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The Ariane 5 launch vehicle is the new addition (as of 1998) to the Arianespace family of launchers. With this new vehicle, Arianespace brings the next generation of heavy lift launch services to the global satellite launch marketplace. Ariane 5 is designed to be even more successful and reliable than Europe's launch workhorse, the Ariane 4. Its simple, clean, modular design provides reliability and performance that is unsurpassed in its class.

Ariane 5 is not so much a single vehicle as it is a modular collection of reliable, well proven parts. Modularity allows maximum versatility for different sizes and styles of payloads, and ensures that Ariane 5 can continue the philosophy of improvement and innovation that began with its predecessors. Future improvements to the launch vehicle will allow the delivery of larger and more diverse payloads to a wide range of possible orbits. Future enhancements will become particularly useful as large satellite constellations become more commonplace.

Ariane 5 was originally proposed as the next in the Ariane line in 1977. The project was approved in 1985, and the design of a new cryogenic engine began. The resulting engine, Vulcain, was first tested in 1990, and has since proven to be a reliable foundation for Ariane 5. The Aestus engine, which is used in the upper stage of the launch vehicle to put payloads in the required orbits, was first tested in 1992 and completed testing in 1994. Development of the solid rocket boosters culminated in the first full scale test in 1993. The combined vehicle made its maiden voyage on June 4th, 1996. The test flight ended 37 seconds after liftoff, when a software error caused it to veer off course and breakup. The second test flight occurred on October 27th, 1997, and the third, completely successful flight flew on October 28th, 1998.

The heart of the Ariane 5 launch vehicle is the main cryogenic stage. This stage houses the equipment bay, the cryogenic propellant, and the Vulcain engine. The vehicle equipment bay contains the electronics that monitor and control the vehicle during its flight. Redundant computers and flight guidance systems help make Ariane 5 as reliable as possible. The cryogenic propellant consists of 132.27 metric tons of liquid oxygen and 25.84 metric tons of liquid hydrogen, which is burned by the Vulcain engine. The cryogenic stage is 30.5 meters long, from the engine bell to the forward skirt, and has a dry mass of 12.2 metric tons. Fully fueled, this stage has a mass of 170.3 metric tons. This stage operates for 589 seconds, at which point it separates from the remaining upper stage. The cryogenic stage then falls back into the atmosphere and is destroyed as it falls back into the ocean.

Solid rocket boosters provide 90% of the enormous thrust required to break free of Earth's gravitational field. The boosters are 30 meters long, and contain 237.8 metric tons of propellant. Both boosters together provide 1,370 metric tons of thrust at liftoff. They burn for 130 seconds, after which they separate from the vehicle and fall into the ocean. The boosters may then be recovered, and post flight analysis can be performed.

The upper, or stored propellant stage, is the part of the vehicle that actually puts the payload into orbit. This stage carries 9.7 metric tons of fuel, and is powered by the Aestus engine. This restartable engine can provide 3 metric tons of thrust, with flight control provided by electrical actuators controlling the engine nozzle.

A number of payload configurations are available for Ariane 5. The vehicle can be configured with one of two fairings, one of nine payload adapters, and, optionally, either a Speltra or a Sylda 5 structure. The Speltra and Sylda 5 structures allow two primary payloads to be launched at the same time. Ariane 5 can also be fitted with the Ariane structure for auxiliary payloads, which can accommodate up to eight micro satellites.

The fairings provided by Ariane 5 protect the payload as it is launched. The acoustic, thermal, and atmospheric protection provided by the fairing ensure that the payload is not damaged during its ascent. The vehicle can be fitted with one of two payload fairings. The short fairing is 12.7 meters long and accommodates payloads up to 11.5 meters long. The long fairing is 17 meters in length and allows for payloads as long as 15.5 meters long. Both the long and the short fairings have a useful interior diameter of 4.57 meters.

To provide maximum versatility, Ariane 5 has nine different payload adapters, allowing payloads ranging in mass from 1,000 kg to 18,000 kg. These adapters give Ariane 5 the ability to launch satellites based on all current satellite platforms.

