vendredi 16 septembre 2011

Space Station Trio Lands Safely In Kazakhstan












ROSCOSMOS - Soyuz TMA-21 Mission patch.

Sept. 16, 2011

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Expedition 28 Crew Undocks from Station

Three International Space Station crew members safely returned to Earth Thursday, Sept. 15, wrapping up a six-month mission of research and exploration.

Soyuz TMA-21 landing

NASA's Ron Garan, Expedition 28 commander Andrey Borisenko and flight engineer Alexander Samokutyaev, both of the Russian Federal Space Agency, landed their Soyuz spacecraft in Kazakhstan at 11:59 a.m. EDT (9:59 a.m. in Kazakhstan). The trio, which arrived at the station on April 6, had been scheduled to land on Sept. 8, but that was postponed because of the Aug. 24 loss of the Progress 44 cargo ship.

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Expedition 28 Crew Lands Safely


Image above: Expedition 28 crew members Andrey Borisenko, Alexander Samokutyaev and Ron Garan. Credit: NASA TV.

Before leaving the station, Borisenko handed over command to NASA's Mike Fossum, who leads Expedition 29. He and Flight Engineers Satoshi Furukawa of Japan and Sergei Volkov of Russia are conducting research and maintenance aboard the station. The launch date for the remaining Expedition 29 crew members, NASA's Dan Burbank, and Russia's Anatoly Ivanishin and Anton Shkaplerov, is under review.

Fossum is blogging about his experiences aboard the space station at: http://blogs.nasa.gov

For more information about Expedition 29 and the space station, visit: http://www.nasa.gov/station

Images, Videos, Text, Credits: ROSCOSMOS / NASA / NASA TV.

Greetings, Orbiter.ch

jeudi 15 septembre 2011

NASA'S Kepler Discovery Confirms First Planet Orbiting Two Stars







NASA - Kepler A Search for Terrestrial Planets logo.

Sept. 15, 2011

NASA's Kepler mission has turned fiction into fact. A world with a double sunset that was first imagined in Star Wars over 30 years ago in a galaxy far, far away has become scientific reality. NASA's Kepler mission has made the first unambiguous detection of a circumbinary planet -- a planet orbiting, not one, but two stars -- 200 light-years from Earth.

The planet is cold and gaseous unlike Star Wars' Tatooine and is not thought to harbor life, but its discovery demonstrates the diversity of planets in our solar system.

Unequivocal evidence for the existence of a circumbinary planet has been limited, until now. Hints of their existence have been presented, but clear confirmation has been elusive. Kepler detected the planet through what is known as a planetary transit -- an event where the brightness of a star dims as a result of a planet crossing in front of it.


Image above: In the Light of Two Suns - This artist's concept illustrates Kepler-16b, the first planet known to definitively orbit two stars -- what's called a circumbinary planet. The planet, which can be seen in the foreground, was discovered by NASA's Kepler mission. Image credit: NASA / JPL-Caltech / T. Pyle.

"This discovery provides confirmation of a new class of planetary systems that could harbor life. Given that most stars in our galaxy are part of a binary system, this means that the opportunities for life are much broader than if planets form only around single stars," said Kepler principal investigator William Borucki. "This milestone discovery confirms a theory that scientists have had for decades but could not be proven until now."

A research team, led by Laurance Doyle of the SETI Institute, used data from the Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets. Kepler is the first NASA mission capable of finding Earth-size planets in or near the "habitable zone," the region in a planetary system where liquid water can exist on the surface of the orbiting planet. This finding provides significant insight into the world of planetary formation.

"Theorists have been debating for years about whether giant planets could form around close binary star systems- some said yes, others said no," said theoretical astrophysicist Alan Boss of the Carnegie Institution of Washington. "Kepler has now answered this question with a resounding 'YES'!"


Image: Where the Sun Sets Twice - NASA's Kepler mission has discovered a world where two suns set over the horizon instead of just one. The planet, called Kepler-16b, is the most "Tatooine-like" planet yet found in our galaxy. Tatooine is the name of Luke Skywalker's home world in the science fiction movie Star Wars. In this case, the planet it not thought to be habitable. It is a cold world, with a gaseous surface, but like Tatooine, it circles two stars. Image credit: NASA / JPL-Caltech / R. Hurt.

This discovery confirms that Kepler-16b is an inhospitable, cold world about the size of Saturn, and thought to be made up of about half rock and half gas. The parent stars are both smaller than our sun; one is 69 percent and the other only 20 percent the mass of the sun. Kepler-16b orbits around both stars every 229 days, similar to Venus’ 225-day orbit, but lies outside the system's habitable zone, where liquid water could exist on the surface, because the stars are cooler than our sun.

