Vega program
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The Vega program (
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
The Vega spacecraft
Bus Instruments
- imaging system
- infrared spectrometer
- ultraviolet, 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
- wave and plasma analyzers
The Venus mission
Vega 1 arrived at Venus on 11 June 1985 and Vega 2 on 15 June 1985, and each delivered a 1,500 kg (3,300 lb), 240 cm (94 in) 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
The landers were identical to that of the previous five
The Vega 1 lander's surface experiments were inadvertently activated at 20 km (12 mi) 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 0.1 km (0.062 mi) above the planetary mean radius. The measured pressure at the landing site was 91 atm and the temperature was 736 K (463 °C; 865 °F). The surface sample was found to be an anorthosite-troctolite. The lander transmitted data from the surface for 56 minutes.[citation needed]
Payload
- 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
Balloon
The two balloon aerobots were designed to float at 54 km (34 mi) from the surface, in the most active layer of the Venusian cloud system. The instrument pack had enough battery power for 60 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 hours from injection to the final transmission.[2]
The balloons were of spherical superpressure types of 3.54 m (11.6 ft) diameter, filled with helium. A gondola assembly weighing 6.9 kg (15 lb) and 1.3 m (4 ft 3 in) long was connected to the balloon envelope by a tether 13 m (43 ft) long. Total mass of the entire assembly was 21 kg (46 lb).
The top section of the gondola assembly was capped by a conical antenna 37 cm (15 in) tall and 13 cm (5.1 in) 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 LED-photodetector optointerrupters.
- A module containing a 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)
The balloons were pulled out of the lander at 180,000 feet (55 km) above the planet's darkside surface, and fell to 164,000 feet (50 km) ASL while they were being inflated. After that, they rose to 177,000 feet (54 km) and stabilized.
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
After their encounters, the Vega motherships were redirected to intercept
Vega 1 made its closest approach on 6 March, around 8,890 km (5,520 mi) from the nucleus, and Vega 2 made its closest approach on 9 March at 8,030 km (4,990 mi). 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
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
Vega 1 and Vega 2 are currently in heliocentric orbits.
See also
- Pioneer Venus Orbiter
- Venera program
References
External links
- Vega mission images from the Space Research Institute (IKI)
- Raw data from Vega 1 and Vega 2 on board instruments
- Soviet Exploration of Venus
- HSAO/NASA Astrophysics Data System (ADS) – A tool for studying atmosphere dynamics on Venus