40 years of exploring space

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By 2017-09-10

Voyager 1 and 2 achieve 40 years of operation and exploration this August and September, 2017. Despite their vast distance, they continue to communicate with NASA daily.

Voyager was born when it was observed that several planets would be aligning in a very convenient fashion in the late '70s – a once-in-several-lifetimes opportunity to visit them all in one trip. Or two, as it turns out. Because it would be difficult and expensive to carry out a trajectory that hit all targets perfectly (not to mention if something went wrong, they were sunk), NASA decided to send two identical craft, one after the other.

Voyager 2 launched on 20 August 1977, from Cape Canaveral, Florida aboard a Titan-Centaur rocket. On 5 September 1977, Voyager 1 launched, also from Cape Canaveral aboard a Titan-Centaur rocket.

Everything – well, mostly everything – worked out as planned, and Voyager has been one of the most productive and surprising missions ever undertaken in space.

The Golden Record

As long as you're sending something into interstellar space, why not prepare it for the possibility of extra-terrestrial interception?

"Moonshot" doesn't adequately describe the ambition of the Golden Record project and the astronomically small odds of it ever being encountered by intelligent life, but that isn't really the point.

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 space farers 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 extra-terrestrials. 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, (including Sri Lanka's "Ayubowan") and printed messages from President Carter and U.N. Secretary General Waldheim.

Each record is encased in a protective aluminium 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."

The definitive work about the Voyager record is Murmurs of Earth by Executive Director Carl Sagan, Technical Director Frank Drake, Creative Director Ann Druyan, Producer Timothy Ferris, Designer Jon Lomberg, and Greetings Organizer Linda Salzman. 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 with 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.

The record and Voyager have inspired generations with the idea that it's worth it to explore and try things just because we can, and because it's part of our makeup. The very human contents of the Golden Record were curated by Carl Sagan, among the most humanitarian of scientists. The idea that our unique presence, from our biology to our ideas of beauty and philosophy, is blasting through outer space is awe-inspiring.

Discoveries

The twin Voyager 1 and 2 spacecraft are exploring where nothing from Earth has flown before. Continuing on their more-than-39-year journey since their 1977 launches, they each are much farther away from Earth and the sun than Pluto. In August 2012, Voyager 1 made the historic entry into interstellar space, the region between stars, filled with material ejected by the death of nearby stars millions of years ago. Scientists hope to learn more about this region when Voyager 2, in the "heliosheath" – the outermost layer of the heliosphere where the solar wind is slowed by the pressure of interstellar medium – also reaches interstellar space. Both spacecraft are still sending scientific information about their surroundings through the Deep Space Network, or DSN.

The primary mission was the exploration of Jupiter and Saturn. After making a string of discoveries there – such as active volcanoes on Jupiter's moon Io and intricacies of Saturn's rings – the mission was extended. Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. The adventurers' current mission, the Voyager Interstellar Mission (VIM), will explore the outermost edge of the Sun's domain. And beyond.

Between them, Voyager 1 and 2 explored all the giant planets of our outer solar system, Jupiter, Saturn, Uranus and Neptune; 48 of their moons; and the unique system of rings and magnetic fields those planets possess.

Closest approach to Jupiter occurred on 5 March 1979 for Voyager 1; 9 July 1979 for Voyager 2.

Closest approach to Saturn occurred on 12 November 1980 for Voyager 1; 25 August 1981 for Voyager 2.

Closest approach to Uranus occurred on 24 January 1986 by Voyager 2.

Closest approach to Neptune occurred on 25 August 1989 by Voyager 2.

The Voyager spacecraft are the third and fourth human spacecraft to fly beyond all the planets in our solar system. Pioneers 10 and 11 preceded Voyager in outstripping the gravitational attraction of the Sun but on 17 February 1998, Voyager 1 passed Pioneer 10 to become the most distant human-made object in space.

Present status

As of August 2017, Voyager 1 was at a distance of 20.8 billion kilometres (139.3 AU) from the Sun. an One Astronomical Unit (AU) is the mean distance of Earth from the Sun, about 150 million kilometres.

Voyager 2 was at a distance of 17.2 billion kilometres (115 AU).

Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year.

Voyager 2 is escaping the solar system at a speed of about 3.3 AU per year.

There are currently five science investigation teams participating in the Interstellar Mission. They are:

1. Magnetic field investigation
2. Low energy charged particle investigation
3. Cosmic ray investigation
4. Plasma Investigation (Voyager 2 only)
5. Plasma wave investigation

Five instruments on board the Voyagers directly support the five science investigations. The five instruments are:

1. Magnetic field instrument (MAG)
2. Low energy charged particle instrument (LECP)
3. Cosmic ray instrument (CRS)
4. Plasma instrument (PLS)
5. Plasma wave instrument (PWS)

One other instrument is collecting data but does not have official science investigation associated with it: the Ultraviolet spectrometer subsystem (UVS), Voyager 1 only.

Termination shock

Voyager 1 crossed the termination shock in December 2004 at about 94 AU from the Sun while Voyager 2 crossed it in August 2007 at about 84 AU. Both spacecraft are now exploring the Heliosheath. The termination shock is the boundary marking one of the outer limits of the Sun's influence, and is one boundary of the Solar System.

The Heliosphere

The heliosphere is a bubble around the sun created by the outward flow of the solar wind from the sun and the opposing inward flow of the interstellar wind. That heliosphere is the region influenced by the dynamic properties of the sun that are carried in the solar wind – such as magnetic fields, energetic particles and solar wind plasma. The heliopause marks the end of the heliosphere and the beginning of interstellar space. Voyager 1, which is traveling up away from the plane of the planets, entered interstellar space on 25 August 2012. Voyager 2, which is headed away from the sun beneath the plane of the planets, is expected to pass beyond the heliosphere and enter interstellar space in the coming years.
(Source: voyager.jpl.nasa.gov, techcrunch.com)

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