Iridium NEXT-5 satellites ride to orbit on SpaceX Falcon 9

by William Graham

SpaceX conducted the fifth launch of its contract with Iridium Communications Friday, deploying ten more satellites to bring Iridium’s next-generation fleet up to a total of fifty satellites in orbit. Falcon 9 lifted off from Vandenberg Air Force Base at 07:13:51 Pacific Daylight Time (14:13 UTC). The launch also saw SpaceX make an unsuccessful attempt to recover half of Falcon 9’s payload fairing.

Friday’s launch was one of eight that SpaceX is conducting for Virginia-based Iridium Communications, to deploy a total of seventy-five Iridium-NEXT satellites into low Earth orbit. SpaceX began deploying the constellation with four launches last year – the remaining launches will take place in 2018 with Saturday’s the first of the year.

Iridium Communications specializes in mobile satellite communications. Instead of using a small number of satellites in geostationary orbit, the company operates a large fleet in low Earth orbit – which relieves its customers of the need to carry around large antennas and results in a lower latency than geostationary communications.

Iridium NEXT-5 on the pad – photo by Jack Beyer for NSF (including lead photo)

The Iridium constellation was originally developed by Iridium SSC, financed by Motorola, with first-generation satellites deploying between 1997 to 2002. The constellation’s name comes from the chemical element Iridium, which has atomic number 77, as the system was originally expected to require seventy-seven satellites to provide worldwide service. The name was retained after the constellation was redesigned, reducing the minimum number of satellites to 66.

A drawback of Iridium’s concept was that the constellation required all of its satellites to be in orbit before commercial service could begin – resulting in high initial outlay. The setup cost of Iridium’s first-generation constellation in the late 1990s was estimated at around five billion US dollars.

To get their satellites into orbit as quickly as possible, Iridium employed a varied, global, fleet of rockets: 55 of the satellites were deployed by twelve US Delta II rockets, carrying five satellites each. Russia launched twenty-five via three Proton-K/DM2 rockets with seven spacecraft aboard, and two dual-satellite launches using Rokot/Briz-KM vehicles. China’s Chang Zheng 2C/SD made six launches, deploying a total of twelve spacecraft.

The cost of building and launching its fleet of satellites, combined with a slower-than-planned uptake from customers, led to Iridium SSC declaring bankruptcy in 1999. Time Magazine described the company’s collapse as one of the “ten biggest tech failures of the […] decade”. A new company, which would become the present-day Iridium Communications, was formed in 2001 and purchased Iridium SSC’s assets – including the satellites – at a fraction of their value.

Iridium’s first-generation satellites were built around Lockheed Martin’s LM-700A bus, with a design life of eight years. Between 2002 and early 2017, no further satellites were launched to replenish the constellation. This changed last January when SpaceX deployed the first ten second-generation Iridium-NEXT satellites.

Iridium has ordered eighty-one new satellites – including ground spares – for a complete overhaul of their constellation. Thales Alenia Space is the prime contractor for the spacecraft, while US-based Orbital ATK is responsible for integration with a production line set up in Gilbert, Arizona.

The 10 Iridium NEXT satellites that will launch on the fifth Iridium NEXT mission. Credit: Iridium Communications

The satellites are built around Thales’ Extended Lifetime Bus – ELiTeBus-1000 – platform. Each one has a mass of 860 kilograms (1,900 lb) and is expected to operate for at least 20 years. The satellites carry L-band transponders for mobile communications and Ka-band transponders to provide crosslinks between satellites and downlink to ground stations.

The Iridium constellation’s crosslink capability allows each satellite to relay data directly to the four other satellites: those immediately ahead of and behind it in the same orbital plane, and those operating parallel to it in the two adjacent planes.

This allows calls to be routed around the network without needing to pass through ground stations, reducing latency and also cost – as fewer ground stations are required. The sixty-six operational Iridium satellites are arranged in six planes of eleven spacecraft, orbiting at an altitude of about 780 kilometers (485 miles, 421 nautical miles) and a near-polar inclination of 86.4 degrees.

Iridium NEXT constellation – via Thales materials

SpaceX was initially contracted to launch seventy Iridium-NEXT satellites, via seven Falcon 9 rockets. Russia’s ISC Kosmotras was also awarded several launches which were to have flown two satellites at a time aboard the Dnepr rocket.

Due to the political situation between Russia and Ukraine – home to the manufacturer of the R-36 missile upon which the Dnepr was based – Dnepr launches were put on hold and now appear to have stopped permanently. Iridium was forced to cancel their contract with Kosmotras and have manifested a further five satellites to fly on another Falcon 9 launch as a rideshare with GRACE Follow-On – a pair of geophysical research satellites that are being launched for NASA and the German Research Centre for Geosciences (GFZ).

When it deploys Iridium satellites, Falcon 9 flies from SpaceX’s West Coast launch site at Vandenberg Air Force Base in California.

Falcon 9 on the SLC-4E pad ahead of Iridium NEXT-5 launch – Photo by Philip Sloss for NSF/L2

Space Launch Complex 4E (SLC-4E) was originally built as part of the US Navy’s Point Arguello launch site in the 1960s, becoming part of the US Air Force’s Vandenberg AFB when the two adjacent facilities merged in 1964.

