Editing Voyager program (section)

==History==
{{Further|Grand Tour program}}

=== Mariner Jupiter-Saturn ===
{{also|Grand Tour program#Mariner Jupiter-Saturn}}
[[File:Voyager Path.svg|right|thumb|The trajectories that enabled the Voyager spacecraft to visit the outer planets and achieve velocity to escape the Solar System]]
[[File:Voyager 2 velocity vs distance from sun.svg|thumb|Plot of ''Voyager 2''{{'}}s heliocentric velocity against its distance from the Sun, illustrating the use of gravity assist to accelerate the spacecraft by Jupiter, Saturn and Uranus. To observe [[Triton (moon)|Triton]], ''Voyager 2'' passed over Neptune's north pole, resulting in an acceleration out of the plane of the ecliptic and reduced its velocity away from the Sun.<ref>{{cite web |author=Dave Doody |url=http://www2.jpl.nasa.gov/basics/bsf4-1.php |title=Basics of Space Flight Section I. The Environment of Space |publisher=.jpl.nasa.gov |date=15 September 2004 |access-date=29 December 2017 |archive-date=17 August 2015 |archive-url=https://web.archive.org/web/20150817051745/http://www2.jpl.nasa.gov/basics/bsf4-1.php |url-status=live }}</ref>]]

{{Blockquote
|text=Voyager did things no one predicted, found scenes no one expected, and promises to outlive its inventors. Like a great painting or an abiding institution, it has acquired an existence of its own, a destiny beyond the grasp of its handlers.
|author=[[Stephen J. Pyne]]<ref name="The Fantastic Voyage of Voyager"/>
}}
The two Voyager space probes were originally conceived as part of the [[Planetary Grand Tour]] planned during the late 1960s and early 70s that aimed to explore  [[Jupiter]], [[Saturn]], Saturn's moon [[Titan (moon)|Titan]], [[Uranus]], [[Neptune]], and [[Pluto]]. The mission originated from the [[Grand Tour program]], conceptualized by [[Gary Flandro]], an [[aerospace engineer]] at the Jet Propulsion Laboratory, in 1964, which leveraged a rare [[Syzygy (astronomy)|planetary alignment]] occurring once every 175 years.<ref>{{cite journal |last=Flandro |first=Gary |title=Fast Reconnaissance Missions to the Outer Solar System Using Energy Derived from the Gravitational Field of Jupiter |journal=Astronautica Acta |volume=12 |pages=329–337 |date=1966 |url=http://www.gravityassist.com/IAF3-2/Ref.%203-143.pdf |access-date=1 June 2024 |archive-date=30 March 2019 |archive-url=https://web.archive.org/web/20190330015134/http://www.gravityassist.com/IAF3-2/Ref.%203-143.pdf |url-status=live }}</ref><ref>{{cite web|url=http://voyager.jpl.nasa.gov/science/planetary.html|archive-url=https://web.archive.org/web/20131127192310/http://voyager.jpl.nasa.gov/science/planetary.html|archive-date=27 November 2013|url-status=dead|title=Planetary Voyage|date=30 October 2013|publisher=USA.gov|access-date=15 October 2013}}</ref> This alignment allowed a craft to reach all [[outer planets]] using [[gravitational assist]]s. The mission was to send several pairs of probes and gained momentum in 1966 when it was endorsed by [[NASA]]'s [[Jet Propulsion Laboratory]]. However, in December 1971, the Grand Tour mission was canceled when funding was redirected to the [[Space Shuttle program]].<ref name="GTN">{{cite book
 |last          = Butrica
 |first         = Andrew J.
 |title         = From Engineering Science to Big Science: The NACA and NASA Collier Trophy Research Project Winners
 |chapter       = Voyager: The Grand Tour of Big Science
 |editor1-last  = Mack
 |editor1-first = Pamela E.
 |url           = https://history.nasa.gov/SP-4219/Chapter11.html
 |access-date   = August 25, 2014
 |location      = Washington, D.C.
 |publisher     = NASA
 |date          = 1998
 |archive-url   = https://web.archive.org/web/20140823084758/http://history.nasa.gov/SP-4219/Chapter11.html
 |archive-date  = August 23, 2014
 |url-status    = live
 |isbn          = 978-1-4102-2531-3
}}</ref>

