Editing Voyager program (section)

== Voyager Interstellar Mission ==
[[File:PIA22835-VoyagerProgram&Heliosphere-Chart-20181210.png|thumb|center|600px|<div class="center">''[[Voyager 1]]'' crossed the heliopause, or the edge of the [[heliosphere]], in August 2012.<br />''[[Voyager 2]]'' crossed the [[heliosheath]] in November 2018.<ref name="NASA-20181210">{{cite news |last1=Brown |first1=Dwayne |last2=Fox |first2=Karen |last3=Cofield |first3=Calia |last4=Potter |first4=Sean |title=Release 18-115 – NASA's Voyager 2 Probe Enters Interstellar Space |url=https://www.nasa.gov/press-release/nasa-s-voyager-2-probe-enters-interstellar-space |date=10 December 2018 |work=[[NASA]] |access-date=10 December 2018 |archive-date=27 June 2023 |archive-url=https://web.archive.org/web/20230627023807/https://www.nasa.gov/press-release/nasa-s-voyager-2-probe-enters-interstellar-space/ |url-status=live }}</ref><ref name="NASA-20181005">{{cite news |last1=Cofield |first1=Calia |last2=Cook |first2=Jia-Rui |last3=Fox |first3=Karen |title=NASA Voyager 2 Could Be Nearing Interstellar Space |url=https://www.jpl.nasa.gov/news/news.php?feature=7252 |date=5 October 2018 |work=[[NASA]] |access-date=6 October 2018 |archive-date=5 October 2018 |archive-url=https://web.archive.org/web/20181005173131/https://www.jpl.nasa.gov/news/news.php?feature=7252 |url-status=live }}</ref></div>]]
The Voyager primary mission was completed in 1989, with the close flyby of Neptune by ''Voyager 2''. The Voyager Interstellar Mission (VIM) is a mission extension, which began when the two spacecraft had already been in flight for over 12 years.<ref>{{cite web |url=http://voyager.jpl.nasa.gov/mission/interstellar.html |title=Interstellar Mission |publisher=NASA |access-date=30 May 2008 |archive-date=15 October 2009 |archive-url=https://web.archive.org/web/20091015172229/http://voyager.jpl.nasa.gov/mission/interstellar.html |url-status=live }}</ref> The Heliophysics Division of the NASA Science Mission Directorate conducted a Heliophysics Senior Review in 2008. The panel found that the VIM "is a mission that is absolutely imperative to continue" and that VIM "funding near the optimal level and increased DSN ([[NASA Deep Space Network|Deep Space Network]]) support is warranted."<ref>{{cite web |url=http://www.igpp.ucla.edu/public/THEMIS/SCI/Pubs/Proposals%20and%20Reports/Senior%20Review%202008%20Report%20Final.pdf |title=Senior Review 2008 of the Mission Operations and Data Analysis Program for the Heliophysics Operating Missions |page=7 |publisher=NASA |access-date=30 May 2008 |archive-url=https://web.archive.org/web/20080626213548/http://www.igpp.ucla.edu/public/THEMIS/SCI/Pubs/Proposals%20and%20Reports/Senior%20Review%202008%20Report%20Final.pdf |archive-date=26 June 2008 |url-status=dead  }}</ref>

The main objective of the VIM was to extend the exploration of the Solar System beyond the outer planets to the [[heliosphere|heliopause]] (the farthest extent at which the Sun's radiation predominates over interstellar winds) and if possible even beyond. Voyager 1 crossed the heliopause boundary in 2012, followed by Voyager 2 in 2018. Passing through the heliopause boundary has allowed both spacecraft to make measurements of the interstellar fields, particles and waves unaffected by the [[solar wind]]. Two significant findings so far have been the discovery of a region of magnetic bubbles<ref>{{cite web | url=https://svs.gsfc.nasa.gov/10790 | title=GMS: Voyager Satellites Find Magnetic Bubbles at Edge of Solar System | date=9 June 2011 | access-date=11 August 2022 | archive-date=5 December 2022 | archive-url=https://web.archive.org/web/20221205112656/https://svs.gsfc.nasa.gov/10790 | url-status=live }}</ref> and no indication of an expected shift in the Solar magnetic field.<ref>{{cite journal | url=https://physicstoday.scitation.org/do/10.1063/pt.6.3.20190215a/full/ | doi=10.1063/pt.6.3.20190215a | title=The confounding magnetic readings of Voyager 1 | journal=Physics Today | year=2019 | last1=Grant | first1=Andrew | issue=2 | page=30645 | bibcode=2019PhT..2019b0645G | s2cid=242207067 | access-date=11 August 2022 | archive-date=15 August 2022 | archive-url=https://web.archive.org/web/20220815164724/https://physicstoday.scitation.org/do/10.1063/PT.6.3.20190215a/full/ | url-status=live | url-access=subscription }}</ref>

