SEOUL, October 07 (AJP) - South Korea's first working satellite constellation reached orbit Wednesday on the country's own Nuri rocket. A university lab and a private company built the small Earth-observation satellites and designed them from the start to fly on a Korean launcher.
A satellite constellation is a group of satellites run as a single system. They are spread across different orbits, so between them they pass over the same place far more often than one satellite can. That lets them photograph a flood zone or a coastline several times a day, without waiting for a single satellite to come around again.
"National satellites had been built and operated by the Korea Aerospace Research Institute, almost without exception," said Lee Chol, head of planning and coordination at KAIST's Satellite Technology Research Institute (SaTReC), which led the program. This time, Lee told AJP in a phone interview Wednesday, the Korea Aerospace Research Institute (KARI) worked alongside SaTReC and the private satellite maker Satrec Initiative.
"We led the way in diversifying the national satellite program," he said.
SaTReC built South Korea's first satellite, Uribyol-1, in 1992. On this program, it oversaw the project and developed the satellite system. Satrec Initiative, founded by former SaTReC researchers, built the satellite body and the optical camera, and KARI developed the ground and image-processing systems.
The Korea AeroSpace Administration (KASA) and KARI declared the launch a success. Nuri lifted off at 12:25 p.m. (0325 GMT) from Naro Space Center in Goheung, on the southern coast, and released five satellites, called NEONSAT, one at a time at an altitude of about 570 kilometers.
Ground controllers made first contact with NEONSAT-6 at about 1:08 p.m. through King Sejong Station in Antarctica. Nine of the 10 cubesats carried as secondary payloads also reached orbit, and one failed to separate from the rocket.
The domestic launch was possible only because of a decision made before any hardware existed. Many satellite parts fall under the U.S. International Traffic in Arms Regulations (ITAR). These rules restrict where satellites carrying American defense-related technology can be launched.
"If we used parts subject to ITAR, a satellite carrying those parts could not be launched on a Korean rocket," Lee said.
"From the start of the program, we planned the satellite with a domestic rocket in mind. So we selected all the parts from those not subject to ITAR."
The constellation itself addresses a different problem. Large observation satellites such as South Korea's Arirang series take sharp images, but each one photographs only a narrow strip of ground as it passes overhead.
"Large satellites perform well, but they are expensive," Lee said. "And because their resolution is high, their observation swath is not wide."
Flying small satellites as a group trades some of that sharpness for reach.
"The performance is somewhat lower, but it is still high resolution, and you can photograph a wide area at a relatively low cost compared to large, full-size satellites," he said.
Each NEONSAT weighs less than 100 kilograms. According to KAIST, its camera can make out objects 1 meter across in black and white and 4 meters across in color.
A single satellite needs time before it passes over the same spot again, so it may not be overhead when a wildfire spreads or a river floods.
The five satellites launched Wednesday fly in an orbit that crosses the Korean Peninsula in the afternoon. Five more will launch on Nuri's sixth flight in 2027, into an orbit that crosses in the morning.
"It is less about linking them to each other and more about doubling the opportunities to take images," Lee said.
Once all 10 production satellites are working, KAIST said, the fleet will be able to photograph the peninsula at least three times a day. In an emergency, it will be able to return to the same spot within 24 hours.
Lee put the total cost of the 10-satellite program at a little over 200 billion won. That figure includes the ground system, the image-processing system and much of the launch cost. He estimated a single multipurpose satellite at roughly 200 billion to 300 billion won, though he said that figure was not exact.
Lee said more constellation programs are now being prepared in South Korea. "What we are doing now for the first time looks like a model others can refer to," he said.
The fleet still has to prove itself in orbit. The launch slipped from June to October after KASA found that thrusters on earlier test satellites needed improvement in space, and the five new satellites carry upgraded thrusters. KAIST said it would check each satellite's condition and image quality step by step. As of Wednesday afternoon, KASA had reported contact with one of the five satellites.
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