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Animation: Three Eclipsing Bodies - This artist's movie illustrates Kepler-16b, the first directly detected circumbinary planet, which is a planet that orbits two stars. The movie begins by showing the gaseous surface of the rotating planet then pans out to show the stars it orbits. Image credit: NASA / JPL-Caltech / T. Pyle.

"Working in film, we are often tasked with creating something never before seen," said visual effects supervisor John Knoll of Industrial Light & Magic. "However, more often than not, scientific discoveries prove to be more spectacular than anything we dare imagine. There is no doubt these discoveries influence and inspire storytellers. Their very existence serves as cause to dream bigger, to open our mind to new possibilities beyond what we think we 'know'."

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Animation: A Dance of Two Suns and One Planet - This artist's animation illustrates the Kepler-16 system from an overhead view, showing the eccentric orbits of the two stars as they twirl around each other every 41 days like figure skaters. The planet, which was discovered by NASA's Kepler mission, orbits in a circle around both of the stars every 229 days. The larger of the stars is about 69 percent of the mass of the sun, and the smaller is about 20 percent of the sun's mass. The planet is about the mass of Saturn. All three bodies orbit in the same plane, which is why Kepler can observe the various planetary and stellar eclipses.
Image credit: NASA / JPL-Caltech / T. Pyle.

For more information about the Kepler-16 discovery, visit: http://kepler.nasa.gov/Mission/discoveries/kepler16b/

For more information about NASA’s Kepler Mission, visit: http://www.nasa.gov/kepler

For more information about NASA’s Ames Research Center, visit: http://www.nasa.gov/ames

Images (mentioned), Videos (mentioned), Text, Credit: NASA / JPL-Caltech.

Greetings, Orbiter.ch

BepiColombo Mercury explorer to be launched on Ariane












ESA - BepiColombo Mission patch.

15 September 2011

Reaching one of the most mysterious planets in our Solar System takes enormous power and finesse. ESA has now firmly entrusted its precious Mercury explorer to Europe’s largest rocket – the Ariane 5.

Ariane 5 liftoff

ESA today signed the contract with Arianespace to launch its BepiColombo mission on an Ariane 5 from Europe’s Spaceport in French Guiana.

Europe's first mission to probe the Solar System's innermost planet will depart in July 2014.

BepiColombo heading towards Mercury

BepiColombo's sensors will completely map Mercury at different wavelengths, charting the planet's mineralogy and elemental composition.

It will reveal the planet's interior structure and probe Mercury's magnetic field.

ESA is leading the mission, flying it in cooperation with the Japan Aerospace Exploration Agency.

The mission's two orbiters will be injected into separate orbits around Mercury: ESA's Mercury Planetary Orbiter and Japan's Mercury Magnetospheric Orbiter.

After signing, ESA Director General Jean-Jacques Dordain said, "With BepiColombo, Europe continues to explore our Solar System.

BepiColombo launch contract signature

"After Mars Express, Venus Express and the Huygens probe to Titan, we are now gearing up to explore a planet that is very close to the Sun, key to understanding the formation of our Solar System, and yet still very mysterious.

"For the European Space Agency, it’s also an excellent example of scientific teamwork, since we are sharing this experience with the Japanese space agency.

"After the successful launch of Herschel and Planck back in 2009 and before the launch of the ATV-3 and Alphasat next year, Ariane 5 again demonstrates its extreme flexibility, which will soon be complemented by Soyuz and Vega."

Jean-Yves Le Gall, Chairman and CEO of Arianespace, added: "We are both proud and honoured to be given this opportunity to support space science and serve the European Space Agency, teaming up with JAXA [Japan Aerospace Exploration Agency] on this programme."

Related links:

ESA Test Centre: http://www.esa.int/SPECIALS/Space_Engineering/SEM8AWZO0WF_0.html

ESA's Large Space Simulator: http://www.esa.int/SPECIALS/Space_Engineering/SEM2MWZO0WF_0.html

BepiColombo at JAXA: http://www.stp.isas.jaxa.jp/mercury/p_bepi.html

ESA BepiColombo team site: http://www.rssd.esa.int/index.php?project=BEPICOLOMBO

BepiColombo in-depth: http://sci.esa.int/bepicolombo

Images, Text, Credits: ESA / N. Imbert-Vier / AOES Medialab / Arianespace.