The entire ''Voyager 2'' scan platform, including all of the platform instruments, was switched off in 1998. All platform instruments on ''Voyager 1'', except for the ultraviolet spectrometer (UVS)<ref>{{cite web | title=Ultraviolet Spectrometer | work=Voyager: The Interstellar Mission | publisher=NASA JPL | url=http://voyager.jpl.nasa.gov/spacecraft/instruments_uvs.html | access-date=11 June 2006 | archive-date=5 March 2006 | archive-url=https://web.archive.org/web/20060305105235/http://voyager.jpl.nasa.gov/spacecraft/instruments_uvs.html | url-status=live }}</ref> have also been switched off.

The ''Voyager 1'' scan platform was scheduled to go off-line in late 2000 but has been left on to investigate UV emission from the upwind direction.
UVS data are still captured but scans are no longer possible.<ref>{{cite web|url=http://voyager.jpl.nasa.gov/Proposal-2010/VGRSR.pdf|title=The Voyager Interstellar Mission Proposal to Senior Review 2010 of the Mission Operations and Data Analysis Program for the Heliophysics Operating Missions|page=24 |author=E. C. Stone |author2=J. D. Richardson |author3=E. B. Massey |publisher=NASA |access-date=20 November 2016|archive-url=https://web.archive.org/web/20161223041419/http://voyager.jpl.nasa.gov/Proposal-2010/VGRSR.pdf|archive-date=23 December 2016|url-status=dead}}</ref>

Gyro operations ended in 2016 for ''Voyager 2'' and in 2017 for ''Voyager 1''. Gyro operations are used to rotate the probe 360 degrees six times per year to measure the magnetic field of the spacecraft, which is then subtracted from the magnetometer science data.<!-- [[File:Voyager 1 entering heliosheath region.jpg|thumb|right|300px|Voyagers as of March 2013]] -->

On 14 November 2023, Voyager 1 stopped sending all telemetry and data, though the signal was still present.  After months of experiments, made considerably more difficult by the 45 hour round trip time, the cause was traced to a bad memory chip.  New software was written to avoid the bad memory block, and engineering data resumed on 20 April 2024.<ref>{{cite web |url=https://www.jpl.nasa.gov/news/nasas-voyager-1-resumes-sending-engineering-updates-to-earth/ |title=NASA’s Voyager 1 Resumes Sending Engineering Updates to Earth}}</ref>  Science data from two instruments resumed in May 2024,<ref>{{cite web |url=https://science.nasa.gov/blogs/voyager/2024/05/22/voyager-1-resumes-sending-science-data-from-two-instruments/ |title=Voyager 1 Resumes Sending Science Data from Two Instruments}}</ref> and full recovery (of all science instruments that were still powered up) was in June 2024.<ref>{{cite web |url=https://www.jpl.nasa.gov/news/voyager-1-returning-science-data-from-all-four-instruments/ |title=Voyager 1 Returning Science Data From All Four Instruments}}</ref>  For more details of this intricate operation, see [[Voyager 1]].

The two spacecraft continue to operate, with some loss in subsystem redundancy but retain the capability to return scientific data from a full complement of Voyager Interstellar Mission (VIM) science instruments.

Both spacecraft also have adequate electrical power and attitude control propellant to continue operating and collecting science data through at least 2026.<ref>{{cite web |url=https://www.jpl.nasa.gov/news/nasas-voyager-will-do-more-science-with-new-power-strategy/ |title=NASA’s Voyager Will Do More Science With New Power Strategy}}</ref>  Though additional science instruments may need to be turned off, the spacecraft are expected to be able to communicate until 2036, in the absence of additional failures.<ref>{{cite web |url=https://science.nasa.gov/mission/voyager/frequently-asked-questions/ |title=Frequently Asked Questions}}</ref>

