The satellite that North Korea launched into space three years ago circles the earth every 95 minutes at an altitude of about 540km, its orbit decaying. No signal has ever been detected from the crude-looking 100kg hunk of black metal that the North said was mounted with cameras to take images and transmit them back to Pyongyang. The North is planning another satellite launch next month, reigniting fears that it is really testing a system to deliver nuclear weapons. The secretive state is already under international sanctions for its nuclear and missile tests. South Korean Foreign Minister Yun Byung-se said this month the North's plan to launch a new satellite, which could be timed around the 70th anniversary of its ruling party on October 10, would be a disguised missile test. The United States has said such a launch could lead to more sanctions. North Korea says its space programme is peaceful and any attempt to stop it is an attack on its sovereignty. While many observers were impressed that Pyongyang managed to put an object into orbit in 2012, German aerospace engineer Markus Schiller said in a 2013 analysis that the mission was a "low performance" event and "not a game changer". "Nothing that has happened in the past years has changed my assessment," Schiller said, despite further short-range missile launches by Pyongyang using existing technology. "Most of these activities still seem to be more motivated by political reasons than by engineering ones," he said. The North's space agency said last week it was building a new satellite and readying it for launch, possibly around October 10, which suggests it has made advances in developing a ballistic missile. South Korea's defence ministry said this week it had not detected any signs of preparations at the main launch site, about 50km from the Chinese border. While a satellite launch utilises technology also found in ballistic missiles, the thrust and speed of the launch vehicle, as well as the point of engine cut-off, are different. Also, a missile must be designed for its warhead to withstand the stress of atmosphere re-entry, which is not the case when putting a satellite into space and leaving it there. The satellite was propelled by North Korea's Unha-3, a home-grown three-stage rocket based on 1950s Soviet Scud missile technology. The design and engineering that made the 30-metre-high Unha 3 suitable to launch a satellite make it a poor vehicle to deliver weapons, largely because launch preparations are difficult to hide due to the time it takes to assemble and fuel the rocket. "It is not a system that can be used for any military objective," said Daniel Pinkston, a visiting fellow at Babes-Bolyai University in Romania. Still, the North's pursuit of long-range rocket technology should be taken seriously because of potential capabilities it might acquire in the future, Pinkston added. "It should be clear how important these capabilities are to the leadership because they are expensive and difficult to acquire," he said.