Space Sunday: Cassini – a journey’s end

An artist’s impression of the Cassini spacecraft entering the upper reaches of Saturn’s atmosphere, high above the cloud tops, and breaking / burning up against the backdrop of the planet’s rings. Credit: NASA

On Friday, September 15th, 2017, just one month short of the 20th anniversary of its launch, the NASA/ Italian Space Agency (ASI) space probe Cassini will plunge into the upper reaches of Saturn’s atmosphere, bringing to a close the momentous NASA / ASI / European Space Agency Cassini-Huygens mission.

It will be a bitter-sweet moment for many the world over – most of all the vast international team who devoted up to fourteen years of their time on the mission – even before it launched. The Cassini vehicle has not only revealed so much about Saturn, its myriad moons, the rich complexities of the gas giant’s ring system- it has also helped inform us on the potential for life to exist elsewhere in the solar system and has even helped test Einstein’s work. It has also over the years returned some of the most stunning and evocative images of other worlds we have yet witnessed. Many of these images have been gathered together by National Geographic and have been put together in a superb interactive web presentation on the mission by Nadia Drake and Brian Jacobs.

A computer model of the hundreds of orbits Cassini has made around Saturn over the years (excluding the more recent orbits of the Grand Finale). Credit: Drake / Jacobs / National Geographic

In all seventeen countries have been directly involved in the conception, design, construction and operation of the Cassini-Huygens mission, both in terms of the Cassini orbiter and the Huygens Titan lander and the science instruments they carry. NASA carries primary responsibility for the orbiter’s design and construction, with the Italian Space Agency providing the all-important, dual-purpose high-gain radio antenna and its associated communications equipment, together with the low-gain communications suite which would provide continuous communications with Earth through the mission. ASI also incorporated a compact radar system in to the high-gain antenna systems, allowing it to function as a synthetic-aperture radar, a radar altimeter, a radiometer, and provide the visible channel portion of the VMS spectrometer package carried by the probe.

ESA was responsible for the Huygens lander, with France designing the vehicle itself, with the descent parachute system provided by Martin-Baker of America, while the science and communications packages were supplied by several European countries and the United States.

Cassini-Huygens stored within the payload fairing of an Atlas 4B rocket on the pad of Launch Complex 40, Canaveral Air Force Station, October 12th, 1997, 3 days ahead of its launch. Credit: NASA

The mission was named for the Italian-French astronomer Giovanni Domenico Cassini, who first observed the divisions within Saturn’s rings system (and after whom one of the divisions is also named) as well as for of the planet’s moons, and  Christiaan Huygens, the Dutch mathematician, physicist and astronomer, who first observed Titan, Saturn’s largest moon.

Work actually commenced on the mission in the 1980s, the goal being to develop a mission which could determine the three-dimensional structure and dynamic behaviour of Saturn’s ring system, investigate Saturn’s atmosphere and magnetosphere, determine the composition and likely structure of Saturn’s moons, including the nature and origin of the dark material on Iapetus‘s leading hemisphere, and, in conjunction with the Huygens lander, characterise Titan’s atmosphere, including the variability of the cloud haze, and characterise the moon’s surface at a regional level.

Initially, the mission was funded for a 10-year period from late 1997 through mid-2008, which included a journey of seven years to reach Saturn. The voyage took so long because at the time of launch, there was no launch vehicle combination capable of sending Cassini directly to Saturn. Instead, it completed a mini-tour of the inner solar system; six months after launch, Cassini flew by Venus, using the planet’s gravity to accelerate it into a wide elliptical orbit. A second encounter in June 2000 again accelerated the spacecraft, slinging it on to a further gravity-assist flyby of Earth in August 2000, which in turn accelerated it and bent it onto an trans-Jovian flight path.

In late 2000, Cassini reached the vicinity of Jupiter, making its closest approach to the planet on December 30th of that year. As well as using Jupiter’s gravity to sling it onwards to its final destination, Cassini used the encounter to study Jupiter and its faint system of rings. In all some 26,000 images of Jupiter, its moons and its rings were taken during the 6-month period of the flyby (October 2000 – March 2001). Cassini’s science suite was powered-up for the flyby, and resulted in some significant discoveries concerning Jupiter’s turbulent atmosphere, including breaking a long-held view. Jupiter’s banded atmosphere comprises a series of alternate bands of darker and lighter zones, in part caused by Jupiter’s rapid rotation. It had also been thought that the lighter bands were the result of the atmosphere rising upwards, giving rise to lighter cloud formations, before circulating downwards once more.

