The Voyager

The Voyager probes were originally conceived as part of the Mariner program, and designated Mariner 11 and Mariner 12, respectively. They were then moved into a separate program named Mariner Jupiter-Saturn, later retitled Voyager because it was felt that the probes' designs had moved sufficiently far from the Mariner family that they merited a separate name. Voyager is essentially a scaled-back version of the Grand Tour program of the late 1960s and early 1970s. The Grand Tour's plan was to send a pair of probes to fly by all the outer planets; it was scaled back because of budget cuts. However, in the end, Voyager fulfilled all the Grand Tour flyby objectives except for Pluto, which at the time was considered a planet by the IAU.

Of the pair, Voyager 2 was launched first. Its trajectory was designed to take advantage of an unusually convenient alignment of the planets allowing the inclusion of Uranus and Neptune fly bys in the probe's mission. Voyager 1 was launched after its sister probe, but on a faster trajectory which enabled it to reach Jupiter and Saturn sooner at the consequence of not visiting the outer planets.

In the 1990s, Voyager 1 overtook the slower traveling Pioneer 10 to become the most distant human made artifact in space. It will keep that record for at least several decades; even the fast (at launch) New Horizons probe will not catch up with it since its final speed will be less than Voyager 1's. Voyager 1 and Pioneer 10 are also the most widely-separated man-made objects in the universe because they are traveling in roughly opposite directions from the sun.

Periodic contact has been maintained with both probes to monitor conditions in the outer expanses of the solar system. The crafts' radioactive power sources are still producing electrical energy, fueling hopes of locating the solar system's heliopause. In late 2003, Voyager 1 began sending data that seemed to indicate it had crossed the termination shock, but interpretations of this data are in dispute. It is now believed that the termination shock was crossed in December 2004, with the heliopause an unknown distance ahead.

Due to budget cuts prompted by President George W. Bush's Vision for Space Exploration, it was questionably stated that the probes were to be deactivated and abandoned[3] as early as October 2005, before they would have observed the heliopause. However, the program continues to be funded into 2009.

As of August 2009, Voyager 1 was over 16.5 terameters (16.5 × 1012 meters, or 16.5 × 109 km, 110.7 AU, or 10.2 billion miles) from the Sun, and has thus entered the heliosheath, the termination shock region between the solar system and interstellar space (or the interstellar medium), a vast area where the Sun's influence has given way to that of the Milky Way galaxy in general. At this distance, light from the sun takes over 15 hours to reach the probe.

As of August 2009, Voyager 2 is at a distance of around 89.7 AU (approximately 13.4 terameters) from the Sun, deep in the scattered disc, and traveling outward at roughly 3.3 AU a year. It is more than twice as far from the Sun as Pluto is. On December 10, 2007, instruments on board Voyager 2 sent data back to Earth indicating that the Solar System is asymmetrical. It has also reached the termination shock, about 10 billion miles from where Voyager 1 first crossed it.

Source: Wikipedia