Originally Landsat’s primary sensor, the Return Beam Vidicon (RBV) flew on the first three Landsats. A vidicon is a television camera tube that formed an image by focusing light onto a photoconductive faceplate. The RBV on Landsat 1 failed just 2 weeks after launch. The RBV on Landsat 3 had higher resolution that could be used for detailed ground mapping and glacier studies. Only RBV imagery from Landsat 3 is available to download.