Space Sunday: Voyager at 40

Voyager: 40 years on. Credit: NASA

August 20th 2017 marks the 40th anniversary of the launch of Voyager 2, which with its sister craft Voyager 1 (launched on September 5th, 1977) are humanity’s furthest-flown operational space vehicles, with Voyager 1 being the most distant human made object from Earth, at some 140 AU (AU= astronomical unit, the average distance between the Earth and the Sun; 140 AU equates to about 20.9 billion kilometres / 13 billion miles).

Despite being so far away from Earth, both craft are still sending data back to Earth as they fly through the interstellar medium in the far reaches of the solar system (the Pioneer 10 and Pioneer 11 craft which pre-date the Voyager programme by some 5 years, ceased transmissions to Earth in January 2003 and September 1995 respectively, although Pioneer 10 is the second most distant human made object from Earth after Voyager 1).

The Voyager programme stands as one of the most remarkable missions of early space exploration. Originally, the two vehicles were to be part of NASA’s Mariner programme, and were at first designated Mariner 11 and Mariner 12 respectively. The initial Mariner missions – 1 through 10 – were focused on studying the interplanetary medium and  Mars, Venus and Mercury (Mariner 10 being the first space vehicle to fly by two planets beyond Earth – Venus and Mercury – in 1974). Mariner 11 and Mariner 12 would have been an expansion of the programme, intended to perform flybys of Jupiter and Saturn.

A drawing of the Voyager vehicles. Credit: NASA/JPL (click for full size)

However, in the late 1960s Gary Flandro, an aerospace engineer at the Jet Propulsion Laboratory (JPL) in California noted that in the late 1970s, the outer planets would be entering a period of orbital alignment which occurs once every 175 years and which could be used to throw a series of probes out from Earth, which could then use the gravities of the worlds they encountered to “slingshot” them on to other targets. This led to the idea of a “Grand Tour” mission: sending pairs of probes which could use these gravity assists to fly by Jupiter, Saturn, Uranus, Neptune and Pluto in various combinations.

Funding limitations eventually brought an end to the “Grand Tour” idea, but the planetary alignment was too good an opportunity to miss, and so elements of the idea were folded into the Voyager Programme, which would utilise Mariner 11 and Mariner 12. However, as the mission scope required some significant changes to the vehicles from the basic Mariner design, they were re-designated as Voyager class craft.

(As an aside, the Mariner class is the longest-lived of NASA’s space probe designs; as well as the ten missions of the 1960s and 1970s which carried the design’s name,  the Mariner baseline vehicle – somewhat enlarged – was used for the Viking 1 and Viking 2 orbiter missions to Mars, and formed the basis of the Magellan probe (1989-1994)  to Venus and the Galileo vehicle (1989-2003) which explored Jupiter. And uprated and updated baseline Mariner vehicle, designated “Mariner Mark II”, formed the basis of the Cassini vehicle, now in the terminal phase of its 13-year study of Saturn and its moons.)

Each of the Voyager mission vehicles is powered by  three plutonium-238 MHW-RTG radioisotope thermoelectric generators (RTGs), which provided approximately 470 W at 30 volts DC when the spacecraft was launched. By 2011, both the decay of the plutonium and associated degradation of the thermocouples that convert heat into electricity has reduced this power output by some 57%, and is continuing at a rate of about 4 watts per year.

To compensate for the loss, various instruments on each of the vehicles have had to be turned off over the years. Voyager 2’s scan platform and the six instruments it supports, including the vehicle’s two camera systems, was powered-down in 1998. While the platform on Voyager 1 remains operational, all but one of the instruments it supports – the ultraviolet spectrometer (UVS) – have also been powered down. In addition, gyro operations ended in 2016 for Voyager 2 and will end in 2017 for Voyager 1. These allow(ed) the craft to rotate through 360 degrees six times per year to measure their own magnetic field, which could then be subtracted from the magnetometer science data to gain  accurate data on the magnetic fields of the space each vehicle is passing through.

However, despite the loss of capabilities, both Voyager 1 and Voyager 2 retain enough power to operate the instruments required for the current phase of their mission – measuring the interstellar medium and reporting findings back to Earth. This phase of the mission, officially called the Voyager Interstellar Mission, essentially commenced in 1989 as Voyager 2 completed its flyby of Neptune, when the missions as a whole was already into their 12th year.

