PARIS — The in-orbit failure of the Orbital Sciences-built Intelsat Galaxy 15 telecommunications satellite April 5 was likely caused by unusually violent solar activity that week that damaged the spacecraft’s ability to communicate with ground controllers, Orbital officials said April 20.

Similar events have occurred, if less severely, on other Orbital spacecraft over the years, and all of these satellites were returned to service. Company officials said they remain confident that once Galaxy 15’s commercial traffic has been off-loaded to another Intelsat satellite and full testing of the stricken spacecraft begins, Galaxy 15 will recover its full operational status.

Dulles, Va.-based Orbital, in a conference call with investors, said a series of minor delays in development of the company’s new Taurus 2 rocket and its Cygnus space station cargo transporter will push the inaugural Taurus 2/Cygnus launch into May or June 2011 instead of the March date earlier targeted.

Orbital Chief Executive David W. Thompson said that Taurus 2 and Cygnus, which are the company’s two biggest development programs, nonetheless are moving forward without major roadblocks. As of March 31, three-quarters of Orbital’s total investment in Taurus 2 and a little over half of its investment in the Cygnus cargo carrier had been completed.

The schedules of both programs are now so tight that any further hiccups likely would delay the launch still further, he said.

The Orbital-built Galaxy 15 satellite suffered failures in its ability to send telemetry to ground teams, and to receive commands, April 5. Satellite fleet operator Intelsat of Luxembourg and Washington is moving a spare in-orbit satellite, the Orbital-built Galaxy 12, to take over commercial service from Galaxy 15.

Operating from 133 degrees west longitude since late 2005, Galaxy 15 carries a 24-transponder C-band payload serving media customers in North America. Intelsat has said these customers should see no service interruption as they are moved to Galaxy 12.

The U.S. Federal Aviation Administration (FAA) is leasing an L-band payload on Galaxy 15 to guide aircraft as part of a satellite-based navigation service that uses the U.S. GPS satellites in medium Earth orbit and payloads on three commercial satellites in higher geostationary orbit.

Intelsat spokeswoman Dianne J. VanBeber said April 21 that the company expects to continue operating the L-band payload even after all other Galaxy 15 customers have been off-loaded. L-band service should continue even as the satellite is put through more-rigorous testing to determine the cause of the communications problem, although signal disruptions are possible during this period, VanBeber said.

Intelsat is coordinating Galaxy 15 testing with the FAA and with Lockheed Martin — the prime contractor for the FAA’s Geostationary Communications and Control Segment (GCCS) program that provides ground stations and broadcast services that, by using signals on the geostationary-orbit satellites, improve the accuracy of GPS signals for aviation.

VanBeber said Intelsat would decline to speculate on the causes of the Galaxy 15 communication failure and the likelihood of a full recovery until the testing has concluded. Thompson said unusually severe solar activity between April 3 and April 5 is “our best-informed guess” of what caused the Galaxy 15 problem.

He said there are no indications that any other Orbital-built satellites were affected by the solar activity, but that over the past 15 to 20 years two or three Orbital spacecraft have suffered similar failures. Once the company has succeeded in reproducing the failure in ground tests, it will be able to design a software patch to send to Galaxy 15.

J.R. Thompson, Orbital’s chief operating officer, said the testing could take three to six weeks, “with the goal of returning Galaxy 15 to full operational status by this summer” if the tests yield the expected results.

Orbital Chief Financial Officer Garrett E. Pierce said the company carries insurance against the loss of its in-orbit incentive payments. Commercial satellite owners often withhold around 10 to 15 percent of a satellite’s cost, and distribute the payments annually as the satellite continues to function as designed in orbit. The incentive payments are canceled in the event of an in-orbit failure.

David Thompson said the company continues to expect 22 to 25 commercial geostationary telecommunications satellites to be purchased worldwide in 2010, with six or seven of these being in the smaller, lower-power class of satellites in which Orbital specializes. Orbital hopes to win three of these.

He said the company also is offering Orbital’s new, higher-power satellite platform to prospective customers this year and might land one contract for this product.          

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