The first launch from the pad – then designated Point Arguello Launch Complex 2-4 (PALC-2-4) – came a few weeks after the merger: an Atlas SLV-3 Agena-D deploying a KH-7 reconnaissance satellite. Atlas-Agena rockets continued to use the pad until 1967.

From 1971 to 2005, SLC-4E was used by heavy-lift versions of the Titan III and later Titan IV rockets, beginning with the Titan III(23)D.

The final launch of any Titan rocket was made by a Titan IV(404)B which lifted off from SLC-4E in October 2005, deploying a KH-11 imaging satellite for the National Reconnaissance Office. SpaceX has used the pad since 2013, with Friday’s launch the ninth Falcon mission to fly from Vandenberg.

SpaceX facility at Vandenberg – Photo by Philip Sloss for NSF/L2

SpaceX made the first four launches of their contract with Iridium last year – with successful missions in January, June, October and December placing forty satellites into orbit. The Falcon 9 is designed to be partially reusable, and December’s mission – designated Iridium-4 by SpaceX – used the same first stage that had been used for the Iridium-2 launch in June. Friday’s launch also featured a “flight-proven”, or previously-flown first stage – which was used in last October’s Iridium-3 mission.

The first stage, B1041, made a successful landing aboard SpaceX’s West Coast Autonomous Spaceport Drone Ship (ASDS), Just Read the Instructions, following its previous launch. The stage was returned to shore and refurbished to fly again on Friday’s mission. It was built to Block 4 specifications and as SpaceX does not intend to fly any version other than Block 5 more than twice, B1041 was not recovered again following its second flight. After completing its role in the Iridium-5 mission, the core still made boostback, entry and/or landing burns, but only to gather data for future recoveries.

One part of the Falcon 9 that SpaceX is attempting to recover is its payload fairing – the structure that protects the rocket’s payload from the atmosphere during the early stages of flight.

SpaceX has been experimenting with fairing recovery over the last year, equipping one half of the fairing thrusters to provide attitude control and a parachute to slow and guide its descent.

To protect the fairing from being damaged or contaminated by the salt water of the ocean, a recovery boat will position itself underneath the fairing as it descends, catching it in a large net suspended between four pillars rising up from the deck. SpaceX’s West Coast fairing recovery ship is named Mr. Steven.

SpaceX Fairing Recovery boat – Mr. Steven – photo from Elon Musk/SpaceX

During Falcon 9’s previous West Coast launch, which carried Spain’s Paz satellite to orbit late last month, Falcon 9 flew with a new payload fairing and the first attempt was made to recover the fairing via the boat. The attempt came close to success, with the fairing half landing intact in the water a few hundred meters away from Mr. Steven. The fairing was hoisted out of the ocean and brought back to California.

Mr. Steven put to sea on Thursday to support the Iridium-5 launch. At liftoff she will be located downrange ready to make another attempt to catch Falcon’s fairing as it descends. The test wasn’t successful.

Falcon 9 first flew in June 2010, with Friday’s mission its fifty-first launch. A two-stage rocket, Falcon 9 burns RP-1 propellant and liquid oxygen. The first stage – the only part of the rocket that is currently reusable – is powered by nine Merlin-1D engines.

The rocket’s second stage has a tenth Merlin-1D, optimized to operate in the vacuum of space. This Merlin Vacuum (MVac) engine is making two burns during Friday’s launch in order to place the Iridium satellites into their planned low Earth orbit.

Friday’s launch began with ignition of the nine first-stage engines about three seconds before the end of the countdown. At the zero second mark, Falcon lifted off to began the climb into orbit. Flying south, the rocket passed through the area of maximum dynamic pressure (Max-Q) about 76 seconds after liftoff. The first stage burned for the first two minutes and 34 seconds of the mission before reaching main engine cutoff (MECO).

Iridium NEXT-2 photo by NSF’s Sam Sun for NSF L2

About three seconds after cutoff, the first stage separated from the second stage. While the first stage performed any post-separation testing or falls back to Earth, the second stage continued on towards orbit with the ten Iridium satellites aboard. The second stage ignited its engine about two seconds after stage separation, while the fairing separated from around its payload about forty-nine seconds into the burn.

The first burn of Falcon 9’s second stage lasted six minutes and 23 seconds, placing the rocket and its cargo into an initial parking orbit.

For reasons that are unclear, NOAA restrictions – according to SpaceX – resulted in the webcast ending just prior to the coast phase, but SpaceX provided additional information via social media.

Following a 43-minute, three-second coast, Falcon restarted its second stage for an eleven-second circularisation burn – raising the perigee – or low point – of the orbit.

The Iridium satellites began separating from the upper stage five minutes after the end of the second burn, with the deployment process lasting fourteen minutes and 47 seconds.

Iridium NEXT satellites deploying on the previous mission – via SpaceX webcast

Friday’s mission was SpaceX’s sixth launch of the year and will be the thirtieth worldwide – twelve up on the same point last year.

This is the first time since 1987 that thirty launches have occurred in the first three months of a year. Of the nine previous years in which thirty or more launches were made in the first quarter, 1987’s 114 launches represents the lowest end-of-year total. There has not been a calendar year with more than 100 launches since 1990.

The Iridium launch is the first of two that SpaceX will conduct over the Easter weekend. Another Falcon 9 is due to lift off from Florida’s Cape Canaveral Air Force Station on Monday carrying an unmanned Dragon spacecraft to orbit on its CRS-14 mission to the International Space Station.

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