structural:summarization, stylistic:style_transfer, structural:expansion
An X-ray telescope (XRT) is a telescope that is designed to observe remote objects in the X-ray spectrum. X-rays are absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. The basic elements of the telescope are the optics, that collects the radiation entering the telescope, and the detector, on which the radiation is collected and measured. A variety of different designs and technologies have been used for these elements. Many X-ray telescopes on satellites are compounded of multiple small detector-telescope systems whose capabilities add up or complement each other, and additional fixed or removable elements that add functionalities to the instrument.