Ariane 5 - Definition and Overview

The Ariane 5 is an expendable launch system, designed and manufactured under the authority of the European Space Agency (ESA) by EADS SPACE Transportation, the Prime Contractor, leading a consortium of many sub-contractors and is operated and marketed by Arianespace as part of the Ariane programme. EADS SPACE Transportation builds the rockets in Europe and Arianespace launches them from a space port at Kourou in French Guiana.

Components

Ariane 5’s cryogenic H155 main stage is called the EPC from the French, Etage Principal Cryotechnique. It consists of a large tank with two compartments: one for liquid oxygen and one for liquid hydrogen, with at the base the Vulcain engine.

Attached to the sides are two solid propellant boosters.

The second stage is on top of the main stage and below the payload.

Use

Ariane 5 usually puts satellites into Earth orbit. It succeeds the Ariane 4, but it does not directly derive from it. Its development took 10 years and cost EUR 7 billion. The ESA originally designed Ariane 5 to launch the manned mini shuttle Hermes too, and thus intended it to be "man rated" from the beginning. After the ESA cancelled Hermes the rocket became a purely commercial launcher. The current payload capability to geostationary transfer orbit (GTO) comprises about 6,200 kg. Upgrades were planned to boost this to 12,000 kg, making it possible to launch two "heavy" satellites at once, but their future is now uncertain.

Although recently much improved, the Ariane 5 could not immediately connect to the stellar success record of the Ariane 4. Ariane 5's first test flight (Ariane 5 Flight 501) on June 4, 1996 failed, with the rocket self-destructing 40 seconds after launch because of a malfunction in the control software, which was arguably one of the most expensive computer bugs in history. A data conversion from 64-bit floating point to 16-bit signed integer value had caused a processor trap (operand error). The floating point number had a value too large to be represented by a 16-bit signed integer. Efficiency considerations had led to the disabling of the software handler (in Ada code) for this trap, although other conversions of comparable variables in the code remained protected.

Subsequent test flights on October 30, 1997 and October 21, 1998 proved successful and the first commercial launch occurred on December 10, 1999 with the launch of the XMM-Newton X-ray observatory satellite.

Another partial failure occurred on July 12, 2001, with the delivery of two satellites into an incorrect orbit. One of these, the ESA Artemis telecommunications satellite, managed to reach its correct orbit using fuel intended for orbit maintenance, but in the process reduced the expected lifetime of the satellite.

The following launch did not occur until March 1, 2002, when the Envisat environmental satellite successfully reached an orbit 800km above the Earth in the 11th launch. This was the rocket's heaviest payload to date at 8500kg.

Ariane 5 lifts off with the Rosetta probe on 2nd of March, 2004.

A new variant of the Ariane 5 intends to increase the GTO launch capacity to 10,500kg. However the first launch of an ESC-A on December 11, 2002 ended in failure when a main booster problem caused the rocket to veer off-course, forcing its self-destruction three minutes into the flight. Its payload of two communications satellites (Stentor and Hot Bird 7) valued at about EUR 630 million was lost in the ocean. The fault was determined to have been caused by a leak in coolant pipes allowing the tail nozzle to overheat. After this failure, Arianespace delayed the expected January 2003 launch for the Rosetta mission to February 26, 2004, but this was again delayed to early March, 2004 due to a minor fault in the foam that protects the cryogenic tanks on the Ariane 5.

On 27 September 2003 an Ariane 5 boosted three satellites (including the first European lunar probe, SMART-1) in Flight 162 and on 17 July 2004 it boosted the heaviest telecommunication satellite ever, weighting almost 6,000kg.

Future developments

The ESC-A upper stage is powered by an HM-7B engine, weighting 6,500kg and carrying 14,000kg of cryogenic propellant and previously used as the third stage of the Ariane 4. A future ESC-B upper stage was planned using a new engine "Vinci", an expander cycle type engine which is to increase the GTO capacity to 12,000kg, but it was put on hold indefinitely due to budget cuts. A 10,000kg GTO capacity version of Ariane 5, using a new Vulcain 2 first stage engine will try launching a satellite by January 2005. The original attempt was to be in October 2004, but additional testing and the military requiring a launch at that time (for an Helios 2A observation satellite) delayed the attempt to 2005.

Ariane 5 Flights

External link

• ESA description of the Ariane 5 (http://www.esa.int/export/SPECIALS/Launchers_Access_to_Space/ASEVLU0TCNC_0.html)