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SUCCESSFUL FLIGHT OF ESA'S REENTRY DEMONSTRATOR

by Christopher Hess

Ariane Flight 503 was successful in two respects. The new European launcher is not only ready for the market introduction, but during her third flight Ariane 5 carried a red brown capsule which was jettisoned 12 minutes after launch and landed on target in the waves of the Pacific Ocean some 90 minutes later. With the flight of the Atmospheric Reentry Demonstrator Europe has for the first time carried out a complete mission from start to finish.

ESA's ARD is an unmanned, automatic test vehicle, which is stabilised via three axis. The fully equipped High-Tech-Capsule recorded more than 200 critical parameters on its short mission. These will help to analyse the flight and the performance of the on-board equipment. For Europe this is an important step towards developing competence in re-entry Technologies.

To save time and money, the design of the ARD was modelled on the proven aerodynamic shape of the American Apollo Capsule. The European Capsule is about 70 per cent of the size of the Apollo Capsule. According to ESA it had roughly half the size of a potential operational re-entry vehicle.

During the flight on 21 October the ARD was released at an altitude of 209km and reached a maximum height of 830km, before the capsule began re-entry into the earthís atmosphere at 120km (altitude) and at a speed of around 27,000km/h.

After release from Arianeís upper stage, the capsule initially flew ballistic. However, for steering control during re-entry the ARD was equipped with an attitude control system with seven thrust-jets, each with an output of up to 400N. ARD splashed down about 4.9km from the planned target point. Still, this was within the 5km target range.

Several factors have contributed to this kind of precision. One was the brilliant performance of the launch rocket. It was important for the capsuleís ballistic flight phase that the main stage of the rocket was working perfectly and that the engine did not switch off prematurely as was the case during the 502 flight. Patrice Amadieu from ESAís Directorate for manned spaceflight claimed that ìevery second, Arianeís main stage had switched off earlier than planned, would have meant a deviation from the capsule's target of 500km.î The capsuleís position control system would not have been able to cope with this discrepancy at re-entry.

The navigation computer, which received data from the Inertia-Navigation-System and the GPS also contributed to ARDís precise landing South of Hawaii. Since GPS Steering had failed during earlier flights of Japanese test vehicles, the ESA could not be certain whether satellite navigation was going to be successful with the ARD, which moved at hyper speed.

The GPS experiment intended to leave steering to the satellite system, (supervised and verified by the inertia system), as long as the navigation results were inside a credibility window. Evaluation of real time telemetric data has now shown that the GPS remained in control throughout the entire flight.

Temperatures of over 1,000 Degrees C were measured at the outside of the capsule. Inside the temperature reached 25 Degrees C. The capsule, which was taken on board a French Naval vessel after splash down, is currently being examined in great detail. One thing is certain: "This flight represents a big push forward for European Spaceflight", says Patrice Amadieu.

From page 42 of FLUG REVUE 1/99