The Hubble Space Telescope Reading Answers

HST (The Hubble Space Telescope) or Hubble is a space telescope that was hurled into lower Earth orbit in 1990 and remains in process till date. There were telescopes that were sent to the space before Hubble, but Hubble Space Telescope is the largest and most versatile of all of them. It is well known to be a vital research tool as well as a public relations boon for astronomy. The Hubble telescope is named after 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. Hubble is constructed wit a 2.4-meter mirror, and its four main instruments observe in the ultraviolet, visible, and near infrared regions of the electromagnetic spectrum. Hubble's orbit outside the gravity of Earth's atmosphere permits it to capture extremely high-resolution images with substantially lower background light than ground-based telescopes. It has chronicled some of the utmost thorough visible light images, allowing a deep view into space. Many Hubble observations have led to many scientific discoveries, such as determining the rate of expansion of the universe. NASA was instrumental in building the Hubble Space Telescope.

There was some assistance from ESA (European Space Agency) as well. The Space Telescope Science Institute (STSI) selects Hubble's targets and processes the resulting data, while the spacecraft is controlled by the Goddard Space Flight Centre. Space telescopes were proposed as early as 1923. Hubble was funded

in the 1970s with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the 1986 Challenger disaster. It was lastly launched by Space Shuttle Discovery in 1990, but its main mirror had been ground incorrectly, resulting in spherical aberration that compromised the telescope's capabilities. The optics were corrected to their planned quality by a servicing mission in 1993. Hubble can be upgraded and repaired by astronauts when required. It is one of its kind and no other telescope can be upgraded or repaired. There have been five space shuttle missions that have repaired, upgraded, and replaced systems on the telescope, including all the five major instruments. At the time, the fifth mission was cancelled on safety grounds following the Columbia disaster (2003), but NASA administrator Michael D. Griffin permitted the fifth servicing mission which was completed in 2009. The telescope is operating as of 2020 and could last until 2030-2040. Its descendant is the James Webb Space Telescope (JWST) which is scheduled to be launched in March 2021. 

The scientific operation of the telescope is functioned by the Space Telescope Science Institute (STSI). This agency is also responsible to deliver the data products to the astronomers. STSI is operated by the Association of Universities for Research in Astronomy (AURA) and is in Baltimore, Maryland on the Homewood campus of Johns Hopkins University, one of the 39 U.S. universities and seven international affiliates that make up the AURA association. STSI was established in 1981 after a power struggle between NASA and the scientific community at large. NASA had sought to keep this function in-house, but scientists wanted it to be founded

in an academic establishment. The Space Telescope European Coordinating Facility (ST-ECF), recognized at Garchingbei München near Munich in 1984, provided similar support for European astronomers until 2011, when these activities were moved to the European Space Astronomy Centre. STSI holds a significant task that includes scheduling observations for the telescope. 

Hubble is in a low-Earth orbit to enable servicing missions, but this means most astronomical targets are obstructed by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes over the South Atlantic Anomaly due to raised radiation levels, and there are also sizable exclusion zones around the Sun (precluding observations of Mercury), Moon and Earth. The solar avoidance angle is around 50°, to retain sunlight from illuminating any part of the OTA. Earth and Moon evasion keeps bright light out of the FGSS and keeps dispersed light from entering the instruments. If the FGSs are turned off, then the Moon and Earth can be observed. Earth observations were used very early in the program to generate flat fields for the WFPC1 instrument. There is a so-called continuous viewing zone (CVZ), at roughly 90° to the plane of Hubble's orbit, in which targets are not hidden for long periods. Owing to the precession of the orbit, the position of the CVZ moves lethargically over a period of eight weeks Because the limb of the Earth is always within about 30° of regions inside the CVZ, the brightness of scattered Earthshine may be elevated for long periods during CVZ observations. 

Hubble Space Telescope orbits in the lower Earth orbit. The altitude of its orbit is about 540 Kilometres. The telescope orbits at an inclination of 28.5°. The position along its orbit alters over time in a way that is not accurately predictable. The density of the upper atmosphere varies according to many factors, and this means Hubble's predicted position for six weeks' time could be in error by up to 4.000 km (2.500 mi). Observation schedules are typically finalised only a few days in advance, as a longer lead time would mean there was a chance the target would be unobservable by the time it was due From its original total cost estimate of about US$400 million, the telescope cost about US $4.7 billion by the time of its launch. Hubble's cumulative costs were estimated to be about USS 10 billion in 2010. twenty years after launch.