CAPE CANAVERAL - Replacement workers are finishing an upper-stage booster for the plutonium-powered spacecraft NASA aims to launch to Pluto in January, Boeing officials.

Striking workers are questioning whether it is safe to do so.

"I think they are playing with dynamite, personally," said Johnny Walker, business representative for the International Association of Machinists and Aerospace Workers Local Lodge 1163 in Cape Canaveral.

"What they are fixing to do is very dangerous, as far as I'm concerned," he said.

Boeing machinists in Florida, California and Alabama went on strike Wednesday after the union and the company failed to reach an agreement on a new three-year contract.

Striking workers had been preparing a Boeing upper-stage booster that will be used to propel NASA's New Horizons spacecraft on the first flight to Pluto.

The solid-fueled motor is the third stage of the Lockheed Martin Atlas 5 rocket that is to fly between Jan. 11 and Feb. 14.

A delay past then would force NASA to postpone the launch until early 2007.

Boeing spokeswoman Tina Lange said the company intends to deliver the upper stage as scheduled on Dec. 1. Replacement technicians and inspectors from Boeing's current work force were trained and certified in advance of the strike to finish work on the upper stage, she said.

"We knew the negotiations were coming, and we wanted to put in place a contingency plan because this mission is very important and has a very strict launch window," Lange said.

The New Horizons spacecraft is equipped with a generator that will convert heat from the natural decay of 24 pounds of plutonium-238 into electricity to power spacecraft systems.

Contact Halvorson at 639-0576 or thalvorson@flatoday.net