Ariane 4 Launch Pad
The last of the Ariane 4 expendable launchers completed its final mission on 15 February 2003. This particular type of launch vehicle design lasted for 15 years and successfully completed 113 launches for a range of government and commercial ventures, capturing 50 per cent of the commercial satellite market at one point during its service career. So what was it about the Ariane 4 that made it so popular across the globe?
Ariane4was the culmination of technology from three generations of Ariane launcher before it. It started out as the European Space Agency’s (ESA’s) attempt to compete with already well-established space organizations like NASA. Europe had tried and failed to develop a space launch vehicle for a decade, so in 1973 the newly formed ESA made a concerted effort to build one, led by France. Ariane 1 first flew in 1979 and, by the time Ariane 4 took to the skies, the launcher was capable of transporting a 2,700-kilogram (5,900-pound) satellite into geostationary orbit.
Key to Ariane 4’s success was its versatility. As well as the payload system that could launch two satellites into orbit, there were four variants across the standard model that allowed additional solid/liquid rocket booster attachments.
The basic Ariane 4 model – the AR 40 – had three stages with a total thrust of 590,000 kilograms-force (1.3 million pounds-force). There were four Viking 2B motors in its first stage, one Viking 4B motor in its second stage and an HM7B liquid hydrogen (with liquid oxygen oxidiser) motor in the third. The Ariane4achieved an exemplary 97 per cent success rate over its career, with only three of its 116 launches ending in failure.
Enter the expendables
Taking even a small object into orbit costs a tremendous amount in resources and requires a particularly capable machine, known as expendable launch vehicles (ELVs), so-called because they aren’t recovered for reuse. This might seem wasteful, but there are good reasons why ELVs are sometimes preferable to reusable launch systems. The cost of a shuttle orbiter can run into tens of billions of dollars, plus recovery and maintenance costs it incurs for each successive launch. The most advanced and expensive version of the Ariane 4 (the 44L), meanwhile, costs in the region of GBP 60 million ($100 million) – pocket change for the likes of NASA and major telecommunications companies interested in sending unmanned craft into orbit. A reusable shuttle also requires a much more protective structure and a recovery system, which reduce its payload capacity.
Getting to LEO
Any object that orbits the Earth below an altitude of 2,000 kilometres (1,240 miles) is considered to be in low-Earth orbit (LEO). Below an altitude of 200 kilometres (120 miles) an object experiences rapid orbital decay and will crash into our planet. Below 300 kilometres (186 miles) atmospheric drag makes changes in trajectory (delta-v) prohibitive in energy costs, so the majority of man-made satellites are placed between 300 and 500 kilometres (186 and 310 miles). This includes the International Space Station (ISS), whose orbit ranges from just above the 300-kilometre (186-mile) threshold to an altitude of about 400 kilometres (248 miles). In fact, all human spaceflight apart from those of the Apollo programme took place in LEO. The rare exception to the LEO rule are global positioning system (GPS), geostationary and geosynchronous satellites, which need much higher altitudes upwards of 20,000 kilometres (12,430 miles) to achieve an extremely precise orbit.