Artist concept of the two Voyager spacecraft as they approach interstellar space. Image credit: NASA/JPL

Voyager 1, already the most distant human-made object in the cosmos, reaches 100 astronomical units from the sun on Tuesday, August 15 at 5:13 p.m. Eastern time (2:13 p.m. Pacific time). That means the spacecraft, which launched nearly three decades ago, will be 100 times more distant from the sun than Earth is.

In more common terms, Voyager 1 will be about 15 billion kilometers (9.3 billion miles) from the sun. Dr. Ed Stone, Voyager project scientist and the former director of NASA's Jet Propulsion Laboratory in Pasadena, Calif., says the Voyager team always predicted that the spacecraft would have enough power to last this long.

"But what you can't predict is that the spacecraft isn't going to wear out or break. Voyager 1 and 2 run 24 hours a day, seven days a week, but they were built to last," Stone said. The spacecraft have really been put to the test during their nearly 30 years of space travel, flying by the outer planets, and enduring such challenges as the harsh radiation environment around Jupiter.

The spacecraft are traveling at a distance where the sun is but a bright point of light and solar energy is not an option for electrical power. The Voyagers owe their longevity to their nuclear power sources, called radioisotope thermoelectric generators, provided by the Department of Energy.

Voyager 1 is now at the outer edge of our solar system, in an area called the heliosheath, the zone where the sun's influence wanes. This region is the outer layer of the 'bubble' surrounding the sun, and no one knows how big this bubble actually is. Voyager 1 is literally venturing into the great unknown and is approaching interstellar space. Traveling at a speed of about one million miles per day, Voyager 1 could cross into interstellar space within the next 10 years.

"Interstellar space is filled with material ejected by explosions of nearby stars," Stone said. "Voyager 1 will be the first human-made object to cross into it."

Voyager Project Manager Ed Massey of JPL says the survival of the two spacecraft is a credit to the robust design of the spacecraft, and to the flight team, which is now down to only 10 people. "But it’s these 10 people who are keeping these spacecraft alive. They're very dedicated. This is sort of a testament to them, that we could get all this done."

Between them, the two Voyagers have explored Jupiter, Uranus, Saturn and Neptune, along with dozens of their moons. In addition, they have been studying the solar wind, the stream of charged particles spewing from the sun at nearly a million miles per hour.

Source: by Jane Platt, JPL NASA

New Discoveries at the Edge of the Solar System
http://www.nasa.gov
05.23.06

As the 28-year-old Voyagers 1 and 2 spacecraft approach the edge of interstellar space, they have found that the heliosphere, the "bubble" within which the sun dominates, bulges outward in the northern hemisphere and is pressed inward in the south. Voyager 1, flying about 34 degrees north of the equator, crossed the termination shock and entered the outermost layer of the heliosphere about 9 billion miles from the sun. Meanwhile Voyager 2, about 26 degrees south of the equator, finds that the shock may be nearly a billion miles closer to the sun.

Scientists believe that the observed discrepancies may be attributed to an interstellar magnetic field pressing inward on the southern hemisphere. Voyager 2 will determine the exact location of the shock in the south when it crosses it sometime before the end of next year. Then scientists will have a better idea of how strong the magnetic field is outside of the heliospheric bubble.

Voyager 2 is also finding that the shock in the south is a source of low energy ions as was discovered by Voyager 1 in the north. Contrary to earlier predictions, however, neither Voyager 1 nor 2 have found the source of higher energy anomalous cosmic rays.

Both Voyager spacecraft were launched from the Cape Canaveral Air Force Station in Florida: Voyager 2 on Aug. 20, 1977 and Voyager 1 on Sept. 5, 1977 on a faster, shorter trajectory than its twin. The mission is managed for NASA by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology.

Voyager Multimedia

"Twenty-five years ago, on November 12, 1980 at 3:56 PM PST, the Voyager 1 spacecraft made its closest approach to Saturn in mankind's first detailed reconnaissance of that giant planet. One hour and 25 minutes later, the signal from that moment arrived at Earth, while the world waited in awe as picture after picture unfolded on monitors at JPL showing never-before-seen details of the Saturn, its rings and satellites. Voyager remains NASA's most successful planetary mission as measured by total number of scientific discoveries.."

"Voyager 1 flew under Saturn's south pole, a requirement to get a close look at Titan. Saturn's gravity caused the trajectory to bend northward out of the ecliptic plane, precluding any further planetary encounters. The success of the Titan encounter (hazy though it was), set the stage for Voyager 2 to continue on to Uranus and Neptune. Had Titan not been successful, Voyager 2 would have followed its in the footsteps of its twin, and the Uranus and Neptune encounters would not have been possible.

Voyager 1 discovered three satellites, a dynamic and complex ring structure with ring spokes, shepherding moons and far more structure than had been previously imagined...
A huge impact crater was found on the satellite Mimas that nearly broke it apart - added to the fact that Mimas, with its crater, appeared as nearly a carbon copy of the Star Wars Death Star, which had been invented only about 2 years earlier here on Earth..."

