Engine Test Preparations and Modernization at Sohae Satellite Launching Station

New activity at the Yunsong Vertical Engine Test Stand, September 27, 2025. Satellite image © 2025 Vantor. Image may not be republished without permission. Please contact [email protected] .

Key Findings

• A unique sequence of four satellite images collected on September 27, 2025, shows likely preparations for a new engine test at the Sohae Satellite Launching Station.
• Throughout the facility, development priorities have shifted over the past year from modernizing the original launch pad and building a large underground facility to constructing a new horizontal processing building, a probable research facility, and an L-shaped pier. These additions will provide the infrastructure needed for North Korea to launch larger and more capable space launch vehicles at Sohae.
• South Korea's National Intelligence Service assessed that North Korea received Russian assistance in reconnaissance satellite and launch platform development in return for supporting the war in Ukraine.
• The human and financial costs of the development of the Sohae facility are considerable and are a clear indication of Kim Jong-un's strong desire to prepare for future operations to launch additional satellites for security, science, and international prestige.
• The observed activities for potential preparation for a new engine test could also be limited to maintenance work at the test stand.

In March 2022, Kim Jong-un visited the Sohae Satellite Launching Station (referred to as the Sohae Satellite Launching Ground in North Korean media). During the visit, he "evaluated the present state of the ground and advanced the task to modernize it on an expansion basis." He also set forth the task of building numerous facilities. Among the more specific items mentioned were:¹

• "Reconstructing on an expansion basis the launching ground zone and the facilities for the general assembly and trial gearing of rocket and for the trial gearing of satellite…
• establishing extra facilities for the injection and supply of fuel…
• modernizing parts of the launch control facility and major technical posts on an expansion basis…
• expanding the capacity of the engine ground jet test site…
• ensuring the convenience of carrier rocket transport…
• improving the ecological environment around the launching ground…
• building a grandstand in the safe zone opposite to the launching ground."

The visit and subsequent development of the site is a clear indication of Kim Jong-un's priorities and a strong desire to prepare for future operations to launch additional satellites for security, science, and international prestige. Additionally, South Korea's National Intelligence Service assessed that North Korea received Russian assistance in reconnaissance satellite and launch platform development in return for supporting the war in Ukraine.²

Satellite imagery of the Sohae Satellite Launching Station in September 2025 show that Kim's directives have led to significant progress and efforts to expand the capabilities of the site will likely continue for the foreseeable future.

New Activity at the Yunsong Vertical Engine Test Stand

An engine test was apparently conducted at the vertical engine test stand, sometimes referred to as the Yunsong Vertical Engine Test Stand, in late June this year, as was evidenced by burnt vegetation at the exit of the stand's exhaust deflector.

More recently, a unique sequence of four satellite images collected on September 27, 2025, by Vantor, previously known as Maxar, shows what appears to be preparations for a new engine test. The activities observed in the series of images collected on September 27, 2025, suggest either preparations for a new test or maintenance work of the test stand.

The first image collected at 9:30 a.m. local time shows the test stand quiet, as it has been for the past two months. The second image collected at 12:49 p.m., shows that the rail-mounted environmental shelter has been pulled back from the test stand, and a truck is present between the two. A third image, collected at 2:29 p.m., shows that the truck is no longer present. However, a large telescoping crane has arrived, and there is evidence of what is likely water draining off the test site's pad. In the past, such cranes have been used to lift a test engine up and into the test stand itself. Finally, an image collected at 3:00 p.m. shows the test stand area once again quiet with no vehicles present, but the rail-mounted environmental shelter is still pulled back away from the test stand and only a small patch of water remaining on the site's pad.

New activity at the Yunsong Vertical Engine Test Stand, September 27, 2025. Satellite image © 2025 Vantor. Image may not be republished without permission. Please contact [email protected] .

The New Yunsong Pier

The most notable development at the Sohae Satellite Launching Station over the past year is the new L-shaped pier to the southeast corner of the perimeter.

Prior to the expansion of the Sohae Satellite Launching Station, the agricultural village of Yunsong was located on a small peninsula in the extreme southeast corner and outside of the Sohae Satellite Launching Station perimeter. With the expansion of the facility beginning in 2022, the area was incorporated into the facility.ⁱⁱⁱ Subsequently, construction of what would become a large L-shaped pier and associated access road began in mid-2022. Construction continued slowly and between June and July 2025, a new seawall and pier with basin were completed. The pier has a total of approximately 350 meters of docking space and an 80-meter-long basin. There is an approximately 110-meter-long surface level rail system that partially encompasses the basin that will likely be used to mount a gantry crane in the future.

