The trickiest thing about space is getting back from it in one piece. Just ask Giorgio Tumino.
Tumino is the programme manager of the European Space Agency’s IXV (Intermediate Experimental Vehicle) project and has spent the last seven years developing Europe’s first spacecraft designed for re-entry. Although the US and Russia have developed capsules and shuttles that re-enter the atmosphere and are recovered, Europe has, up until now, never solved the problem.
The IXV spaceplane changes that. It is a demonstrator vehicle intended to validate under real conditions, the main atmospheric re-entry technologies – the aerodynamics and aerothermodynamics, the thermal projection and navigation and control systems.
The IXV demonstrator will launch on top of a Vega rocket from French Guiana. After separating from Vega 320 km above Earth, the 5m long, 2 tonne vehicle will climb to a height of around 450 km and then descend for re-entry. After manoeuvring to decelerate from hypersonic to supersonic speeds, IXV deploys a parachute to slow down further before splashdown in the Pacific Ocean, where it will be recovered for detailed analysis. The entire flight lasts about 100 minutes.
IXV in its mobile gantry pre-launch
As well as being Europe’s first steps into re-entry spacecraft, the IXV demonstrator is also the first time a full re-entry for a lifting body shape has been attempted by anyone. The lifting body has no wings, instead it features an aerodynamic shape that creates the lift it requires to fly through the atmosphere. It uses a combination of flaps, thrusters and an autonomous navigation and control system to steer through the atmosphere.
Tumino says: “Usually spacecraft are capsules, which are very simple but have high limitations in manoeuvrability and control. The opposite extreme is winged spacecraft, like the space shuttle. But these are costly and impractical. We are trying to optimise a lifting body without wings. It is the most desirable shape if we can do it.”
Re-entry into the atmosphere is tough. Spacecraft and satellites in orbit travel at speeds of more than 15,000 mph. When they re-enter the atmosphere they hit air molecules and several things happen. The spacecraft experiences extreme forces in the form of gravity, lift and drag. The friction from hitting the air molecules at such high velocities also creates aerothermodynamic effects. One of the principal aims of IXV is to study these effects. The in-flight experimentation is integrated at the vehicle’s system level – it is equipped with more than 300 sensors and a thermal camera that will map the flow of heat across its body as it re-enters Earth’s atmosphere.
“We will learn what is really going on during supersonic flight,” says Tumino. “There are huge uncertainties in aerothermodynamics. We know it very well at slow speeds up to Mach 1. When you go higher than Mach 4, up to Mach 25, the air becomes so hot it creates a plasma which means the nitrogen and oxygen parts of the air break apart to become separate gases. This changes the way the aerodynamic tools work for you and creates uncertainties with things like the flaps. To deal with these uncertainties you have to have larger margins and, for example, design the skin thicker, adding mass.”
The carbon fibre matrix and silicon carbide thermal protection system
One of the key technology areas that governs the re-entry of IXV is its thermal protection system. The spaceplane uses a ceramic matrix composite that is one of the most advanced thermocomposites in the world, carbon fibres imbued in silicon carbide that can provide resistance to heat up to 1700 degrees C. This protects the underside of the vehicle including the nose, leading edges, lower surface of the wing and flaps. The material is also used in the nuts and bolts and the bearing system of the flaps.
The leeward, lateral and base of IXV are covered by an ablative material, cork, to provide heat adsorption and and removal. A white silicon elastomer material is used where there are antennae.
The final area that governs the re-entry is the ground navigation and control system, which activates the flaps and the thrusters automatically. IXV will be the first European spacecraft to control flight this way, relying on improved guidance algorithms and enhanced navigation obtained through the coupling of inertial measurements and GPS.
The IXV during integration at Thales Alenia in Italy
Tumino says: “Europe is extraordinarily good at reaching orbit with Ariane and Vega rockets. We can also operate in orbit. But where we are behind is how to come back from orbit. This is the first real time we have done this. This is an experiment to understand the performance of the lifting body, but we have had to avoid putting too much risk into the mission.”
The data from IXV is “fundamental” to many of ESA’s future missions. First, the flight data will be used in ESA’s “Pride” (Programme for a Reusable In-orbit Demonstrator for Europe) project, which will be able to deploy satellites then re-enter and land on a runway. It will also help shape and mould the technologies required to bring back launcher stages and the retrieval of materials from other planets.
Whatever European spacecraft look like after IXV, Tumino is confident that it will be based on the demonstrator. “Whatever is next will start from the IXV design,” he says. “The ship is the result of extensive aerodynamic testing – thousands of simulations and hundreds of wind tunnel tests. IXV will be the starting point, but if the shape needs to be modified it will be.”