Voyager Finds Three Surprises Near Our Solar System's Edge
physorg.com
Sep 27, 2005 The surprises come as the hardy, long-lived spacecraft approaches the edge of our solar system, called the heliopause, where the sun's influence ends and the solar wind smashes into the thin gas between the stars.

"These are just the most recent of many surprises Voyager has revealed in its 28-year journey of discovery. They tell us that the interaction of our sun with the surrounding interstellar matter from other stars is more dynamic and complex than we had imagined, and that there is more yet to be learned as Voyager begins the final leg of its race to the edge of interstellar space," said Dr. Edward Stone, Voyager project scientist at the California Institute of Technology in Pasadena.

Voyager 1 is expected to pass beyond the heliopause into interstellar space in eight to 10 years, with Voyager 2 expected to follow about five years later.

Voyager 1 has already passed the termination shock, where the million-mile-per-hour solar wind abruptly slows and becomes denser and hotter as it presses against interstellar gas. It was expected the wind beyond the shock would slow to a few hundred thousand miles per hour. But the Voyager scientists were surprised to find that the speed was much less, and at times the wind appeared to be flowing back inward toward the sun.

"This could mean that the outward pressure of wind was decreasing as the sun entered the less active phase of its 11-year cycle of sunspot activity," said Stone.

Another surprise: the direction of the interplanetary magnetic field in the outer solar system varied more slowly beyond the termination shock. As the sun rotates every 26 days, the direction of the field alternates every 13 days.

That field is carried out by the solar wind, with the alternating directions forming a pattern of zebra stripes moving outward past the spacecraft. One could imagine a zebra with giant "magnetic stripes" running past the spacecraft and Voyager 1 "observing" an alternating stripe every 13 days. After the shock, the "zebra" with its stripe pattern was moving at nearly the same speed as Voyager, so that it took more than 100 days for the stripe to pass the spacecraft and for the magnetic field to switch directions.

Perhaps the most puzzling surprise is what Voyager 1 did not find at the shock. It had been predicted that interstellar ions would bounce back and forth across the shock, slowly gaining energy with each bounce to become high speed cosmic rays.

Because of this, scientists expected those cosmic ray ions would become most intense at the shock. However, the intensity did not reach a maximum at the shock, but has been steadily increasing as Voyager 1 has been moving farther beyond the shock. This means that the source of those cosmic rays is in a region of the outer solar system yet to be discovered.

Still operating in remote, cold and dark conditions billions of miles from the sun, the Voyager 1 and 2 spacecraft owe their longevity to radioisotope thermoelectric generators which produce electricity from the heat generated by the natural decay of plutonium.

Caltech manages NASA's Jet Propulsion Laboratory in Pasadena, which built and operates Voyager 1 2. NASA's Goddard Space Flight Center, Greenbelt, Md., built the magnetometers.

Golden Record
http://voyager.jpl.nasa.gov/

Pioneers 10 and 11, which preceded Voyager, both carried small metal plaques identifying their time and place of origin for the benefit of any other spacefarers that might find them in the distant future. With this example before them, NASA placed a more ambitious message aboard Voyager 1 and 2-a kind of time capsule, intended to communicate a story of our world to extraterrestrials. The Voyager message is carried by a phonograph record-a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth. The contents of the record were selected for NASA by a committee chaired by Carl Sagan of Cornell University.

Dr. Sagan and his associates assembled 115 images and a variety of natural sounds, such as those made by surf, wind and thunder, birds, whales, and other animals. To this they added musical selections from different cultures and eras, and spoken greetings from Earth-people in fifty-five languages, and printed messages from President Carter and U.N. Secretary General Waldheim. Each record is encased in a protective aluminum jacket, together with a cartridge and a needle. Instructions, in symbolic language, explain the origin of the spacecraft and indicate how the record is to be played.

The 115 images are encoded in analog form. The remainder of the record is in audio, designed to be played at 16-2/3 revolutions per minute. It contains the spoken greetings, beginning with Akkadian, which was spoken in Sumer about six thousand years ago, and ending with Wu, a modern Chinese dialect. Following the section on the sounds of Earth, there is an eclectic 90-minute selection of music, including both Eastern and Western classics and a variety of ethnic music. Once the Voyager spacecraft leave the solar system (by 1990, both will be beyond the orbit of Pluto), they will find themselves in empty space. It will be forty thousand years before they make a close approach to any other planetary system. As Carl Sagan has noted, “The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space. But the launching of this bottle into the cosmic ocean says something very hopeful about life on this planet.”

Information About the Earth and Its Inhabitants Included on the Record Want to know more about Voyager's record?

The definitive work about the Voyager record is "Murmurs of Earth" by Sagan, Drake, Lomberg et.al. Basically, this book is the story behind the creation of the record, and includes a full list of everything on the record. "Murmurs of Earth", originally published in 1978, was reissued in 1992 by Warner News Media and includes a CD-ROM that replicates the Voyager record. Unfortunately, this book is now out of print, but it is worth the effort to try and find a used copy or browse through a library copy.