BR-138-COVER 30-09-1998 11:34 Page 1 BR-138 October 1998 The Atmospheric Reentry Demonstrator nn > < Contact: ESA Publications Division c/o ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands > Tel. (31) 71 565 3400 - Fax (31) 71 565 5433 < Directorate of Manned Spaceflight and Microgravity Direction des Vols Habités et de la Microgravité ARD 29-09-1998 17:02 Page 1 BR-138 October 1998 The Atmospheric Reentry nDemonstrator n <> The Atmospheric Reentry Demonstrator What is the Atmospheric atmosphere. It will test and qualify reentry Reentry Demonstrator? technologies and flight control algorithms ESA’s Atmospheric Reentry Demonstrator under actual flight conditions. (ARD) is a major step towards developing and operating space transportation In particular, the ARD has the following vehicles that can return to Earth, whether main demonstration objectives: carrying payloads or people. For the first – validation of theoretical time, Europe will fly a complete space aerothermodynamic predictions, mission – launching a vehicle into space – qualification of the design of the and recovering it safely. thermal protection system and of thermal protection materials, Seven thrusters will The ARD is an unmanned, 3-axis stabilised – assessment of navigation, guidance orient the ARD during automatic capsule that will be launched and control system performances. atmospheric entry. on top of an Ariane-5 from the European space port at the Guiana Space Centre in Kourou, French Guiana. Its suborbital ballistic path will take it to a maximum altitude of 830 km before bringing it back into the atmosphere at 27 000 km/h. Atmospheric friction and a series of parachutes will slow it down for a relatively soft landing in the Pacific Ocean, some 100 min after launch and three-quarters of the way around the world from its Kourou starting point. The ARD is a heavily-instrumented test vehicle. During the flight, it will record and transmit to the ground more than 200 critical parameters for analysis of the flight and the behaviour of the onboard equipment. It is also planned to locate the capsule after splashdown and, if possible, to retrieve it for return to Europe and a more detailed technical analysis. What are the objectives of the ARD? The ARD will allow Europe to study the physical environment to which future space transportation systems will be exposed when they reenter the Earth’s 3 Further objectives are: Why is this flight historic? – the assessment of the parachute and So far, Europe has built satellites for all recovery system, possible scientific, governmental and – the study of radio communications commercial applications, and carried during atmospheric reentry. them into space on its Ariane launchers. It has also developed and operated As a pilot project, the ARD is automatic platforms (Eureca, Spas) and a demonstrating that Europe can develop a manned laboratory (Spacelab). However, complete space vehicle in a shorter time it relies on other partners to carry these and with a smaller budget than in the elements into space, deploy and retrieve past. Last, but not least, the ARD is also a them, and to return them safely to Earth. historic flight for Europe. To date, only the US and Russia have fully 4 Artist’s impression of the assembly of the ARD on Ariane-5’s Speltra in Kourou. mastered the technical and operational know-how for both the ascent and return phases of space vehicles. With the flight of the ARD, Europe is undertaking a complete spaceflight cycle, from launch to landing, with its own expertise for the first time. Why is the ARD important Ariane-5 and other advanced space for Europe? transportation systems have reached the Flight through the Earth’s atmosphere limits of what is achievable today using imposes an enormous stress on a space classical mechanical and power designs. vehicle. This is true in both directions: Further improvements in payload-carrying during ascent after launch, and during capability, accompanied by a significant reentry at the end of the mission. The reduction in launch costs, require a real speeds associated with spaceflight are quantum leap in the technical and very high: at least 27 000 km/h is operational approach: instead of necessary to achieve low Earth orbit. discarding the launch vehicle, or at least Space vehicles suffer considerable important parts of it, after each launch, it buffeting and heating from the will be recovered whole for reuse on aerodynamic friction created by such high further missions. speeds. Without the appropriate aerodynamic shape, robust mechanical This will not be easy. The road to reusable structures, heat-resistant materials and space transportation systems will be intelligent automatic flight control difficult, but if Europe is to maintain the systems, the vehicle would simply break remarkable position it has achieved with up and burn under the harsh conditions. the Ariane launcher family, and if it intends to take up the