In 1972, a scaled-down (four planets, two identical spacecraft) mission was proposed, utilizing a spacecraft derived from the [[Mariner program|Mariner]] series, initially intended to be [[Mariner 11]] and [[Mariner 12]]. The [[gravity-assist]] technique, successfully demonstrated by [[Mariner 10]], would be used to achieve significant velocity changes by maneuvering through an intermediate planet's [[gravitational field]] to minimize time towards Saturn.<ref name="HMSmurmeier1974">{{cite web |last1=Smurmeier |first1=H. M. |title=The Mariner Jupiter/Saturn 1977 Mission" (1974) |url=https://commons.erau.edu/cgi/viewcontent.cgi?article=2830&context=space-congress-proceedings |website=[[Embry–Riddle Aeronautical University]] |access-date=May 16, 2024 |date=April 1, 1974 |archive-date=20 April 2023 |archive-url=https://web.archive.org/web/20230420101913/https://commons.erau.edu/cgi/viewcontent.cgi?article=2830&context=space-congress-proceedings |url-status=live }}</ref> The spacecrafts were then moved into a separate program named '''Mariner Jupiter-Saturn''' (also '''Mariner Jupiter-Saturn-Uranus''',<ref>{{cite web |title=The Voyagers: An unprecedented on-going mission of exploration |url=https://www.nasaspaceflight.com/2011/08/voyagers-unprecedented-on-going-mission-exploration/ |website=[[NASASpaceFlight.com]] |publisher=Jeff Goldader, Chris Gebhardt |access-date=May 17, 2024 |date=August 7, 2011 |archive-date=17 May 2024 |archive-url=https://web.archive.org/web/20240517013934/https://www.nasaspaceflight.com/2011/08/voyagers-unprecedented-on-going-mission-exploration/ |url-status=live }}</ref> '''MJS''', or '''MJSU'''), part of the [[Mariner program]], later renamed because it was thought that the design of the two space probes had progressed sufficiently beyond that of the Mariner family to merit a separate name.<ref>[https://history.nasa.gov/SP-4219/Chapter11.html '' Chapter 11 "Voyager: The Grand Tour of Big Science"''] {{Webarchive|url=https://web.archive.org/web/20200229064831/https://history.nasa.gov/SP-4219/Chapter11.html |date=29 February 2020 }} (sec. 268.), by Andrew,J. Butrica, found in ''From Engineering Science To Big Science'' {{ISBN|978-0-16-049640-0}} edited by Pamela E. Mack, NASA, 1998</ref>

=== Voyager probes ===
[[File:Voyager Probe.stl|thumb|left|304x304px|Interactive 3D model of the Voyager spacecraft .]]

On March 4, 1977, [[NASA]] announced a competition to rename the mission, believing the existing name was not appropriate as the mission had differed significantly from previous [[Mariner program|Mariner]] missions. ''Voyager'' was chosen as the new name, referencing an earlier suggestion by [[Bill Pickering (rocket scientist)|William Pickering]], who had proposed the name ''Navigator''. Due to the name change occurring close to launch, the probes were still occasionally referred to as Mariner 11 and Mariner 12, or even Voyager 11 and Voyager 12.<ref name="GTN" /><!-- cf page 269 of source -->

