Question: Which observatory/satellite was launched into space first, Hakucho or Chandra X-ray Observatory?

Context articles: X-ray Astronomy Recovery Mission
Hubble Space Telescope
Leon Van Speybroeck
Advanced Telescope for High Energy Astrophysics
Chandra Deep Field South
RX J0806.3+1527
STS-37
Martin C. Weisskopf
Chandra X-ray Observatory
Hakucho

The X-ray Astronomy Recovery Mission (XARM, pronounced "charm") is an X-ray astronomy satellite project of the Japan Aerospace Exploration Agency (JAXA) to provide breakthroughs in the study of structure formation of the universe, outflows from galaxy nuclei, and dark matter.
 It is a replacement for the failed X-ray astronomy mission Hitomi.
 As the only international X-ray observatory project of its period, XARM will function as a next generation space telescope in the X-ray astronomy field, similar to how the James Webb Space Telescope, Fermi Space Telescope, and the ALMA Observatory are placed in their respective fields.
 The mission will crosslink X-ray telescopes of the present (Chandra, XMM-Newton) with that of the future (ATHENA, Lynx/X-Ray Surveyor), thus preventing the formation of a blank period in X-ray astronomy in the early 2020s resulting from the loss of Hitomi.
 During its formulation, XARM was also known as the "ASTRO-H Successor", "ASTRO-H2".
The Hubble Space Telescope (HST) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation.
 Although not the first space telescope, Hubble is one of the largest and most versatile, and is well known as both a vital research tool and a public relations boon for astronomy.
 The HST is named after the astronomer Edwin Hubble, and is one of NASA's Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope.
Leon P. Van Speybroeck (1935 – December 25, 2002) served as Telescope Scientist for the Chandra X-Ray Observatory and designed the mirrors that made possible its spectacular X-ray images of nearby and remote celestial objects, including comets, exploding stars, jets of gas spewing from nearby black holes, and powerful quasars more than 10 billion light years from Earth.
 Chandra data prompted new discoveries about the evolution of stars and galaxies, the nature of the black holes, dark matter, and the shape and dimensions of the universe.
The Advanced Telescope for High ENergy Astrophysics (ATHENA) is a future X-ray telescope of the European Space Agency, under development for launch around 2028.
 It is the second (L2) large class mission within ESA Cosmic Vision Program.
 ATHENA will be one hundred times more sensitive than the best of existing X-ray telescopes—Chandra X-ray Observatory, and XMM-Newton.
The Chandra Deep Field South (CDF-S) is an image taken by the Chandra X-ray Observatory satellite.
 The location was chosen because, like the Lockman Hole, it is a relatively clear "window" through the ubiquitous clouds of neutral hydrogen gas in our Milky Way galaxy, which allows us to clearly see the rest of the universe in X-rays.
 The image is centered on RA 3 32 28.0 DEC −27 ° 48′ 30″ (J2000.0), covering 0.11 square degrees, measuring 16 arcminutes across.
 This patch of sky lies in the Fornax constellation.
RX J0806.3+1527 or HM Cancri (sometimes shortened to "HM Cnc" or "J0806" after establishing identity) is an X-ray binary star system about 1600 ly away.
 It comprises two dense white dwarfs orbiting each other once every 321.5 seconds (in this system the "year" duration is of only 5.4 minutes), at an estimated distance of only 80000 km apart (about 1/5 the distance between the Earth and the Moon).
 The two stars orbit each other at speeds in excess of 400 km/s .
 The stars are estimated to be about half as massive as the Sun.
 Like typical white dwarfs, they are extremely dense, being composed of degenerate matter, and so have radii of order the radius of Earth.
 Astronomers believe that the two stars will eventually merge, based on data from many X-ray satellites, such as Chandra X-Ray Observatory, XMM-Newton and the Swift Gamma-Ray Burst Mission.
 These data show that the orbital period of the two stars is steadily decreasing at a rate of 1.2 milliseconds per year as they thus are getting closer by approximately 60 cm per day.
 At this rate, they can be expected to merge in approximately 340,000 years.
 With a revolution period of 5.4 minutes RX J0806 is the shortest orbital period binary system currently known.
STS-37, the eighth flight of the Space Shuttle "Atlantis", was a six-day mission with the primary objective of launching the Compton Gamma Ray Observatory (CGRO), the second of the Great Observatories program which included the visible-spectrum Hubble Space Telescope, the Chandra X-ray Observatory and the infrared Spitzer Space Telescope.
 The mission also featured two spacewalks, the first since 1985.
Dr. Martin C. Weisskopf (born April 21., 1942) is project scientist for NASA's Chandra X-ray Observatory and Chief Scientist for X-ray Astronomy in the Space Sciences Department at NASA's Marshall Space Flight Center in Huntsville, Ala.
The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space observatory launched on STS-93 by NASA on July 23, 1999.
 Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors.
 Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations.
 Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2017 .
Hakucho (also known as CORSA-b before launch) was Japan's first X-ray astronomy satellite, developed by the Institute of Space and Aeronautical Science (then a division of the University of Tokyo).
 It was launched by the ISAS M-3C-4 rocket on February 21, 1979 and reentered the atmosphere on April 16, 1985 .