A machinists' strike is hitting some US space projects hard. It has already delayed the launch of three atmospheric satellites and it could derail a major Pluto mission if it is left unresolved.

About 1,500 Boeing machinists and engineers walked off the job at facilities across the United States on 2 November, after talks between the union and the company on health care broke down. The machinists are responsible for the assembly and launch preparation of the company's Delta rockets, commonly used in scientific missions for NASA.

The strike stopped the countdown of the National Oceanic and Atmospheric Administration's hurricane-tracking satellite GOES-N, scheduled to launch on 5 November, leaving it stranded atop its Delta IV rocket in Cape Canaveral, Florida. Boeing officials are now assessing whether it will be possible to restart the countdown using non-union employees, says Robert Villanueva, a spokesman for the company.

And delayed indefinitely are NASA's CloudSat and CALIPSO satellites, which will study the global distribution of aerosols (see Nature 437, 468–469; 2005). They were set to launch on a single Delta II rocket in November, but those plans are now on hold. David Winker, principal investigator for CALIPSO, says that the delay is especially worrying because the satellites are meant to take part in international projects in which many teams collect climate data at the same time. “These things are going to go ahead whether we launch or not,” he says. “It's close to being critical.”

If the strike becomes protracted, it may even affect a mission to Pluto. New Horizons would be the first spacecraft to visit the Solar System's most distant planet, and the final stage of the vehicle is propelled by a Boeing engine. If the mission misses its month-long launch window early next year, its next chance will not be until February 2007. But Villanueva says it should be possible to complete the necessary work using replacement technicians and inspectors.

He adds that there is no schedule for resolving the strike: “Basically both sides are sitting back and leaving lines of communication open.”