PARIS — Europe’s Ariane 5 rocket likely will be grounded until May as the Arianespace launch consortium investigates a helium-pressurization issue that stopped the most recent launch attempt and conducts a parallel inquiry into quality control following delays affecting the last two launch campaigns, Arianespace Chief Executive Jean-Yves Le Gall said April 16.

The Evry, France-based company has created a board of inquiry and a separate, outside committee to review overall quality control following three postponements of the first Ariane 5 launch in 2010 and a similar series of delays in last December’s launch of France’s Helios 2B reconnaissance satellite.

The latest launch cancellation occurred April 9 less than a minute before the scheduled liftoff, when the helium tank that keeps the Ariane 5 rocket’s main cryogenic stage pressurized showed a pressure level that was outside of permissible bounds.

A similar problem occurred in December and was determined to have been caused by a small leak in the helium-pressurization system. Helium is used to maintain pressure in the Ariane 5’s main stage tanks that hold the liquid hydrogen and liquid oxygen the rocket burns on its way to orbit. The Helios 2B satellite was successfully launched on Dec. 18, nine days after the problem was discovered.

In an April 16 interview, Le Gall said the company has identified the defective part in the April 9 postponement as a helium pressure regulator that adjusts pressure between the Ariane 5’s helium tank and its feed lines. An unacceptably high pressure reading in the feed lines forced the automatic shutdown of the April 9 launch sequence.

Le Gall said the regulator was removed from the Ariane 5 at the Guiana Space Center spaceport in French Guiana and returned to its manufacturer in Italy the week of April 12. He said the problem is unlikely to be related to the device’s design insofar as it has been used on 49 previous launches without incident.

The task force looking into the issue made an initial report April 16, but a more-precise estimation of when the Ariane 5 will resume its launch campaign will await further review the week of April 19, he said.

Nonetheless, Le Gall said the launch is unlikely to occur before the first half of May. While it will be Arianespace’s first Ariane 5 launch of the year, the company still plans seven launches in 2010 and likely will shorten or eliminate a planned mid-summer break to reach the target. “Recall that we launched nine times between August 2007 and August 2008, so performing seven campaigns this year, even starting in May, is certainly within our reach,” Le Gall said.

The separate quality-control audit being managed by outside experts will determine if any of Arianespace’s procedures needs review following the series of launch postponements.

“In light of what happened with the Helios 2B delays and now these recent postponements, I would like to have an outside team look at our practices to see where we can improve,” Le Gall said April 12. “There have been a few too many issues of late. What I am expecting is at least a preliminary set of conclusions from the quality audit before we proceed with the launch.”

In addition to its Ariane 5 schedule, Arianespace is preparing for the inaugural launch — now expected no sooner than late September — of the European version of Russia’s Soyuz rocket from the Guiana Space Center.

The helium-pressure anomaly discovered April 9 forced a third postponement of the launch of the Astra 3B commercial direct-broadcast television satellite, owned by SES of Luxembourg, and the COMSATBw-2 military telecommunications satellite to be operated by the German Defense Ministry in partnership with a commercial consortium made up of Astrium Services and ND Satcom, both of Europe.

The two satellites have been insured for a total of more than $700 million, making it the most highly insured commercial launch mission ever, according to insurance officials.

Peter B. de Selding was the Paris bureau chief for SpaceNews.