Greetings, Orbiter.ch

mercredi 14 septembre 2011

NASA Announces Design for New Deep Space Exploration System










NASA logo.

Sept. 14, 2011

NASA is ready to move forward with the development of the Space Launch System -- an advanced heavy-lift launch vehicle that will provide an entirely new national capability for human exploration beyond Earth's orbit. The Space Launch System will give the nation a safe, affordable and sustainable means of reaching beyond our current limits and opening up new discoveries from the unique vantage point of space.

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Space Launch System, or SLS

The Space Launch System, or SLS, will be designed to carry the Orion Multi-Purpose Crew Vehicle, as well as important cargo, equipment and science experiments to Earth's orbit and destinations beyond. Additionally, the SLS will serve as a back up for commercial and international partner transportation services to the International Space Station.

Artist concept of SLS on launchpad

"This launch system will create good-paying American jobs, ensure continued U.S. leadership in space, and inspire millions around the world," NASA Administrator Charles Bolden said. "President Obama challenged us to be bold and dream big, and that's exactly what we are doing at NASA. While I was proud to fly on the space shuttle, kids today can now dream of one day walking on Mars."

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NASA Administrator Charles Bolden

The SLS rocket will incorporate technological investments from the Space Shuttle program and the Constellation program in order to take advantage of proven hardware and cutting-edge tooling and manufacturing technology that will significantly reduce development and operations costs. It will use a liquid hydrogen and liquid oxygen propulsion system, which will include the RS-25D/E from the Space Shuttle program for the core stage and the J-2X engine for the upper stage. SLS will also use solid rocket boosters for the initial development flights, while follow-on boosters will be competed based on performance requirements and affordability considerations. The SLS will have an initial lift capacity of 70 metric tons (mT) and will be evolvable to 130 mT. The first developmental flight, or mission, is targeted for the end of 2017.

Artist concept of SLS launching. (NASA)

This specific architecture was selected, largely because it utilizes an evolvable development approach, which allows NASA to address high-cost development activities early on in the program and take advantage of higher buying power before inflation erodes the available funding of a fixed budget. This architecture also enables NASA to leverage existing capabilities and lower development costs by using liquid hydrogen and liquid oxygen for both the core and upper stages. Additionally, this architecture provides a modular launch vehicle that can be configured for specific mission needs using a variation of common elements. NASA may not need to lift 130 mT for each mission and the flexibility of this modular architecture allows the agency to use different core stage, upper stage, and first-stage booster combinations to achieve the most efficient launch vehicle for the desired mission.

"NASA has been making steady progress toward realizing the president's goal of deep space exploration, while doing so in a more affordable way," NASA Deputy Administrator Lori Garver said. "We have been driving down the costs on the Space Launch System and Orion contracts by adopting new ways of doing business and project hundreds of millions of dollars of savings each year."

Artist concept of future destinations

The Space Launch System will be NASA's first exploration-class vehicle since the Saturn V took American astronauts to the moon over 40 years ago. With its superior lift capability, the SLS will expand our reach in the solar system and allow us to explore cis-lunar space, near-Earth asteroids, Mars and its moons and beyond. We will learn more about how the solar system formed, where Earth' water and organics originated and how life might be sustained in places far from our Earth's atmosphere and expand the boundaries of human exploration. These discoveries will change the way we understand ourselves, our planet, and its place in the universe.

Images, Videos, Text, Credits: NASA / Michael Braukus / J.D. Harrington / Marshall Space Flight Center / Dan Kanigan.

Best regards, Orbiter.ch

Arctic ice nears record low












ESA - ENVISAT-1 Mission patch.

14 September 2011

A new record low could soon be set for ice in the Arctic. The past five years have seen the lowest extent of sea ice since satellite measurements began in the 1970s.

Earth observing satellites make it possible to measure the amount of sea ice in inaccessible areas such as the Arctic.

This year, the extent of Arctic sea ice is comparable to the record low set in 2007.

According to scientists at the University of Bremen in Germany, sea ice extent in early September has dropped below even that record.

 Envisat image of the Arctic

Their maps are based on observations made by Japan’s microwave sensor on NASA’s Aqua satellite.

According to other teams, like the US National Snow and Ice Data Center, the 2007 record has not yet been reached but is very close.

International teams use various methods to measure sea ice based on different satellite observations, but the slight differences in their results are trivial.

“It seems to be clear that this is a further consequence of the man-made global warming with global consequences,” said Dr Georg Heygster from the University of Bremen.

Arctic sea ice since 2003

“Directly, the livelihoods of small animals, algae, fish and mammals – like polar bears and seals – are further reduced.”

