Electrotelescope Although somewhat primitive , the electrotelescope was an electo - optical device that was used for surveying the surroundings . Electrotelescopes were once used on starships , but were phased out in favor of sensor arrays . Portable versions were still used throughout the galaxy for millennia since they had greater power and resolution than most electrobinoculars . Electroscopes were electro - optical devices used to observe nearby planets , moons , and asteroids . Similar in concept to electro - and macrobinoculars but much more powerful , electroscopes provided a tremendous degree of magnification through the use of optics and computers that electronically enhanced existing light sources and reduced atmospheric haze and other sources of visual distortion . Electroscopes were equipped with sensors that scanned for energy emissions or communication transmissions , making even smaller models capable of detecting small freighters at distances of up to five light minutes , with larger ground or satellite based models having significantly farther range ; as many were used as sensor backups for space stations and deep space observatories . Electroscopes used a two - stage scanning system . The general scanning mode observed a large area , but with limited resolution and detail . When the control computer detected an anomaly or came across energy emissions that might indicate nearby starships , the electroscope ’ s detailed scan mode focused on the specified area to gather as much information as possible . Most models featured controls and standard dataport s and astromech droid interfaces . External comm transceivers could transmit data from a central base or link multiple units for composite imaging with tremendous detail . Smaller units , such as the Neuro - Saav Technologies VXI - 3 electrotelescope used by the Rebels on Hoth , could weigh as little as thirty - five pounds , and their repulsorlift generators allowed them to be moved easily . Larger electroscopes provided much greater resolution , but were so large that they had to be stationed permanently at an observatory , on a planet , or placed aboard an orbiting satellite . Electroscopes often were installed as sensor backups for starports and space stations and were used on deep - space stations and observation stations for inhabited planets . Smaller colonies used these devices to scan for asteroids and comets that might be on collision vectors . Since these devices were passive , only detecting incoming light and energy emissions , they could be used without fear of detection by passing starships . They were perfectly suited to the Rebel Alliance ' s and other outlaws ' many outposts , such as on Tierfon , Thila , and Derra IV . When the Rebel Alliance established Echo Base on Hoth , secrecy was vital to its survival . Active sensors or orbital satellites were out of the question ; instead , the Alliance relied on over a dozen Neuro - Saav VXI - 3 electroscopes positioned at the main base and at remote observations posts to provide an early - detection scanning system . Unfortunately , this network was hampered by the Hoth system ’ s numerous asteroids and comets , and a Viper probe droid managed to land on the planet undetected , alerting the Empire to the Rebel ’ s presence .