Iridium NEXT Satellite Constellation, United States of America
Iridium NEXT is a second-generation global satellite constellation being developed by Iridium Communications. It will become the world's largest commercial satellite constellation upon its scheduled completion in 2018.
Iridium NEXT development
Orbiting Carbon Observatory-2 (OCO-2) is the first Earth remote-sensing satellite mission intended to monitor and provide observations of atmospheric carbon dioxide (CO2).
The first ten of the 66-satellite low-earth orbit (LEO) constellation were launched in January 2017, while the remaining spacecraft are scheduled for launch by 2018. Each satellite is designed to deliver a service life of 15 years.
The satellite constellation is intended to offer higher bandwidth and data speeds, allowing Iridium to cater to the growing demand for worldwide mobile communications.
Iridium NEXT development
The Iridium NEXT programme was initiated by Iridium Communications in 2007. System requirements review of the constellation was concluded in the first quarter of 2009.
Thales Alenia Space was selected as the prime contractor to design, build, and integrate 66 operational satellites, as well as six in-orbit and nine ground spares for the Iridium NEXT constellation in June 2010.
The €1.7bn ($2.2bn) full-scale development contract between Iridium and Thales Alenia Space was finalised in October 2010.
Space Exploration Technologies (SpaceX) was awarded a $492 contract in June 2010 by Iridium Communications, in order to supply 70 Iridium NEXT satellites for use aboard the Falcon 9 launch vehicle.
Thales Alenia Space signed an agreement with the Orbital Sciences Corporation for systems integration and testing of the communications payloads and platforms of the Iridium NEXT satellites, which were manufactured by Thales in January 2011.
International Space Company (ISC) Kosmotras was awarded a supplementary launch services contract in June 2011, in order to launch the Iridium NEXT satellites aboard the Dnepr launch vehicle.
Primary design reviews of the system and space segment were completed in the second quarter of 2012 and March 2012 respectively, followed by critical design review (CDR) of the satellite network system in October 2013.
The payload-to-bus integration on the first Iridium NEXT satellite was completed in June 2015.
Payload details of Iridium NEXT
Each of the Iridium Next satellites can carry a single 48-beam transmit / receive L-band phased array antenna, a Ka-band feeder link and cross-link antennae, and 2,000W two-axis solar array wings.
The satellites have a launch mass of approximately 860kg, and the spacecraft supports the integration of a hosted payload of up to 50kg in weight.
The satellite is equipped with sophisticated onboard processing hardware and software, including a regenerative processing payload with on-board processor (OBP) and a time-division duplex (TDD) architecture, as well as a telemetry, tracking, and control (TT&C) subsystem.
Iridium Communications secured a contract from the joint venture between Iridium and NAV Canada, Aireon, for the primary payload space on Iridium NEXT constellation in 2012.
Aireon will pay hosting fees and a data communications service fee to Iridium under the deal, in return for the integration and launch of its payloads aboard each Iridium NEXT satellite.
Iridium signed an agreement with Harris Corporation in 2013 for the hosting of the Harris AppSTAR reconfigurable payload platform as a secondary payload.
The Iridium NEXT constellation
Iridium NEXT will use a unique mesh architecture of 66 cross-linked LEO satellites, forming a global network in space. It will ensure the delivery of high-quality voice and data coverage across any location on Earth.
Each Iridium NEXT satellite is connected to two satellites in the same orbital plane, as well as one in each neighbouring plane.
This unique configuration avoids the need for dependency on terrestrial infrastructure for routing, as the dynamic mesh network routes traffic between the cross-linked satellites.
The independent constellation offers uninterrupted services in the event of natural disasters that often damage ground telecom networks.
Launch vehicles for the Iridium NEXT satellites
The Iridium NEXT satellites can be launched aboard SpaceX Falcon 9 and Kosmotras Dnepr rockets. The Falcon 9 rocket carries ten satellites in a single launch mission.
Falcon 9 is a two-stage launch vehicle with a launch mass of 505,846kg. It can deliver 13,150kg of payload to LEO and 4,850kg of payload to geostationary transit orbit (GTO).
Its first stage is powered by nine Merlin engines, whereas the second stage is powered by a single Merlin vacuum engine.
The Dnepr launch vehicle is based on the SS-18 inter-continental ballistic missile (ICBM). It has a launch mass of 210t and can carry a maximum payload of 3,200kg in standard space head module (SHM) configuration.
The three-stage rocket is powered by unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (N2O4).