Ariane

With a stretched first stage augmented by a mix of strap-ons, the Ariane 4 could put payloads of between 2,000 and 4,900 kilograms into geosynchronous transfer orbit.

The launch of an Ariane 40, the basic variant of this launch vehicle, on 7 July 1995 with a number of payloads including the Cerise satellite.

The basic three-stage vehicle was the Ariane 40; the 42P had two solid strap-ons; the 44P had four solid strap-ons; the 42L had two liquid strap-ons; the 44LP had four strap-ons (two solid and two liquid); and the 44L (the most powerful variant) had four liquid strap-ons. Within a year of its introduction on 15 June 1988, the previous models had been retired.

The first failure was on 22 February 1990 when an Ariane 44L lost Superbird B and BS-2X, which were American-built communications satellites that were being launched for Japanese companies.44 In this configuration, the Viking 6 liquid engines of the strap-ons ignite for lift-off and burn for 144 seconds; they are shed 10 seconds later, 1 minute before the first stage shuts down. In this case, the telemetry indicated that one of the four engines in the core stage had had a problem very early on. It was clear, however, that this fault was upstream of the engine.45 The Ariane 4 drew water from a tank located at the top of the stage to pressurise the propellant tanks and to regulate the combustion chamber pressure via the gas generator. In the case of the 44L, water was also fed through pipes to the strap-on engines. In this case the eight engines ran up to full power and at T+3.3 seconds the vehicle was released. Within the space of half a second, at T + 6 seconds, the chamber pressure of one of the main engines dropped from the nominal 58 bars to about half of this value, and never recovered. The flight control system promptly gimballed the other three engines to compensate for the asymmetric thrust. Even so, as the vehicle rose from the pad it side-slipped towards the 77-metre-tall umbilical tower, clearing it by a mere 2 metres. At T + 90 seconds, the gimballed engines reached their maximum angle of 5 degrees and the vehicle began to tip over, and at T+101 seconds the aerodynamic stress began to tear it apart and it finally exploded at an altitude of 9 kilometres. On a previous mission, air trapped in a water feed pipe had caused a momentary dip in combustion chamber pressure in one of the strap-ons. The design had been changed, but it appeared that once again the flow of water had been impeded. With the Atlas-Centaur now operating in competition, Arianespace could ill afford a lengthy grounding.

The launch of an Ariane 40, the basic variant of this launch vehicle, on 7 July 1995 with a number of payloads including the Cerise satellite.

The launch of an Ariane 44L, the most powerful variant of this launch vehicle, on 29 March 2002 with Astra 3A and JCSAT 8.

A record insurance loss

On 24 January 1994 the third stage of an Ariane 44LP shut down 80 seconds into its 750-second burn.46 This was only the second failure in 35 launches. At T + 60 seconds the bearing of the oxygen turbopump, which spun at 13,000 revolutions per minute and was cooled by being immersed in the liquid oxygen, began to rapidly overheat. Nineteen seconds later, the speed of the bearing and the outlet pressure both fell, and the engine shut down one second later as the bearing rup-tured.47 The investigation conducted 100 tests on 30 bearings (in some cases in a complete engine) to further characterise the heat dissipation parameters of the bearing. In order to preclude a recurrence, the bearing would henceforth be coated with molybdenum disulphide to make it self-lubricating, and a purge line would be added to the bearing cavity to ensure that the cooling and helium flushing systems would be more reli-able.48,49,5° The loss of Eutelsat 2F5 and Turksat 1, both of which were of the Aerospatiale Spacebus 2000 series, resulted in a total insurance claim of $350 million - one of the greatest to date. By mid-1994 Arianespace had hoped to ramp up the pace of Ariane 4 launches to one every three weeks, but this failure had undermined that as-piration.51 The Ariane 44LP resumed operations on 17 June 1994 with Intelsat 702.

The launch of an Ariane 44L, the most powerful variant of this launch vehicle, on 29 March 2002 with Astra 3A and JCSAT 8.

Telstar 402

Within 10 minutes of being released by its Ariane 42L on 8 September 1994, Telstar 402 suffered a leak of the helium gas that was to pressurise the propellant for its attitude control thrusters, which prevented it from orienting itself, and the following day AT&T Skynet Satellite Services declared it a write-off.5V3 The fact that the satellite had fallen silent in the act of pressurising its propellant suggested an explosion.54 The investigation focused on the explosively actuated valves used to pressurise the propulsion system.55 At first, such valves had been made of stainless steel, but over recent years there had been a trend towards titanium in order to save mass. It was concluded that when the second of the redundant pair of pyrovalves opened the hydrazine line, this set off an explosion.56 As such valves were believed to have been responsible for the losses of Mars Observer and Landsat 6, AT&T sued Martin Marietta, whose Astro Space had supplied all of these spacecraft, citing incompetence and deception for failing to correct "known defects" in the propulsion system. The case was settled out of court in May 1995.57 Meanwhile, in October 1994 NASA had organised an industry-wide teleconference to review the use of such valves and, in view of concern about how titanium reacted with hydrazine, it was concluded that the performance margins were ill understood. It was therefore decided to revert to stainless steel in some cases - notably for Mars Global Surveyor and Cassini.58 AT&T had put Telstar 402 on an Ariane in an effort to jump the queue on the repeated grounding of the Atlas. Although the loss was not a launch vehicle failure, Arianespace promised to launch a replacement as a matter of priority, and the third satellite, known as Telstar 402R, went up on an Ariane 42L on 23 September 1995.

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