Instrument Host Overview

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The Vega 1 Lander/Balloon capsule entered the Venus atmosphere (125 km
altitude) at 2:06:10 UT (Earth received time; Moscow time 5:06:10 a.m.)
on 11 June 1985 at roughly 11 km/sec. At approximately 2:06:25 UT the
parachute attached to the landing craft cap opened at an altitude of 64 km.
The cap and parachute were released 15 seconds later at 63 km altitude.
The balloon package was pulled out of its compartment by parachute 40 seconds
later at 61 km altitude, at 8.1 degrees N, 176.9 degrees east. A second
parachute opened at an altitude of 55 km, 200 seconds after entry, extracting
the furled balloon. The balloon was inflated 100 seconds later at 54 km and
the parachute and inflation system were jettisoned. The ballast was
jettisoned when the balloon reached roughly 50 km and the balloon floated
back to a stable height between 53 and 54 km some 15 to 25 minutes after
entry. The mean stable height was 53.6 km, with a pressure of 535 mbar and
a temperature of 300-310 K in the middle, most active layer of the Venus
three-tiered cloud system. The balloon drifted westward in the zonal wind
flow with an average speed of about 69 m/s at nearly constant latitude.
The probe crossed the terminator from night to day at 12:20 UT on 12 June
after traversing 8500 km. The probe continued to operate in the daytime until
the final transmission was received at 00:38 UT on 13 June from 8.1 N, 68.8 E
after a total traverse distance of 11,600 km. It is not known how much
further the balloon travelled after the final communication.

The Vega 2 capsule similarly entered around 02:00 hrs UT, on 15 June 1985,
about 3-7 degrees south of the equator and followed a broadly similar
mission profile, floating due westwards. Notably, its more southerly
trajectory overflew the mountainous terrain Aphrodite Terra and experienced
more violent vertical winds, perhaps associated with gravity waves excited
by the terrain.

The landers carried a variety of instrumentation for atmosphere (a 'Meteo'
package for pressure and temperature, a mass spectrometer, a UV spectrometer,
etc.) and surface (a drill and X-ray fluorescence experiment) investigations.
The drill on Vega-1 actuated prematurely, apparently a gust or similar anomaly
during descent triggered surface operations. The results from the Vega-1
descent 'Meteo' measurements were also not reported.

The Vega-1 landing site was 8.10 N, 175.85 E, where it operated for 20
minutes.  The Vega-2 lander reached the surface at 7.14 S, 177.67 E.