EXPO-SEDE_ET_2007_381405_EN.pdf — page 7

However, development and acquisition of high-end Medium-Altitude Long Endurance (MALE) 
and High-Altitude Long Endurance (HALE) systems demands major investments. For Fiscal 
Year 2007 the US Air Force requested US$287m for the acquisition of 26 RQ-1 Predator UAVs 
and US$504m for six Global Hawk UAVs. In Fiscal Years 2004, 2005 and 2006 the US spent a 
total of US$2.66bn on 295 UAVs of different types6.  
 
2.2 UAV/UCAV Types 
 
UAVs are often categorized based on performance (linked often to size). There are several 
categorizations from producers, users and researchers. (These are listed in Appendix I.) UAVs 
can be classified according to the way their flight is controlled, of which there are three 
methods: pre-programmed; remote control; self-thinking (which can be combined). Each means 
of control provides both challenges and opportunities.  
 
• The most basic control is by pre-programmed flight. This is simple, does not need 
technically difficult and disturbance-sensitive data-links for control, and gives ranges 
beyond the line-of-sight. However, the system is inflexible. Once airborne the UAV 
follows a fixed path. It cannot ‘take a second look’ at something that seems interesting. If 
the UAV needs to fly as low as possible, it is also dependent on good information of the 
terrain. 
 
• Remote-control is the most common control system for UAVs. By radio, the operator 
receives flight data from the UAV and sends flight commands back. The weak points of 
this system lie in the vulnerability of the continuous radio links, which reveal the 
positions of both the controller and the UAV, and the fact that radio links limit the 
UAV’s range. More advanced, less vulnerable radio links and indirect radio links (e.g. 
via satellites or relay UAVs) are a partial solution. 
 
• Self-thinking UAVs are still a futuristic option. The technical challenges to develop a 
fully autonomous UAV are still insurmountable. Nevertheless, an element of self-
thinking has been achieved in as much as UAVs are able to react to threats, for example, 
when attacked by an air-defence missile. 
 
UAVs and UCAVs are themselves just ‘aircraft’ with onboard systems. However, they are 
usually linked to additional equipment outside, such as the remote-control and launching 
equipment. In addition, UAVs often have an interchangeable ‘mission package’, which includes 
the sensors and, if necessary, the link for transferring data collected by the sensors. Together, 
this equipment forms the UAV system7, the main components of which are listed in Appendix 
II. 
 
2.3 UCAV 
 
A UCAV is a sub-category of UAVs. It is basically nothing more than an armed UAV. The 
border between UAV and UCAV is a thin and grey one. Generally, all UAVs have an inherent 
combat capacity – one just has to replace a non-deadly payload with a deadly one. The US 
Predator was modified from a reconnaissance UAV to a UCAV by simply adding Hellfire 
                                                 
6 The Military Balance 2006, IISS, p. 20-22 and p. 26 (Routledge, UK, May 2006). 
7 The US uses the term UAS – Unmanned Air System – for the complete package, reserving UAV for the airborne 
component, the ‘aircraft’, itself. 
 
 
 
3