A plume rises 160 km (100 mi) above Loki Patera, the largest volcanic depression on Io, captured in March 1979 by Voyager 1. Credit: NASA/JPL

Voyager 2 was launched on August 20th, 1977. Of the two vehicles, it was tasked with the longer of the planned interplanetary missions, with the aim of flying by Jupiter, Saturn, Uranus and Neptune. However, the latter two were seen as “optional”, and dependent upon the success of Voyager 1.

This was because scientists wanted the opportunity to look at Saturn’s moon Titan. But doing so would mean the Voyager craft doing so would have to fly a trajectory which would leave it unable to use Saturn’s gravity to swing it on towards an encounter with Uranus. Instead, it would head directly towards interstellar space.

So it was decided that Voyager 1, which although launched after Voyager 2 would be able to travel faster, would attempt the Titan flyby. If it failed for any reason, Voyager 2 could be re-tasked to perform the fly-past, although that would also mean no encounters with Uranus or Neptune. In the end, Voyager 1 was successful, and Voyager 2 was free to complete its surveys of all four gas giants.

Along the way, both missions revolutionised our understanding of the gas giant planets and revealed much that hadn’t been expected, such as discovering the first active volcanoes beyond Earth, with nine eruptions imaged on Io as the vehicles swept past Jupiter. The Voyager missions were also the first to find evidence that Jupiter’s moon Europa might harbour a subsurface liquid water ocean and to return the first images of Jupiter’s tenuous and almost invisible ring system. Voyager 1 was responsible for the first detailed examination of Titan’s dense, nitrogen-rich atmosphere, and Voyager 2 for the discovery of giant ice geysers erupting on Neptune’s largest moon, Triton. In addition, both of the Voyager vehicles added to our catalogues of moons in orbit around Jupiter and Saturn, and probed the mysteries of both planet’s atmospheres, whilst Voyager 2 presented us with our first images of mysterious Uranus and Neptune – and thus far remains the only vehicle from Earth to have visited these two worlds.

This is the last full planet image captured of Neptune. Taken by Voyager 2 on August 21st, 1989, from a distance of 7 million km (4.4. million mi). A true colour image white balanced to reveal the planet under typical Earth lighting conditions, it shows Neptune’s “Great Dark Spot” and surrounding streaks of lighter coloured clouds, all of which persisted through the period of Voyager 2’s flyby. More recent Hubble Space Telescope images suggest the “Great Dark Spot”, initially thought to be a possible cloud / storm formation, similar to Jupiter’s Great Red Spot, has vanished, leading to speculation that it may have actually been a “hole” in a  layer of Neptune’s layered clouds. Credit: NASA/JPL

The flyby of Neptune also sealed Voyager 2’s future. Scientists were keen to use the flyby of the planet to take a look at Triton, Neptune’s largest moon. However, because Triton’s orbit around Neptune is tilted significantly with respect to the plane of the ecliptic, Voyager 2’s course to Neptune  had to be adjusted by way of a gravitational assist from Uranus and a number of mid-course corrections both before and after that encounter, so that on Reaching Neptune, it would pass over the north pole, allowing it to bent “bent” down onto an intercept with Triton while the Moon was at  apoapsis – the point furthest from Neptune in its orbit – and well below the plane of the ecliptic. As a result, Voyager 2 passed over Triton’s north pole 24 hours after its closest approach to Neptune, its course now pointing it towards “southern” edge of the solar system.

Continue reading “Space Sunday: Voyager at 40”

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Garridebs, beyond human, summer recalled and sisterhood

Seanchai Library, Holly Kai Park

It’s time to kick-off another week of storytelling in Voice by the staff and volunteers at the Seanchai Library. As always, all times SLT, and events are held at the Library’s home at Holly Kai Park, unless otherwise indicated.

Sunday, August 13th

13:30: Tea-Time at Baker Street

Tea-time at Baker Street continues with readings from The Casebook of Sherlock Holmes, the final set of twelve Sherlock Holmes short stories first published in the Strand Magazine between October 1921 and April 1927.

This week: The Adventure of the Three Garridebs.

When is a Garrideb not a Garrideb? That’s the question that vexes Sherlock Holmes. or more correctly, Why is a Garrideb not, in fact, a Garrideb; it’s not a particularly common name.

So when he hears from one and is confronted by another, his suspicions are aroused even before the Garrideb – or the man claiming to be Mr. John Garrideb, formerly of Kansas, in the United States – who visits him starts spouting an unlikely tale of inheritances and land tycoons full of its own inconsistencies.

