This flight initially was delayed in March at the request of Arianespace's customer — the European Space Agency (ESA) — to allow time for additional checks on ground segment operations for the Herschel and Planck payloads. While the validation of these ground-based operational procedures was successfully concluded, separate concerns arose during final reviews with the Herschel space telescope, and another delay was implemented in setting the launch date. The new postponement will allow for a final and independent check of the spacecraft's safety margins by ESA and Arianespace.
Herschel's telescope mirror — the largest ever to be launched in space — uses 12 silicon carbide petals brazed together into a single piece. As one of the major technological highlights for this space science mission, the mirror structure's complexity and uniqueness requires that great care be taken to ensure that stresses experienced during launch are well understood, according to ESA program managers. Over the next few days, a panel of independent experts led by the ESA Inspector General and Arianespace will carry out final documentation cross-checks to demonstrate that required safety margins will be met during the telescope's ascent on Ariane 5. Both the Herschel space telescope and Planck observatory are on standby in perfect condition at Europe's Spaceport in French Guiana. Engineers are awaiting the new launch date in order to resume final pre-launch preparations, including fueling of the two satellites and the helium filling of Herschel's cryostat (which provides for cooling of the space telescope's scientific instrument package during operations in space).