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{{Short description|1985 Soviet space program with the first balloon flight on Venus}}
{{More citations needed|date=May 2018}}
{{Use American English|date=June 2019}}<!-- Please, do not change into British English, because British use 'programme'. Please see the talk page-->

[[Image:Vega-mission.jpg|thumb|Vega mission description]]

The '''''Vega'' program''' ({{langx|ru|Вега}}) was a series of [[Venus missions]] that also took advantage of the appearance of comet [[1P/Halley]] in 1986. ''[[Vega 1]]'' and ''[[Vega 2]]'' were uncrewed [[spacecraft]] launched in a cooperative effort among the [[Soviet Union]] (who also provided the spacecraft and launch vehicle) and [[Austria]], [[Bulgaria]], [[France]], [[Hungary]], the [[East Germany|German Democratic Republic]], [[Poland]], [[Czechoslovakia]], and the [[West Germany|Federal Republic of Germany]] in December 1984. They had a two-part mission to investigate [[Venus]] and also flyby [[Halley's Comet]].

The flyby of Halley's Comet had been a late mission change in the [[Venera]] program, following on from the cancellation of the American Halley mission in 1981. A later Venera mission was canceled and the Venus part of the ''Vega 1'' mission was reduced. Because of this, the craft was designated VeGa, a contraction of ''Venera'' and ''Gallei'' (Венера and Галлей respectively, the Russian words for "Venus" and "Halley"). The spacecraft design was based on the previous [[Venera 9]] and [[Venera 10]] missions.

The two spacecraft were launched on 15 and 21 December 1984, respectively. With their redesignated dual missions, the Vega probes became part of the [[Halley Armada]], a group of space probes that studied Halley's Comet during its 1985/1986 [[perihelion]].

==The Vega spacecraft==
[[File:Vega model - Udvar-Hazy Center.JPG|thumb|A ''Vega'' probe bus on display at the [[National Air and Space Museum]]]]
''[[Vega 1]]'' and ''[[Vega 2]]'' were identical sister ships developed from the earlier ''[[Venera]]'' craft. They were of the [[5VK]] type, designed by [[Babakin Space Centre|Babakin Space Center]] and constructed by [[Lavochkin]] at [[Khimki]]. The craft were powered by twin large solar panels and instruments included an antenna dish, cameras, [[spectrometer]], infrared sounder, [[magnetometer]]s (MISCHA; Austrian and Soviet),<ref name="Besser European Space Agency 2004 p. ">{{cite book | last=Besser | first=Bruno Philipp | author2=European Space Agency | title=Austria's history in space | publisher=ESA Publications Division | publication-place=Noordwijk, the Netherlands | date=2004 | isbn=92-9092-545-0 | oclc=56103655 | page=}}</ref>  and plasma probes. The {{cvt|4,920|kg}} craft were launched by a [[Proton-K|Proton 8K82K rocket]] from [[Baikonur Cosmodrome]], [[Tyuratam]], [[Kazakh SSR]] (current [[Kazakhstan]]). Both ''Vega 1'' and ''Vega 2'' were three-axis stabilized spacecraft. The spacecraft were equipped with a dual bumper shield for dust protection from Halley's comet.

===Bus Instruments===
{{div col|colwidth=50em}}
* imaging system
* infrared spectrometer
* [[ultraviolet]], [[light|visible]], infrared imaging [[spectrometer]]
* shield penetration detector
* dust detectors
* dust mass spectrometer
* neutral gas mass spectrometer
* APV-V plasma energy analyzer
* energetic-particle analyzer
* [[magnetometer]] (Austrian-Soviet)
* wave and plasma analyzers
{{div col end}}

==The Venus mission==
[[File:VenusLanderTopo.jpg|thumb|300px|Position of Vega landing sites. Red points denote sites returning images from the surface, black central dots sites of surface sample analysis. Map based on mapping from ''[[Pioneer Venus Orbiter]]'', ''[[Magellan (spacecraft)|Magellan]]'', and ''[[Venera 15 and 16|Venera 15/16]]''.]] 
''Vega 1'' arrived at Venus on 11 June 1985 and ''Vega 2'' on 15 June 1985, and each delivered a {{convert|1500|kg|lb|abbr=on}}, {{cvt|240|cm}} diameter spherical descent unit. The units were released some days before each arrived at Venus and entered the atmosphere without active inclination changes. Each contained a lander and a balloon explorer.

