Historical Tales

As Voyager I continues its 35-year mission exploring the solar system, it is about to cross the 'final frontier' of the heliopause into interstellar space.

On September 5, 1977, Chicago Bulls' center Nazr Mohammed was born. The much-anticipated "Fonzie Moves In" episode of Happy Days was a short four days from airing. The Emotions' Best of My Love topped the pop charts. Hurricane Babe made landfall in Louisiana. Dweezil Zappa turned seven.

Oh, and as Columbo would say just before exiting the premises, just just one more thing: Voyager 1 launched from Space Launch 41 at Cape Canaveral, Florida.

Thirty-five years later, all have diminished or become mere shadows of their former selves, except for one: the venerable, undeniable Voyager I spacecraft. With its twin sister Voyager 2 not far behind, new data suggests both are close to crossing the last vestiges of our solar system and into interstellar space — a first for a man-made object.

Voyager specifications

Given that both probes are still functional and sending back data after more than a third of a century of space travel and given that Pong was the state-of-the-art video game at the time, one might think the Voyager spacecrafts were exceedingly primitive, not much more than reinforced-steel garbage cans with blinking lights like R2D2 in Star Wars. Au contraire:

• Spacecraft mass: 2,080 kilograms (4,586 pounds)
• Launch vehicle: Titan III E-Centaur (TC-6 / Titan no. 23E-6 / Centaur D-1T
• Spacecraft Instruments: 1) imaging system; 2) ultraviolet spectrometer; 3) infrared spectrometer; 4) planetary radio astronomy experiment; 5) photopolarimeter; 6) magnetometers; 7) plasma particles experiment; 8) low-energy charged-particles experiment; 9) plasma waves experiment and 10) cosmic-ray telescope
• Spacecraft Power: 3 plutonium oxide radioisotope thermoelectric generators (RTGs)
• Total Cost: $875 million for Voyager 1 and 2 through the end of the Neptune phase of the Voyager 2 mission. An additional $30 million was allocated for the first 2 years of the Voyager Interstellar Mission.
• NASA center: Jet Propulsion Laboratory, La Canada/Flintridge, CA

With the exception of Voyager 1's Plasma Science instrument, the remainder are still functioning properly. Humorously, the DTR (Digital Tape Recorder) utilizes disco-era 8-track tape technology. In space, no one can hear you dance.

Voyager mission highlights

Although Voyager 2 launched sixteen days earlier, Voyager 1 reached Jupiter and Saturn in 1979 and 1980, respectively, months ahead of its slower-speed twin probe. Following spectacular encounters by each spacecraft with the massive gas giant planets, their paths forever separated. Voyager 1 veered on a trajectory just below the orbital plane on its way out of the solar system, while Voyager 2 flew by Uranus in 1986 and Neptune in 1989, the first such visits to either planet. After more groundbreaking images and discoveries, Voyager 2 proceeded on its long journey out of the solar system.

Today, Voyager 1 is 11.2 billion miles away, hurtling through the cosmos at over 38,000 miles per hour. Traveling at the speed of light, its communications take over 16 hours to reach the Earth. Voyager 2 is 9.1 billion miles away, cruising at roughly 34,500 miles per hour. As a point of reference, the New Horizons probe heading inexorably toward a 2015 Pluto encounter is 2.14 billion miles from Earth — less than one-fifth the distance of Voyager 1.

Voyager 1 and interstellar space

The solar system is surrounded by the heliosphere, a "bubble" consisting of charged particles emitted by the Sun and carried by the solar wind. For over six billion miles of its radius, the solar wind travels at speeds in excess of 600,000 miles per hour. The point in which its speed begins to decrease is called the termination shock. It further slows in the heliosheath, leading to a point where the interstellar medium and solar wind pressures balance called the heliopause, the very edge of the sun's influence. Beyond that is interstellar space.

Recent data transmitted from Voyager 1 suggests the craft is approaching the heliopause. On July 28, high-energy cosmic rays from outside the solar system spiked by 5%. On that same day, charged particles emanating from within the solar system decreased by roughly 50%. Both sets of data have fluctuated since since that time. Scientists are analyzing readings with respect to the direction of the magnetic field, another key indicator as to the end of the solar system, and thus the beginning of interstellar space.

"These are thrilling times for the Voyager team,' said Edward Stone, Voyager project scientist. "The data are changing in ways that we didn't expect, but Voyager has always surprised us with new discoveries." Suzanne Dodd, Voyager project manager, agreed. "We know they will cross into interstellar space," she said. "It's just a question of when."

Live long and prosper, Voyager. In about 40,000 years or so, you might even fly past the planet Vulcan — assuming its host star is AC+79 3888.

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