The cratered moon Tethys slips behind Saturn’s largest moon, Titan, as seen by Cassini on November 26th, 2009. Credit: NASA/JPL / Space Science Institute

However, Cassini revealed the dark bands were peppered with individual storm cells of upwelling bright-white clouds too small to see from Earth, suggesting the vertical circulation of Jupiter’s atmosphere to be far more uniform than thought. The probe’s findings also showed that Jupiter’s thin and dusty rings to be made up from small, irregularly shaped particles, most likely created by ejacta from micrometeorites impacting the Jovian moons.

Cassini reached Saturn in 2004, officially entering orbit around the planet on July 1st of the year. Prior to doing so, the vehicle was part of a test of Einstein’s theory of general relativity. This states that any massive object like the Sun causes space-time to curve, causing a beam of light or any other form of electromagnetic radiation that passes close to it to travel farther (the Shapiro time delay). In 2003, with the Sun coming between Earth and Cassini, scientists on Earth measured the frequency shift in radio signals being received from the spacecraft. Similar experiments had been carried out with the Voyager and Viking missions, but Cassini provided for much more refined measurements to be taken, and firmly validated Einstein’s theory.

A geyser sprays water ice and vapour from the south polar region of Saturn’s moon Enceladus. Cassini’s first hint of this plume came during the spacecraft’s first close flyby of the icy moon on February 17, 2005. Credit: NASA/JPL / Space Science Institute

Cassini‘s primary mission at Saturn commenced as it approached the planet for orbital insertion. Although the orbiter was capable of functioning – all things being equal – through until around 2017, this primary mission was scheduled to last just 3 years and 261 days, ending in mid-2008. This was sufficient time for the primary goals of the mission to be achieved, but Cassini was always designed to achieve so much more. With this in mind, the programme was granted two funding extensions. The first, called the Equinox Mission, funded the project through until the end of 2010, and gave a particular focus on Titan (15 flybys) Saturn’s ice-covered moon Enceladus, thought two of the locations in the Saturnian system where life might have taken hold.

The second extension, granted funding in 2010 to the tune of around US $60 million a year, is referred to as the Solstice mission (as it would end a few months past Saturn’s summer solstice). It guaranteed that, avoiding any spacecraft failures, the mission would continue through to the point where Cassini’s manoeuvring propellants would be practically depleted. This phase of the mission allowed for a more extended study of Saturn, its rings and moons. It meant Cassini could witness never before seen seasonal changes in the planet’s atmosphere and study. It also meant Cassini could study Saturn’s atmosphere and magnetosphere at exactly the same time as NASA Juno mission studied Jupiter’s atmosphere and magnetosphere, allowing a direct comparison of the two. Finally, the extension would carry the mission through its 5-month “grand finale”, probing the region between Saturn and its complex ring system.

Continue reading “Space Sunday: Cassini – a journey’s end”

Advertisements

A Creeping Man, a wizard, pirates and a saloon

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, September 10th

13:30: Tea Time at Baker Street

Seanchai Library once again opens the pages of 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 Creeping Man

“MR. SHERLOCK HOLMES was always of opinion that I should publish the singular facts connected with Professor Presbury, if only to dispel once for all the ugly rumours which some twenty years ago agitated the university and were echoed in the learned societies of London …”

So it is that John Watson puts pen to paper to tell the strange tale of the professor, his secretary, who is also engaged to the professor’s daughter, a trip to Prague and the creepers growing up the side of the professor’s house.

The tale is a most peculiar one indeed, and not just for the story itself; The Adventure of the Creeping Man veers somewhat away from Conan Doyle’s usual scientific approach to the unravelling of the mysteries Holmes and Watson face; so much so that it has met with much debate among critics down the years.

To find out more, be sure to turn up on time for a spot of afternoon tea at Baker Street!

16:00 Magicland Storytime: The Black Cauldron

Join Caledonia Skytower at Magicland Park.

Monday, September 11th 19:00: A Wizard of Earthsea

Gyro Muggins reads Ursula K. Le Guin’s first Earthsea Cycle. 

The boy is born on the island of Gont in the archipelago of Earthsea. This is a world infused with magic. Not everyone can control this magic, but those who know the right words and have a wizard soul can learn to utilize the power of the Earth to manipulate objects and events. The boy’s name is Duny; I can tell you that name because the name has no power over him. His true name is something he can only reveal to those he trusts absolutely beyond question.

I know his true name, but fair reader, I’m not sure yet that I can share it with you.

His aunt knows a few things, a handful of words, that can be used to bind things or call animals to her. Duny is particularly adept at calling falcons and other birds of prey. His agile mind soon surpasses what his aunt can teach him. He burns to know more. He is assigned to a mage, Ogion, who tries to teach him about the balance of magic with the Earth. There is always a cost for using magic. Understanding the levy for sorcery is the difference between being just impulsively talented and being wise about what you know.

(Commentary by Jeffrey Keeten.)

