/6/14

SES-8 Mission: Ku- and Ka-band Launch: 12/3/13

Azerspace/Africasat-1a Mission: C- and Ku-band FSS Launch: 2/7/13

Mexsat Bicentenario Mission: C- and Ku-band FSS Launch: 12/19/12

Star One C3 Mission: C- and Ku-band FSS Launch: 11/10/12

Intelsat 23 Mission: Ku- and C-band Launch: 10/14/12

HYLAS 2 Mission: Two-way Ka-band Communications Launch: 8/2/12

Intelsat 18 Mission: Ku- and C-band Launch: 10/5/11

Intelsat 28 Mission: Ku- and C-band FSS Launch: 4/22/11

KOREASAT 6 Mission: Ku-band DBS and FSS Launch: 12/29/10

SES-1, SES-2 and SES-3 Mission: Ku-band BSS, C-band FSS and Ka-band Launch: SES-1: 4/24/10; SES-2: 2011; SES-3: 2011

NSS-9 Mission: C-band FSS Launch: 2/12/09

MEASAT-3a Mission: Ku-band DTH, C-band FSS Launch: 6/21/09

AMC-21 Mission: Ku-band FSS Launch: 8/14/08

Thor 5 Mission: Ku-band FSS and BSS Launch: 2/11/08

Horizons-2 Mission: Ku-band FSS Launch: 12/21/07

Intelsat 16 Mission: Ku-band DTH Launch: 2/11/10

Intelsat 15 Mission: Ku-band FSS and BSS Launch: 11/30/09

Intelsat 11 Mission: Ku-band DTH, C-band FSS Launch: 10/5/07

Optus D-Series Mission: Ku-band DTH and FSS Launch: D1: 10/13/06; D2: 10/5/07; D3: 8/21/09

TELKOM-2 Mission: C-band FSS Launch: 11/16/05

Galaxy 12, 14 and 15 Mission: C-band FSS (G-15: C-band FSS and L-band Navigation) Launch: G-12: 4/9/03; G-14: 8/14/05; G-15: 10/13/05

N-STAR c Mission: S-band MSS Launch: 7/5/02


Core Bus Features

Bus Dry Mass: 800-1,500 kg Max. Launch Mass: 3,325 kg Payload Mass Capability: 500 kg Orbit: Geosynchronous Typical Mission Lifetime: >15 years Delivery: 24 months (typical) after receipt of order Launch Vehicle Compatibility: Ariane, Soyuz, Land Launch, Proton, H2A, Falcon-9, Sea Launch Reference[5]


Bus Dimensions (HxWxL): 1.75 m x 1.7 m x 1.8 m Construction: Composite/Al Reference[6]

Power Subsystem

Payload Power: Up to 5,550 W orbit average @ 15 years Bus Voltage: 24-36 VDC (nominal) Solar Arrays: Multi-junction GaAs cells Batteries: Li-Ion Reference[7]

Attitude Control Subsystem

Stability Mode: 3-axis; zero momentum Propulsion Subsystem Transfer Orbit System: Liquid bi-propellant On Orbit: Monopropellant (hydrazine) Reference[8]

Command & Data Handling Subsystem

Flight Processor: MIL-STD-1750A Interface Architecture: MIL-STD 1553B, CCSDS Reference[9]

Shared Launch Opportunities

Due to the size and mass envelope of the satellite, the GEOStar-2 Bus is compatible with almost all commercially available launch vehicles, maximizing opportunity for launch and access to space. While dedicated or single launch services are more readily available, the GEOStar-2 Bus targets shared launch opportunities, where launch cost and launch-sharing opportunities are favorable. Reference[10]

Mission Services

Customers can purchase the GEOStar-2 Bus spacecraft bus alone, or as part of a turn-key service that includes an integrated payload, network operations center and launch vehicle. Orbital conducts spacecraft commissioning from its own ground station prior to transferring spacecraft control to the customer’s operations center. Reference[11]


The GEOStar-2 Bus fills a market niche for small, high power geosynchronous communications spacecraft. Orbital’s first application of the GEOStar-2 Bus design, N-STAR c, was successfully launched in July 2002 on an Ariane rocket. Since then, Orbital has launched 27 GEOStar-2 Bus spacecraft with three in production Reference[12]


Several available options augment the basic bus to provide improved pointing, more payload power, secure communications, higher downlink data rates or enhanced payload computing power. Reference[13]


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