=== Mission details ===
[[File:Transitional regions.jpg|thumb|right|350x350px|This diagram about the heliosphere was released on 28 June 2013 and incorporates results from the Voyager spacecraft.<ref>{{Cite web|url=http://voyager.jpl.nasa.gov/news/transitional_regions.html|archive-url=https://web.archive.org/web/20130708092850/http://voyager.jpl.nasa.gov/news/transitional_regions.html|url-status=dead|title=NASA – Transitional Regions at the Heliosphere's Outer Limits|archive-date=8 July 2013}}</ref>]]
By the start of VIM, ''Voyager 1'' was at a distance of 40 [[Astronomical unit|AU]] from the Earth, while ''Voyager 2'' was at 31 AU. VIM is in three phases: termination shock, heliosheath exploration, and interstellar exploration phase. The spacecraft began VIM in an environment controlled by the Sun's magnetic field, with the plasma particles being dominated by those contained in the expanding supersonic solar wind. This is the characteristic environment of the termination shock phase. At some distance from the Sun, the supersonic solar wind will be held back from further expansion by the interstellar wind. The first feature encountered by a spacecraft as a result of this interaction – between interstellar wind and solar wind – was the termination shock, where the solar wind slows to subsonic speed, and large changes in plasma flow direction and magnetic field orientation occur. ''Voyager 1'' completed the phase of termination shock in December 2004 at a distance of 94 AU, while ''Voyager 2'' completed it in August 2007 at a distance of 84 AU. After entering into the heliosheath, the spacecraft were in an area that is dominated by the Sun's magnetic field and solar wind particles. After passing through the heliosheath, the two Voyagers began the phase of interstellar exploration. The outer boundary of the heliosheath is called the heliopause. This is the region where the Sun's influence begins to decrease and interstellar space can be detected.<ref>{{cite web|url=http://voyager.jpl.nasa.gov/mission/interstellar.html|title=Voyager – The Interstellar Mission|last=JPL.NASA.GOV|website=voyager.jpl.nasa.gov|access-date=2016-05-27|archive-date=15 October 2009|archive-url=https://web.archive.org/web/20091015172229/http://voyager.jpl.nasa.gov/mission/interstellar.html|url-status=live}}</ref> 

''Voyager 1'' is escaping the Solar System at the speed of 3.6 AU per year 35° north of the [[ecliptic]] in the general direction of the [[solar apex]] in [[Hercules (constellation)|Hercules]], while ''Voyager 2''{{'}}s speed is about 3.3 AU per year, heading 48° south of the ecliptic. The Voyager spacecraft will eventually go on to the stars. In about [[Timeline of the far future#Spacecraft and space exploration|40,000 years]], ''Voyager 1'' will be within 1.6 [[Light-year|light years]] (ly) of AC+79 3888, also known as [[Gliese 445]], which is approaching the Sun. In 40,000 years ''Voyager 2'' will be within 1.7 ly of [[Ross 248]] (another star which is approaching the Sun), and in [[Timeline of the far future#Spacecreaft and space exploration|296,000 years]] it will pass within 4.6 ly of [[Sirius]], which is the brightest star in the night-sky.<ref name="JPL.NASA">{{cite web |author=Jpl.Nasa.Gov |url=http://www.jpl.nasa.gov/interstellarvoyager/ |title=Voyager Enters Interstellar Space – NASA Jet Propulsion Laboratory |publisher=Jpl.nasa.gov |access-date=14 September 2013 |archive-date=13 April 2020 |archive-url=https://web.archive.org/web/20200413080732/https://voyager.jpl.nasa.gov/mission/interstellar-mission// |url-status=live }}</ref> The spacecraft are not expected to collide with a star for 1 sextillion (10<sup>20</sup>) years.<ref name=lavender>{{Cite journal|title = Future stellar flybys of the Voyager and Pioneer spacecraft|journal = Research Notes of the American Astronomical Society|volume= 3|pages = 59|number=4|doi=10.3847/2515-5172/ab158e|date = 3 April 2019|author = Coryn A.L. Bailer-Jones, Davide Farnocchia|arxiv = 1912.03503|bibcode = 2019RNAAS...3...59B|s2cid = 134524048 | doi-access=free }}</ref>

In October 2020, astronomers reported a significant unexpected increase in density in the [[Outer space|space]] beyond the [[Solar System]], as detected by the Voyager [[space probe]]s. According to the researchers, this implies that "the density gradient is a large-scale feature of the [[Interstellar medium#Structures|VLISM]] (very local [[interstellar medium]]) in the general direction of the [[Heliosphere#Edge structure|heliospheric nose]]".<ref name="SA-20201019">{{cite news |last=Starr |first=Michelle |title=Voyager Spacecraft Detect an Increase in The Density of Space Outside The Solar System |url=https://www.sciencealert.com/for-some-reason-the-density-of-space-is-higher-just-outside-the-solar-system |date=19 October 2020 |work=[[ScienceAlert]] |access-date=19 October 2020 |archive-date=19 October 2020 |archive-url=https://web.archive.org/web/20201019133221/https://www.sciencealert.com/for-some-reason-the-density-of-space-is-higher-just-outside-the-solar-system |url-status=live }}</ref><ref name="AJL-20200825">{{cite journal |last1=Kurth |first1=W.S. |last2=Gurnett |first2=D.A. |title=Observations of a Radial Density Gradient in the Very Local Interstellar Medium by Voyager 2 |date=25 August 2020 |journal=[[The Astrophysical Journal Letters]] |volume=900 |number=1 |pages=L1 |doi=10.3847/2041-8213/abae58 |bibcode=2020ApJ...900L...1K |s2cid=225312823 |doi-access=free }}</ref>