|
''Venus Express'' (VEX) was the first Venus exploration mission of the European Space Agency (ESA). Launched in November 2005, it arrived at Venus in April 2006 and began continuously sending back science data from its polar orbit around Venus. Equipped with seven scientific instruments, the main objective of the mission was the long term observation of the Venusian atmosphere. The observation over such long periods of time had never been done in previous missions to Venus, and was key to a better understanding of the atmospheric dynamics. It was hoped that such studies can contribute to an understanding of atmospheric dynamics in general, while also contributing to an understanding of climate change on Earth. ESA concluded the mission in December 2014. ==History== The mission was proposed in 2001 to reuse the design of the ''Mars Express'' mission. However, some mission characteristics led to design changes: primarily in the areas of thermal control, communications and electrical power. For example, since Mars is approximately twice as far from the Sun as Venus is, the radiant heating of the spacecraft is four times greater for ''Venus Express'' than ''Mars Express''. Also, the ionizing radiation environment is harsher. On the other hand, the more intense illumination of the solar panels results in more generated photovoltaic power. The ''Venus Express'' mission also uses some spare instruments developed for the ''Rosetta'' spacecraft. The mission was proposed by a consortium led by D. Titov (Germany), E. Lellouch (France) and F. Taylor (United Kingdom). The launch window for ''Venus Express'' was open from 26 October to 23 November 2005, with the launch initially set for 26 October 4:43 UTC. However, problems with the insulation from the Fregat upper stage led to a two-week launch delay to inspect and clear out the small insulation debris that migrated on the spacecraft. It was eventually launched by a Soyuz-FG/Fregat rocket from the Baikonur Cosmodrome in Kazakhstan on 9 November 2005 at 03:33:34 UTC into a parking Earth orbit and 1 h 36 min after launch put into its transfer orbit to Venus. A first trajectory correction maneuver was successfully performed on 11 November 2005. It arrived at Venus on 11 April 2006, after 153 days of journey, and fired its main engine between 07:10:29 and 08:00:42 UTC SCET to reduce its velocity so that it could be captured by Venusian gravity into a nine-day orbit of .〔(【引用サイトリンク】title=Venus Express )〕 The burn was monitored from ESA's Control Centre, ESOC, in Darmstadt, Germany. Seven further orbit control maneuvers, two with the main engine and five with the thrusters, were required for ''Venus Express'' to reach its final operational 24-hour orbit around Venus.〔 ''Venus Express'' entered its target orbit at apoapsis on 7 May 2006 at 13:31 UTC, when the spacecraft was from Earth. At this point the spacecraft was running on an ellipse substantially closer to the planet than during the initial orbit. The polar orbit ranged between over Venus. The periapsis is located almost above the North pole (80° North latitude), and it takes 24 hours for the spacecraft to travel around the planet. ''Venus Express'' studied the Venusian atmosphere and clouds in detail, the plasma environment and the surface characteristics of Venus from orbit. It is also made global maps of the Venusian surface temperatures. Its nominal mission was originally planned to last for 500 Earth days (approximately two Venusian sidereal days), but the mission has been extended three times: first on 28 February 2007 until early May 2009; then on 4 February 2009 until 31 December 2009; and then on 7 October 2009 until 31 December 2012.〔(【引用サイトリンク】title=Mission extensions approved for science missions )〕 On 22 November 2010, the mission was extended to 2014.〔(【引用サイトリンク】date=22 November 2010 )〕 On 20 June 2013, the mission was extended until 2015.〔(【引用サイトリンク】date=20 June 2013 )〕 There were on-board resources for an additional 500 Earth days. On 28 November 2014, mission control lost contact with ''Venus Express''. Intermittent contact was reestablished on 3 December 2014, though there was no control over the spacecraft, likely due to exhaustion of propellant.〔 On 16 December 2014, ESA announced that the ''Venus Express'' mission had ended.〔 A carrier signal was still being received from the vehicle, but no data was being transmitted. Mission manager Patrick Martin expected the spacecraft would fall below in early January 2015, with destruction occurring in late January or early February. The spacecraft's carrier signal was last detected by ESA on 18 January 2015.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Venus Express」の詳細全文を読む スポンサード リンク
|