TRIAL BY FIRE
The story behind ESA’s new spacecraft.
Watch a handful of the many sci-fi films set among the stars and you’ll soon notice that there is an incredible diversity of spacecraft exploring our Galaxy and beyond. But if you wanted to travel into space and re-enter Earth’s atmosphere safely right now, you’ve only got a few design options. In fact, says the European Space Agency’s Giorgio Tumino, you can categorise them all into three distinct classes.
First are the capsules. These have been the mainstay of numerous space missions for decades, from the early US Mercury programme right up to the present-day Russian Soyuz craft used to take astronauts and cosmonauts to and from the International Space Station. While their design is relatively simple, capsules are not particularly manoeuvrable. “When you re-enter with a capsule you have to start from the right place if you want to end up in the place you intend,” says Tumino.
At the opposite end of the spectrum is the design Tumino calls the ‘winged body’. These include the now retired Space Shuttle and the US military’s enigmatic X-37B space plane. “Here you have very complex systems but you get a highly manoeuvrable and controllable craft, so you can really tackle precision landing because you have wings and rudders and so on,” he says.
The downside is that this design brings with it high costs and high risk. “You need the wings for the last five minutes of the flight to bring you down to a runway,” he explains. “But you have to bring all this hardware, all this complexity, all these structures that can fail during the flight with you, just for these last five minutes.”
The third spacecraft design is different. It’s what’s known as a ‘lifting body’. “A lifting body means
“The IXV marries the best of both capsules and winged craft while steering clear of their drawbacks”
“The IXV will have a suborbital trajectory – a long distance ‘lob’ across the globe”
that the shape of the spacecraft on its own has the capability to provide lift, and fly like a plane,” says Tumino.
For the last decade or so, Tumino and his colleagues across Europe have been designing and developing a new lifting body test spacecraft called the Intermediate eXperimental Vehicle (IXV). The IXV’s design marries the best elements of both capsules and winged craft while steering clear of their drawbacks, explains Tumino, who is the programme manager for the project. “It means that we have the capability to manoeuvre and control our system in such a way that we get to a precision landing point without the need for wings.”
Start at the bottom
Years of work by the ESA team have produced an unusually shaped spacecraft – somewhat reminiscent of a 5m black and white rockclimbing shoe – that today is being made ready for its maiden test flight into space. Rather than having one specific celestial destination in mind for the IXV, ESA’s plan is to first use it to test the advanced technology and components needed to make a safe re-entry into Earth’s atmosphere. It’s a bottom-up approach to space exploration.
“ESA’s idea was to create, consolidate and grow the technological foundations of these atmospheric re-entry capabilities to build on them,” Tumino explains. One of the crucial pieces of technology being tested on this first flight is the IXV’s thermal protection system. This comprises the heat shield as well as the special protective coatings on the rest of the craft, all of which are needed if it is to survive the heat of re-entry. “We have the most advanced thermal protection systems ever built in Europe,” he adds.
The heat shield itself is made up of a number of large, black panels made of a material known as a ceramic matrix composite. “These have carbon fibres embedded into ceramic/silicon carbide matrixes. So they have the strength of the carbon fibre and the resistance to the heat of the silicon carbide,” says Tumino. “It’s a very high performing material.”
On the surface the heat shield looks very similar to that found on the US Space Shuttle. However there’s an important difference: “On the Shuttle you had small tiles that sometimes flew off. These pieces are really bolted on panels.” In addition to the main heat shield, the rest of the IXV is protected by a white ‘ablative’
coating. Together these two materials should protect the sensitive electronics and instruments inside the spacecraft from outside re-entry temperatures of around 1,700ºC.
Sending the IXV into space and getting it to re-enter our atmosphere is the only way to fully examine if it can withstand this environment.
“In-flight testing is something very important for re-entry because on the ground you’re not able to reproduce the actual flight conditions,” he says. “You can do a lot of work on the ground to develop the technology, the manufacturing processes, the way the material resists the heat and so on. But at the end you never get the combination of all the elements that you will face during flight, like the right temperature at the right pressure at the right moment of the flight.”
The IXV’s test flight will begin at the spaceport in Kourou, French Guiana. Here the spacecraft will be mounted on top of one of ESA’s Vega rockets, which will launch it out over the Atlantic Ocean and into space.
Sub-orbital manoeuvres
Unlike most of the satellites and spacecraft that launch from Kourou, the IXV won’t be going into orbit. “To have fully representative conditions of a return from orbit you don’t need to go to orbit,” explains Tumino. “You just need to hit the atmosphere at a height of 120km under the same conditions as if you had come down from orbit – the speed, the flight path angle and so on.”
To meet these requirements the IXV only has to follow a suborbital trajectory – essentially a long distance ‘lob’ across the globe (briefly going into space) rather than completing a full circuit of the planet. The entire flight is expected to last around 100 minutes. Throughout, teams on the ground will be gathering and scrutinising test data sent back by a multitude of sensors on the craft.
“We have more than 300 sensors, including infrared cameras, pressure gauges, strain gauges, pressure ports and displacement sensors,” says Tumino. All this onboard instrumentation hints at why the IXV won’t be deploying anything – like a satellite – during this first trip into space: as Tumino notes, it is the subject of the experiments.
“As it is experimental hardware, the vehicle itself is the payload,” he says. “We do not have a payload bay in the sense that we do not have one single payload. In fact the whole mission is integrating hundreds of payloads – the sensors.”
The Vega rocket will take the IXV up to an altitude of 320-330km. At that point the two will part ways and the IXV will continue on up to a height of 420km. While in space, the IXV will be able to make small pointing manoeuvres using a set of built-in rocket thrusters – the same as those used by ESA’s Ariane 5 rocket. Its sub-orbital trajectory will take it east towards the Pacific Ocean, but there will be no one on Earth piloting it during the flight.
“It’s completely autonomous, but we will be following it from the ground using the flight data it will be sending us,” says Tumino.
The moment of truth for the IXV will be the re-entry. Here it will not only have to withstand scorching temperatures, but also navigate along a very specific route, known as a ‘re-entry corridor’. It’ll be up to the onboard computers to get the IXV through.
“Basically it has a preprogrammed landing spot in its brain,” explains Tumino. As it interacts with the atmosphere during re-entry the IXV’s instruments will constantly monitor its position to keep it on course. Any steering adjustments needed during this period will be made by the onboard thrusters and two aerodynamic ‘flaps’ mounted at the tail end of the vehicle. “If they move together they adapt the pitch angle,” says Tumino. “If they move in a differential way then they will create yaw and roll so the vehicle can steer. It has to steer. It won’t come down in a straight line because it is necessary to steer and to have banking manoeuvres to be able to survive re-entry.”
Once safely through the atmosphere the IXV will open a parachute before splashing down in the Pacific (see ‘Anatomy of a flight test’, page 64). During the last part of the flight, a special recovery ship will be on hand to track its descent and eventually pluck the IXV out of the water.
Although the project doesn’t have a Kennedyesque goal to aim for, there is no shortage of future uses for the technology it’s testing. “Without being able to re-enter the atmosphere it is hard, if not impossible, to plan sample-return missions,” says Tumino. “If you need to bring back samples from other planets, asteroids or comets, you need to return in one piece.
“It’s the same for human spaceflight – if one day Europe ever has the ambition to have European systems to bring astronauts back, this is a necessary step.”
It’s even hoped that future tests may include landings on the ground or a runway. Perhaps, then, it’s the IXV, not the silver screen, which presents a truer vision of the future of spacecraft design.