After a month-long review of nagging problems with the Ariane 5 rocket's helium pressurization system, the commercial workhorse is scheduled to return to flight May 21 with two communications satellites, Arianespace's top executive said Wednesday.

The Ariane 5 rocket sits on the launch pad in early April. Credit: Arianespace

"We corrected what went wrong, which is a helium subsystem that regulates the pressurization of the launch vehicle," said Jean-Yves Le Gall, Arianespace's chairman and CEO. "Now, we are ready and we will launch on the 21st of May."

The company's first launch of the year has been postponed three times since mid-March, including a last-minute scrub April 9 attributed to a faulty pressure regulator on the Ariane 5 rocket's first stage.

According to Le Gall, the component is used to keep the Ariane 5's hydrogen and oxygen propellant tanks pressurized during the flight. Helium is used to pressurize the tanks during the countdown.

The helium pressurization system was also blamed for a scrub of the last Ariane 5 launch in December. Engineers resolved that problem and the rocket successfully lifted off nine days later, after another unrelated delay.

Arianespace officials announced parallel inquiries into the technical cause of the helium subsystem glitches and an overall audit of the Ariane 5's quality control procedures.

"This is the first time we have done this without a launch failure because we had some trouble with parts, and this is why we needed to perform this quality control [review]."

Le Gall said managers replaced parts of the troublesome helium pressure regulator and the new hardware has passed ground testing. In a meeting Wednesday at the Guiana Space Center, officials signed off on the repairs and gave the green light for launch next week.

Liftoff is scheduled for a launch window that opens at 2201 GMT (6:01 p.m. EDT) May 21. The 50th Ariane 5 mission will haul into orbit the ASTRA 3B broadcasting satellite and the German military's COMSATBw 2 communications platform.

But the top-level inquiry into Ariane 5 quality issues is still continuing as workers in French Guiana prep the next rocket for liftoff.

"In parallel, we are proceeding with the quality audit to be sure that the rest of the launch vehicle is not affected by other problems," Le Gall said Wednesday. "Today we got the preliminary report of this quality review, which cleared the way for this launch, but we will have the full report by the end of June."

Arianespace will be playing catch-up the rest of the year to overcome the two-month delay of its first launch of 2010. Le Gall said he still expects the company to fly seven Ariane 5 rockets this year, ending with the launch of the second Automated Transfer Vehicle for the International Space Station.

A communications satellite for the Middle East and a South Korean multi-purpose spacecraft are due for launch in late June. Another Ariane 5 will blast off in late July, followed by more missions at a pace of nearly one per month through December, Le Gall said.