SpaceX launches Inmarsat I-6 F2 on 12th mission of 2023

by Trevor Sesnic

SpaceX has launched the Inmarsat I-6 F2 satellite into geostationary transfer orbit atop a Falcon 9. The vehicle lifted off from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Space Force Station in Florida at the opening of the 89-minute long launch window on Feb. 17 at 10:59 PM EST (03:59 UTC on Feb. 18). This launch marked 2023’s 24th orbital launch and SpaceX’s 12th of the year — an average launch cadence of 4.1 days per launch.

SLC-40 supported the Starlink Group 5-4 mission just 5.95 days before the planned liftoff time of this mission; this marked the third-fastest turnaround of the pad after 5.15 days between the Amazonas Nexus mission and Starlink Group 5-4 and 5.63 days between Hakuto-R Mission 1 and O3b mPOWER 1 & 2.

Citing the thick cloud layers and cumulus cloud rules, Space Launch Delta 45 initially listed the probability of violating weather constraints at 25%. This improved to just 15% closer to launch.

The Inmarsat I-6 F2 payload is a dual-payload satellite that can transmit signals in both L-band and Ka-band frequencies. It is part of Inmarsat’s network of the future, ORCHESTRA, which will provide seamless, high-capacity, low-latency connectivity for global mobility.

The I-6 F2 satellite was built by Airbus and is the second I-6 satellite built; the first satellite, I-6 F1, was launched atop an H-IIA rocket in December 2021. Inmarsat-6 F2 will provide coverage over the Atlantic Ocean and will be supported by two new ground station antennas in Spain.

Inmarsat designed the payload to offer maximum flexibility and adaptability for its customers. It features a multi-beam, digitally processed payload that can dynamically allocate capacity to different regions and user groups.

It also has a software-defined radio that can switch between L-band and Ka-band modes depending on the demand and availability of the spectrum. This will allow the satellite to offer full routing flexibility over more than 8,000 channels and dynamic power allocation of more than 200 spot beams in the L-band.

The I-6 F2 payload is a key component of Inmarsat’s ORCHESTRA network, which will integrate geostationary, low Earth orbit, and terrestrial 5G technologies into a single solution. ORCHESTRA will leverage the strengths of each technology to deliver the best performance and user experience for different applications and environments. This constellation will also enable dynamic mesh connectivity, allowing satellites and ground stations to communicate with each other and share resources.

Inmarsat I-6 F2 being prepared for thermal vacuum testing. (Credit: Airbus)

With the I-6 F2 payload, Inmarsat aims to enhance its services and offer connectivity for its customers in the aviation, maritime, government, enterprise, and humanitarian sectors. The I-6 F2 payload will support Inmarsat’s ELERA and Global Xpress network components of ORCHESTRA.

The satellite masses 5,500 kg and is built on the Airbus Eurostar-3000EOR satellite bus. It utilizes the Fakel SPT140D propulsion unit and has two deployable solar arrays.

Inmarsat-6 F2 sat in the payload fairing of Falcon 9, attached to the second stage. Following payload fairing separation, both fairing halves will softly splash down in the ocean and be recovered by SpaceX’s multi-purpose recovery vessel Bob.

Serving as the first stage, B1077 flew for the third time, with its previous flight occurring just 31 days prior on the GPS-III-SV06 mission. The booster’s first flight was on the Crew-5 mission, which launched in October 2022.

Following first stage separation, B1077 conducted two burns. First, the booster ignited three of its engines for the entry burn, slowing it down ahead of atmospheric reentry. Shortly after, it ignited its single, center engine and softly touched down on Just Read the Instructions (JRTI).

The now familiar Falcon 9 countdown sequence began at T-38 minutes when the Launch Director verified that the vehicle was go for propellant loading. Three minutes later, at T-35 minutes, SpaceX began loading subcooled RP-1 onto both the first and second stages, as well as superchilled liquid oxygen (LOX) onto the first stage. 

Around T-20 minutes, a large cloud vented from the strong back, signifying the second stage was fully fueled with RP-1 and the Transporter-Erector was being readied for Stage 2 LOX loading, which began at T-16 minutes.

At T-7 minutes, the Falcon 9 ran small amounts of liquid oxygen through the nine Merlin 1D engines on the first stage. Known as engine chill, this process cools the engines slowly, ensuring they do not crack from thermal shock when superchilled LOX flows through them at engine ignition.

At T-1 minute, Falcon 9 entered startup and began tank pressurization for flight. At this time, the Falcon 9 was in command of its countdown.

Forty-five seconds before launch, the Launch Director verified that all systems were go for launch. Manual aborts could be called by the launch operators up until T-10 seconds, after which technical aborts are only handled by the vehicle itself and not the ground operators.

At T-3 seconds, the booster’s flight computer commanded the ignition of the first stage’s nine Merlin 1D engines. The engines on the first stage ignite in pairs to reduce startup transients and loads on the vehicle. 

Falcon 9 shortly after liftoff on the Starlink Group 4-36 mission in October 2022. (Credit: SpaceX)

Once Falcon 9 ensured all systems were nominal, it commanded the hydraulic clamps at the base of the vehicle to release, letting the rocket lift off from the pad.

B1077 burned for approximately two minutes and 31 seconds before it commanded shutdown of all nine of its engines. The stages then separated, and the second stage ignited its single vacuum-optimized Merlin engine, in an event known as SES-1. At T+3:23, the fairing halves deployed from the second stage, exposing the Inmarsat I-6 F2 payload to the vacuum of space.

The second stage continued burning until approximately T+8:09 when it then shut down the MVac engine. Booster B1077-3 then landed atop JRTI, becoming B1077-4. This marked SpaceX’s 99th consecutive successful landing.

After an 18-minute long coast, the second stage ignited again for 63 seconds before shutting down. Five minutes later, the satellite was deployed, marking SpaceX’s 182nd consecutive successful launch.

This launch marked SpaceX’s fifth mission of February. The next two launches planned from the space coast include Starlink Group 6-1 (the first batch of Starlink v2.0 satellites) and Crew-6.

(Lead image: Falcon 9 lifts off from SLC-40 with Inmarsat I-6 F2. Credit: Stephen Marr for NSF)

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