Engine inspections ground Atlas V until early summer

 James Dean, FLORIDA TODAY

An Atlas V rocket launches from Cape Canaveral Air Force Station on a mission to the International Space Station. NASA video. March 22, 2016 Wochit

United Launch Alliance's next Atlas V rocket launch is now targeted for early summer, after the company inspects its inventory of Russian main engines for a flaw believed responsible an early engine shutdown that threatened a mission last month.

During the March 22 launch of International Space Station supplies from Cape Canaveral Air Force Station, the rocket's Russian-made RD-180 main engine shut down six seconds early. The upper stage engine fired for an extra minute to save the mission, ensuring an Orbital ATK Cygnus spacecraft reached its proper orbit.

ULA on Friday said engineers have traced the premature shutdown to a "mixture ratio control valve" that limited the flow of kerosene fuel to the engine

"In addition to analysis and testing, all RD-180 engines are being inspected," the company said in a statement.

An Atlas booster recently was placed on a stand at Launch Complex 41 to support inspections that ULA hopes will "confirm all engine components are ready for launch."

That rocket had been targeting a May 5 launch of a heavy U.S. Navy communications satellite, but the mission was put on hold indefinitely after the last flight's problem.

It now appears the valve issue will delay launch of the Navy's fifth Mobile User Objective System satellite at least six weeks, until sometime after the first day of summer on June 20.

ULA is reviewing dates for Atlas V missions to follow, but said no missions scheduled this year will slip into next year.

"Expect all 2016 missions to launch this year," CEO Tory Bruno said on Twitter

Of particular importance is a planned early September launch of NASA's OSIRIS-REx mission to collect an asteroid sample. Missing the mission's 39-day window would delay it for a year.

Before the next Atlas V launches, ULA is preparing a Delta IV Heavy rocket for a June 4 launch of a classified intelligence mission from Cape Canaveral.

SpaceX is next up on the Eastern Range, with a Falcon 9 rocket targeting a 1:22 a.m. Wednesday blastoff with a Japanese communications satellite

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