Two mission trajectories were established: JST aimed at Jupiter, Saturn, and enhancing a [[Titan (moon)|Titan]] flyby, while JSX served as a contingency plan. JST focused on a Titan flyby, while JSX provided a flexible mission plan. If JST succeeded, JSX could proceed with the Grand Tour, but in case of failure, JSX could be redirected for a separate Titan flyby, forfeiting the Grand Tour opportunity.<ref name="HMSmurmeier1974" /> The second probe, now [[Voyager 2]], followed the JSX trajectory, granting it the option to continue on to Uranus and Neptune. Upon [[Voyager 1]] completing its main objectives at Saturn, Voyager 2 received a mission extension, enabling it to proceed to Uranus and Neptune. This allowed Voyager 2 to diverge from the originally planned JST trajectory.<ref name="GTN" />

The probes would be launched in August or September 1977, with their main objective being to compare the characteristics of Jupiter and Saturn, such as their [[atmospheres]], [[magnetic field]]s, particle environments, [[ring system]]s, and [[moons]]. They would fly by planets and moons in either a JST or JSX trajectory. After completing their flybys, the probes would communicate with Earth, relaying vital data using their [[magnetometer]]s, [[spectrometer]]s, and other instruments to detect [[Interstellar medium|interstellar]], [[solar radiation|solar]], and [[cosmic radiation]]. Their radioisotope thermoelectric generators (RTGs) would limit the maximum communication time with the probes to roughly a [[decade]]. Following their primary missions, the probes would continue to drift into interstellar space.<ref name="HMSmurmeier1974" />

''[[Voyager 2]]'' was the first to be launched. Its trajectory was designed to allow flybys of Jupiter, Saturn, Uranus, and Neptune. ''Voyager 1'' was launched after ''Voyager 2'', but along a shorter and faster trajectory that was designed to provide an optimal flyby of Saturn's moon [[Titan (moon)|Titan]],<ref name="Swift1997">{{cite book|author=David W. Swift|title=Voyager Tales: Personal Views of the Grand Tour|url=https://books.google.com/books?id=E-NGFqfq1LsC&pg=PA69|date=1 January 1997|publisher=AIAA|isbn=978-1-56347-252-7|page=69}}</ref> which was known to be quite large and to possess a dense atmosphere. This encounter sent ''Voyager 1'' out of the plane of the ecliptic, ending its planetary science mission.<ref>{{cite web|title=Voyager FAQ|url=http://voyager.jpl.nasa.gov/faq.html|website=Jet Propulsion Laboratory|access-date=1 January 2015|url-status=dead|archive-url=https://web.archive.org/web/20110721050617/http://voyager.jpl.nasa.gov/faq.html|archive-date=21 July 2011}}</ref> Had ''Voyager 1'' been unable to perform the Titan flyby, the trajectory of ''Voyager 2'' could have been altered to explore Titan, forgoing any visit to Uranus and Neptune.<ref name="Bell2015">{{cite book|author=Jim Bell|title=The Interstellar Age: Inside the Forty-Year Voyager Mission|url=https://books.google.com/books?id=KXPoAwAAQBAJ&pg=PT94|date=24 February 2015|publisher=Penguin Publishing Group|isbn=978-0-698-18615-6|page=94|access-date=9 February 2016|archive-date=24 July 2024|archive-url=https://web.archive.org/web/20240724092318/https://books.google.com/books?id=KXPoAwAAQBAJ&pg=PT94#v=onepage&q&f=false|url-status=live}}</ref> ''Voyager 1'' was not launched on a trajectory that would have allowed it to continue to Uranus and Neptune, but could have continued from Saturn to Pluto without exploring Titan.<ref name="Stern">{{cite web <!-- |  alternate url=http://www.spacedaily.com/reports/What_If_Voyager_Had_Explored_Pluto_999.html --> |url=http://pluto.jhuapl.edu/News-Center/PI-Perspectives.php?page=piPerspective_06_23_2014  | title=The PI's Perspective: What If Voyager Had Explored Pluto? | access-date=29 August 2020 |date=23 June 2014 |author=[[Alan Stern]] |website=New Horizons: NASA's Mission to Pluto and the Kuiper Belt }}</ref>

During the 1990s, ''Voyager 1'' overtook the slower deep-space probes [[Pioneer 10]] and [[Pioneer 11]] to become the most distant human-made object from Earth, a record that it will keep for the foreseeable future. The ''[[New Horizons]]'' probe, which had a higher launch velocity than ''Voyager 1'', is travelling more slowly due to the extra speed ''Voyager 1'' gained from its flybys of Jupiter and Saturn. ''Voyager 1'' and Pioneer 10 are the most widely separated human-made objects anywhere since they are travelling in roughly opposite directions from the [[Solar System]].

