The aim of the EXPERT project is to validate aero-thermodynamic models, numeric codes and ground test facilities by data, which was collected in a representative flight environment. Hereby a better understanding for the processes of the analysis, the tests and the extrapolation of the results to actual flight conditions shall be achieved and the design process for spacecraft shall be improved.The Institute of Structures and Design of DLR in Stuttgart will build the CMC nose for the EXPERT cap.
EXPERT as CFD simulation (Source: ESA)
Former developments in Europe for Hermes or for X-38 showed that there is a large need of measured data from hypersonic flights or from the re-entry in order to be able to verify the methods of the aero-thermodynamic design of such vehicles.
Data for atmospheric re-entry is therefore collected in Europe since the early 90s with the help of flight experiments.This information is needed during the design process for spacecraft of the most diverse kind. These can be re-usable space planes as well as ballistic return capsules or probes, which fly to other planets. In 1998 the flight of the Atmospheric Re-entry Demonstrator (ARD) was completed with success. Beside this flight other research vehicles (EXPRESS, Mirka) were flown, whereas all these systems were characterized by a very simple shape and the thermal protections system consisted mainly of ablator.
In order to make a good design of future spacecraft more precise data is needed particularly for the following aero-thermodynamic problems:
- Effectiveness and heating of control surfaces
- Interaction between shock and boundary layer
- Transition of boundary layer from laminar to turbulent flow
- High temperature and gas chemistry effects
- Interaction between gas and surface such as catalysis and oxidation
EXPERT was conceived to yield data collected in flight to answer precisely these questions. A substantial consequence of this target is the demand of a non-ablative thermal protection system in order to avoid the contamination of the boundary layer by chemical species or solid particles. For this reason materials were selected for the TPS of the capsule which are in general also candidates for the use on re-usable spacecraft. On the nose these materials are C/C-SiC as fiber-reinforced ceramic and PM1000 as high temperature nickel based alloy.
The EXPERT capsule is designed in a simple geometry and consists of an ellipsoid in the nose region, which attaches to a conic body over a clothoide. Four even surfaces are cut into the conic body with four fixed flaps, which are made of CMC as well (figure 1).
EXPERT will be launched on a Russian Volna rocket from a submarine in the Pacific and accomplish a sub-orbital flight. The speed of the capsule will amount to a maximum of 5 km/s. The capsule mass adds up to approx. 400 kg. During the re-entry the aerodynamic loads will be carried mainly by the ceramic nose. This is as well where the maximum heat loads are expected. The maximum heat flux amounts to 1.4 MW/m ². Thus temperatures in the range of 2050°C are caused within the stagnation point. A further critical factor is the stagnation pressure, which adds up to 1,5 bar. The entire re-entry takes approx. 150 seconds.
The fiber-ceramic nose contains sensors for the collection of environment data during the re-entry into the atmosphere. The surface temperature, the heat flux and the aerodynamic pressure are thereby concerned. Furthermore a window is located in the nose through which a spectrometer collects data on the chemical species present in the boundary layer during the re-entry. The sensor systems are provided as payloads by the company HTG (Hypersonic Technology Goettingen) and the Institute for Space Systems of the University of Stuttgart.