Scientists had been anticipating this year’s potential for a new record because satellites have seen the rare occurrence of two major shipping routes in the Arctic Ocean open simultaneously in August – indicating a significant reduction in sea-ice cover.

During the last 30 years, satellites observing the Arctic have witnessed a halving of the minimum ice extent at the end of summer from around 8 million sq km in the early 1980s to 2007’s historic minimum of just over 4 million sq km.

Sea ice can be measured by different types of satellite data. Radars on satellites such as ESA’s Envisat can acquire high-resolution images through clouds and darkness. This is particularly useful when observing the inaccessible Arctic, which is also prone to long periods of bad weather and extended darkness.

ESA’s CryoSat ice mission, launched in April 2010, is also helping our understanding of how the thickness of sea ice is changing.

Yearly sea ice minima
  
Once we have several years of CryoSat measurements, it will be possible to detect precise changes.

ESA’s SMOS mission is providing complementary information on sea-ice cover and the thickness of thin ice.

Observations from space greatly assist in understanding and managing climate change. Measurements over long periods provide a reliable long-term record of Earth’s climate and improve our understanding of the changing planet.

ESA’s Climate Change Initiative is using archived data going back three decades from Agency and Member-State satellites.

Combined with data from new missions, this information is used to produce new, verified information on a wide range of climate variables, including sea-ice extent and thickness.

The GMES Global Monitoring for Environment and Security programme is keeping an eye on Arctic ice coverage through its Polar View project.

Related links:

Climate Change Initiative: http://www.esa-cci.org/

University of Bremen: http://www.iup.uni-bremen.de/seaice/amsr/

Polar View: http://www.polarview.org/

Danish Meteorological Institute: http://www.dmi.dk/dmi/index

US National Snow and Ice Data Center: http://nsidc.org/

US National Ice Center: http://www.natice.noaa.gov/

GMES: http://www.esa.int/esaLP/LPgmes.html

Space for our climate: http://www.esa.int/SPECIALS/Space_for_our_climate/index.html

Image, Graphics, Text, Credits: ESA / DMI / NIC / University of Bremen.

Best regards, Orbiter.ch

Star CoRoT-2a Fries Nearby Planet












NASA - Chandra X-ray Observatory patch.

Sept. 14, 2011

 (click on the image for enlarge)

This graphic contains an image and illustration of a nearby star, named CoRoT-2a, which has a planet in close orbit around it. The separation between the star and planet is only about three percent of the distance between the Earth and the sun, causing some exotic effects not seen in our solar system.

The planet-hosting star is located in the center of the image. Data from NASA's Chandra X-ray Observatory are shown in purple, along with optical and infrared data from the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes, or PROMPT, and the Two Micron All Sky Survey, or 2MASS. CoRoT-2a is surrounded by a purple glow showing that it is an X-ray source.

This star is pummeling its companion planet -- not visible in this image -- with a barrage of X-rays 100,000 times more intense than the Earth receives from the sun. Data from Chandra suggest that high-energy radiation from CoRoT-2a is evaporating about five million tons of matter from the nearby planet every second, giving insight into the difficult survival path for some planets. The artist's representation shows the material, in blue, being stripped off the planet.

The Chandra observations provide evidence that CoRoT-2a is a very active star, with bright X-ray emission produced by powerful, turbulent magnetic fields. This magnetic activity is represented by the prominences and eruptions on the surface of the star in the illustration.

Such strong activity is usually found in much younger stars and may be caused by the proximity of the planet. The planet may be speeding up the star's rotation, causing its magnetic fields to remain active longer than expected. Support for this idea comes from observations of a likely companion star to CoRoT-2a that orbits at a distance about a thousand times greater than the distance between the Earth and the sun. This star is visible in the image as the faint, nearby star located below and to the right of CoRoT-2a. It is also shown as the bright background star in the illustration. This star is not detected in X-rays, perhaps because it does not have a close-in planet like CoRoT-2b to cause it to stay active.

The planet, CoRoT-2b, was discovered by the French Space Agency's Convection, Rotation and planetary Transits, or CoRoT, satellite in 2008. It is located about 880 light years from Earth and has a mass about three times that of Jupiter.

Read more/access all images: http://www.chandra.harvard.edu/photo/2011/corot/

Image , Text, Credits: Optical: NASA / NSF / IPAC-Caltech / UMass / 2MASS, PROMPT; Wide field image: DSS; X-ray: NASA / CXC / Univ of Hamburg / S.Schröter et al; Illustration: CXC / M. Weiss.

