B2. Istanbul 2004 
PEGASUS: DESIGN OF A STRATOSPHERIC LONG ENDURANCE UAV SYSTEM FOR 
REMOTE SENSING 
* . 
J. Everaerts , N. Lewyckyj, D. Fransaer 
Vito, Flemish Institute for Technological Research, Boeretang 200, BE-2400 Belgium - (jurgen.everaerts, 
nicolas.lewyckyj, dirk.fransaer)@vito.be 
KEY WORDS: High resolution, Multisensor, Multispectral, LIDAR, SAR, Thermal, Atmosphere 
ABSTRACT: 
The PEGASUS (Policy support for European Governments by Acquisition of information from Satellite and UAV borne Sensors) 
projects aim is to provide an economic way to gather high resolution data (visual, IR and thermal imagery, LIDAR, SAR, 
atmospheric measurements) from a high altitude platform. Because the platform will not be manned, it will be able to operate 
continuously for weeks or months. 
The paper describes the various aspects involved in the design of both platform and instruments. These include optical design, 
weight considerations, power consumption, data transmission, processing and archiving. The design is driven by the requirements of 
many remote sensing applications. 
RÉSUMÉ: 
Le projet PEGASUS (Policy support for European Governments by Acquisition of information from Satellite and UAV borne 
Sensors) a pour but de fournir des images à trés haute résolution spatiale au moyen de capteurs aéroportés (visible, infrarouge, 
thermique, LIDAR, SAR et mesures atmosphériques) placés sur une plateforme opérant à trés haute altitude. De par le caractère 
inhabité de la plateforme, celle-ci pourra acquérir les données requises de façon continue durant des semaines, voir des mois. 
Ce document décrit les différents aspects concernant les concepts tant de la plateforme porteuse que des instruments se trouvant à 
son bord. Sont décrit ci-dessous l’optique nécessaire, les considérations liées au poids et à la puissance électrique des divers 
instruments, les besoins en matière de transmission des données, de leur traitement ainsi que de leur archivage. Toutes ces 
considérations sont fondées sur les besoins réels rencontrés par de nombreuses applications de télédétection. 
1. INTRODUCTION several months. The instruments that will be installed have been 
selected to optimally satisfy the user community requirements 
Remote sensing is traditionally performed by either airborne or (Fransaer et al, 2004). The first flight of the system is 
spaceborne systems, each having distinct advantages and scheduled for the late summer of 2005, when it will perform 
disadvantages. demonstration flights over Flanders (Belgium). 
Spaceborne systems offer a very stable platform and allow The system will deliver data and information that is directly 
global coverage (e.g. SPOT Végétation produces a global usable for GMES (Global Monitoring for Environment and 
coverage every day, at 1km ground pixel size). Although the Security) applications as well as for medium and small scale 
resolution of the satellites has improved significantly mapping applications (map scales 1:2 500 — 1: 20 000). The 
(IKONOS,...), it still is about one order of magnitude worse combination of its sensors gives it an all weather, 24 hour 
than that of airborne systems. Moreover, due to orbital observing capability, which is critical in emergency situations, 
mechanics, the satellite always passes over a certain spot on such as flooding, forest fires, earthquakes, etc., ... 
earth at the same local time. In case of frequent cloud cover, it 
may take a long time before an area is completely imaged. 
2. LONG ENDURANCE STRATOSPHERIC UAV 
Airborne systems offer great flexibility, short response times 
and are able to generate very high resolution data. They are 2.1 Unmanned Aerial Vehicle 
expensive to operate, though, and their operation is usually 
limited by air traffic constraints. Operating in an unstable part Unmanned aerial vehicles are widely used in military 
of the atmosphere, the instruments are subjected to severe applications (Butterworth-Hayes, 2003; Aldrige et al., 2002). 
vibrations, and it is not easy to navigate the aircraft along the They are often used for tasks that are described as "dull, dirty 
planned lines. and dangerous". Some are less than 10 cm tall, others, such as 
the Helios prototype and the Global Hawk, have wingspans up 
As an alternative to these traditional platforms, it is proposed to to 75 m. The Helios prototype, powered by solar cells, holds the 
use an unmanned aerial vehicle (UAV), capable of operating in world altitude record for non-rocket powered aircraft by flying 
the stratosphere (12 — 20 km altitude) and powered by solar to 96,863 ft in August 2001 (Hindle, 2001). 
energy and batteries or fuel cells, so that it can remain aloft for 
  
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Corresponding author 
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