The US Space Shuttle Columbia took off on July 23, 1999, sending the Chandra X-ray Observatory into space. This space telescope will help astronomers search for black holes and dark matter in the universe, thereby gaining a deeper understanding of the origin and evolution of the universe.
The Chandra Space Telescope was originally called the Advanced X-ray Astrophysics Facility (AXAF), but was later named after the Indian-American astrophysicist Chandrasekhar. Chandra Sika immigrated to the United States in the 1930s, won the Nobel Prize in 1983 for his research on the structure and evolution of stars, and died in 1995. “Chandra” is the name given to him by friends and colleagues. Sanskrit means “moon” and “shining”.
The Chandra Telescope is the third in NASA’s “Great Observatory” series of space astronomy observation satellites. The series consists of 4 satellites, among which the Compton Gamma-ray Observatory and the Hubble Space Telescope (HST) were launched in 1990 and 1991 respectively, and the other satellite is called the Space Infrared Telescope Facility (SIRTF), the Spitzer Space Telescope, was successfully launched in 2003.
The Hubble Space Telescope, an optical telescope in orbit, observes visible light, while the “Chandra” in another orbit captures X-rays. The Chandra X-ray Space Telescope is designed to observe X-rays from the hottest regions of the universe. Compared with the photons of visible light, X-rays have more energy and can penetrate the parabolic mirrors used in optical telescopes like bullets. But when it passes over the mirror surface, it changes direction like a bullet. To this end, the Chandra X-ray Space Telescope has 4 mirrors (4 parabolic mirrors, 4 hyperboloid mirrors), which concentrate the X-rays into the high-quality camera like a “funnel”. The manufacturing precision of the mirror has reached an unprecedented height: the distance between the two ends of the optical system is 2.7 meters, and the error is 1.3×10-6 meters (1/5 of a hair strand). The instruments on the Chandra X-ray Space Telescope can take high-resolution photos while measuring the energy of X-rays. In addition, the accuracy of the aiming system is also very high. It can aim at an egg-sized object 1 km away with an error of 3 mm.
The construction cost of the Chandra telescope is as high as US$1.55 billion, and the total cost of the project is as high as US$2.8 billion, plus the space shuttle launch and in-orbit operation costs. It is the most advanced and complex space telescope built by mankind so far, and is known as the “Hubble in the X-ray field.”
Before that, humans had launched smaller X-ray telescopes. Compared with them, Chandra’s sensitivity is 20-50 times higher. In addition to high resolution, it also has the characteristics of strong light collection ability and wide imaging energy range, and can accurately decompose the spectrum into different energy components. The high-energy X-ray data it obtains will make up for the data obtained by Compton and Hubble in other regions of the electromagnetic spectrum, and deepen human understanding of black holes, colliding galaxies and supernova remnants.
The distance of the Chandra telescope from the earth at its furthest point is about one-third of the distance from the earth to the moon. The choice of this large elliptical orbit is to have as much time as possible to keep the telescope out of the earth’s radiation belt, and to avoid some observational restrictions caused by running very close to the earth.
The Chandra telescope is equipped with a high-resolution mirror assembly (HRMA) and an 8-meter-long optical bench. The main instruments used for observation include a charge-coupled device imaging spectrometer for imaging and spectral analysis, a high-resolution camera, and high-energy transmission grating and low-energy transmission grating. The biggest challenge encountered in the development of the telescope is the development of the 10-meter focal length X-ray telescope, especially the manufacturing of the reflector, the development of the non-deformable mounting system and the maintenance of the precise collimation of the mirror, which is extremely difficult.
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