The key to the mystery appears to reside in, or with the personage of Mr. Nathan Garrideb, an elderly eccentric who has every appearance of being a genuine Garrideb. So what is going on? An attempt to defraud the old man? An attempt to steal something of value from him? Yet “John Garrideb”, having already been in contact with Nathan Garrideb, has never requested money from the older man; and while the elder Garrideb is a collector of just about anything he can keep in his rooms, none of it would appear to be of any intrinsic value.

Yet something is clearly going on, particularly when “John Garrideb” arrives at Nathan’s Garrideb’s rooms announcing he has found a third Garrideb – this one in Birmingham. A visit with Inspector Lestrade helps to confirm Holmes’ suspicions…

18:00: Magicland Storytime: The Black Cauldron

Join Caledonia Skytower at Magicland Park.

Monday, August 14th 19:00: More Than Human

Gyro Muggins reads Theodore Sturgeon’s genre-bending 1953 novel which brings together three of her earlier works   to weave a story about people with extraordinary abilities which can be combined – “bleshed” (itself a blending of “blend” and “mesh”) to make them even more extraordinary.

Take, for example, Lone, the simpleton who can hear other people’s thoughts and make a man blow his brains out just by looking at him; or Janie, who moves things without touching them. Then there are the teleporting twins, who can travel ten feet or ten miles, and Baby, who invented an anti-gravity engine while still in the cradle, and Gerry, who has everything it takes to run the world except for a conscience.

Six people struggling to find who they are and whether they are meant to help humanity, destroy it, or represent the next step in evolution, the final chapter in the history of the human race. Through them, Theodore Sturgeon explores questions of power and morality, individuality and belonging, with suspense, pathos, and a lyricism rarely seen in science fiction.

Tuesday, August 15th 19:00: One Summer, America 1927

The summer of 1927 was, for the United States, a signature period of the 20th Century. On May 21st, Charles Lindbergh became the first man to make a non-stop crossing of the Atlantic in an aeroplane when The Spirit of St Louis arrived at Le Bourget airfield, near Paris.

Through that summer, Babe Ruth was setting his record for the number of home runs in baseball, while one of the most infamous murder trials in New York’s history took place: that of  Ruth Snyder and her married lover, Henry Judd Gray. They stood accused – and were eventually found guilty of – garrotting of Snyder’s husband in what was a tabloid sensation case.

Meanwhile, in the south the Mississippi burst its banks, leading to widespread flooding and a huge human disaster. Far to the north, Al Capone continued his reign of criminal terror in Chicago, while on the west coast, history was being made with the filming of the world’s first “talking picture” in the form of Al Jolson’s The Jazz Singer, released in October 1927.

All of this  and more is charted by Bill Bryson, in a book written with his characteristic eye for telling detail, and delicious humour. 1927 was the year America stepped out onto the world stage as the main event, and One Summer transforms it all into narrative non-fiction of the highest order. Join Kayden Oconnell for a trip through history as seen by Bryson.

Wednesday, August 16th 19:00: Secrets of the Divine Ya-Ya Sisterhood

Caledonia Skytower reads Rebecca Wells’ 2014 tale.

When Siddalee Walker, oldest daughter of Vivi Abbott Walker, Ya-Ya extraordinaire, is interviewed in the New York Times about a hit play she’s directed, her mother gets described as a “tap-dancing child abuser.”

Enraged, Vivi disowns Sidda. Devastated, Sidda begs forgiveness, and postpones her upcoming wedding. All looks bleak until the Ya-Yas step in and convince Vivi to send Sidda a scrapbook of their girlhood mementos, called “Divine Secrets of the Ya-Ya Sisterhood.”

As Sidda struggles to analyze her mother, she comes face to face with the tangled beauty of imperfect love, and the fact that forgiveness, more than understanding, is often what the heart longs for.

Also presented in Kitely (hop://grid.kitely.com:8002/Seanchai/108/609/1528).

Thursday, August 17th 19:00: A book of Days

Caledonia previews her newest WIP – a collection of art inspired micro-fiction and poetry written for both physical and virtual art exhibitions. Also presented in Kitely (hop://grid.kitely.com:8002/Seanchai/108/609/1528).

 


Please check with the Seanchai Library’s blog for updates and for additions or changes to the week’s schedule.

The featured charity for August and September is Little Kids Rock, transforming lives by restoring, expanding, and innovating music education in schools.