The Speltra and Sylda 5 structures allow two primary payloads to be launched on the same flight. The Speltra structure is mounted on the stored propellant stage and contains one of the primary payloads. The second primary payload is mounted on top of the Speltra structure and is enclosed in the payload fairing. Speltra comes in three versions, tall, standard, and short. The standard version is seven meters in length and all Speltra structures can house payloads 4.57 meters in diameter. The Sylda 5 structure is similar to the Speltra structure, except that it is entirely enclosed by the payload fairing. The Sylda 5 structure comes in six different versions, and can carry payloads from 2.9 meters to 4.4 meters in length, with a maximum diameter of 4 meters.

All in all, Ariane 5 is a modern, reliable, heavy lift launcher. It is operated by France based Arianespace, and is flown from the Guiana Space Center in French Guiana.

Resources

Arianespace, Jan 17th 2001, http://www.arianespace.com/

Arianespace, Ariane 5 Technical Information, 1999, http://www.arianespace.com/interior/ARIANE5\_tech\_GB.pdf

Node your homework!

The Failure of Ariane 5


Ariane 5 was scheduled for launch June 4th 1996. Everything went smooth until 37 seconds after launch when Ariane 5 suddenly, during its maiden voyage, tilted over and exploded approximately 3700m above sea level.


The event:
In Kourou, French Guiana, the weather was acceptable in the morning, and presented no obstacle for the shuttle transport to the launch pad. All criterias were fine, apart from the visibility, which made the launch committee delay the launch by 59 minutes.

59 seconds past 09:33 (local time) the Vulcain engine and the two solid boosters were ignited, and the shuttle lifted off. Everything went smoothly until +37 seconds when the shuttle veered off its flight path, and turned sideways. 39 seconds after the launch, the angle of attack was more than 20 degrees. The aerodynamical pressure on the hull was too great, so the shuttle broke up and exploded.

The Failure:
  • The tilt of the shuttle was caused by nozzle deflections of the solid boosters and the Vulcain main engine.

  • These nozzle deflections were commanded by the shuttle's On-Board Computer (OBC), on the basis of information supplied by the active Inertial Reference System (SRI2*). This information was not proper flight data, but a diagnostic bit pattern from the SRI 2, which was interpreted by the OBC as flight data.

    *SRI stands for Système de Référence Inertielle

  • SRI2 sent the diagnostic pattern after a failure caused by a software exception.

  • OBC was unable to switch on SRI1 (the backup), because SRI1 had encountered the same error, one data cycle (72 milliseconds) earlier.

  • The software exceptions in both SRI1 and SRI2 were caused by a data conversion from 64-bit floating point to 16-bit signed integer value. The floating point number that was being converted was greater than what could be represented as a 16-bit integer. The result was an operand error.

  • This error occurred in a part of the software that serves no purpose after lift-off (for Ariane 5, this was +3 seconds after ignition) but the software still remains operative for approx. 40 seconds. This time is based on the requirements of Ariane 4, but Ariane 5 does not require this.

  • The error was caused by an unexpected high result of an internal alignment function called 'Horizontal Bias' (BH). This value is calculated as an indicator for alignment precision over time. The reason for the high BH-result was that the trajectory of Ariane 5 differs from Ariane 4 (which the function was programmed for), which results in a much higher horizontal velocity.
(The telemetry data showed many other anomalies, but none of these are considered significant to the accident.)


The Result:
The self-destruct sequence was initiated, which made the shuttle explode in an height of aprox 3700 metres, and aprox. 1km from the launch pad. The debris was scattered over an area of 5 x 2.5 km2. Amongst the debris the two SRIs were found, and used for analysis.

It took the European Space Agency 10 years and $7 billion to produce Ariane 5. In addition to the building costs, the shuttle contained 4 research-satellites (The satellites were not insured).

The shuttle was unmanned, so no lives were lost, and since the launch area wasn't populated, none were injured by debris.



Sources:
  • CNN
  • The report made by the Ariane 5 Inquiry Board
  • Various documents regarding the accident

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