IN THE late 1800s Jules Verne spun long before humans had ever left their planet. Now his namesake is undertaking an autonomous space manoeuvre even the great author couldn鈥檛 have imagined. At stake is Europe鈥檚 future role in international space missions and the fate of technology that could be used to explore Mars and other planets.
The European Space Agency (ESA) launched the on 9 March, with just one small glitch that has now been fixed. But the true test of its mettle comes on 3 April, when it is due to dock with the Zvezda module of the International Space Station (ISS), while travelling at 28,000 kilometres per hour, 400 kilometres above the Earth鈥檚 surface. It鈥檚 a delicate manoeuvre: if the ATV makes an error of just a few centimetres, it could puncture the side of the space station, jeopardising the lives of the astronauts on board.
Of course, docking is a routine procedure for the ISS, which regularly receives food, water, oxygen, nitrogen, equipment and letters for its occupants from Earth. But this particular manoeuvre has one important difference. Unlike the crewed craft that usually dock with the ISS, the 20-tonne Jules Verne will perform the finely coordinated dance by itself, without the guiding hand of a human controller. 鈥淲hen docking using an unmanned mode you need to be pretty confident that the software will do the business,鈥� says Stuart Eves of the company in the UK. 鈥淚t鈥檚 still a challenge for current engineering to do this reliably.鈥�
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If ESA鈥檚 ATV performs successfully, it could be a safer way to supply the ISS than today鈥檚 shuttle missions, as well as being the first step towards autonomous uncrewed spacecraft that could explore Mars and other planets. It might also signal the start of greater European participation in big space programmes. 鈥淭his is by far the most complicated spacecraft ever built in Europe,鈥� says David Berthelier, a computer scientist from based in Stevenage, UK, who helped to build Jules Verne.
Today, crewed spacecraft such as NASA鈥檚 space shuttles and the Russian Soyuz spacecraft carry supplies to the ISS, but this is costly and potentially dangerous for astronauts on board. A completely autonomous system such as Jules Verne would solve these problems.
Such a system might also be safer for the occupants of the ISS. Since the 1980s a fleet of Russian autonomous spacecraft known as the Progress vehicles carried supplies to the former Russian space station Mir. Although these pilot themselves, human ground controllers step in at the last minute to take over the docking procedure via remote control. It was during this procedure in June 1997, that a Progress vehicle crashed into Mir (New Scientist, 5 July 1997, p 14), damaging its solar panels and air supply. It is not known exactly what sparked the problem in the first place, but if the ATV had been totally autonomous, it might not have crashed. Because its control mechanisms can be connected to its sensors and programmed to self-correct, an autonomous vehicle can potentially respond to problems faster than a human, says Berthelier.
So how will Jules Verne accomplish its autonomous tasks? Currently orbiting at 250 km above the Earth, the ATV is a safe 150 km below the orbit of the ISS, where it is performing a series of test manoeuvres that exactly copy the docking process. When the controllers are sure the ATV is up to the job, they will instruct it to move to within 30 km of the ISS, where it will begin its complex docking procedure.
Precision control
Like an automobile satnav, Jules Verne calculates its position using radio signals from GPS satellites and compares this with the GPS coordinates of the ISS. It then calculates its path and feeds this to the vehicle鈥檚 three computers, which will work out which of the craft鈥檚 28 rocket thrusters to fire and for how long. The ATV recalibrates this GPS information every second and reprograms the thrusters accordingly.
When the rocket is just 250 metres behind the station it must ensure that it is correctly aligned with Zvezda鈥檚 docking port. So at this point, Jules Verne will begin to use a laser measurement system, similar to radar. The vehicle will fire short laser pulses at reflective targets distributed around the docking port and cameras will capture the reflected light. The time it takes for this light to be reflected will tell the vehicle how far it is from the ISS. By detecting where the light comes from, the craft can also work out how these targets are distributed relative to one another and calculate its inclination. To double-check, it also captures images of the constellations of stars in the sky. It compares these to star maps, allowing it to work out its orientation relative to the rest of the sky, and, from that, its orientation relative to the ISS.
Finally, when it is just 12 m away from the ISS, Jules Verne will shoot out a 鈥渉arpoon鈥� into a socket on the space station (see Diagram) and reel itself into the station. Eight latches will then lock it to the socket to achieve an airtight connection. The ATV鈥檚 impact with the ISS should be less severe than two cars touching in a car park. 鈥淭he ATV鈥檚 kinetic energy will be a lot less than what most of us have experienced when meeting uncautious drivers in parking lots,鈥� said Franco Bonacina of ESA, based in Paris, France.
As well as handling docking, the software controls the position of the ATV鈥檚 solar panels, how it divides up power between its components and the heating and cooling systems that protect its contents from the extreme conditions of space. While humans on the ground and the ISS will monitor the vehicle, their control can go no further than to stall the vehicle during its flight if it has gone drastically off course or move it into a 鈥減arking鈥� position a safe distance away from the ISS while they decide whether it is capable of carrying out the rest of its mission. Both these manoeuvres involve a pre-programmed set of actions that the humans simply activate.
Once the astronauts on the ISS have emptied Jules Verne of its supplies, which include a first edition of Verne鈥檚 From the Earth to the Moon, the ISS occupants will fill the craft with trash and send it back by activating a pre-programmed procedure.
While it is designed to burn up as it enters Earth鈥檚 atmosphere, ATVs in future could be equipped with a heat shield that will make them reusable. NASA is planning on phasing out its current line of shuttles and ATVs might be a safer alternative. They might even ferry astronauts, who could leave the docking to the ATV.
The ATV鈥檚 autonomous software might also be ideal for exploring other planets or deep space, where it takes longer for communication signals to travel the distances between spacecraft and ground control on Earth. Current equipment, such as the Mars rovers spend long periods unemployed, waiting to receive signals from Earth. 鈥淏ut if this kind of automation was running, you wouldn鈥檛 need to dedicate massive resources on ground control to nursemaid it,鈥� says Adam Baker of Surrey Satellite Technology.
鈥淭he ATV鈥檚 autonomous software might be ideal for exploring other planets or deep space鈥�
Jules Verne鈥檚 biggest impact will likely be political, however. By far ESA鈥檚 most ambitious project, its success may prompt NASA to share responsibilities more evenly between international space agencies. 鈥淚t may well embolden America to withdraw from their majority position,鈥� says Tim Stevenson, the chief engineer at the Space Research Centre of the University of Leicester in the UK.
