less sensitive than focusing optics and imaging quality and identification of source position is much poorer, however it offers a larger field of view and can be employed at higher energies, where grazing incidence optics become ineffective. Also the imaging is not direct, but the image is rather reconstructed by post-processing of the signal. Detectors Several technologies have been employed on detectors for X-ray telescopes, ranging from counters like Ionization chambers, geiger counters or scintillators to imaging detectors like CCDs or CMOS sensors. The use of micro-calorimeters, that offer the added capability of measuring with great accuracy the energy of the radiation, is planned for future missions. Missions employing X-ray telescopes History of X-ray telescopes The first X-ray telescope employing Wolter Type I grazing-incidence optics was employed in a rocket-borne experiment on October 15, 1963, 1605 UT at White Sands New Mexico using a Ball Brothers Corporation pointing control on an Aerobee 150 rocket to obtain the X-ray images of the Sun in the 8–20 angstrom region. The second flight was in 1965 at the same launch site (R. Giacconi et al., ApJ 142, 1274 (1965)). The Einstein Observatory (1978–1981), also known as HEAO-2, was the first orbiting X-ray observatory with a Wolter Type I telescope (R. Giacconi et al., ApJ 230,540 (1979)). It obtained high-resolution X-ray images in the energy range from 0.1 to 4 keV of stars of all types, supernova remnants, galaxies, and clusters of galaxies. HEAO-1 (1977–1979) and HEAO-3 (1979–1981) were others in that series. Another large project was ROSAT (active from 1990 to 1999), which was a heavy X-ray space observatory with focusing X-ray optics. The Chandra X-Ray Observatory is among the recent satellite observatories launched by NASA, and by the Space Agencies of Europe, Japan, and Russia. Chandra has operated for more than 10 years in a high elliptical orbit, returning thousands 0.5 arc-second images and high-resolution spectra of all kinds of astronomical objects in the energy range from 0.5 to 8.0 keV. Many of the spectacular images from Chandra can be seen on the NASA/Goddard website. NuStar is one of the latest X-ray space telescopes, launched in June 2012. The telescope observes radiation in a high-energy range (3–79 keV), and with high resolution. NuStar is sensitive to the 68 and 78 keV signals from decay of 44Ti in supernovae. Gravity and Extreme Magnetism (GEMS) would have measured X-ray polarization but was canceled in