Voyager Program - History

History

The Voyager space probes were originally conceived as part of the Mariner program, and they were thus named Mariner 11 and Mariner 12, respectively. They were then moved into a separate program named Mariner Jupiter-Saturn, later renamed the Voyager Program because it was thought that the design of the two space probes had progressed sufficiently above those of the Mariner family that they merited a separate name.

The Voyager Program is essentially a scaled-back version of the program "Grand Tour" of the Outer Planets planned during the late 1960s and early 70s. Gary Flandro, an aerospace engineer at the Jet Propulsion Laboratory on the study team, discovered that the alignment of the outer planets would make it possible to use gravitational assists from Jupiter to go to Saturn, and thence and on to Uranus and Neptune. The plan of the "Grand Tour" was to send several pairs of probes to fly by all the outer planets, including Pluto, along various trajectories, including Jupiter-Saturn-Pluto and Jupiter-Uranus-Neptune.

The major plans for the "Grand Tour" were dramatically scaled back because of lack of money appropriated by Congress. In the end, the Voyager Program fulfilled many of the flyby objectives of the "Grand Tour" excepting any mission to Pluto, and dual missions to Uranus and Neptune.

Of the two space probes of the Voyager Program, Voyager 2 was launched first. Its trajectory was designed to take advantage of an unusual alignment of the planets (that occurs once every 177 years) that allowed one space probe to fly by Jupiter, Saturn, Uranus, and Neptune, if everything went well. Of course, in case of a serious malfunction, such as in all of the space probe's radio transmitters or receivers, then that would have been the end of the long mission (to four planets), since there was not a second space probe to fill the gap. That was the gamble that NASA and the JPL were forced to take.

Voyager 1 was launched after its sister probe, but along a shorter and faster trajectory that sent it to Jupiter and Saturn sooner -- but at the cost of not visiting any more of the outer planets. Voyager 1 also had the high-priority mission of making a close fly-by of the saturnian moon Titan, which was known to be quite large and to possess a dense atmosphere very much worth studying.

During the 1990s, Voyager 1 overtook the slower deep-space probes Pioneer 10 and Pioneer 11 to become the most distant manmade object from Earth, a record that it will keep for the foreseeable future. Even the faster (at its launch) New Horizons space probe will not pass it, since the final speed of New Horizons (after maneuvering within the solar system) will be less than the current speed of Voyager 1.

Voyager 1 and Pioneer 10 are the most widely separated manmade objects anywhere, since they are traveling in roughly opposite directions from the Solar System.

Periodic contact has been maintained with Voyager 1 and Voyager 2 to monitor conditions in the outer expanses of the Solar System. The radioactive power sources of both spacecraft were still producing significant amounts of electric power as of 2012, keeping them operational, and it is hoped that this will allow the heliopause of the Solar System to be located and investigated.

In late 2003 Voyager 1 began sending data that seemed to indicate it had crossed the termination shock, but interpretations of these data are in dispute, and it was later believed that the termination shock was crossed in December 2004. The heliopause remains an unknown distance ahead.

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, and is traveling outward at roughly 3.3 AU per year.

In 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 thus had entered the heliosheath region between the solar wind's termination shock and the heliopause (the limit of the solar wind). Beyond the heliopause is the bow shock of the interstellar medium, beyond which the probes enter interstellar space and the Sun's gravitational influence on them is exceeded by that of the Milky Way galaxy in general. At the heliopause, light from the Sun takes over 16 hours to reach the probe.

By December 2010 Voyager 1 had reached a region of space where there was no net velocity of the solar wind. At this point, the wind from the Sun may be canceled out by the interstellar wind. It does not appear that the spacecraft has yet crossed the heliosheath into interstellar space.

On June 10, 2011, scientists studying the Voyager data noticed what may be giant magnetic bubbles located in the heliosphere, the region of our solar system that separates us from the violent solar winds of interstellar space. The bubbles, scientists theorize, form when the magnetic field of the Sun becomes warped at the edge of our Solar System.