Japan succesfully launched the Inmarsat-6 Flight 1 (I-6 F1) satellite Wednesday as a part of Inmarsat’s next-generation satellite broadband service. I-6 F1 launched aboard an H-IIA 204 rocket at 12:32 AM local time Thursday (15:32 UTC Wednesday).
Designated H-IIA F45, Wednesday’s launch is Japan’s third orbital flight of 2021 and H-IIA’s second mission of the year, marking the 45th flight of the H-IIA vehicle overall.
Rocket and Payload Overview
H-IIA is Japan’s flagship and currently largest rocket operated by Mitsubishi Heavy Industries (MHI) for the Japan Aerospace Exploration Agency (JAXA).
Since H-IIA’s first launch in 2001, it has become the longest-serving and most-flown liquid-fueled rocket to be operated by Japan. In 1975, Japan launched its first liquid-powered rocket to orbit as part of a partnership with the American company McDonnell Douglas, with its early liquid-fuelled rockets derived from the US Thor-Delta series.
Building on its experience with the initial rockets, named N-I and N-II, Japan then began work on a new vehicle, known as H-I. This rocket was the first Japanese rocket to utilize the power of liquid hydrogen as fuel. The first stage was the American-designed, kerosene and liquid oxygen (kerolox) powered, Extended Long Tank Thor (ELTT) with Castor-2 solid rocket boosters (SRBs). Its second stage was a Japanese-designed and built hydrogen/liquid oxygen (hydrolox) second stage using the LE-5 engine. The H-I was flown nine times from 1986 to 1992 with all of its flights being successful.
Starting with the H-I’s successor, H-II, all future rockets would only use liquid hydrogen, with the design and construction occurring in Japan. H-II was used from 1994 to 1999, and had a strong start with its first five flights all reaching orbit. However, due to the high cost and the complexity of the rocket, a replacement was already in the works. The final two flights of the H-II ended in failures.
The new rocket, now known as H-IIA, was created to lower costs with less complexity, allowing it to be more competitive in the satellite market. The H-IIA used a similar but updated design to the H-II.
The first stage is powered by a LE-7A hydrolox engine. The LE-7A can produce 1,098 kN of thrust with a specific impulse of 440 seconds while in a vacuum. It is four meters in diameter with a height of 37.2 meters. During the launch, the stage will burn for 390 seconds.
To support the initial part of the flight, two or four SRBs are used. Known as SRB-A, these provide the initial push to leave the atmosphere. Each booster provides 2,020 kN of thrust with a burn time of 100 seconds.
H-IIA’s second stage is powered by a single LE-5B hydrolox engine. This engine can produce 137 kN of thrust with a specific impulse of 448 seconds while in a vacuum. The stage is the same four meters in diameter but with a height of 9.2 meters. To place its payloads into orbit, the stage can burn for 530 seconds.
A four meter diameter payload fairing, placed on top of the second stage, is used to protect the payloads before and during launch. There is also an option for a five meter fairing to accommodate larger payloads.
Meet the #H2A204 rocket, rolled out of @MHI_GroupJP’s factory today. Standing 53 metres tall & weighing 443 metric tons, it’s scheduled to launch #I6F1, our @AirbusSpace satellite that’s almost as large as a London double-decker bus, into space on 21 Dec! https://t.co/b9Aep9GEQ8 pic.twitter.com/CWRoTrWcXV
— Inmarsat (@InmarsatGlobal) November 8, 2021
To signify which version the H-IIA is using, a numbering system was created. The first number signifies how many stages are used – although in all flown configurations two stages have been used. The second digit signifies how many liquid boosters would be used, however this was canceled before the first flight of H-IIA. Thus, the first two numbers in the system are always fixed at “20”.
A third number signifies how many SRB-As boosters are used, while an optional fourth digit signified how many Castor-4XL Solid Strap-On Boosters (SSBs) would be used. Early H-IIA rockets had the option to use up to four Castor-4AXL along with two SRB-As. This option was retired in 2010.
Using the most powerful version, the H-IIA 204 with four SRB-As, as much as 15 metric tons can be lifted to Low-Earth Orbit (LEO), or six metric tons to Geostationary Transfer Orbit (GTO).
The H-IIA rocket was selected to launch I-6 F1 in 2017. Designated H-IIA F45, Wednesday’s launch used this H-IIA 204 variant to lift the I-6 F1 satellite into orbit. This is expected to be the final flight of the 204 configuration, leaving 202 as the only active H-IIA variant as JAXA winds down H-IIA operations in preparation for its replacement by the upcoming H3.