In December 2004, ''Voyager 1'' crossed the [[termination shock]], where the solar wind is slowed to subsonic speed, and entered the [[heliosheath]], where the solar wind is compressed and made turbulent due to interactions with the [[interstellar medium]]. On 10 December 2007, ''Voyager 2'' also reached the termination shock, about {{convert|1|e9mi|e9km|abbr=off|order=flip}} closer to the Sun than from where ''Voyager 1'' first crossed it, indicating that the Solar System is [[Asymmetry|asymmetrical]].<ref>{{Cite web|url=https://www.nasa.gov/mission_pages/voyager/voyager-20071210.html|title=NASA - Voyager 2 Proves Solar System Is Squashed|website=www.nasa.gov|access-date=6 February 2020|archive-date=13 April 2020|archive-url=https://web.archive.org/web/20200413080741/https://www.nasa.gov/mission_pages/voyager/voyager-20071210.html|url-status=dead}}</ref>

In 2010 ''Voyager 1'' reported that the outward velocity of the solar wind had dropped to zero, and scientists predicted it was nearing [[interstellar space]].<ref>{{cite news
 |author = Brown, Dwayne
 |author2 = Cook, Jia-Rui
 |author3 = Buckley, M.
 |title = Nearing Interstellar Space, NASA Probe Sees Solar Wind Decline
 |publisher = Applied Physics Lab, Johns Hopkins University
 |date = 14 December 2010
 |url = http://www.jhuapl.edu/newscenter/pressreleases/2010/101214.asp
 |archive-url = https://web.archive.org/web/20101215061146/http://www.jhuapl.edu/newscenter/pressreleases/2010/101214.asp
 |archive-date = 15 December 2010
 |url-status = dead
 |df = dmy-all
}}</ref> In 2011, data from the Voyagers determined that the heliosheath is not smooth, but filled with giant [[magnetic]] bubbles, theorized to form when the [[magnetic field]] of the Sun becomes warped at the edge of the Solar System.<ref>{{cite news | url=http://www.huffingtonpost.com/2011/06/10/nasa-voyager-bubbles-solar-system-heliosphere_n_874733.html?icid=maing-grid7%7Cmain5%7Cdl1%7Csec3_lnk3%7C69958 | work=Huffington Post | first=Catharine | last=Smith | title=WATCH: NASA Discovers 'Bubbles' At Solar System's Edge | date=10 June 2011 | access-date=11 June 2011 | archive-date=13 April 2020 | archive-url=https://web.archive.org/web/20200413080729/https://www.huffpost.com/entry/nasa-voyager-bubbles-solar-system-heliosphere_n_874733?icid=maing-grid7%7Cmain5%7Cdl1%7Csec3_lnk3%7C69958 | url-status=live }}</ref>