Tuesday, September 12th 19:00: Adventure on the High Seas

Selected adventures to whet your appetite for International Talk Like A Pirate Day with Caledonia Skytower

Wednesday, September 13th 19:00: Callahan’s Crosstime Saloon

Corwyn Allen reads Spider Robinson’s 1999 anthology.

callahansThe titular saloon is a haven for lost souls; a place where the patrons come for one drink and a chance for a second – but only if they offer an unburdening toast at the fireplace. Mike Callahan, the owner, never judges but sometimes advises in as few words as possible.

The stories in the volume are:

  • “The Guy with the Eyes”
  • “The Time-Traveler”
  • “The Centipede’s Dilemma”
  • “Two Heads Are Better Than One”
  • “The Law of Conservation of Pain”
  • “Just Dessert”
  • “A Voice is Heard in Ramah…”
  • “Unnatural Causes”
  • “The Wonderful Conspiracy”

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

Thursday, September 14th 19:00: Blueskin the Pirate

Shandon Loring  reads a short story from Howard Pyle’s Masterpieces.

Cape May and Cape Henlopen form, as it were, the upper and lower jaws of a gigantic mouth, which disgorges from its monstrous gullet the cloudy waters of the Delaware Bay into the heaving, sparkling blue-green of the Atlantic Ocean.

From Cape Henlopen as the lower jaw there juts out a long, curving fang of high, smooth-rolling sand dunes, cutting sharp and clean against the still, blue sky above-silent, naked, utterly deserted, excepting for the squat, white-walled lighthouse standing upon the crest of the highest hill.

Sunday, September 17th 13:00-16:30: The Pirates Are Coming!

A special event to mark International Talk Like A pirate Day – ARRRR! On Tuesday, September 19th. Stories from 13:00 and music and dancing from 14:30. Full details to follow on the Seanchai Library and Holly Kai Park websites.

 


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.

Seven lilies, seven virtues and seven artists in Second Life

DaphneArts: Lilium

Now open at DaphneArts is Lilium, the second in a series of exhibitions focus on the mystical number seven, following on from The Endless (reviewed here).

The curators of DaphneArts, Angelika Corral and Sheldon Bergman (SheldonBR), who are also two of the seven artists participating in the exhibition, describe it in part thus:

Number seven is sacred and powerful. Pythagoras, the father of numerology, considered seven as the most spiritual of all the numbers. Seven is the number of divine perfection. Seven are the colors of the rainbow. Seven are the notes of the diatonic scale. There are seven ancient wonders of the world, seven days of the week, seven letters in the Roman numeral system, seven arts…

When Pope Gregory defined the Seven deadly sins, he also included a counter-balancing set of values, in a way to protect one against temptation from the deadly sins. The seven [heavenly] virtues … For this exhibition, seven photographers were invited to create a photo, each of them representing one of the seven virtues.

DaphneArt: Lilium – Temperance by Fenris

Lilium is itself Latin for “lily”, a symbol of virtue, as Angelika and Sheldon also note in their curator’s introduction to the exhibit, illustrating the point with the inclusion of an image The Annunciation by Paolo de Matteis.

Thus it is, with viewer correctly set, visitors to the exhibition start their journey in the chancel of a marble-like white cathedral (white obviously symbolic of virtue). A HUD is offered on arrival and should be worn, while overhead is a set of easy-to-follow steps guide people through ensuring they have their viewer correctly set-up (e.g. ensuring the required Windlight is selected and Advanced Lighting Model is enabled).

DaphneArts: Lilium – Patience by Magic Marker

From here, a walk through the nave of the cathedral to the porch brings people to the main exhibition space, progress to it marked by the lyrics – in Latin of the Elven Song, or Elfen Lied, as featured in the Japanese manga series of that name, the lyrics based on biblical passages and the hymn Ave Mundi Spes Maria. Beyond the porch is an open platform set against a uniform backdrop and on which are arranged seven gilded lilies.

Approaching any of these lilies will cause it to open, revealing the art apparently “held” inside it. At the same time, the title of the art – the virtue it represents – and the name of the artist are revealed by the HUD.

DaphneArt: Liluim

The images / virtues are, by artist: Charity – Inexorably; Chastity – Sheldon Bergman; Diligence – Harbour Galaxy; Humility – Kimeu Kamolla; Kindness – Angelika Corral; Patience – Magic Marker, and Temperance – Fenris. Each is obviously a personal representation of the virtue it depicts, however each carries a degree of symbolism which may be related to the virtue it represents, to virtue as a whole or to the mysticism of seven.

Lilium is a further nuanced ensemble exhibition built around a central theme, rich in symbolism and interpretation. And for those curious about Elfin Lied, I’ll leave you with this.

SLurl Details