Astronomy

Past Spacecraft sent to Venus



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Venus is the most visited of the other planets in our solar system. This may be surprising to many: since the fall of the Soviet Union, the space program of which specialized in Venus exploration, and the rise of interest in the possible history of primitive life on Mars, the red planet has become the dominant target of planetary probe missions. Nevertheless, a large number of space probes have been sent to Venus, beginning with the Soviet Venera 1 (1961) and American Mariner 2 (1962), and extending to the European Venus Express, which arrived in 2006 and is still engaged in studying the planet.

- Soviet Venus Program -

Even today, the most accomplished series of space probes sent to Venus were those launched by the former Soviet Union, beginning with Venera 1 in 1961, which was the first interplanetary spacecraft and did manage to enter Venusian orbit, though it malfunctioned and failed soon after doing so. The Zond 1 probe, launched in 1964, suffered a similar fate; by the time it reached Venus in July of that year, Soviet scientists had already lost all contact and given up the probe for dead.

Despite the inauspicious beginnings, the Venera program continued, becoming arguably the most successful series of planetary landing missions until the Mars rover missions launched by NASA over the last decade or so. Venera 2 and Venera 3 were launched in 1966 to crash-land on Venus, the standard approach to lunar and planetary exploration at a time when landing technology was still technically unfeasible; Venera 2 failed, but Venera 3 managed to land, but not to communicate. The next entry vehicle, Venera 4, was promptly sent on a similar mission, and finally transmitted atmospheric data on its way down.

More Venera missions followed, leading to the first successful landing by Venera 7 in 1970. Several more Venera landers followed, with impressive achievements interspersed with occasional dramatic failures. However, the harsh environment on the surface of Venus meant that such missions were necessarily short-lived and limited. Venera 13, which sent back colour photographs of Venus for the first time in the 1980s, was designed for a simple half-hour mission in the several-hundred-degree heat; when instead it lasted for slightly over two hours, this was considered an impressive achievement. (By contrast, NASA probes on Mars have been able to survive and operate for many years.)

Its last pair of probes to Venus departed from the Venera model, and were instead designated as Vega 1 and Vega 2. For these probes, launched in late 1984, the Soviets chose to design balloons rather than landers, so that the probes were able to spend roughly two days floating in the upper atmosphere before failing. The Vega spacecraft, having discharged their balloon probe payload, later went on to make approaches to Halley's Comet, which plunges through the inner solar system about once every 75 years.

- American Venus Program -

Given the context of the Cold War space race, NASA was understandably reluctant to tolerate unchallenged Soviet exploration of Venus. As a result, Mariner 2 was hastily sent to Venus the following year on a flyby mission. Mariner 2 was a modified version of the Ranger probe used by NASA on lunar missions of the time, but was able to take several basic observations of Venus for the first time, confirming that the planet has no magnetic field but does have an extraordinarily high surface temperature (both very unlike Earth). Two subsequent flybys, Mariner 5 and Mariner 10, added to the early American understanding of Venus.

Having staked their claim, however, American space scientists generally returned to Mars, where they had considerably more success (in contrast, Soviet and Russian probes have had a string of bad luck at Mars). Two Pioneer spacecraft were finally sent back to Venus in 1978, and four probes were launched, one of which survived landing and operated for nearly an hour on the surface of the overheated planet.

The more successful American achievement at Venus, however, was in orbit, where the Magellan spacecraft arrived in 1990 and conducted a comprehensive radar-based mapping survey of the planet's surface, the most detailed yet made of the planet. Magellan is no longer in orbit: after its four-year mapping mission was complete, it was allowed to enter the atmosphere. Most or all of the probe would have been destroyed during entry, although it is possible that some debris now lies on Venus's surface.

- European Space Agency -

The only currently operational probe at Venus is a European Space Agency spacecraft, the Venus Express, which arrived in 2006 and has been studying the planet from polar orbit. Reflecting current scientific priorities here, Venus Express is principally interested in temperature and climate, hoping to understand why Venus has become so incredibly hot and whether this holds implications for the future of Earth's own climate. (Venus's extremely high carbon dioxide levels, coupled with its blistering heat, has led to the general understanding that the planet's temperature is so high because of a runaway greenhouse effect.) Venus Express has found evidence that the surface used to contain oceans and active tectonic plates, meaning that at some point in its history, it would have been roughly similar to Earth's surface today.

- Current Plans -

One probe, the Japanese-built Akatsuki, has already been launched as of May 2010, but will not reach Venus until December 2010. Other planned probes to Venus, including NASA's VISE spacecraft, and Russia's Venera-D are currently in development, but will not be launched for at least several years, if ever.

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