===Descent craft===
[[File:Vega balloon probe.jpg|thumb|Artist's impression of the ''Vega'' probe on Venus]]
The landers were identical to that of the previous five ''[[Venera]]'' missions and were to study the atmosphere and surface. Each had instruments to study temperature and pressure, a [[UV]] spectrometer, a water concentration meter, a [[Gas-liquid chromatography|gas-phase chromatograph]], an [[X-ray]] [[spectrometer]], a [[mass spectrometer]], and a surface sampling device.

The ''Vega 1'' lander's surface experiments were inadvertently activated at {{cvt|20|km}} from the surface by an especially hard wind jolt, and so failed to provide results. It landed at 7.5°N, 177.7°E.

The ''Vega 2'' lander touched down at 03:00:50 UT on 15 June 1985 at 8.5° S, 164.5° E, in eastern [[Aphrodite Terra]]. The altitude of the touchdown site was {{cvt|0.1|km}} above the planetary mean radius. The measured pressure at the landing site was 91 atm and the temperature was {{convert|736|K}}. The surface sample was found to be an [[anorthosite]]-[[troctolite]]. The lander transmitted data from the surface for 56 minutes.{{Citation needed|date=November 2023}}

====Payload====
{{div col|colwidth=50em}}
* Meteocomplex T,P sensors
* Sigma-3 gas chromatograph
* LSA particle size spectrometer
* IFP aerosol analyzer
* VM-4 hygrometer
* ISAV-A nephelometer/scatterometer
* Malakhit-V mass spectrometer
* ISAV-S UV spectrometer
* GZU VB-02 drill + BDRP-AM25 soil X-ray fluorescence spectrometer
* GS-15-STsV gamma ray spectrometer
* PrOP-V penetrometer
* MSB small solar batteries
{{div col end}}

===Balloon===
[[File:Russian "Vega" balloon mission to Venus on display at the Udvar-Hazy museum.jpg|thumb|Vega balloon probe on display at the [[Steven F. Udvar-Hazy Center|Udvar-Hazy Center]] of the Smithsonian Institution. Photo by Geoffrey A. Landis.]]
The two balloon [[aerobot]]s were designed to float at {{cvt|54|km}} from the surface, in the most active layer of the Venusian cloud system. The instrument pack had enough battery power for 60&nbsp;hours of operation and measured temperature, pressure, wind speed, and aerosol density. The balloon envelopes were surfaced with [[polytetrafluoroethylene]] to resist attack by the corrosive atmosphere. Both Vega-1 and Vega-2 balloons operated for more than 46&nbsp;hours from injection to the final transmission.<ref>{{cite journal|author=Preston|display-authors=etal|year=1986|title=Determination of Venus Winds by Ground-Based Radio Tracking of the VEGA Balloons|journal=Science|volume=231|issue=4744|pages=1414–1416|doi=10.1126/science.231.4744.1414|bibcode=1986Sci...231.1414P|pmid=17748082|s2cid=29444555}}<!-- orig ref specified p. 1416 --></ref>

The balloons were of spherical superpressure types of {{cvt|3.54|m}} diameter, filled with [[helium]]. A gondola assembly weighing {{cvt|6.9|kg}} and {{cvt|1.3|m}} long was connected to the balloon envelope by a tether {{cvt|13|m}} long. Total mass of the entire assembly was {{cvt|21|kg}}.

The top section of the gondola assembly was capped by a conical antenna {{cvt|37|cm}} tall and {{cvt|13|cm}} wide at the base. Beneath the antenna was a module containing the radio transmitter and system control electronics. The lower section of the gondola assembly carried the instrument payload and batteries.

The instruments consisted of:
* An arm carrying thin-film resistance thermometers and a [[anemometer|velocity anemometer]]. The anemometer consisted of a free-spinning plastic propeller, whose spin was measured by [[LED]]-photodetector optointerrupters.
* A module containing a [[PIN diode]] [[photodetector]] to measure light levels and a vibrating-[[quartz]]-beam [[pressure sensor]].
* A package at the bottom carrying the batteries and a [[nephelometer]] to measure cloud density through light reflection.

The small low-power (5 watt)<ref name=FF/> transmitter only allowed a data transmission rate of 2,048&nbsp;bit/s, though the system performed data compression to squeeze more information through the narrow bandwidth. Nonetheless, the sampling rate for most of the instruments was only once every 75&nbsp;seconds. The balloons were tracked by two networks (20 radio telescopes total) back on Earth: the Soviet network, coordinated by the [[USSR Academy of Sciences|Soviet Academy of Sciences]], and the international network, coordinated by {{lang|fr|Centre national d'études spatiales}} of France ([[CNES]]).

