Nuri places 15 satellites in orbit on its fifth flight from Goheung

South Korea's Nuri rocket lifted off from the Naro Space Center in Goheung at 12:25 p.m. on Wednesday and placed 15 satellites into orbit on its fifth flight. The Korea AeroSpace Administration said the 200-ton vehicle separated its first and second stages, then released the satellites at about 575 kilometres. Administrator Oh Tae-seog said the rocket had reached its target orbit on the planned sequence, and that all five NEONSAT microsatellites had separated in the planned order.

The flight lasted about 20 minutes and ended near 12:45 p.m., after the third stage finished its autopilot run. Oh said the satellites appeared to have deployed as planned, and that a detailed reading of the telemetry was still under way before a final verdict on mission performance. The Korea Times put the release near 12:40 p.m. at about 570 kilometres. The two figures describe the same window: deployment between roughly 810 and 960 seconds after liftoff.

The payload was five New-space Earth Observation Satellite Constellation for National Safety microsatellites, numbered 2 through 6, and 10 CubeSats. Each NEONSAT weighs under 100 kilograms. They are meant to work as a swarm, watching the Korean peninsula at a revisit rate a single satellite cannot give. The CubeSats carry smaller experiments, including work on pharmaceuticals, industrial parts, radiation and the Earth's magnetic field, according to the Korea Herald's account of the manifest.

The release sequence was built to keep the satellites from hitting one another. The five NEONSATs went out at intervals of 35 to 40 seconds. Between each separation the upper stage rotated about 45 degrees. The 10 CubeSats then left in pairs, every 10 seconds. After the last release, the upper stage was to make a collision-avoidance burn and vent the fuel it still carried. It stays in orbit for a time, then re-enters and burns up. That is the standard end for a Nuri upper stage. It is not recovered.

Goheung sits about 400 kilometres southwest of Seoul, on the south coast of South Jeolla. The rocket left the second launch pad. Preparations had started early. The Korea Herald reported that checks on the propellant system were done near 7:50 a.m., fuel and oxidizer loading finished near 11:06 a.m., and the support structure was pulled back near 11:55 a.m. Liftoff followed half an hour later.

Nuri, also called KSLV-II, is a three-stage rocket. The first stage uses four clustered engines. The second stage uses one. The third stage uses a smaller engine suited to the final push into orbit. On this flight the first stage was due to separate about 123 seconds after liftoff, and the second about 268 seconds. Those times are the planned marks Yonhap published before the result was in. KASA later said both separations had succeeded.

This was the first Nuri flight asked to put out several primary satellites, one after another, for the same mission. Earlier flights proved the rocket could reach orbit and could carry a mix of a main satellite and rideshares. A swarm is a different job. The upper stage has to point, wait, release, turn, and release again, without the satellites drifting into the same slot. A 45-degree turn between NEONSATs is the practical answer to that problem.

The constellation is aimed at national safety, which in Korean programme language covers disaster monitoring, maritime watch and security imaging. Five microsatellites will not match the revisit of a large commercial constellation. They do give Seoul a domestic string of eyes, launched on a domestic rocket, rather than a purchase of foreign rides. That is the point of the Nuri programme: a launcher the country can fly without asking another state for the slot.

KASA was created to pull together work that had sat at the Korea Aerospace Research Institute and in the ministry. Oh's statement on Wednesday is the agency's public claim on the flight. He was careful. He confirmed the orbit and the order of the five NEONSAT separations. He did not declare the telemetry closed. A final assessment still depends on whether each satellite talks back from the right orbit, with the right power and the right attitude. Separation from the rocket is the launch provider's job. Health of the satellite is the satellite team's job. Both have to land before the mission is marked complete.

The next practical test is contact. Ground stations will look for beacons from the five NEONSATs and the 10 CubeSats over the coming passes. A satellite that separated cleanly can still fail to open a panel or to answer. Until those calls come in, the flight is a launch success with the satellite check unfinished. That is the state Oh described at the pad.