Cheers, Orbiter.ch

mardi 13 septembre 2011

Herschel paints new story of galaxy evolution












ESA - Herschel Mission patch.

13 September 2011

ESA's Herschel infrared space observatory has discovered that galaxies do not need to collide with each other to drive vigorous star birth. The finding overturns this long-held assumption and paints a more stately picture of how galaxies evolve.

The conclusion is based on Herschel's observations of two patches of sky, each about a third of the size of the full Moon.

Galaxy forming stars

It's like looking through a keyhole across the Universe – Herschel has seen more than a thousand galaxies at a variety of distances from the Earth, spanning 80% of the age of the cosmos.

These observations are unique because Herschel can study a wide range of infrared light and reveal a more complete picture of star birth than ever seen before.

It has been known for some years that the rate of star formation peaked in the early Universe, about 10 billion years ago. Back then, some galaxies were forming stars ten or even a hundred times more vigorously than is happening in our Galaxy today.

In the nearby, present-day Universe, such high birth rates are very rare and always seem to be triggered by galaxies colliding with each other. So, astronomers had assumed that this was true throughout history.

Herschel's view of GOODS-North

Herschel now shows that this is not the case by looking at galaxies that are very far away and thus seen as they were billions of years ago.

David Elbaz, CEA Saclay, France, and collaborators have analysed the Herschel data and find that galaxy collisions played only a minor role in triggering star births in the past, even though some young galaxies were creating stars at furious rates.

By comparing the amount of infrared light released at different wavelengths by these galaxies, the team has shown that the star birth rate depends on the quantity of gas they contain, not whether they are colliding.

Gas is the raw building material for stars and this work reveals a simple link: the more gas a galaxy contains, the more stars are born.

Herschel's view of GOODS-South

"It's only in those galaxies that do not already have a lot of gas that collisions are needed to provide the gas and trigger high rates of star formation", says Dr Elbaz.

This applies to today's galaxies because, after forming stars for more than 10 billion years, they have used up most of their gaseous raw material.

The research paints a much more stately picture of star births than before, with most galaxies sitting in space, growing slowly and naturally from the gas they attract from their surroundings.

"Herschel was conceived to study the history of star formation across cosmic time", says Göran Pilbratt, ESA Herschel Project Scientist.

"These new observations now change our perception of the history of the Universe."

More informations:

Herschel first science results in depth: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=46985

Herschel in depth: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=16

Herschel Science Centre: http://herschel.esac.esa.int/

Images, Text, Credits: ESA / AOES Medialab / GOODS-Herschel consortium / David Elbaz / NASA / JPL-Caltech.

Greetings, Orbiter.ch

lundi 12 septembre 2011

Fermi's Latest Gamma-ray Census Highlights Cosmic Mysteries











NASA - Fermi Gamma-ray Space Telescope logo.

Sept. 12, 2011

Every three hours, NASA's Fermi Gamma-ray Space Telescope scans the entire sky and deepens its portrait of the high-energy universe. Every year, the satellite's scientists reanalyze all of the data it has collected, exploiting updated analysis methods to tease out new sources. These relatively steady sources are in addition to the numerous transient events Fermi detects, such as gamma-ray bursts in the distant universe and flares from the sun.

Earlier this year, the Fermi team released its second catalog of sources detected by the satellite's Large Area Telescope (LAT), producing an inventory of 1,873 objects shining with the highest-energy form of light. "More than half of these sources are active galaxies, whose massive black holes are responsible for the gamma-ray emissions that the LAT detects," said Gino Tosti, an astrophysicist at the University of Perugia in Italy and currently a visiting scientist at SLAC National Accelerator Laboratory in Menlo Park, Calif.


This all-sky image, constructed from two years of observations by NASA's Fermi Gamma-ray Space Telescope, shows how the sky appears at energies greater than 1 billion electron volts (1 GeV). Brighter colors indicate brighter gamma-ray sources. For comparison, the energy of visible light is between 2 and 3 electron volts. A diffuse glow fills the sky and is brightest along the plane of our galaxy (middle). Discrete gamma-ray sources include pulsars and supernova remnants within our galaxy as well as distant galaxies powered by supermassive black holes. (Credit: NASA/DOE/Fermi LAT Collaboration).

One of the scientists who led the new compilation, Tosti today presented a paper on the catalog at a meeting of the American Astronomical Society's High Energy Astrophysics Division in Newport, R.I. "What is perhaps the most intriguing aspect of our new catalog is the large number of sources not associated with objects detected at any other wavelength," he noted.

