Vega 1

Infobox_Spacecraft
Name = Vega 1 spacecraft


Caption = Vega 1
Organization = USSR
Major_Contractors =
Mission_Type = Flyby, balloon and lander
Flyby_Of = Venus, Halley
Flyby_Date = June 11, 1985 (Venus) and
March 6, 1986 (Halley)
Launch = 1984-12-15 at 09:16:24 UTC
Launch_Vehicle = Proton 8K82K rocket
Decay =
Mission_Duration =
NSSDC_ID = 1984-125A
Webpage =
Mass = 4920 kg
Power =
Orbital_elements =
Semimajor_Axis =
Eccentricity =
Inclination =
Orbital_Period =
Apoapsis =
Periapsis =
Orbits =

Vega 1 (along with its twin Vega 2) is a soviet space probe part of the Vega program. The spacecraft was a development of the earlier "Venera" craft. They were designed by Babakin Space Center and constructed as 5VK by Lavochkin at Khimki.

The craft was powered by twin large solar panels and instruments included an antenna dish, cameras, spectrometer, infrared sounder, magnetometers (MISCHA), and plasma probes. The 4,920 kg craft was launched by a Proton 8K82K rocket from Baikonur Cosmodrome, Tyuratam, Kazakh SSR. Both Vega 1 and 2 were three-axis stablized spacecraft. The spacecraft were equipped with a dual bumper shield for dust protection from Halley's comet.

The Venus mission

Vega 1 arrived at Venus on June 11, 1985 delivering a 1500 kg, 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

Infobox_Spacecraft
Name = Vega 1 Descent Craft


Caption = Vega 1 Descent Craft
Organization = USSR
Major_Contractors =
Mission_Type = Venus Lander
Flyby_Of =
Flyby_Date =
Launch =
Launch_Vehicle = Vega 1
Decay =
Mission_Duration =
NSSDC_ID = 1984-125E
Webpage =
Mass =
Power =
Orbital_elements =
Semimajor_Axis =
Eccentricity =
Inclination =
Orbital_Period =
Apoapsis =
Periapsis =
Orbits = 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, pressure, a UV spectrometer, a water concentration meter, a 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 20 km from the surface by an especially hard wind jolt and so failed to provide results. It landed at Venus coords and quad cat|7.2|N|177.8|E in the Mermaid Plain north of Aphrodite Terra.

Balloon

Infobox_Spacecraft
Name = Vega 1 Balloon


Caption = Vega 1 Balloon
Organization = USSR
Major_Contractors =
Mission_Type = Venus balloon
Flyby_Of =
Flyby_Date =
Launch =
Launch_Vehicle = Vega 1 Descent Craft
Decay =
Mission_Duration = 11 June to 13 June 1985
NSSDC_ID = 1984-125F
Webpage =
Mass = 21.5 kg
Power =
Orbital_elements =
Semimajor_Axis =
Eccentricity =
Inclination =
Orbital_Period =
Apoapsis =
Periapsis =
Orbits = 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/s. 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 Halley mission

After their encounters, the Vegas' motherships were redirected by Venus' gravity to intercept Halley's Comet.

Images started to be returned on March 4, 1986, and were used to help pinpoint Giotto's upcoming close flyby of the comet. The early images from Vega that showed two bright areas on the comet, which were initially interpreted as a double nucleus. The bright areas would later turn out to be two jets emitting from the comet. The images also showed the nucleus to be dark, and the infrared spectrometer readings measured a nucleus temperature of 300 K to 400 K, much warmer than expected for an ice body. The conclusion was that the comet had a thin layer on its surface covering an icy body.

Vega 1 made its closest approach on March 6 at around 8,889 kilometers (at 07:20:06 UT) of the nucleus. It took more than 500 pictures via different filters as it flew through the gas cloud around the coma. Although the spacecraft was battered by dust, none of the instruments were disabled during the encounter.

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, 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.

The Vega images showed the nucleus to be about 14 km long with a rotation period of about 53 hours. The dust mass spectrometer detected material similar to the composition of carbonaceous chondrites meteorites and also detected clathrate ice.

After subsequent imaging sessions on 7 and 8 March 1986, Vega 1 headed out to deep space. In total Vega 1 and Vega 2 returned about 1500 images of Comet Halley. Spacecraft operations were discontinued a few weeks after the Halley encounters.

Vega 1 and Vega 2 are currently in heliocentric orbits.

ee also

*Venera program
*Vega program

External links

* [http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Vega_01 Vega 1 Measuring Mission Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://arc.iki.rssi.ru/IPL/vega.html Vega mission images from the Space Research Institute (IKI)]
* [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]