PARIS — The launch of Europe’s Herschel and Planck astronomy satellites, which had been scheduled for April 16, has been delayed for about two weeks to give Europe’s Esoc mission control center time to verify recently added flight-simulation software, European Space Agency (ESA) officials said March 13.

Jacques Louet, ESA’s head of science projects, said the two satellites are in good shape at Europe’s Guiana Space Center in French Guiana and that the delay is only to give the Darmstadt, Germany-based Esoc control center time to de-bug a new software system that will monitor the satellites during their launch and early operations phase.

Louet said Esoc teams expect to complete the work by March 27. If that occurs, the launch campaign will resume, starting with the fueling of the satellites and their integration onto a single Ariane 5 heavy-lift rocket. Under current planning, Louet said, the launch would occur April 29 or April 30.

The combined Herschel-Planck mission is the most expensive science package ever launched in Europe. Its budget is estimated at about 1.6 billion euros ($2 billion), including the satellites’ construction, launch and in-orbit operations.

The Arianespace launch consortium typically needs about four weeks between launches. The Evry, France-based company is preparing the launch of SkyTerra Corp.’s TerreStar-1 mobile communications satellite for May 28. The 6,700-kilogram TerreStar-1 will be a rare solo commercial passenger on Ariane 5. Arianespace officials said that the late-May TerreStar-1 launch does not need to be delayed if the Herschel-Planck mission is completed by April 30.

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