Inmarsat is a world-leading satellite communications provider with its origins in the 1970s as an intergovernmental organization. Now privatized, the UK-based company provides satellite communication around the world.
Inmarsat’s first satellite constellation was inherited from its predecessor organization, Marisat, consisting of three spacecraft that had been launched on Delta rockets in the 1970s. These were followed by two MARECS satellites launched on Ariane rockets in the 1980s, with a third lost in a launch failure.
The next generation of satellites began to be launched in the 1990s using the Airbus-built Eurostar-1000 satellite bus. Named Inmarsat-2, four were launched on Delta II and Ariane 4 rockets.
From 1996 to 2013, nine satellites were launched as a part of the Inmarsat-3 and 4 series of satellites. Many of these satellites are still in use today. These satellites mainly used L-Band transponders for communications as a part of the ELERA network.
Beginning in 2013, Inmarsat began launching its fifth generation set of satellites known as Inmarsat-5. Instead of using the L-Band, like the company’s previous spacecraft, it used Ka-Band transponders as part of a new broadband internet constellation called Global Xpress (GX). The first four satellites used the Boeing 702 high-power satellite bus.
The fifth and most recent satellite was launched on an Ariane 5 ECA in 2019. Inmarsat-5 F5 used the Spacebus-4000B2 satellite bus. These five satellites allow global coverage to provide broadband internet. Future satellites will use mainly Ka-Band transponders.
I-6 F1 is the first of two satellites in the Inmarsat 6 series, and the newest satellite in Inmarsat’s ever-growing satellite fleet. Inmarsat ordered the two I-6 satellites from Airbus in 2015. I-6 is based on the Eurostar-3000 electric orbit raising (E3000-EOR) satellite bus.
Artist impression of Inmarsat-6 in orbit. (Credit: Airbus/Inmarsat)
The Eurostar satellites bus is Airbus’s primary offering for modular satellites in Geostationary Orbit (GEO). Eurostar began in the 1990s with the Inmarsat-2 satellites. Since then the Eurostar bus has become the most reliable bus, with no in-orbit failures.
E3000-EOR is Airbus’s first all-electric-propulsion GEO satellite bus. This allowed Airbus to remove the standard propulsion module to cut the weight of any satellite. A new satellite bus, Eurostar-NEO, was born and is a more evolved version of the E3000-EOR.
The reduced mass of the satellite allowed Inmarsat to outfit it with dual payloads and a next-generation digital processor. This will be the first time an Inmarsat satellite supports dual payloads. I-6 will support L-Band and Ka-Band transponders for the ELERA and GX networks.
To support the L-Band transponder, a large nine meter antenna will be used on I-6. The new capabilities added by I-6 will expand ELERA services to support the Industrial Internet of Things (IIoT), maritime and aviation safety services, and allow support to autonomous vehicles.
The Ka-Band transponders on I-6 are also known as GX6A. GX6A is a set of nine multibeam antennas used to provide additional capacities to key demand and growth areas. The new capabilities will be used to help grow Inmarsat’s GX network to the world. I-6 will provide coverage over the Indian Ocean with support by ground stations in Australia.
As a part of the plan to launch seven satellites by 2024, I-6 will also be used as a part of the Inmarsat ORCHESTRA network. The network will use satellites from both GEO, LEO, highly elliptical orbits (HEO), along with 5G to allow one continuous global mobile network.
With the size of the spacecraft, dual payloads, and electric propulsion, the I-6 satellites are some of the largest and most advanced commercial communications satellites ever launched.
I-6 F1 packing before delivery. (Credit: Airbus)
Large twin solar arrays are used on the spacecraft to provide electrical power. When extended, the solar arrays will have a wingspan of 47 meters, nearly as long as a wingspan of a Boeing 767 aircraft. The two solar arrays will provide 21 kW of power.
Using electric propulsion, I-6 F1 will operate in GEO for at least 15 years. Fully fueled the satellite has a mass of around 5,470 kg.
In late 2020, the first I-6 spacecraft was completed and began pre-launch testing. Once testing was completed, I-6 F1 was loaded with one ton of Xenon propellant for its electric propulsion system. By November 2021, final preparations were completed and the spacecraft was delivered to the Tanegashima Space Center via an Antonov An-124 cargo aircraft.
Around the same time, the H-IIA F45 first and second stages arrived at Tanegashima. The two were installed in the Vehicle Assembly Building (VAB) at the Yoshinobu Launch Complex. In early December, the four SRB-A boosters were added to the H-IIA rocket.
