BUTTE - A 24-inch rocket exploded during an experimental test Tuesday afternoon at the Butte Aerotec facility, seriously damaging a new building but causing no injuries.

Dave Micheletti, president of Montana Aerospace Development Association, confirmed there was a "malfunction" during a SPG Inc. rocket test, and that no one was hurt. The cause of the explosion is unknown.

"It was the first test of the big 24-inch rocket," Micheletti said. "It was a hot-fire test. As to what happened, we have some ideas, but we won't know for sure until we finish an investigation."

Last year, SPG Inc., a Stanford University-affiliated company, had tested an 11-inch rocket on the site in the Tax Increment Financing Industrial District located off Interstate 15, about 10 miles west of Butte. Butte-Silver Bow built a $168,000 steel-sided structure nearby, so the company could test a larger rocket in which paraffin wax is used as the main fuel. Tuesday's test was among the first in the new facility.

Micheletti said explosion happened after 1:30 p.m., causing a "big bang" that was heard by people working in the industrial district. It created a large flame, which is normal during the rocket tests, he said.