Editing Vega program (section)

===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.