The first cargo vessel observed in readily available commercial imagery at the new pier was an approximately 65-meter-long vessel, seen through cloud cover on September 28, 2025. Although clouds and haze partially obscure the view of the pier, a barge, potentially two, is also present in the same image.

The construction of the L-shaped pier was likely undertaken as part of Kim's desire to ensure "the convenience of carrier rocket transport."³ However, the addition of this pier is intriguing as mud flats exposed during routine tidal swings surround the area, preventing vessel access or stranding vessels. Furthermore, the waters around the small peninsula are often clogged with ice in the winter. Such environmental factors have likely led to North Korea's intention to bring large cargo here by barge, as suggested by the presence of the surface-level rail system along the basin. There is also speculation that it could be used to transport large rocket components or that the Nampo submersible missile launch barge may alternately be transferred here in the basin.⁴

Rail Station, Assembly Buildings, and New Railroad Spur Line

Approximately 4.5 kilometers northwest of the L-shaped pier and into the more central area of the Sohae Satellite Launching is an area that has also undergone considerable development during the past three years. The development includes a new railroad spur line with two new bridges and branches off the existing spur line, which leads to the original launch pad. This new branch line leads to the new high-bay horizontal assembly/processing building and underground facility. Additionally, the area includes a new rail-served high-bay horizontal assembly/processing building located alongside the covered railroad station, as well as a horizontal assembly/processing building that existed prior to the last three years' development.

The most notable new development in this area is the new rail-served high-bay horizontal assembly/processing building that measures approximately 200 by 49 meters. This building consists of a long central assembly/processing hall with workshops, offices, and storage rooms located along its length.⁵ Processing buildings support the assembly, integration, testing, and checkout of SLVs or ballistic missiles before they are transported to the launch pad.

The layout and size of the new horizontal processing building indicates that it can handle all existing North Korean space launch vehicles (SLV) and ballistic missiles, as well as those estimated to come into service in the foreseeable future. As of September 9, 2025, the building is externally complete but activity around it indicates that interior work to finish construction is slowly continuing.

The new railroad spur line servicing the building and the nearby underground facility is in its initial stages of construction. Depending upon resources allocated, the spur line could be completed during early 2026.

Except for minor changes to the types and numbers of equipment and supplies present, little has changed at the original horizontal assembly/processing building. The 12 large trailer tanks first observed during mid-2024 remain, the southern access road to the building remains blocked, and the rail spur line leading from the covered rail station to the original launch pad that passes the building remains usable.

Entrance, Headquarters, and Warehouse

At the entrance, headquarters, and warehouse of the Sohae site, minor activity has been observed in satellite imagery during the past year. While the rail-served warehouse facility remains active, no equipment or supplies are presently stored out in the open. ⁶ The main entrance and checkpoint, as well as the administration and security headquarters area, remain quiet. The latter has only two small unidentified vehicles present in the courtyard. No railcars, construction equipment, or piles of sand or gravel are observed at the temporary rail-served delivery point immediately south of the administration and security headquarters area. The current level of activity observed at these locations is typical of what has been observed throughout 2025.

Underground Facility

Construction of the large underground facility (UGF) east of the new high-bay horizontal assembly/processing building, which began in 2022, continues at its west portal and access roads.⁷ While details concerning the interior layout of the facility are unknown, its overall length, including current portals, is approximately 695 meters. If it is similar to other strategic UGFs, it is likely to include smaller interior branch tunnels and a railroad siding. Notably, the west portal has been extended some 130 meters from the original excavation point since 2022 but remains incomplete with construction suspended since mid-2024. The reason for this apparent suspension is unknown.

As noted above, the road and rail spur line work to the west portal is ongoing. At the east portal, construction on the portal itself appears complete, but vehicle and personnel activity around the portal indicates that access road work continues. Furthermore, excavation from the portal to the southeast is ongoing. Since March 2025, the excavation work has extended to approximately 940 meters to the southeast. It is too early to determine whether this is for a new road or for a roadbed to continue the new railroad spur line through the UGF and onto the coastal launch pad 760 meters further to the southeast. Alternately, if it is a continuation of the spur line, it could lead to a new railroad siding to support the coastal launch pad.

Original Launch Pad

Approximately 1 kilometer south of the original horizontal assembly/processing building is the original launch pad. Barring occasional activity, there have been no significant developments observed here over the past year. An earlier renovation program, which began in 2022 to replace the existing fuel and oxidizer storage facilities and the construction of two large water tanks, has been suspended or cancelled since 2023. Work on refurbishing the rail-mounted transfer structure and entrance to the underground rail terminal was completed in 2023.⁸ As of September 2025, the original launch pad appears to be in caretaker status.

