Falcon 9 conducts static fire test ahead of the fifth Iridium NEXT mission

by Ian Atkinson

SpaceX has static fired its Falcon 9 rocket at Vandenberg Air Force Base SLC-4E ahead of the fifth of eight planned Iridium NEXT launches. The vehicle, which includes the flight-proven booster 1041.2, will lift the fifth batch of 10 Iridium NEXT satellites into a 625 km polar orbit. The static fire test was conducted near the 7 AM local time (14:00 UTC) opening of the test window on March 25. The launch, which will be SpaceX’s sixth mission this year, is expected to lift off at 7:19 AM local time (14:19 UTC) on March 29.

The test was centered on the flight-proven booster 1041.2, a Block 4 booster which first flew supporting the third Iridium NEXT mission in October 2017.

The test is essentially a full countdown simulation, beginning with the Falcon 9 rocket – minus its payload – rolling out from the Horizontal Integration Facility (HIF) and being raised to vertical on the launch pad. The vehicle is then powered up and propellant is loaded into the tanks of both stages.

A Falcon 9 rocket performing a static fire test at Vandenberg AFB, ahead of the Formosat-5 mission. Credit: SpaceX

The launch control team and Falcon 9 flight computers work their way through the countdown, mirroring exactly what will occur on the actual launch day.

In the last few seconds of the test, the nine Merlin 1D engines on the first stage perform a 3.5 or 7-second test firing while still being firmly held down on the pad. The duration of the burn depends on whether or not the first stage is a reused or new booster. For missions using a new, unflown first stage, the test firing is usually 3.5 seconds long, and 7 seconds long if the first stage is a flight-proven booster.

Since the first stage – B1041.2 –  is a flight-proven booster, the test burn of the nine engines was expected to be 7 seconds long. On this mission, the first stage is expected to be expended, although an open-ocean landing test may be performed to gain additional data on booster landings.

Following the engine test, the fuel in both stages is drained and the vehicle and strongback are lowered horizontal. The rocket is then rolled back into the HIF for final pre-launch processing, which includes integration of the payloads in the fairing onto the vehicle.

Right after the static fire test, SpaceX controllers and engineers conduct a “quick look” review of the data gathered from the test, and SpaceX tweets out whether or not the test was a success soon after, as was the case on Sunday.

Throughout the next few days, and up until the launch day, a much more thorough review of the data is performed, which is fed into the Launch Readiness Review (LRR). The launch date confirmation is determined based on the results of this review.

Few other companies or agencies perform an on-pad static fire, making the test another unique feature of the SpaceX rocket family.

B1041 was first flown supporting the third Iridium NEXT flight in October 2017, which also launched from SLC-4E at Vandenberg.

Liftoff of the third Iridium NEXT mission from Vandenberg AFB. Credit: SpaceX

After completing acceptance testing at SpaceX’s McGregor test facility in September 2017 – which notably includes either a minute-long or full flight duration test firing of the nine engines on the first stage – B1041 was moved to Vandenberg for pre-launch preparations. It lifted off on October 9, 2017, and successfully landed on the Autonomous Spaceport Drone Ship (ASDS) Just Read The Instructions.

The booster was then refurbished at SpaceX’s Hawthrone facilities from late October 2017 to early February 2018, and was shipped to Vandenberg for the second time in late February 2018 to be prepared and processed for this mission.

The payloads on this launch are the fifth set of 10 Iridium NEXT satellites, owned and operated by Iridium Communications, Inc. All of the Iridium NEXT satellites were built by Thales Alenia Space in Arizona.

10 Iridium NEXT satellites being encapsulated in the Falcon payload fairing at Vandenberg AFB, ahead of the third Iridium NEXT flight. Credit: Iridium Communications

The previous four sets of satellites were launched on Falcon 9 rockets from Vandenberg throughout last year. After this launch, there will be three more Iridium flights, all on Falcon 9 rockets.

Two will be additional sets of 10 satellites, and one – the Iridium 6 + GRACE-FO mission – will have five Iridium NEXT satellites and the two GRACE Follow-On satellites, launched for NASA and the GFZ German Research Center for Geosciences in Germany.

The Iridium NEXT satellites will replace the original Iridium satellite constellation. The original satellites were launched on American Delta II, Russian Proton-K and Chinese Long March 2C rockets throughout the late 1990s and early 2000s.

Iridium satellites are used for mobile voice communications on satellite phones. Iridium phones are commonly used by first-responders during natural disasters when conventional cell phone towers are offline or damaged. Iridium phones are also useful for communication across the world while in uninhabited areas, such as on the ocean.

All 10 Iridium NEXT satellites are currently at Vandenberg and are being processed ahead of their upcoming launch. The satellites have been mated to the payload adapters, which will be connected to the Falcon 9 second stage. The total mass of all 10 satellites plus their dispenser is approximately 9.6 metric tons.

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

The 10 satellites will go into service and replace the original Iridium satellites following any needed on-orbit maneuvers throughout the next few months.

The original Iridium satellite constellation is expected to be completely replaced by the new NEXT satellites at the end of summer 2018.

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