Hershel-Planck Launch Incident Prompts Scrutiny of Ariane 5 Upgrade

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LE BOURGET, France — Arianespace and the European Space Agency (ESA) have established a board of inquiry to examine whether a new fairing-separation system, used for the first time during the May 14 launch of ESA’s Herschel and Planck science satellites, propelled the two fairing halves too close to the satellites, according to ESA and Arianespace officials.

Officials said the telemetry data at the moment of fairing separation suggests that the new HSS-3, or horizontal separation system, sent the fairing closer than forecast to the satellites and the Ariane 5 upper stage that was carrying them to their orbital drop-off point.

Officials denied industry rumors that fairing components came close to hitting the satellites or the launch vehicle and that the launch narrowly averted a catastrophe. But indications from the available telemetry are that the separation did throw the fairing halves from the vehicle in such a way as to bring them closer than predicted to the two satellites.

Costing a combined 1.8 billion euros ($2.5 billion), Hershel and Planck represent Europe’s most expensive space science mission to date.

“I would not yet call this an anomaly, that is going a bit too far,” ESA Launcher Director Antonio Fabrizi said in a June 18 interview. “What we observed in the recorded data is that the separation occurred in a way that the engineers had not modeled. We want first to verify this, and then to determine appropriate action if we conclude that there is a problem. But at no time did the separated fairing violate the ‘respect area’ around the [satellite and upper stage] composite.”

Satellite owners and manufacturers have long asked launch services provider Arianespace to reduce the shock created when the Ariane 5 fairing splits in two about two minutes after liftoff to expose the satellites. The fairing separation occurs at an altitude of some 120 kilometers — high enough above that the fairing is no longer needed to protect the satellites. Pyrotechnic charges separate the fairing halves vertically, with a separate charge needed to provide horizontal separation so that the fairing — 17 meters long, 5.4 meters wide and weighing some 2,675 kilograms — can fall away harmlessly as the rocket continues its ascent.

Oerlikon Space AG of Zurich, which builds the HSS-3 fairing separation system, said the new hardware is designed to reduce shock levels felt by Ariane 5’s satellite payloads by a factor of 100 compared to the currently used Ariane 5 separation system. For satellites whose electronic or other components are viewed as especially sensitive, Arianespace occasionally uses shock-reducing rings, but these can weigh hundreds of kilograms and thus reduce the vehicle’s payload-carrying capacity.

In a prelaunch statement on the new system, Oerlikon Space described the HSS-3 this way: “While the old system consisted of a ring in which a fuse was lit, the HSS-3 system is made up of two symmetrically arranged rings that are set in such a way that the shock waves generated by the separation cancel each other out. This particular setup allowed the Oerlikon Space specialists to reduce the mechanical stress on the payload at separation to about one-hundredth of the earlier value.”

Fabrizi and Arianespace officials said the HSS-3 appears to have met the goal of reducing mechanical shock to the satellites caused by the fairing separation. HSS-3 had been tested during two campaigns using the large vacuum chamber at NASA’s Plum Brook Station in Ohio. One official said HSS-3 had been scheduled for a second flight, set for late 2009, but will not be used until the inquiry has more data on how it performed during the Herschel-Planck launch. Fabrizi said the inquiry is expected to conclude by mid-July. “By then we should know if a problem exists,” he said.