In June 2012, Scientists at NASA reported that ''[[Voyager 1]]'' was very close to entering interstellar space, indicated by a sharp rise in [[cosmic ray|high-energy particles]] from outside the Solar System.<ref name="BBC-20120615">{{cite news |last=Amos |first=Jonathan |title=Particles point way for Nasa's Voyager |url=https://www.bbc.co.uk/news/science-environment-18458478 |date=15 June 2012 |work=BBC News |access-date=15 June 2012 |archive-date=15 June 2012 |archive-url=https://web.archive.org/web/20120615183422/http://www.bbc.co.uk/news/science-environment-18458478 |url-status=live }}</ref><ref name="Ferris-201205">{{cite magazine |last=Ferris |first=Timothy |title=Timothy Ferris on Voyagers' Never-Ending Journey |url=http://www.smithsonianmag.com/science-nature/Timothy-Ferris-on-Voyagers-Never-Ending-Journey.html |date=May 2012 |magazine=[[Smithsonian (magazine)|Smithsonian Magazine]] |access-date=15 June 2012 |archive-date=4 November 2013 |archive-url=https://web.archive.org/web/20131104221550/http://www.smithsonianmag.com/science-nature/Timothy-Ferris-on-Voyagers-Never-Ending-Journey.html |url-status=dead }}</ref> In September 2013, NASA announced that ''Voyager 1'' had crossed the [[Heliopause (astronomy)|heliopause]] on 25 August 2012, making it the first spacecraft to enter interstellar space.<ref name="NASA-20130912">{{cite web |last1=Cook |first1=Jia-Rui C. |last2=Agle |first2=D. C. |last3=Brown |first3=Dwayne |title=NASA Spacecraft Embarks on Historic Journey into Interstellar Space |url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html |work=[[NASA]] |date=12 September 2013 |access-date=12 September 2013 |archive-date=11 June 2020 |archive-url=https://web.archive.org/web/20200611233345/https://www.nasa.gov/mission_pages/voyager/voyager20130912.html |url-status=dead }}</ref><ref name="agu">{{cite web|title=Voyager 1 has entered a new region of space, sudden changes in cosmic rays indicate|url=http://www.agu.org/news/press/pr_archives/2013/2013-11.shtml|access-date=20 March 2013|archive-url=https://web.archive.org/web/20130322025117/http://www.agu.org/news/press/pr_archives/2013/2013-11.shtml|archive-date=22 March 2013|url-status=dead}}</ref><ref name="NASA">{{cite web|title=Report: NASA Voyager Status Update on Voyager 1 Location|url=http://www.jpl.nasa.gov/news/news.php?release=2013-117&cid=release_2013-107&msource=2013107|publisher=NASA|access-date=20 March 2013|archive-date=13 April 2020|archive-url=https://web.archive.org/web/20200413080743/http://www.jpl.nasa.gov/news/news.php?release=2013-117&cid=release_2013-107&msource=2013107|url-status=dead}}</ref>

In December 2018, NASA announced that ''Voyager 2'' had crossed the heliopause on 5 November 2018, making it the second spacecraft to enter interstellar space.<ref name="NASA-20181210"/>

{{As of|2017}} ''Voyager 1'' and ''Voyager 2'' continue to monitor conditions in the outer expanses of the Solar System.<ref name="NYT-20170905">{{cite news |last=Krauss |first=Lawrence M. |author-link=Lawrence M. Krauss |title=Pondering Voyagers' Interstellar Journeys, and Our Own |url=https://www.nytimes.com/2017/09/05/opinion/pondering-voyagers-interstellar-journeys-and-our-own.html |date=5 September 2017 |work=[[The New York Times]] |access-date=5 September 2017 |archive-date=13 April 2020 |archive-url=https://web.archive.org/web/20200413080730/https://www.nytimes.com/2017/09/05/opinion/pondering-voyagers-interstellar-journeys-and-our-own.html |url-status=live }}</ref> The Voyager spacecraft are expected to be able to operate science instruments through 2020, when limited power will require instruments to be deactivated one by one. Sometime around 2025, there will no longer be sufficient power to operate any science instruments.

In July 2019, a revised power management plan was implemented to better manage the two probes' dwindling power supply.<ref name="NASA-20190712">{{cite news |last=Cofield |first=Calla |title=A New Plan for Keeping NASA's Oldest Explorers Going |url=https://www.jpl.nasa.gov/news/news.php?feature=7446 |date=8 July 2019 |work=[[NASA]] |access-date=12 July 2019 |archive-date=13 April 2020 |archive-url=https://web.archive.org/web/20200413080726/https://www.jpl.nasa.gov/news/news.php?feature=7446 |url-status=live }}</ref>