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HEAT SHIELD MADE IN GERMANY

A second life for Hermes? Not entirely. However, after development of the re-usable space transport was stopped at the beginning of the 90's, and it seemed that Germany had completely lost interest in re-entry systems, the technologies that were being developed at the time can be advanced further and finally be verified in flight.

The German Technology Program Tetra for future space transport systems has been running since October 1997. DM 80 million are available for this program, which will last until 30th June 2002. This sum consists of DM 21 million put up by the industrial partners involved. The Bavarian Ministry for the Economy, Transport and Technology is supporting Tetra with around DM 30 million. A further DM 19 million are supplied by the client, the German Ministry for Education, Science, Research and Technology, which is also making an additional DM 10 million available for complementary ESA programs.

The German Aerospace Centre (DLR) is in charge of the project. MAN Technology leads and co-ordinates the program activities of the partners. Among them are the DLR, Dasa, Kayser-Threde, OHB, the IABG as well as some universities.

Tetra's aim is "the creation of a technology base for future re-usable space-transport systems". In order to achieve this, key technologies for re-entry systems are to be validated. This will be carried out mainly through flight trials during other space flight programs but also during trials on the ground. Dr. Jens Peter Kemper, Head of MAN Technology's technology project department stresses, that "the development of any technology without the chance to test it during flight is just an academic exercise".

However, there is no chance to test these technologies in flight in Europe for the foreseeable future. It is no coincidence that Tetra is basically geared toward the Experimental Space Glider X-38. This craft is currently being developed by NASA, in conjunction with the European Space Agency (ESA) as a forerunner to the Crew Rescue Vehicle (CRV). Tetra complements the existing German and European work programs for the X-38 and is separated from these distinctly by the project management.

The CRV is intended to be available from 2003 as a rescue vehicle for the crew of the International Space Station. First flights with test vehicles at low altitudes are currently being undertaken. The X-38 will be launched with the Space Shuttle in the fourth quarter of the year 2000. It will then carry out a re-entry into the atmosphere.

Since the X-38/CRV is far smaller than the Space Shuttle, the re-entry speed of the new Space Glider will be considerably higher. As a result of this, temperatures at critical places like around the nose and the body flap on the tail of the fuselage will be very much higher than on the Shuttle. Consequently the Thermal Protection System (TPS) of the American craft cannot be used to protect critical places on the X-38. This is where Tetra fits in smoothly, because half of Tetra's budget is intended for work with hot structures and re-usable thermal protection systems.

The highest temperatures are expected around the glider's nose area. A nose tile that will withstand high temperatures, is being developed at the Institute for Building and Construction Research by the DLR in Stuttgart. The unit will be a ceramic structure with strengthened fibres. The material being used is Silicon Carbide, the fibres of which have been strengthened with carbon (C/SiC). It is claimed to withstands temperatures of up to 1,800 Degrees C.

Between the nose tile and the first row of heat protection tiles a nose ring will be used. It is also made of laminated ceramic. These side panels are 2.4 mm thick on average and can withstand temperatures of up to 1,650 Degrees C. The Dasa Space Flight Infrastructure Section in Bremen bears the main responsibility for the thermal protection of the nose ring.

The lifting bodies tiles on the fuselage tail will also be exposed to temperatures of between 1,600 to 1,700 degrees C on re-entry. That is why this component is also made of laminated fibre ceramic. MAN Technology is responsible for carrying out this work. This company also developed the tail structure when co-operating with ESA on the experimental vehicle. The flap, which consists of two steering surfaces, is made entirely out of ceramic high temperature components - this includes all fittings and is an absolutely unique technology.

The upper side of the X-38 will be covered with flexible thermal mats similar to those covering the Space Shuttle. The so-called FEI-Mats, (Flexible External Isolation), consist of ceramic, silicon or fibreglass cloths, which surround a fleece or felt. They are sewn together with thread and can be used in various shapes and thickness, which makes them ideal to fit to surfaces.

Dasa had already developed an FEI-650 with heat resistance of up to 650 Degrees C for Hermes and declared fit for up to 100 deployments. For Tetra only a small area of the Space Glider was to be covered with the newly developed low temperature-FEI. However, in the meantime, Dasa has been asked by NASA to cover the entire upper surface of the X-38 with FEIs of various degrees of heat resistance, (up to 1,000 Degrees C).

Originally planned as a national technology program, the activities of the German space industry in the areas of high temperature resistant laminated fibre ceramic and of re-usable thermal protection systems are indispensably connected with the development of the X-38. Jens Peter Kemper claims that "without Hermes, Tetra would not have been possible". The technologies in question were at least partially in place through the research carried out during the Hermes-Project, and they could be continued for Tetra.

There is not much time for new developments. As early as June 1999, NASA is to be supplied with the flight hardware. Before then the hot structures and thermal protection systems have to be certified. In spring 1999 the Industrial Plant Company wants to start operations in a new thermodynamic experimental test cell under the auspices of Tetra. Here temperatures between 1,800 and 2,000 Degrees C can be tested and mechanical loads can be introduced in hot areas.

For Germany's space iIndustry a lot is at stake with the X-38. Through Tetra the industry has taken on the role of NASA's equal partner by developing the experimental Space Glider. It can now demonstrate its know-how. This provides much better conditions for future co-operation on the Crew Rescue Vehicle.

From page 42 of FLUG REVUE 12/98