Spaceflight Insider

SpaceX set to launch rare Falcon 9 for Inmarsat-5 F4 mission

An artist’s depiction of the Inmarsat-5 F4 satellite in orbit. Image credit: Boeing

KENNEDY SPACE CENTER, Fla. — With the static fire successfully concluded, SpaceX is clear to begin final launch preparations of the rarest variant of the company’s active Falcon 9 launch fleet as it readies to loft the fourth of the Inmarsat-5 series of communications satellites. The company is targeting a 50-minute launch window opening at 7:20 p.m. EDT (23:20 GMT) May 15, 2017, at Launch Complex 39A (LC-39A).

Fourth of its kind

Sitting atop the Falcon 9 is the fourth of the Inmarsat-5 series of telecommunications satellites. Initially meant to only be a trio of spacecraft, Inmarsat triggered the option in 2013 to have a fourth built in order to enhance the capabilities of the company’s Global Xpress (GX) satellite broadband network.

An archive photo of a Falcon 9 in its expendable configuration, similar to what will be used for the Inmarsat-5 F4 mission. Photo credit: Mike Howard / SpaceFlight Insider

Like its three predecessors, Inmarsat-5 F1 through F3, the fourth satellite will provide up to 50 megabits per second of data and voice services to terrestrial terminals. The spacecraft will operate in the Ka- and L-band spectrum and will be powered by two solar “wings” generating a total of 15 kilowatts at the beginning of its life, dropping to 13.8 kilowatts at the end of its 15-year design life.

The Inmarsat-5 family of spacecraft is built on the Boeing 702HP satellite bus. Tipping the scales at more than 13,000 pounds (5,900 kilograms), the satellite is slightly too massive to allow for a recovery attempt of the Falcon 9 first stage.

In contrast to the constellation planned by SpaceX, Inmarsat’s satellites are positioned above the equator in a geostationary orbit, which allows as few as three satellites to provide global coverage.

Rare bird

While most of the company’s recent launches feature either a barge recovery of the first stage or a return of the booster back to a ground-based landing pad, this mission is noteworthy for something quite the opposite: a completely expendable launch vehicle.

Perhaps nothing is more a testament to SpaceX’s success of recovering as much of its rockets as practical than is the newsworthiness of the expendable nature of this particular Falcon 9. Indeed, when much of the excitement surrounding a SpaceX mission centers on the recovery of the booster, discarding the first stage almost seems an anathema.

Recovering the booster is crucial to SpaceX’s goal of reducing launch costs. However, the hardware necessary to perform this feat adds considerable heft to the rocket. With this satellite’s mass at the upper end of the Falcon 9’s capability, every ounce saved in launch vehicle weight directly translates into mass-to-orbit performance.

Therefore, once the first stage has completed its job and separates from the second stage, it will be left to follow a ballistic arc and splashdown into the Atlantic Ocean, not to be recovered.

Quick turnaround at LC-39A

Although the company has received criticism for unmet launch projections, SpaceX has made significant progress toward ramping up its launch cadence. While some of this efficiency can be credited to improved familiarity with procedures and workflows with the pad and vehicle, a great portion of the improvement belongs to the actions of the Transporter Erector Launcher (TEL) at liftoff.

At Cape Canaveral Air Force Station’s Space Launch Complex 40, the TEL would retract several minutes before liftoff. This necessitated the use of extended-length umbilical connections to bridge the gap between the retracted strongback and the rocket. This would leave a significant portion of hoses and feed lines exposed to the rocket’s exhaust as the vehicle climbed from the pad.

The procedure at LC-39A differs markedly in that it only retracts a few degrees from vertical before liftoff and only fully retracts as the rocket begins to rise from the pad. This greatly decreases damage to equipment on the TEL, allowing SpaceX to more quickly ready the complex for the next launch.

Indeed, CRS-11 is set to launch 17 days after Inmarsat-5 F4, an accomplishment that would be difficult to reach without this change in procedures.

For the May 15 launch, the weather forecast three days out calls for an 80 percent chance of favorable conditions at the opening of the window, with the primary concern being cumulus and anvil clouds.

Video courtesy of Inmarsat



Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.

Reader Comments

Andrew Goetsch

The satellite is not too massive to allow 1st stage recovery. SpaceX decided to go to an SSTO so they could burn to depletion and give the customer a few hundred extra meters per second to compensate the customer for the delay.

Garth Woodworth

I don’t doubt your knowledge of the parameters for the Falcon 9 recovery. If the satellite could successfully achieve the desired orbit without the extra momentum, why would it be worth expending all the equipment in the first stage to add more? If you have data about the cutoff between possible and not possible recovery, please post a link to it.

Inmarsat F4 was originally to be launched on top of Falcon Heavy, but since a further delay of the Heavy variant and more capable Falcon 9 single core variant, they decided to go with expandable version as the contract still might be needed to boost the satellite extra on the orbit.

Aleksander Suur

Can’t give you a ref on that but for GTO i read the cutoff point is 5500kg for FT, they would have tried to recover Amos-6(5500kg to GTO) had it not blown up, they did not attempt EcoStar23(5600kg to GTO) Inmarsat-5 F4 is beyond that at 6070kg to GTO so its not surprising they will go expendable on it.

Clive Bashford

I hope they will align the spent first stage tail first and monitor its reentry and destruction. They could find out just how much it could take, and the video would be interesting.

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