With the Space Shuttle set for imminent retirement, the only operational vehicle capable of re-entering the atmosphere from low-Earth orbit will be Russia's venerable Soyuz capsules.
The Soyuz capsules are not a replacement for the Shuttle as they can accommodate three crew and a small amount of cargo. SpaceX has also tested a capsule designed to supply the International Space Station and bring cargo home. Also being tested is the US Air Force's X-37B unmanned experimental spaceplane.
So a European Space Agency push towards testing its IXV - Intermediate eXperimental Vehicle - in 2013 is a programme with significant implications for space transportation, exploration and robotic servicing of space infrastructure.
At the Paris air show, ESA signed the contract with Thales Alenia Space Italia to build the vehicle. ESA's project manager, Giorgio Tumino, says it is too early to say what will follow the 2013 test flight. His team will begin seriously considering further evolution of the lifting-body spaceplane concept after returning from the summer holidays.
IXV will be launched into a suborbital trajectory on ESA's small Vega rocket and return to Earth as if from a low-orbit mission, to test and qualify new critical re-entry technologies such as advanced ceramic and ablative thermal protection.
The 2-tonne lifting body will attain an altitude of around 450km, allowing it to reach a velocity of 7.5 km/s on entering the atmosphere, which Tumino describes as fully representing a return from a low-Earth orbit mission - for example from the International Space Station.
IXV will collect a large amount of data during its hypersonic and supersonic flight, controlled by thrusters and aerodynamic flaps before a parachute descent to the Pacific Ocean to await recovery and analysis.
Lifting body IXV will test never-before-flown technologies
IXV is the "intermediate" step in a European drive to develop re-entry technology, following the 1998 flight of the less-manoeuvrable Atmospheric Re-entry Demonstrator. What comes after IXV is likely to be a multipurpose vehicle, or series of design evolutions, possibly capable of landing on a runway, to return cargo or crew to Earth, or even to return following a deep-space exploration mission.
Tumino stresses that ESA is developing a small vehicle capable of going to orbit and back to Earth, but is not trying to replace the Space Shuttle, which he calls an "extremely expensive machine". Alluding to budgets, he says: "We're always about millions, not billions." And, he adds: "We always want to be affordable; to have concrete technological achievements."
IXV, then, is the start of what Tumino calls a "bottom-up approach" to development, so any subsequent European re-entry vehicle programme may take IXV as a starting point for further evolution, or it may take advantage of technologies validated by the IXV project.
Overall, IXV has two main objectives. IXV is a demonstrator for systems integration in a lifting-body vehicle, and it is also a test-bed for modern re-entry technologies that have never flown before, dealing with aerothermodynamics, guidance navigation and control, and thermal protection, says Tumino.
In aerothermodynamics, ESA hopes to fill gaps in current knowledge, which force designers of re-entry vehicles to build in large margins for safety. For example, when re-entering from low-Earth orbit the oxygen and nitrogen molecules in the air break apart to dissipate the high energies involved. When this happens, the ideal-gas laws normally used for simulations are replaced by complex, real-gas laws that are governed by phenomena that are difficult to predict.
Guidance navigation and control in the hypersonic phase of re-entry is also not well understood, so there is scope to improve guidance algorithms and the coupling of inertial measurement units with GPS for the control of flaps and thrusters.
IXV will also test the performance of thermal protection materials and design solutions such as thermal expansion junctions.