challenges of the Reentry technology is not only important future launcher market, it has to master for space vehicles returning to Earth from the reentry technologies that will play an space, but also for space transportation increasingly important role in the launch vehicles that carry payloads into space. vehicles that are expected to come after These vehicles, or at least their lower Ariane-5. stages in the case of a multi-stage vehicle, generally fall back towards Earth after Acquiring its own competence in these completing their transport missions. The key technologies is also important if Ariane-5 core stage reenters the Europe wants to become an appreciated atmosphere at almost the same speed as and respected partner in the possible a vehicle returning from low Earth orbit. governmental and industrial cooperation Mastering reentry technology is not only structures of the future for the important for guiding the upper stages of development of such vehicles. expendable launch vehicles into safe trajectories back to Earth, but it will be The Atmospheric Reentry Demonstrator is even more important for the development an important step for Europe in achieving of future space transportation systems. these strategic goals. 5 What is the overall design of the ARD? The ARD has an external diameter of 2.80 m, an overall height of 2.04 m and a launch mass of 2800 kg. Roughly speaking, it looks like a 70%-scale Apollo capsule, with the remarkable difference that it incorporates modern technologies. The ARD has an air- and water-tight pressurised structure. In principle, it is designed to float by itself. However, after landing, two balloons will make sure that it floats upright, with the heatshield fully immersed in the water. This position contributes to better thermal equilibrium and ensures that the Sarsat (satellite search and rescue) radio beacon and flashing light that guide the recovery ship are not immersed. The ARD comprises four main elements: – a bulkhead structure that carries the heatshield, – a conical section that incorporates the reaction control system and houses an internal secondary structure, – a secondary structure inside the conical part to support the electrical equipment, – a back cover to protect the descent and recovery systems during flight. All structural elements are made of mechanical-fastened aluminium alloy parts. The outer surface of the ARD is covered with heat-protection material of different types. What are the main system functions of the ARD? Aerodynamics and automatic flight control ARD’s flight can be divided into three phases: ascent into orbit as a payload of 6 ARD vehicle architecture. Ariane-5; a free ballistic flight through based on Ariane-5’s performance space; and an aerodynamic, automatically capabilities and on ballistic reentry guided flight through the atmosphere. parameters that could be representative for a later Crew Transport Vehicle. As a As soon as it reenters the atmosphere, the result, the ARD is a spheroidal-conical ARD will become an aerodynamic vehicle capsule very similar in shape to a NASA that automatically controls its flight path Apollo capsule and, roughly speaking, a with the help of the onboard navigation, 50%-scale model of what could be an guidance and attitude control system. It operational transportation vehicle capable will be like an aircraft in autopilot mode, of reentry. with the substantial difference, however, that the ARD will be travelling at The ARD’s automatic navigation, guidance hypersonic speed and, in place of control and control system consists of a Global surfaces such as ailerons, elevators and Positioning System (GPS) receiver, an rudders, it will use small rocket thrusters inertial navigation system, a computer, to change flight attitude. the associated data bus and power supply and distribution system, and a To save time and money by avoiding the reaction control system. The reaction need for a long aerothermodynamic control system is derived from Ariane-5’s selection process, an existing attitude control system, using seven aerodynamic shape was adopted. The 400 N thrusters drawing on hydrazine dimensions and masses were defined (N2H4) carried in two 58-litre tanks 7 pressurised by nitrogen. The thrusters are positioned so that three provide control in pitch, two in roll and two in yaw. One of ARD’s objectives is to validate the flight control algorithms that were developed as part of the former Hermes spaceplane programme. The guidance calculation complexity and storage algorithm is similar to that used by NASA’s requirements. The accuracy is expected to ARD’s conical surface is Space Shuttle, based on a reference be 5 km, equivalent to kicking a goal with coated with thermal deceleration profile and also used by a football from a distance of 25 km. ESA’s protection consisting mainly of cork powder Apollo. This approach allows a good final initial requirement for landing precision and phenolic resin.