Indeed, if the Fermi catalog were a recipe, the two major ingredients would be active galaxies and pure mystery. To them, add in a pinch of pulsars, a dollop of supernova remnants, and a dash of other celestial objects, such as globular star clusters and galaxies like our own Milky Way.


Graphic above: Active galaxies called blazars constitute the single largest source class in the second Fermi LAT catalog, but nearly a third of the sources are unassociated with objects at any other wavelength. Their natures are unknown. (Credit: NASA's Goddard Space Flight Center).

Astronomers delight in the possibility of finding new types of gamma-ray-emitting objects within the "unassociated sources" that constitute roughly a third of the catalog. But Fermi's LAT is revealing gamma-rays from an increasing -- and sometimes, surprising -- variety of astronomical objects. To highlight the range of LAT discoveries, the Fermi team created the following "top ten" list of five sources within the Milky Way and five beyond our galaxy.

The top five sources within our galaxy are:

The Crab Nebula. The famous Crab Nebula, located in the constellation Taurus, is the wreckage of an exploded star whose light reached Earth in 1054. Located 6,500 light-years away, the Crab is one of the most studied objects in the sky. At the heart of an expanding gas cloud lies what's left of the original star's core, a superdense neutron star (also called a pulsar) that spins 30 times a second. Until recently, all of the Crab's high-energy emissions were thought to be the result of physical processes near the pulsar that tapped into this rapid spin.

For decades, most astronomers regarded the Crab Nebula as the steadiest beacon at X-ray energies. But data from several orbiting instruments -- including Fermi's Gamma-ray Burst Monitor -- now show unexpected variations. Astronomers have shown that since 2008, the nebula has faded by 7 percent at high energies, a reduction likely tied to the environment around its central neutron star.

Since 2007, Fermi and the Italian Space Agency's AGILE satellite have detected several short-lived gamma-ray flares at energies hundreds of times higher than the nebula's observed X-ray variations. In April, the satellites detected two of the most powerful yet recorded.

To account for these "superflares," scientists say that electrons near the pulsar must be accelerated to energies a thousand trillion (1015) times greater than that of visible light -- and far beyond what can be achieved by the Large Hadron Collider near Geneva, Switzerland, now the most powerful particle accelerator on Earth.


Image above: Fermi's LAT mapped GeV-gamma-ray emission (magenta) from the W44 supernova remnant. The features clearly align with filaments detectable in other wavelengths. This composite merges X-rays (blue) from the Germany-led ROSAT mission, infrared (red) from NASA's Spitzer Space Telescope, and radio (orange) from the NRAO's Very Large Array near Socorro, N.M. Credit: NASA/DOE/Fermi LAT Collaboration, ROSAT, JPL-Caltech, and NRAO/AUI.

W44. Another interesting supernova remnant detected by Fermi's LAT is W44. Thought to be about 20,000 years old -- middle-age for a supernova remnant -- W44 is located about 9,800 light-years away in the constellation Aquila. The LAT not only detects this remnant, it actually reveals GeV gamma rays coming from places where the remnant's expanding shock wave is known to be interacting with cold, dense gas clouds.

Such observations are important in solving a long-standing problem in astrophysics: the origin of cosmic rays. Cosmic rays are particles -- mainly protons -- that move through space at nearly the speed of light. Magnetic fields deflect the particles as they race across the galaxy, and this scrambles their paths and masks their origins. Scientists can't say for sure where the highest-energy cosmic rays come from, but they regard supernova remnants as a best bet.

In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of gas clouds. In the decades that followed, astronomers showed that the magnetic fields in the expanding shock wave of a supernova remnant is just about the best location for this process to work.

So far, LAT observations of W44 and several other remnants strongly suggest that the gamma-ray emission arises from accelerated protons as they collide with gas atoms.

V407 Cygni. V407 Cygni is a so-called symbiotic binary system, one that contains a compact white dwarf and a red giant star that has swollen to about 500 times the size of the sun. Lying about 9,000 light-years away in the constellation Cygnus, the system occasionally flares up when gas from the red giant accumulates on the dwarf's surface and eventually explodes. The event is sometimes called a nova (after a Latin term meaning "new star").

When the system's most recent eruption occurred in March 2010, Fermi's LAT defied expectations and detected the nova as a brilliant source. Scientists simply didn't expect that this type of outburst had the power to produce high-energy gamma rays.

