In the cold dark recesses of space a single mission carries the torch for humanity. Voyager 1 and 2 are soon to leave the solar system completely, entering deep space with its sensors being our eye’s and ears. Will they be required to stay left unless overtaking on some inter-galactic super highway ? That’s the adventure, we don’t know. The Voyager space craft have a history of surprising us, a tradition that will continue as long as the batteries hold up.

“They are about to break free of the solar system,” Ed Stone, Voyager project scientist at Caltech in Pasadena, Calif., said during a media teleconference (April 28). “We are trying to get outside of our bubble, into interstellar space, to directly measure what is there.”

The Voyager craft have reached the outer border of our solar system, the heliosphere. The heliosphere is the border-land between our solar system and deep space, like the shiny surface of a bubble. The heliosphere marks the end of the Sun’s sphere of influence, it is where the solar winds run out of steam and the furthest point of the magnetic field. Voyager 1 passed the first layer of the heliosphere, the termination shock and entered the heliosheath in the middle of December 2004.

The Termination Shock is the first layer of the heliosphere, marking the point the solar winds have slowed to subsonic speeds as it starts to mix with the interstellar medium – the matter, gas and plasma that makes up the space between the stars -. The second layer, the Heliosheath is an area of turbulence caused by the slowing solar wind and interaction or mixing with the interstellar medium. Heliopause is the next region the Voyager will move through, an region where the solar wind has stopped due to its force being balanced by the pressure of the interstellar medium. Then it’s on to deep space, Voyager will then be humanities first inter-stellar space craft.

“The heliosheath looks to be about 3 to 4 billion miles (4.8 to 6.4 billion km) thick, and the spacecraft are already well into it. Based on their speed, they should be out in about five years.” Stone said.

Launched in 1977 the Voyager space craft were dispatched to study the giant planets of our solar system, Jupiter and Saturn. Also on their itinerary were the many moons of both planets. By March and July of 1979 both craft had encountered Jupiter collecting some of the most detailed information and pictures ever. By 1982 both craft had completed their original missions, Saturn and her associated moons had been documented, Europa’s oceans measured. The volcano’s of Io captured in pictures. After the success of the Jupiter and Saturn flyby’s the Voyager program was extended to study the outer planets Uranus and Neptune. Between them, the two spacecraft have explored all of the giant outer planets of our solar system; Jupiter, Saturn, Uranus and Neptune, their 49 moons, ring systems and magnetic fields.

To this day the Voyager craft continues to play an important role in many new discoveries. Recently scientists used data from voyager to confirm the existence of powerful magnet fields and clouds of fluffy dust just outside our solar systems protective bubble, the Heliosphere. This along with direct measurements of the solar winds within the heliosphere are helping scientists to better explain how the solar winds and inter-stellar winds interact.

The sensors of both craft are incredibly still operational after 33 years – originally a 4 year mission -. The cosmic ray detector, magnetometer, plasma wave detector and low-energy charged particle detector are all still functioning. Voyager 1’s ultraviolet spectrometer and Voyager 2’s plasma science instrument continue to transmit data. During the extended part of their mission’s the Voyagers have sent home 65 billion bits of information. Information that is transmitted in real-time by the 20watt transmitter on each Voyager, this faint signal takes 14 hours to reach Earth – even at the speed of light – and is picked up by NASA’s 34-meter Deep Space Network antennas in California, Australia and Spain.

The original Voyager program was called the Grand Tour an extension of the Mariner Inter-planetary exploration program. It was to include 4 Voyager space craft studying all of the outer planets. NASA usual habit of spoiling the party occurred early on, budget cuts reduced the number space craft from 4 to 2, the mission was also reduced to the study of Jupiter and Saturn. Six months before the launch one final change was made and the program was renamed Voyager.

It hasn’t been all smooth sailing for the Voyager space-craft either, early on there were problems directing the antenna. Both space-craft have been re-programmed a number of times to work around problems. At one point the recording tape for a camera become corrupted in the middle so it was reprogrammed to only use the outer edges.

The design of the Voyager craft was the culmination of many years of experience building and launching exploration satellites, that was the Mariner program. The Mariner program was NASA’s early testing grounds, from 1963 to 1973 Mariner taught NASA everything that went into the Voyager craft. Of the ten vehicles in the Mariner series, seven were successful and three were lost. The earlier Mariner missions concentrated on the inner planets, Mars, Mercury and Venus. Voyager 1 & 2 were initially designated as Mariner 11 and 12, before the budget cuts to the Grand Tour missions, they were still considered a part of Mariner program. Of the many lessons learned from Mariner was flexibility, lesson number one. The ability to reprogram the craft on the fly was essential to their continued success. The flexibility of the design wasn’t just for emergencies either, both Voyager craft had flight plan changes mid mission. This was seen through-out the early years with changes to the flight path being common. Once the intended missions were completed this flexibility allowed flight control to continue with the extended flight plan including Pluto and Neptune and now 33 years after their launch, the Heliosphere.

The greatest limitation for any space-craft is battery power and rocket fuel. Voyager 1 and 2 both use nuclear batteries, radioisotope thermal electric generators (RTGs). RTG’s use the heat – radioactive decay – from a chunk of plutonium to generate electricity, this form of battery has extremely long life, enough to keep both Voyager’s running until 2020 and maybe beyond. Both craft also have enough hydrazine fuel left to perform maneuvers for another 60 years.

Both space-craft carry a copy of the Golden Record, a time capsule introduction to humanity. On the record are sounds of our world, greetings in many languages, 116 images, where Earth is located and other information about us. The Golden Records have gained a lot of pop culture credibility, appearing in films like Beast Wars – it was the disk – , Star Trek the original motion picture featured V’Ger the remnants of the ancient Voyager’s Satellite with Golden Record and Futurama treats Voyager as bug kill on their spaceships windscreen. Fitting too that the disks were placed on the craft furthest away from earth. Humanities torch. On February 17, 1998 Voyager 1 passed the Pioneer 10 space-craft as the furthest away man-made object, a record now shared by both voyager space-craft. Voyager 1 is now over 17 billion km’s from Earth while Voyager 2 is close behind at 14 billion km’s from Earth.

Recently Voyager 2 has been making the headlines for all of the wrong reasons. The head-lines read “Have aliens hijacked Voyager 2 spacecraft “, no really. On April 22, 2010 Voyager 2 changed the language it spoke to NASA in. NASA were no longer able to decode Voyager 2’s instrument data transmissions. Technicians quickly began working to fix the glitch, sending new commands and testing systems. By May 25 transmissions had resumed, with the problem found to be a single bit had flipped itself from one to zero in it’s central computer. Still the incident drew some interesting commentary, so called alien expert Hartwig Hausdorf said:”It seems almost as if someone had reprogrammed or hijacked the probe – thus perhaps we do not yet know the whole truth”.

By far our favorite interplanetary and now inter-stellar craft the Voyager 1 and 2 have been our eyes and ears on this expedition of discovery. There are a number of danger periods ahead, the Heliosphere is a big unknown with deep space beyond that being even more of an unknown quantity. Hopefully our two scouts will continue on to deep space, keep blipping bits of information back to us about what is really out there.

More information at NASA