The balloons were pulled out of the lander at {{convert|180,000|ft|km}} above the planet's darkside surface, and fell to {{convert|164,000|ft|km}} ASL while they were being inflated. After that, they rose to {{convert|177,000|ft|km}} and stabilized.<ref name=FF>{{cite web|url=https://www.airspacemag.com/daily-planet/ireali-first-flight-another-world-180977540/|work=Air & Space Smithsonian|title=The First Flight on Another Planet (from ''Infinity Beckoned'')|author=Jay Gallentine|date=2016|access-date=20 April 2021}}</ref> At this altitude, pressure and temperature conditions of Venus are similar to those of [[Earth]] at 18,000 feet MSL (5,5&nbsp;km),<ref name=FF/> though the planet's winds move at hurricane velocity, and the [[carbon dioxide]] atmosphere is laced with [[sulphuric acid]], along with smaller concentrations of [[hydrochloric acid|hydrochloric]] and [[hydrofluoric acid]].

The balloons moved swiftly across the night side of the planet into the light side, where their batteries finally died, and contact was lost. Tracking indicated that the motion of the balloons included a surprising vertical component, revealing vertical motions of air masses that had not been detected by earlier probe missions.

==The Halley mission==
[[File:1986 venera galley nh.jpg|thumb|250px|1985 [[USSR]] [[miniature sheet]] dedicated to the program, depicting the ''[[Vega 1]]'' spacecraft, [[Comet Halley]], and the [[Interkosmos]] logo]]
After their encounters, the Vega motherships were redirected to intercept [[Comet Halley]], utilizing the gravity of Venus to alter their trajectory.

''Vega 1'' made its closest approach on 6 March, around {{cvt|8,890|km}} from the nucleus, and ''Vega 2'' made its closest approach on 9 March at {{cvt|8,030|km}}. The data intensive examination of the comet covered only the three hours around closest approach. They were intended to measure the physical parameters of the nucleus, such as dimensions, shape, temperature, and surface properties, as well as to study the structure and dynamics of the [[Coma (cometary)|coma]], the gas composition close to the nucleus, the dust particles' composition and mass distribution as functions of distance to the nucleus, and the cometary-[[solar wind]] interaction.

In total ''Vega 1'' and ''Vega 2'' returned about 1,500 images of Comet Halley. Spacecraft operations were discontinued a few weeks after the Halley encounters.

The on-board TV system was created in international cooperation of the scientific and industrial facilities from the [[USSR]], [[People's Republic of Hungary|Hungary]], France, and [[Czechoslovakia]]. The TV data was processed by an international team, including scientists from the Soviet Union, Hungary, France, [[East Germany]], and the [[United States]]. The basic steps of data acquisition and preprocessing were performed in [[Russian Space Research Institute|IKI]] using an image processing computer system based on a [[PDP-11|PDP-11/40]] compatible host.

''Vega 1'' and ''Vega 2'' are currently in [[heliocentric orbit]]s.

==See also==
* [[Pioneer Venus Orbiter]]
* [[Venera program]]

==References==
{{Reflist}}

==External links==
{{Commons category}}
*[http://arc.iki.rssi.ru/IPL/vega.html Vega mission images from the Space Research Institute (IKI)]
*[https://web.archive.org/web/20070311040927/http://starbase.jpl.nasa.gov/archive/vega2-c-tvs-5-rdr-halley-transform-v1.0/hal_0026/ Raw data from ''Vega 1'' and ''Vega 2'' on board instruments]
*[http://www.mentallandscape.com/V_Vega.htm Soviet Exploration of Venus]
*[http://articles.adsabs.harvard.edu/full/1986SvAL...12....7K HSAO/NASA Astrophysics Data System (ADS)] – A tool for studying atmosphere dynamics on Venus

{{Venus}}
{{Venus spacecraft}}
{{Comet spacecraft}}
{{URSS space probes}}
{{Authority control}}

[[Category:Vega program| ]]
[[Category:Missions to Halley's Comet]]
[[Category:France–Soviet Union relations]]
[[Category:Czechoslovakia–Soviet Union relations]]
[[Category:Hungary–Soviet Union relations]]
[[Category:Austria–Soviet Union relations]]
[[Category:Germany–Soviet Union relations]]
[[Category:Poland–Soviet Union relations]]
[[Category:Bulgaria–Soviet Union relations]]