The image is indeed an impotent one. A special missile failing to leave its booster rocket and scuppering an experimental mission to shoot down a mock warhead before it really got started. It is a metaphor for the wider failures surrounding the United States' controversial programme to build a National Missile Defence (NMD) system. The US$100 million (HK$779 million) failure of the test in space above the Pacific at the weekend may thwart any domestic political benefit to Vice-President Al Gore. It is also sure to further embolden the chorus of international and scientific critics against a plan they insist provides little real protection and could spark a new arms race. It was also a timely reminder of exactly what NMD is - an attempt to defend US cities from limited strikes from 'rogue' states such as North Korea - rather than a bullet-proof shield from a quiver of missiles from China or Russia. A successful test could have led to a positive recommendation on the system's technical viability over the summer from Defence Secretary William Cohen. President Bill Clinton would then have had to consider the wider picture before giving the go-ahead in the autumn to build X-band radar sites on Alaska's Aleutian Island chain - the first stage of a system that will link satellites, radars and land-based interceptor rockets fitted with 'kill vehicles'. The timetable is essential to meeting the perceived threat of a North Korean nuclear-tipped missile reaching the US - a capability intelligence says Pyongyang will have by 2005. That decision, while internationally difficult for the White House, would have reflected well on Mr Gore as he moves into full campaign mode for the presidency; Democrats never like to look weak on the military front going into elections. Now, with two out of three tests failures, Republicans are questioning the management of the project's implementation. Their presidential hopeful, George W. Bush, has stressed he will push ahead with NMD - possibly even beyond the limited US$60 billion plan proposed by the Clinton administration. Mr Bush has even called for renewed studies of Reagan-era 'Star Wars' laser defences - space-based weapons even more risky than any counterpart fired from land. 'I remain confident that, given the right leadership, America can develop an effective NMD system,' Mr Bush said. Politicians in both parties urged Mr Clinton to keep the programme moving to at least give his successor the chance of making a final decision next year. What is certain is that there will be more tests. Eight more are planned before 2003. 'Basically, we learned nothing,' said a Clinton administration official of Saturday's attempted test. Like many observers, rather than a high-speed explosion in space, he was watching piped-in footage of a deserted rocket launch pad on the Marshall Islands surrounded by swaying palms. 'Believe me, the sense of doom was palpable . . . but we'll keep on plugging away.'