Pulsar PSR J0101-6422. Pulsars -- rapidly rotating neutron stars -- constitute about six percent of the new catalog. In some cases the LAT can detect gamma-ray pulses directly, but in many cases pulses were first found at radio wavelengths based on suspicions that a faint LAT source might be a pulsar. PSR J0101-6422 is located in the southern constellation of Tucana, its quirky name reflecting its position in the sky.

"This pulsar turns out to be a great example of the cooperation between the Fermi team and radio astronomers -- scientists working in widely separated parts of the electromagnetic spectrum," said David Thompson at NASA's Goddard Space Flight Center in Greenbelt, Md., who co-led the catalog team.

The Fermi team originally took notice of the object as a fairly bright but unidentified gamma-ray source in an earlier LAT catalog. Because the distribution of gamma-ray energies in the source resembled what is normally seen in pulsars, radio astronomers in Australia took a look at it using their Parkes radio telescope.

Pulsars are neutron stars, compact objects packing more mass than the sun's into a sphere roughly the size of Washington, D.C. Lighthouse-like beams of radiation powered by the pulsar's rapid rotation and strong magnetic field sweep across the sky with every spin, and astronomers can detect these beams if they happen to sweep toward Earth.

The Parkes study found radio signals from a pulsar rotating at nearly 400 times a second -- comparable to the spin of a kitchen blender -- at the same position as the unknown Fermi source. With this information, the LAT team was able to discover that PSR J0101-6422 also blinks in gamma rays at the same incredible rate.

2FGL J0359.5+5410. Fermi scientists don't know what to make of this source, located in the constellation Camelopardalis. It resides near the populous midplane of our galaxy, which increases the chance that it's actually an object in the Milky Way. While its gamma-ray spectrum resembles that of a pulsar, pulsations have not been detected and it isn't associated with a known object at other wavelengths.


This radio, optical and gamma-ray composite illustrates the full extent of Cen A's vast radio-emitting lobes. Radio data (orange) reveal that the structures span more than 1.4 million light-years, and Fermi's LAT data (purple) show that they also emit gamma rays. Credit: NASA/DOE/Fermi LAT Collaboration, Capella Observatory, and Ilana Feain, Tim Cornwell, and Ron Ekers (CSIRO/ATNF), R. Morganti (ASTRON), and N. Junkes (MPIfR).

The top five sources beyond our galaxy are:

Centaurus A. The giant elliptical galaxy NGC 5128 is located 12 million light-years away in the southern constellation Centaurus. One of the closest active galaxies, it hosts the bright radio source designated Cen A. Much of the radio emission arises from million-light-year-wide lobes of gas hurled out by the supermassive black hole at the galaxy's center.

Fermi's LAT detects high-energy gamma rays from an extended region around the galaxy that corresponds to the radio-emitting lobes. The radio emission comes from fast-moving particles. When a lower-energy photon collides with one of these particles, the photon receives a kick that boosts its energy into the gamma-ray regime. It's a process that sounds more like billiards than astrophysics, but Fermi's LAT shows that it's happening in Cen A.

The Andromeda Galaxy (M31). At a distance of 2.5 million light-years, the Andromeda Galaxy is the nearest spiral galaxy, one of similar size and structure as our own Milky Way. Easily visible to the naked eye in a dark sky, it's also a favorite target of sky gazers.

The LAT team expected to detect M31 because it's so similar to our own galaxy, where a bright band of diffuse emission creates the most prominent feature in the gamma-ray sky. These gamma rays are mostly produced when high-energy cosmic rays smash into the gas between the stars.

"It took two years of LAT observations to detect M31," said Jürgen Knödlseder at the Research Institute for Astrophysics and Planetology in Toulouse, France. Currently a visiting scientist at the SLAC National Accelerator Laboratory, he worked on the M31 study. "We concluded that the Andromeda Galaxy has fewer cosmic rays than our own Milky Way, probably because M31 forms stars -- including those that die as supernovae, which help produce cosmic rays -- more slowly than our galaxy."


Plumes of glowing hydrogen blast from the center of M82, a well known galaxy undergoing a torrent of star formation. This mosaic of six images taken in 2006 by the Hubble Space Telescope is the sharpest ever obtained of the entire galaxy. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

The Cigar Galaxy (M82). What works for the Andromeda Galaxy works even better for M82, a so-called starburst galaxy that is also a favorite of amateur astronomers. M82 is located 12 million light-years away in the constellation Ursa Major.

M82's central region forms young stars at a rate some 10 times higher than the Milky Way does, activity that also guarantees a high rate of supernovae as the most short-lived stars come to explosive ends. Eventually, M82's superpowered star formation will subside as the gas needed to make new stars is consumed, but that may be tens of millions of years in the future. For now, it's a bright source of gamma rays for Fermi.

