Getting to space is difficult, and coming back is just as hard. ESA will test the science and technology of reentry by sending the new Expert experimental vehicle on a fast and fiery return trip to space next year.
The Expert (European Experimental Reentry Testbed) spacecraft is being built in Italy by Thales Alenia Space and is revealed in detail on the new Expert web site.
The information from Expert’s flight will test the computer models of the harsh heating and aerodynamic conditions encountered by space vehicles during their passage through Earth’s atmosphere.
This is not the first time that ESA has studied the challenging art of reentry. In October 1998 the Atmospheric Reentry Demonstrator (ARD) was launched by an Ariane 5 rocket on a suborbital arc reaching up to an altitude of 830 km. It splashed safely into the Pacific Ocean after a 101-minute flight and was recovered for detailed technical analysis.
Blunt nose and four flaps
ARD had a ‘classical’ Apollo-type capsule shape, but Expert will use a novel elongated conical pyramid. Its very small angle of attack means it will hit the atmosphere very much like a bullet: nose ahead, straight and fast – at about 5 km/s.
The blunt nose will create a detached shockwave that will carry off much of the heat generated by the friction with the air.
The nose is made of heat-resistant ceramic material attached by a complex mechanism to the metallic conical body. The junction allows for differential expansion of the ceramic and metallic parts while maintaining a smooth surface and minimising disturbances to the airflow.
Four flat sides with four fixed flaps and rear thermal blankets complete the shape. Flaps will control the flight in the atmosphere and reduce the speed before the parachute is released.
The flight conditions will be recorded by temperature, heat-flux and pressure sensors, spectrometers and an infrared camera. The reentry trajectory will be tracked for Expert to be recovered for detailed analysis in Europe.
Looking to a full-sized return vehicle
The refrigerator-sized Expert, weighing about 430 kg, will be launched on a Russian submarine-based Volna rocket on a suborbital path, hitting the upper layers of the atmosphere on the way back down at an altitude of about 100 km.
The 5 km/s is not quite as fast as a spacecraft returning from orbit, but it is enough for a realistic test and for comparing the measurements with simulations and wind tunnel tests.
Fresh and detailed experimental data will allow designers to refine the aerodynamic and aerothermodynamic models for the future. For example, a full-sized European spacecraft could bring back scientific samples from the International Space Station – and possibly, one day, astronauts home from space.
Expert project is conducted under the responsibility of ESA’s Directorate of Human Spaceflight by an integrated team including specialists from the Directorate of Technical and Quality Management.