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<\/p>\nSpaceX conducted its final launch of 2017 Friday, with a Falcon 9 lifting off from Vandenberg Air Force Base to deploy ten more Iridium-NEXT communications satellites. The launch, which occurred at 17:27:23 Pacific Time (01:27 UTC on Saturday), took place 61 seconds after a Japanese H-IIA rocket is lifted off on the other side of the Pacific.\n<\/p>\n
Friday\u2019s launch carried the fourth group of ten satellites in Iridium Communications\u2019 second-generation Iridium-NEXT constellation. Iridium provides global mobile satellite communications through a fleet of satellites in low Earth orbit. The company was formed in 2001 as Iridium Satellite LLC, taking over the assets of Motorola-backed Iridium SSC, which had deployed the first-generation Iridium constellation but bankrupted itself in the process.<\/p>\n
To provide worldwide communications, the Iridium constellation uses six orbital planes with eleven satellites per plane. As well as sixty-six operational satellites, Iridium keeps several more spacecraft available as on-orbit spares. The first-generation constellation was deployed between 1997 and 2002, with satellites built by Lockheed Martin around the LM-700A platform, which had an expected design life of seven years. The satellites significantly out-performed this expectation, with some operating for over twenty years before replacements finally began to launch earlier this year.<\/p>\n
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Iridium-NEXT satellites \u2013 Credit Iridium<\/p>\n
The Iridium-NEXT satellites, which are built by a partnership of Thales Alenia Space and Orbital ATK, will replace and modernize Iridium\u2019s fleet. The first ten spacecraft were launched in January, with subsequent launches in June and October bringing the total number of new-generation satellites on orbit up to thirty. Iridium has begun decommissioning its older satellites: as of early November, the oldest spacecraft still in service were Iridium 10, 12 and 13, which were part of a seven-satellite launch atop a Proton-K rocket in June 1997.<\/p>\n<\/p>\n
The new satellites are based around Thales\u2019 Extended Lifetime Bus 1000, or ELiTeBus-1000, platform. Also used by Iridium\u2019s rivals Globalstar and O3b, the ELiTeBus platform provides the satellites with a ten-year design life, however Iridium is optimistic that the spacecraft will be able to operate for fifteen years. Each satellite has a mass of 860 kilograms (1,900 lb), and carries L- and Ka-band communications payloads.<\/p>\n
Iridium uses L-band signals to communicate with users\u2019 handsets, while Ka-band transponders are used to cross-link between satellites \u2013 allowing a call to be routed across the Iridium network without needing to transmit it via ground stations. Additional Ka-band transponders are used to provide a downlink where necessary.<\/p>\n
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Iridium CEO Matt Desch on an Iridium handset \u2013 Photo from Jay L. DeShetler\u200f for NSF\/L2<\/p>\n
The fourth launch in SpaceX\u2019s contract with Iridium, which calls for the launch of seventy-five satellites aboard eight Falcon 9 rockets, Saturday\u2019s launch was the first Iridium launch to use a \u201cflight-proven\u201d \u2013 or previously-flown \u2013 first stage. The booster in question, Core 1036, is the same one that was used for SpaceX\u2019s second Iridium launch which took place on 25 June.<\/p>\n
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SpaceX designed the Falcon 9 to be at least partially reusable. Where its primary mission allows, following separation the first-stage booster returns to Earth \u2013 landing either on a landing pad near to the launch site, or an Autonomous Spaceport Drone Ship (ASDS) at sea. Following June\u2019s launch, Core 1036 landed aboard the West Coast ASDS, named Just Read the Instructions, in the Pacific Ocean.<\/p>\n
Friday\u2019s launch was the fifth time SpaceX have launched a flight-proven Falcon 9, and the first such mission to fly from Falcon\u2019s west-coast launch pad at Vandenberg Air Force Base. Core 1036 is a Block 3 booster, part of an earlier production series that has now been superseded by a more powerful Block 4 version. As Block 3 stages are only flown twice \u2013 at most \u2013 before they are retired, SpaceX has opted to fly Friday\u2019s mission in an expendable configuration.<\/p>\n
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Falcon 9 for Iridium-4 at Vandenberg. Photo by Philip Sloss for NSF\/L2<\/p>\n
No landing legs were fitted to the first stage. However, photos of the rocket being prepared for launch showed that the rocket was still sporting grid fins, which are not typically flown on expendable missions. Their presence suggested that SpaceX would attempt to guide the stage to a controlled landing in the ocean \u2013 a technique used on several early Falcon 9 missions to test landing procedures before the first recoveries were attempted \u2013 instead of simply letting it fall back to Earth.<\/p>\n
Core 1036 was the first flight-proven booster not to be recovered a second time, and only the second expendable Falcon 9 to be flown from Vandenberg \u2013 the first being 2013\u2019s deployment of CASSIOPE, which took place before SpaceX had begun attempting to recover its stages.<\/p>\n
Friday\u2019s launch was likely to see another attempt to recover the rocket\u2019s payload fairing. A recovery ship, named Mr Steven, left the port of Los Angeles on Thursday bound for Guadalupe Island, off the coast of Mexico.<\/p>\n