Arianespace has set a comprehensive recovery plan to address the upper stage
malfunction that occurred during Flight 142, and expects to return Ariane 5
to commercial service by late November.

The recovery plan takes into account all recommendations made by the
independent inquiry board that investigated the malfunction, and targets the
next Ariane 5 mission for late November. This represents a delay of only two
months compared to the original launch manifest, and will cause relatively
minor schedule implications for the remainder of 2001 and early 2002.

The seven-member inquiry board identified combustion instability during
upper stage engine ignition as the source of Flight 142’s malfunction. The
origin of the combustion instability is attributed to an unfavorable
hydraulic dynamic coupling between the propellant feed system and the
internal fluid cavities of the combustion chamber.

The upper stage malfunction, which occurred during Flight 142’s final
propulsion phase on July 12, resulted in the mission’s dual satellite
payload being delivered to a lower than expected orbit.

Among the primary action items identified by the board are: improved
hydraulic modeling of the upper stage’s ignition sequence, definition and
qualification of modifications to the engine’s ignition sequence, and
modification of the test bench used to qualify the engines to more closely
duplicate flight conditions.

Edouard Perez, Arianespace’s senior vice president of engineering, said the
goal of these actions is to improve the Aestus ignition sequence to make it
more progressive and smooth. An intensive program of vacuum test firings is
planned before the next Ariane 5 flight occurs. As part of the recovery
plan, the next engine to fly on Ariane 5 will go through a ground test
firing to be qualified for launch.

The storable propellant upper stage performs the final part of Ariane 5’s
mission, propelling the payload to the point of orbit injection. The upper
stage’s Aestus engine is fed by 9.7 metric tons of propellant (MMH fuel and
N204 oxidizer). There is no turbopump in the upper stage, so the flow of
fuel and oxidizer to the Aestus engine is created by helium pressurization
of the propellant tanks.

Perez said the recovery plan has been structured, and will begin with the
dynamic modeling of the upper stage’s ignition sequence. The modeling will
be main tool driving the test firing plan for the Aestus engine . “The
modeling will be used to set new qualification and acceptance test criteria
for the Aestus engine,” he explained.

According to Perez, the inquiry board confirmed that all processing and
countdown operations for Flight 142 proceeded nominally, as did the
Ariane5’s flight prior to ignition of the upper stage’s Aestus engine. The
Board therefore concluded that nothing had affected the stage prior to the
ignition of its Aestus engine.

In addition, The Board clearly stated that no relationship or link was found
between the Ariane 5 anomaly and the Ariane 4 vehicle. Preparations continue
for the next Ariane 4 mission, which is planned for late August.

The Flight 142 inquiry board was headed by Roger Vignelles, who said his
team worked in complete independence, and received all information and
support it requested from Arianespace and its industrial team. The board was
made up of veteran space industry engineers and managers, headed by
Vignelles – who is considered one of the “fathers” of the Ariane program.

“Arianespace’s choice of the board was excellent – all of the members had
extensive space sector experience, and we quickly found our ‘working
rhythm,'” Vignelles said. “We worked together as a group, but I gave each
member lead responsibility for one of the major areas of reflection as we
studied the data and worked to pinpoint the causes.”

As part of its activity, the inquiry board traveled to Germany to see the
EPS upper stage motor and visit the site where it is produced and qualified.
The members worked through the first weekend, and were quickly able to focus
on the origin of the Aestus engine’s “hard start” during the flight.

The board’s report was submitted on August 1, meeting the two-week timing
requested by Arianespace. The recommendations were accepted by Arianespace,
and the action plan was given the go-ahead two days later. Arianespace
rapidly notified its customers of the inquiry board’s findings, meeting its
commitment to keep the lines of communications open following Flight 142.