OrbitalHub

NASA dixit:

“June 21, 2006. The slim crescent of the moon Rhea glides silently onto the featureless, golden face of Saturn in this mesmerizing color image. In an interplay of contrast and shadow, the moon goes dark against the planet, and then its crescent suddenly brightens as it slips in front of Saturn’s night side. This view looks down onto the unlit side of Saturn’s rings, which cast soft, linear shadows onto the planet’s northern hemisphere. The images were acquired by the Cassini spacecraft wide-angle camera on March 21, 2006, at a distance of approximately 221,000 kilometers (137,000 miles) from Rhea. The image scale is approximately 13 kilometers (8 miles) per pixel.”

“After almost 20 years in space, NASA’s Cassini spacecraft begins the final chapter of its remarkable story of exploration: its Grand Finale. Between April and September 2017, Cassini will undertake a daring set of orbits that is, in many ways, like a whole new mission. Following a final close flyby of Saturn’s moon Titan, Cassini will leap over the planet’s icy rings and begin a series of 22 weekly dives between the planet and the rings.

No other mission has ever explored this unique region. What we learn from these final orbits will help to improve our understanding of how giant planets – and planetary systems everywhere – form and evolve.

On the final orbit, Cassini will plunge into Saturn’s atmosphere, sending back new and unique science to the very end. After losing contact with Earth, the spacecraft will burn up like a meteor, becoming part of the planet itself.

Cassini’s Grand Finale is about so much more than the spacecraft’s final dive into Saturn. That dramatic event is the capstone of six months of daring exploration and scientific discovery. And those six months are the thrilling final chapter in a historic 20-year journey.”

Image credit: NASA

ESA dixit:

“The motion of two million stars is traced 5 million years into the future using data from the Tycho-Gaia Astrometric Solution, one of the products of the first Gaia data release. This provides a preview of the stellar motions that will be revealed in Gaia’s future data releases, which will enable scientists to investigate the formation history of our Galaxy.

Stars move through our Galaxy, the Milky Way, although the changes in their positions on the sky are too small and slow to be appreciated with the naked eye over human timescales. These changes were first discovered in the eighteenth century by Edmond Halley, who compared stellar catalogues from his time to a catalogue compiled by the astronomer Hipparchus some two thousand years before. Nowadays, stellar motions can be detected with a few years’ worth of high-precision astrometric observations, and ESA’s Gaia satellite is currently leading the effort to pin them down at unprecedented accuracy.

A star’s velocity through space is described by the proper motion, which can be measured by monitoring the movement of a star across the sky, and the radial velocity, which quantifies the star’s motion towards or away from us. The latter can be inferred from the shift towards blue or red wavelengths of certain features – absorption lines – in the star’s spectrum.

Launched in 2013, Gaia started scientific operations in July 2014, scanning the sky repeatedly to obtain the most detailed 3D map of our Galaxy ever made. The first data release, published in September 2016, was based on data collected during Gaia’s first 14 months of observations and comprised a list of 2D positions – on the plane of the sky – for more than one billion stars, as well as distances and proper motions for a subset of more than two million stars in the combined Tycho–Gaia Astrometric Solution, or TGAS.
The TGAS dataset consists of stars in common between Gaia’s first year and the earlier Hipparcos and Tycho-2 Catalogues, both derived from ESA’s Hipparcos mission, which charted the sky more than two decades ago.

This video shows the 2 057 050 stars from the TGAS sample, with the addition of 24 320 bright stars from the Hipparcos Catalogue that are not included in Gaia’s first data release. The stars are plotted in Galactic coordinates and using a rectangular projection: in this, the plane of the Milky Way stands out as the horizontal band with greater density of stars. Brighter stars are shown as larger circles, and an indication of the true colour of each star is also provided; information about brightness and colour is based on the Tycho-2 catalogue from the Hipparcos mission.

The video starts from the positions of stars as measured by Gaia between 2014 and 2015, and shows how these positions are expected to evolve in the future, based on the proper motions from TGAS. The frames in the video are separated by 750 years, and the overall sequence covers 5 million years. The stripes visible in the early frames reflect the way Gaia scans the sky and the preliminary nature of the first data release; these artefacts are gradually washed out in the video as stars move across the sky.”

Video credit: ESA

NASA dixit:

“March 31, 2005. NASA’s Cassini spacecraft successfully flew by Saturn’s largest moon, Titan, at about 2,400 kilometers (1,500 miles) above the surface.”

“After almost 20 years in space, NASA’s Cassini spacecraft begins the final chapter of its remarkable story of exploration: its Grand Finale. Between April and September 2017, Cassini will undertake a daring set of orbits that is, in many ways, like a whole new mission. Following a final close flyby of Saturn’s moon Titan, Cassini will leap over the planet’s icy rings and begin a series of 22 weekly dives between the planet and the rings.

No other mission has ever explored this unique region. What we learn from these final orbits will help to improve our understanding of how giant planets – and planetary systems everywhere – form and evolve.

On the final orbit, Cassini will plunge into Saturn’s atmosphere, sending back new and unique science to the very end. After losing contact with Earth, the spacecraft will burn up like a meteor, becoming part of the planet itself.