Located approximately 650 meters to the east of the original launch pad is one of the two primary construction support compounds. It is from here that workers and heavy construction equipment have been dispatched to work on projects around the Sohae facility. Satellite imagery from the past year has shown continuing activity and changes in the quantities and types of supplies, equipment, and vehicles present, providing further indication of the ongoing construction activity at Sohae.

VIP Observation Facility and Horizontal Engine Test Stand

On the hill mass looking over the original launch pad and the two engine test stands is one of two VIP observation facilities at Sohae. While no activity of significance is observed here in recent imagery, the observation building has undergone minor development during the past nine months, with a structure added to its roof. The reason for this addition is unclear. Although nothing of significance has recently changed at the nearby support building, a new approximately 6-meter-diameter radome, likely associated with tracking or telemetry download, was installed on its roof during 2023.

Below and to the east of the VIP observation facilities are the vertical and horizontal rocket engine test stands and the ballistic missile test silo. As noted above, activities for either preparation for an engine test or maintenance were observed at the Yunsong vertical engine test stand in recent imagery. At the horizontal engine test stand, sometimes referred to as the Yunsong Horizontal Engine Test Stand, a test supervised by Kim Jong-un was reportedly conducted two weeks ago on September 9, 2025. According to Rodong Sinmun, the test was of "a high-thrust solid-fuel engine using the composite carbon fiber material" and "heralds major changes in expanding and strengthening the nuclear strategic forces of the DPRK."⁹ The Korean Central News Agency (KCNA) announced that this was the "ninth ground launch test of the engine [and that it] will be the final test in the development process." And that the "maximum thrust of the new engine is 1,971 kN."¹⁰

Approximately 125 meters north of the horizontal engine test stand is the underground test silo built in 2023. It was from here that North Korea conducted a test launch of a potentially navalized version of the KN-23 on March 19, 2023. Since then, no activity has been observed at the underground test silo.

East Coast VIP Observation Facility, Coastal Launch Pad, and Support Facilities

During the past several years, North Korea has shifted construction efforts to the east side of the Sohae facility. These efforts have been focused upon construction of a VIP observation facility, a coastal launch pad for solid fuel SLVs, and several support facilities.

Between 2022 and 2023, North Korea began construction of a new VIP observation facility on the east coast of the Sohae facility, approximately 1.3 kilometers north-northwest of the coastal launch pad, to observe and film SLV launches from the new east coast launch pad. No activity has been observed here since construction was suspended mid-2024 and remains incomplete in recent imagery.

Construction of the coastal launch pad for solid fuel SLVs, sometimes identified as the Yunsong Launch Pad, began in April 2023 and was generally complete by the end of May 2023. Since that time there have been four reported launches of a Chollima 1 SLV (May 30, 2023, August 23, 2023, November 21, 2023, and May 27, 2024) from the facility. All of these are reported to have been for launching a "military reconnaissance satellite." Of these, only the November 21, 2023, launch was successful and placed the Malligyong-1-3 satellite into orbit.¹¹ As of September 25, 2025, the Malligyong-1-3 remains on orbit at approximately 500 kilometers above the Earth. Its ability to capture and transmit images is uncertain. The coastal launch pad has remained quiet since the May 27, 2024, launch attempt, however, it maintains the capability to conduct a surprise launch at any time of Kim Jong-un's choosing.

Approximately 1.1 kilometers northwest of the coastal launch pad is a small probable research facility built between 2022 and 2023. The facility consists of four buildings (one a high-bay building), two storage tanks (potentially nitrogen and liquid oxygen), nearby water tank, and a small pond. The nature of the work conducted here is unknown but may be related to satellite processing before launch. No significant activity has been observed here over the past year.

Approximately 300-meters south of the coastal launch pad are a barracks and warehouse and support area that were constructed in 2023 and 2024, respectively.

Activity on the Western Side of the Facility

Located within the western half of the Sohae Satellite Launching Station are a small number of facilities, including the National Aerospace Technology Administration (NATA) Launch Control and Observation building, NATA support facility, livestock facility, and a former warehouse and support facility.¹² No activity of any significance has been observed here during the past year, and all these facilities appear to be in caretaker status. It should be noted that in 2019, a network of dirt roads was developed throughout the western side of the facility. At that time and subsequently in 2022 when Kim announced plans for expansion, it was believed that these roads would connect future support facilities. However, this has not happened to date.

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