Editing Hubble Space Telescope (section)

=== Ground support ===
{{Main|Space Telescope Science Institute}}
[[File:Hubble Control Centre.jpg|thumb|upright=1.0|right|Hubble Control Center at Goddard Space Flight Center, 1999]]

The Space Telescope Science Institute (STScI) is responsible for the scientific operation of the telescope and the delivery of data products to astronomers. STScI is operated by the [[Association of Universities for Research in Astronomy]] (AURA) and is physically located 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 consortium. STScI was established in 1981<ref name="Edmondson1997">{{cite book |url=https://books.google.com/books?id=jEurac1jvsAC&pg=PA244 |title=AURA and Its US National Observatories |publisher=Cambridge University Press |first=Frank K. |last=Edmondson |page=244 |date=1997 |isbn=978-0-521-55345-2 |access-date=January 7, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150041/https://books.google.com/books?id=jEurac1jvsAC&pg=PA244 |url-status=live }}</ref><ref>{{cite web |url=http://www.aura-astronomy.org/about.asp |title=About AURA |publisher=AURA |access-date=November 6, 2012 |archive-date=September 29, 2018 |archive-url=https://web.archive.org/web/20180929155829/http://www.aura-astronomy.org/about.asp |url-status=live }}</ref> after something of a power struggle between NASA and the scientific community at large. NASA had wanted to keep this function in-house, but scientists wanted it to be based in an [[academia|academic]] establishment.{{sfn|Dunar|Waring|1999|pp=486–487}}<ref>Roman, Nancy Grace. "Exploring the Universe: Space-Based Astronomy and Astrophysics", in [https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf ''NASA SP-2001-4407: Exploring the Unknown''] {{Webarchive|url=https://web.archive.org/web/20170120024958/https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf |date=January 20, 2017 }} (PDF). NASA. Chapter 3, p. 536.</ref> The [[Space Telescope European Coordinating Facility]] (ST-ECF), established at [[Garching bei München]] near [[Munich]] in 1984, provided similar support for European astronomers until 2011, when these activities were moved to the European Space Astronomy Centre.<ref>{{Cite web |title=Closure of ST-ECF |url=http://www.stecf.org/ECFclosure.php |access-date=April 7, 2022 |website=www.stecf.org}}</ref>

One complex task that falls to STScI is scheduling observations for the telescope.<ref name="Team Hubble">{{cite web |url=https://www.stsci.edu/hst/observing/scheduling |title=Scheduling |publisher=[[Space Telescope Science Institute]] |website=stsci.edu |access-date=April 7, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715144805/https://www.stsci.edu/hst/observing/scheduling |url-status=live }}</ref> Hubble is in a low-Earth orbit to enable servicing missions, which results in most astronomical targets being [[occultation|occulted]] by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes through the [[South Atlantic Anomaly]] due to elevated [[radiation]] levels, and there are also sizable exclusion zones around the Sun (precluding observations of [[Mercury (planet)|Mercury]]), Moon and Earth. The solar avoidance angle is about 50°, to keep sunlight from illuminating any part of the OTA. Earth and Moon avoidance keeps bright light out of the FGSs, and keeps scattered light from entering the instruments. If the FGSs are turned off, 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), within roughly 24° of Hubble's [[orbital pole]]s, in which targets are not [[occultation|occulted]] for long periods.<ref>{{Cite web |date=January 15, 1996 |title=Hubble's Deepest View of the Universe Unveils Bewildering Galaxies across Billions of Years |url=http://hubblesite.org/contents/news-releases/1996/news-1996-01 |access-date=April 7, 2022 |website=HubbleSite.org |publisher=[[Space Telescope Science Institute]] |language=en |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150044/https://hubblesite.org/contents/news-releases/1996/news-1996-01.html |url-status=live }}</ref><ref>{{Cite journal |last1=Adler |first1=David S. |last2=Kinzel |first2=Wayne |last3=Jordan |first3=Ian |date=August 6, 2014 |editor-last=Peck |editor-first=Alison B. |editor2-last=Benn |editor2-first=Chris R. |editor3-last=Seaman |editor3-first=Robert L. |title=Planning and scheduling at STScI: from Hubble to the James Webb Space Telescope |url=http://proceedings.spiedigitallibrary.org/proceeding.aspx?doi=10.1117/12.2054932 |journal=Proc. SPIE 9149, Observatory Operations: Strategies, Processes, and Systems V |series=Observatory Operations: Strategies, Processes, and Systems V |volume=9149 |location=Montréal, Quebec, Canada |pages=91490D |doi=10.1117/12.2054932 |bibcode=2014SPIE.9149E..0DA |s2cid=122694163 |access-date=July 15, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150044/https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9149/1/Planning-and-scheduling-at-STScI--from-Hubble-to-the/10.1117/12.2054932.short?SSO=1 |url-status=live }}</ref><ref>{{Cite web |title=HST Cycle 26 Primer Orbital Constraints – HST User Documentation |url=https://hst-docs.stsci.edu/hsp/past-hst-proposal-opportunities/the-hubble-space-telescope-primer-for-cycle-26/hst-cycle-26-primer-orbital-constraints |access-date=July 16, 2022 |website=hst-docs.stsci.edu |archive-date=July 16, 2022 |archive-url=https://web.archive.org/web/20220716221122/https://hst-docs.stsci.edu/hsp/past-hst-proposal-opportunities/the-hubble-space-telescope-primer-for-cycle-26/hst-cycle-26-primer-orbital-constraints |url-status=live }}</ref>

{{multiple image
| align             = right
| direction         = horizontal
| total_width       = 400
| image1            = Diagram of Hubble's orbit.jpg
| caption1          = Hubble's low orbit means many targets are visible for slightly more than half of an orbit's elapsed time, since they are blocked from view by the [[Earth]] for almost one-half of each orbit.
| image2            = Animation of Hubble Space Telescope trajectory.gif
| caption2          = Animation of Hubble's orbit from October 31, 2018, to December 25, 2018; Earth is not shown.
}}
Due to the [[precession]] of the orbit, the location of the CVZ moves slowly over a period of eight weeks. Because the [[wikt:limb#Etymology 2|limb]] of the Earth is always within about 30° of regions within the CVZ, the brightness of scattered [[earthshine]] may be elevated for long periods during CVZ observations. Hubble orbits in low Earth orbit at an altitude of approximately {{convert|540|km|sp=us}} and an inclination of 28.5°.<ref name="heavens-above" /> The position along its orbit changes 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 {{convert|4000|km|abbr=on}}. Observation schedules are typically finalized 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 to be observed.{{sfn|Strolger|Rose|2017|p=46}} Engineering support for HST is provided by NASA and contractor personnel at the Goddard Space Flight Center in [[Greenbelt, Maryland]], {{convert|48|km|abbr=on}} south of the STScI. Hubble's operation is monitored 24&nbsp;hours per day by four teams of flight controllers who make up Hubble's Flight Operations Team.<ref name="Team Hubble" />