Cassini’s Grand Finale is about so much more than the spacecraft’s final dive into Saturn. That dramatic event is the capstone of six months of daring exploration and scientific discovery. And those six months are the thrilling final chapter in a historic 20-year journey.”

Image credit: NASA

ESA dixit:

“The JUpiter ICy moons Explorer (JUICE) is the first L-class mission within ESA’s Cosmic Vision programme. It aims at a comprehensive exploration of the Jovian system with particular emphasis on Jupiter, its environment, and Galilean moons Ganymede, Europa and Callisto by investigating them as planetary bodies and potential habitats.

Scheduled for launch in 2022, with arrival in the Jovian system in 2029, JUICE will spend three-and-a-half years examining the giant planet’s turbulent atmosphere, enormous magnetosphere, its set of tenuous dark rings and its satellites. It will study the large icy moons Ganymede, Europa and Callisto, which are thought to have oceans of liquid water beneath their icy crusts – perhaps even harbouring habitable environments. The mission will culminate in a dedicated, eight-month tour around Ganymede, the first time any moon beyond our own has been orbited by a spacecraft.

JUICE will be equipped with 10 state-of-the-art instruments, including cameras, an ice-penetrating radar, an altimeter, radio-science experiments, and sensors to monitor the magnetic fields and charged particles in the Jovian system. In order to ensure it can address these goals in the challenging Jovian environment, the spacecraft’s design has to meet stringent requirements. An important milestone was reached earlier this month, when the preliminary design of JUICE and its interfaces with the scientific instruments and the ground stations were fixed, which will now allow a prototype spacecraft to be built for rigorous testing. The review also confirmed that the 5.3 tonne spacecraft will be compatible with its Ariane 5 launcher.

Operating in the outer Solar System, far from the Sun, means that JUICE needs a large solar array: two wings of five panels each are foreseen, which will cover a total surface area of nearly 100 m², capable of providing 820 W at Jupiter by the end of the mission. After launch, JUICE will make five gravity-assist flybys in total: one each at Mars and Venus, and three at Earth, to set it on course for Jupiter. Its solar panels will have to cope with a range of temperatures such that when it is flying closer to the Sun during the Venus flyby, the solar wings will be tilted to avoid excessive temperatures damaging the solar cells.

The spacecraft’s main engine will be used to enter orbit around the giant planet, and later around Jupiter’s largest moon, Ganymede. As such, the engine design has also been critically reviewed at this stage. Special measures will allow JUICE to cope with the extremely harsh radiation that it must endure for several years around Jupiter. This means careful selection of components and materials, as well as radiation shielding. One particularly important topic is JUICE’s electromagnetic ‘cleanliness’. Because a key goal is to monitor the magnetic fields and charged particles at Jupiter, it is imperative that any electromagnetic fields generated by the spacecraft itself do not interfere with the sensitive scientific measurements. This will be achieved by the careful design of the solar array electrical architecture, the power distribution unit, and the reaction wheels – a type of flywheel that stabilizes the attitude.

[…]JUICE will meet strict planetary protection guidelines, because it is imperative to minimize the risk that the potentially habitable ocean moons, particularly Europa, might be contaminated by viruses, bacteria or spores carried by the spacecraft from Earth. Therefore, mission plans ensure that JUICE will not crash into Europa, on a timescale of hundreds of years.”

Video credit: ESA

NASA dixit:

“January 14, 2005. This is an artist’s interpretation of the area surrounding the Huygens landing site, based on images and data returned.”

“After almost 20 years in space, NASA’s Cassini spacecraft begins the final chapter of its remarkable story of exploration: its Grand Finale. Between April and September 2017, Cassini will undertake a daring set of orbits that is, in many ways, like a whole new mission. Following a final close flyby of Saturn’s moon Titan, Cassini will leap over the planet’s icy rings and begin a series of 22 weekly dives between the planet and the rings.

No other mission has ever explored this unique region. What we learn from these final orbits will help to improve our understanding of how giant planets – and planetary systems everywhere – form and evolve.

On the final orbit, Cassini will plunge into Saturn’s atmosphere, sending back new and unique science to the very end. After losing contact with Earth, the spacecraft will burn up like a meteor, becoming part of the planet itself.

Cassini’s Grand Finale is about so much more than the spacecraft’s final dive into Saturn. That dramatic event is the capstone of six months of daring exploration and scientific discovery. (And those six months are the thrilling final chapter in a historic 20-year journey.)”

Image credit: NASA

NASA dixit:

“Arctic sea ice extent ebbs and flows with the seasons. During the summer months, the ice melts and the edge recedes northward, usually reaching its annual minimum sometime in September. The ice extent is shaped by a variety of factors, including warmer temperatures, storms, and changes in the ocean, which makes it difficult to predict. Sea ice plays an important role in maintaining Earths temperature, so predicting how the ice extent might change helps us understand the warming climate. Scientists have developed a new model to predict the sea ice minimum extent, using historical measurements and real-time satellite data. The model can begin predictions up to six months before the predicted minimum and continue to improve each day.”

Video credit: NASA Goddard