The payload riding on the first flight of the H3-24L is HTV-X1, Japan’s next-generation cargo spacecraft for the International Space Station. Built by Mitsubishi Heavy Industries for JAXA, HTV-X1 is the direct successor to the H-II Transfer Vehicle (HTV, also called Kounotori). Its design keeps the reliability of the original HTV but introduces major improvements in cost efficiency, operational flexibility, and cargo capacity. With the ISS program extended into the late 2020s, HTV-X is set to continue Japan’s vital role in resupply missions while also serving as a platform for testing technologies for future exploration.

Specs

Length: ~8 m (26 ft)

Max. Diameter: ~4.4 m (14 ft)

Launching Weight: ~16 metric tons (35,300 lb)

Loading Weight: ~6 metric tons (13,200 lb)

HTV-X1 consists of three main sections: an unpressurized cargo module for large external hardware, a central service module that houses the spacecraft’s solar arrays, batteries, and propulsion thrusters, and a pressurized logistics module for supplies, experiments, and equipment bound for astronauts inside the ISS. Unlike its predecessor, HTV-X features simplified wiring and externalized components, making astronaut servicing easier and reducing overall mass. Its upgraded power and communication systems allow for more robust operations, and it can support extended missions after leaving the ISS.

In terms of capability, HTV-X1 is impressive. It has a launch mass of about 16,000 kg (35,000 lb) and can carry up to 4,070 kg (8,970 lb) of pressurized cargo and 1,750 kg (3,860 lb) of unpressurized cargo. The pressurized volume available to astronauts is 78 m³ (2,800 cu ft), and its solar power system generates 3 kW. Once berthed to the ISS, HTV-X1 can remain attached for up to six months, and after departure, it can continue operating independently for as long as 1.5 years. This gives JAXA the opportunity to use the spacecraft for technology demonstrations well beyond its cargo delivery mission.

For its maiden voyage, HTV-X1 will serve not just as a supply ship but also as a technology demonstrator. Potential applications under study include using the unpressurized module for external sensor packages, testing autonomous docking systems, carrying small satellites, or even acting as a tug for orbital logistics. Future evolutions, such as the proposed HTV-XG, could see the vehicle adapted for lunar missions under NASA’s Artemis program. In this way, HTV-X1 is both a workhorse for ISS operations and a stepping stone toward Japan’s participation in deeper-space exploration.

Courtesy of Wikipedia and JAXA.

The H3-24L is the most powerful configuration of Japan’s new H3 launch vehicle, developed by Mitsubishi Heavy Industries and JAXA as the successor to the long-serving H-IIA. Designed with modularity in mind, the H3 family can be configured with different numbers of engines, boosters, and fairing sizes to suit a wide variety of missions. The “24L” designation means the rocket has two LE-9 engines in its core stage, four solid rocket boosters (SRBs) strapped to the sides, and the long payload fairing to accommodate large spacecraft. This makes the H3-24L the heavy-lift workhorse of the fleet, capable of launching the heaviest payloads, including cargo craft for the ISS like HTV-X1.

Specs

Height: 69 m (226 ft)

Liftoff mass: ~574 metric tons (1.26 million lb)

Core stage engines: 2 × LE-9 (liquid hydrogen / liquid oxygen)

Solid boosters: 4 × SRB-3

Liftoff thrust: ~12,142 kN (2.73 million lbf)

Payload capacity to Low Earth Orbit (LEO): 16,500 kg (36,400 lb)

Payload capacity to Geostationary Transfer Orbit (GTO): 6,500 kg (14,300 lb)

Payload fairing: Long type (L), 16 m tall (52 ft)

The rocket emphasizes not only raw performance but also cost efficiency and flexibility. Japan has pushed for lower launch costs to compete in the global market while still ensuring reliability. By using fewer unique parts and simplifying the assembly process, the H3 is intended to reduce launch costs by nearly half compared to the H-IIA. With its scalable design, the H3-24L can handle government missions, commercial satellite deployments, and international collaborations, ensuring Japan’s continued independent access to space.

Photo courtesy of Mitsubishi Heavy Industries (MHI).

Launch Area Y2 (LA-Y2) at the Tanegashima Space Center (TNSC) in Japan is one of the country’s primary rocket launch sites. TNSC is located on the southeast coast of Tanegashima Island in Kagoshima Prefecture, offering an advantageous position near the equator that allows rockets to take better advantage of Earth’s rotational speed. This location provides efficiency benefits for launches into orbit and has made the site central to Japan’s space program.

LA-Y2 is specifically used for H-IIA and H-IIB rocket launches, which are Japan’s main medium-to-heavy lift vehicles. The H-IIA has been in service since 2001 and is used to place satellites into orbit, support interplanetary missions, and resupply the International Space Station (ISS). Its larger counterpart, the H-IIB, was used to launch the HTV cargo spacecraft for ISS resupply missions from 2009 to 2020. Both vehicles relied on LA-Y2 as their launch pad, with the site equipped with extensive ground support infrastructure, including mobile service towers, fueling systems, and flame trenches to safely handle the rockets.

The launch pad has seen many significant missions. Notable examples include the deployment of satellites for weather monitoring, Earth observation, and communications, as well as high-profile missions such as the Hayabusa 2 asteroid explorer launched in 2014 and cargo deliveries to the ISS. After the retirement of the H-IIB, LA-Y2 is still active for H-IIA launches, but with Japan’s new H3 rocket entering service, the center’s operations are gradually shifting focus to LA-Y3, the dedicated pad for H3.

Image courtesy of Wikipedia.

After launch, Cygnus will spend several days boosting itself up to the International Space Station. Upon arrival, two crew members will capture it with the Station’s robotic arm, Canadarm2, and berth it to the Earth-facing, or nadir, port on the Unity module.

Unity, also called Node-1, was the second module of the ISS to be launched. Carried into orbit on the STS-88 mission of the Shuttle Endeavour, Unity was joined to the Russian Zarya (“dawn”) module on December 6, 1998. Its nadir port later hosted two Space Shuttle dockings, STS-97 aboard Endeavour in December 2000 and STS-98 aboard Atlantis in February 2001, and since December 2015 has served as the sole berthing port for Cygnus cargo spacecraft.

Picture

The Unity module (without solar panels), with its nadir port visible at its center, is joined via spacewalk (an astronaut is visible to the right of the Unity–Zarya connection) to the Zarya module during STS-88 in December 1998.

Courtesy of NASA

Download the Supercluster app to track spacecraft traffic and view crewmembers aboard the International Space Station and China’s Tiangong Space Station.

Alternatively, you can use the web version of our Stations Dashboard on Supercluster's website.

We now track "Arrivals and Departures" for both stations through a new "Timetable" feature, covering crew rotations and cargo resupply missions.

You can also switch between the ISS and Tiangong to see their relative positions over Earth on our mini-map.

A recent update allows users to enable push alerts for notifications when space stations pass over their location.

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