The WorldView-1 satellite caught a picture of North Korea's rocket moments after launch.DigitalGlobe Image Library

A photograph snapped by a passing commercial satellite has one arms-control expert questioning whether North Korea's rocket launch on 5 April was intended for peaceful purposes, as initially claimed. But other analysts are sceptical.

WorldView-1, an orbiting imaging satellite owned by DigitalGlobe in Longmont, Colorado, snapped the photograph of North Korea's TaepoDong-2 (TD-2) rocket just moments after it lifted off from the country's Musudan-ri launch site. The photo (right) shows the contrail left by the rocket's first stage as it streaked out over the Sea of Japan. Minutes later, say officials from the United States and South Korea, the upper stages and satellite payload of the TD-2 plunged into the Pacific Ocean several thousand kilometers away from the launch site (see 'Korean satellite misses orbit').

North Korea claims that the mission was a peaceful attempt to launch a communications satellite into orbit, but the image suggests otherwise, according to Geoffrey Forden, a physicist and arms-control analyst at the Massachusetts Institute of Technology in Cambridge. Forden triangulated the trajectory of the rocket using the contrail in the image, the position of the satellite taking the picture, and North Korea's declared 'splashdown zones' for the first and second stages.

Based on his analysis, the TD-2's course appears to be too shallow to be a space launch. To reach orbit, Forden says, the rocket should have been travelling almost vertically in an attempt to gain altitude early on in its flight. Instead, it appears to be pitching horizontally, sacrificing height for distance in a trajectory that would allow it to sling a warhead as far as possible. Such a trajectory could be consistent with that of an intercontinental ballistic missile (ICBM).

Rocketing ahead

North Korea is explicitly prohibited from undertaking ballistic missile tests under the United Nations Security Council resolution 1718, which was passed shortly after the country carried out an underground nuclear test in 2006. The United States claims that the launch constitutes a clear violation of the resolution, but China and Russia have said that North Korea's actions, if peaceful, did not break the rules.

Forden says that the evidence is not conclusive. "You can use an ICBM trajectory for space launches, but you lose a considerable amount in terms of payload capacity." Regardless, he says that it seems likely that North Korea has gained more from its failed satellite attempt than was previously believed. It now seems that the first and second stages of the rocket, as well as its guidance system, worked more or less fine, and "that's all that they would probably use for an ICBM," he says.

TaepoDong-2 — missile test or satellite launch?AP Photo/KRT TV

But not everyone is convinced. "If this is true, it's a very surprising result," says David Wright, an analyst with the Union of Concerned Scientists, a non-profit group based in Cambridge, Massachusetts. Wright says that the trajectory suggested by Forden "seems shallow for either a ballistic missile or a space-launch vehicle". If the trajectory was as shallow as Forden claims, Wright believes the TD-2 would not have made it as far out over the Pacific as press reports claim it did.

Ground-based images and video of the rocket launch released by North Korea are also providing new clues about the TD-2, which until now has been shrouded in secrecy. Early analysis indicates that the rocket's first stage seems to be slightly smaller and less powerful than previous estimates. It also looks as though it may be more sophisticated, using a single turbo pump to feed fuel and oxidizer into its multiple engines. Forden says that more details about the type of fuel used, the number of engines and the rocket's guidance system could emerge as independent analysts pore over the publicly available images.