The satellite was encapsulated in the four meter payload fairing also in early December. Due to the size of the satellite, only 21 mm are spared between the wall of the fairing and the spacecraft. In mid-December, the satellite and fairing were installed on top of the second stage, completing the H-IIA rocket.
Launch
About 18 hours before launch, the completed H-IIA rocket was rolled out to Pad 1 of the Yoshinobu Launch Complex, also known as Y1. launch site. From the VAB to the launch site is ~500 meters and the journey takes ~30 minutes. Once at Pad Y1, the vehicle was connected to the ground support systems.
Once final checkouts are completed, a Go/No-Go poll is completed before propellant loading begins. The terminal count is started shortly afterwards, with final launch vehicle tests continuing through the countdown. Loading of the LH2 and LOX propellants is completed about six hours before launch.
At the one-hour mark in the countdown – termed X-1 hour in Japanese terminology – the final launch countdown begins. The automated launch countdown sequence begins at X-4 minutes and 40 seconds. The water suppression system is activated about 35 seconds before launch.
The LE-7A engine ignites three seconds before launch. At X-0, the four SRB-As ignite and H-IIA lifted off with the I-6 F1 satellite.
Launch of H-IIA F44. (Credit: MHI Launch Services)
A few seconds after liftoff, the H-IIA begins a pitch maneuver to head due East towards its geostationary transfer orbit (GTO).
At X+1 minute and 40 seconds, the four SRBs burn out. The four SRB-A are then separated in pairs, the first at X+2 minutes and 5 seconds followed by the second pair a few seconds later.
Once the rocket reaches space, the payload fairing is no longer needed and is jettisoned approximately four minutes into the flight.
After burning for six and a half minutes, propellent levels in the first stage are depleted and the LE-7A engine will shut down. A few seconds later the second stage separates and its LE-5A engine ignites.
Following an approximately five and a half minute burn, the second stage reaches its initial Low-Earth parking orbit and shut down its engine. From there, the second stage enters a coast phase ahead of its second burn.
Once the coast is complete, the second burn accelerates the rocket to reach the planned transfer orbit. This burn lasts approximately three minutes. After the burn is complete, the I-6 F1 satellite separates from the second stage. From there, the spacecraft’s twin solar arrays will deploy and its onboard propulsion will be used to place the satellite into its final geostationary orbit (GEO).
Once in GEO, the satellite will begin on-orbit testing. Following the testing, I-6 will join the rest of the Inmarsat satellite fleet in providing global communication.
Japan’s and Inmarsat’s future
With 2021 coming to a close, 2022 is set to be a big year for both Inmarsat and Japan. Japan is set to launch its next-generation H3 rocket early in the year. The H3 rocket is planned to replace the H-II rocket family to lower complexity and cost. After the I-6 F1 launch, five H-IIA rockets remain to fly before its retirement.
In March 2021, the first H3 rocket completed a Wet Dress Rehearsal to test the rocket’s systems. Shortly after, the rocket was de-stacked before being re-stacked in August 2021. Currently, the rocket is undergoing final engine certification for its first test flight. H3’s maiden flight will launch the Advanced Land Observation Satellite (ALOS)-3 to orbit.
An artist impression of all Inmarsat’s Global Xpress satellites in orbit. (Credit: Inmarsat)
Following the I-6 F1 mission, 2022 will see the launch of three more Inmarsat satellites. In Q2 2022, the I-6 F2 satellite will be launched on board a SpaceX rocket, with the exact launch vehicle (Falcon 9 or Falcon Heavy) not yet announced.
In Q4 2022, a SpaceX Falcon 9 will launch the twin Arctic Satellite Broadband Mission (ASBM) satellites, also known as GX 10A/10B. In a partnership with Inmarsat and the Norwegian Ministry of Defense, the ASBM satellites will provide communication to the Arctic. ASBM will use the Northrop Grumman GEOStar-3 satellite bus. The satellites will use Ka and X-band transponders with an EHF payload. The Falcon 9 will launch the two satellites into highly elliptical orbits with an orbital period of 16 hours.
In 2023 and 2024, will see the launch of the seventh generation Inmarsat satellites. The I-7 constellation will consist of three spacecraft, also known as GX 7, 8, and 9. The I-7 will use the Airbus OneSat satellite bus and will carry a reconfigurable Ka-band payload.
(Lead Image Credit: MHI Launch Services)