programmes along with multiple new-generation materials, the latter of which had been principally included for testing purposes. During reentry, the ARD's head shield loses only 0.5 mm of its thickness, keeping its aerodynamic shape relatively constant, which in turn simplifies the flight control algorithms. The vehicle is equipped with a Descent Recovery System (DRS), deployed prior to splashdown in order to limit the impact loads and to ensure its flotation for up to 36 hours. This system involving the deployment of multiple parachutes, stored within the internal space of the tip of the nose cone; in total, one flat ribbon pilot chute, one conical ribbon drogue chute with a single reefing stage, and three slotted ribbon main parachutes with two reefing stages are typically deployed. For buoyancy purposes, a pair of inflatable balloons are also present in the DRS, helping to keep the vehicle upright. To aid in its recovery, the ARD is furnished with both a satellite-based search and rescue radio beacon and flashing light. The internal space of the ARD and was packed with the most advanced technologies to test and qualify new technologies and flight control capabilities for atmospheric reentry and landing. The avionics of the vehicle were primarily sourced from existing equipment used upon the Ariane 5 launcher. The guidance and navigation systems used a computerised inertial navigation system which, via a databus, would be automatically corrected by GPS during the ballistic phase of flight. However, the ARD was designed to be tolerant to instances of GPS failure; this is achieved via a series of control loop algorithms that verify the GPS-derived data to be within a pre-established ‘credibility window’, defined by the inertial navigation readings. During the vehicle's sole mission, it continuously recorded and transmitted to the ground in excess of 200 critical parameters that were used to analyse the ARD's flight performance as well as the behaviour of the equipment on board. Operational history The ARD only performed a single spaceflight. On 21 October 1998, the ARD was launched upon the third flight of the Ariane 5 expendable launch system. It was released shortly after separation of the launcher's cryogenic main stage (at an altitude of about 216 km) 12 minutes after lift-off from the Guiana Space Centre, Europe's spaceport in Kourou, French Guiana. The ARD attained a recorded altitude of 830 km, after which a guided reentry into the atmosphere was conducted. It