Blazar PKS 0537-286. At the core of an active galaxy is a massive black hole that drives jets of particles moving near the speed of light. Astronomers call the galaxy a blazar when one of these jets is pointed our way -- the best view for seeing dramatic flares as conditions change within the jet.

PKS 0537-286 is a variable blazar in the constellation Leo and the second most distant LAT object. Astronomers have determined that the galaxy lies at a redshift of 3.1, more than 11.7 billion light-years away. (Expressed more precisely, the blazar's gamma-ray photons have been traveling for at least 11.7 billion years before being detected by Fermi's LAT).

The blazar is the farthest active galaxy in the Fermi catalog to show variability. Astronomers are witnessing changes in the jet powered by this galaxy's supermassive black hole that occurred when the universe was just 2 billion years old, or 15 percent of its current age.

video

Video above: Active galaxies called blazars make up the largest class of objects detected by Fermi's Large Area Telescope (LAT). Massive black holes in the hearts of these galaxies fire particle jets in our direction. Fermi team member Elizabeth Hays narrates this quick tour of blazars, which includes LAT movies showing how rapidly their emissions can change. (Credit: NASA's Goddard Space Flight Center).

2FGL J1305.0+1152. The last item is another mystery object, one located in the constellation Virgo and high above our galaxy's midplane. It remains faint even after two years of LAT observations.

One clue to classifying these objects lies in their gamma-ray spectrum -- that is, the relative number of gamma rays seen at different energies. At some energy, the spectra of many objects display what astronomers call a "spectral break," that is, a greater-than-expected drop-off in the number of gamma rays seen at increasing energies.

If this were a pulsar, it would show a fast cutoff at higher energies. Many blazars exhibit much more gradual cutoffs. But 2FGL J1305.0+1152 shows no evidence of a spectral break at all, leaving its nature -- for the time being, anyway -- a true mystery.

Related Links:

› Fermi Spots 'Superflares' in the Crab Nebula: http://www.nasa.gov/mission_pages/GLAST/news/crab-flare.html

› NASA Satellites Find High-Energy Surprises in 'Constant' Crab Nebula: http://www.nasa.gov/mission_pages/GLAST/news/crab-nebula-surprise.html

› Fermi Closes on Source of Cosmic Rays: http://www.nasa.gov/mission_pages/GLAST/news/cosmic-rays-source.html

› Fermi Detects 'Shocking' Surprise from Supernova's Little Cousin: http://www.nasa.gov/mission_pages/GLAST/news/shocking-nova.html

› Fermi Maps an Active Galaxy's 'Smokestack Plumes': http://www.nasa.gov/mission_pages/GLAST/news/smokestack-plumes.html

› Fermi's Best-Ever Look at the Gamma-Ray Sky: http://www.nasa.gov/mission_pages/GLAST/news/gammaray_best.html

› Active Galaxies Flare and Fade in Fermi Telescope All-Sky Movie: http://www.nasa.gov/mission_pages/GLAST/news/flare_fade.html

› Fermi Sees Brightest-Ever Blazar Flare: http://www.nasa.gov/mission_pages/GLAST/news/brightest-blazar.html

Images (mentioned), Video (mentioned), Text, Credit: NASA / Goddard Space Flight Center / Francis Reddy.

Greetings, Orbiter.ch

Fifty New Exoplanets Discovered by HARPS












ESO - European Southern Observatory logo.

12 September 2011

Richest haul of planets so far includes 16 new super-Earths

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Video above: Artists’s impression of one of more than 50 new exoplanets found by HARPS: the rocky super-Earth HD 85512 b.

Astronomers using ESO’s world-leading exoplanet hunter HARPS have today announced a rich haul of more than 50 new exoplanets, including 16 super-Earths, one of which orbits at the edge of the habitable zone of its star. By studying the properties of all the HARPS planets found so far, the team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.

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Fifty New Exoplanets

The HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile is the world’s most successful planet finder [1]. The HARPS team, led by Michel Mayor (University of Geneva, Switzerland), today announced the discovery of more than 50 new exoplanets orbiting nearby stars, including sixteen super-Earths [2]. This is the largest number of such planets ever announced at one time [3]. The new findings are being presented at a conference on Extreme Solar Systems where 350 exoplanet experts are meeting in Wyoming, USA.


This artist’s impression shows the planet orbiting the Sun-like star HD 85512 in the southern constellation of Vela (The Sail). This planet is one of sixteen super-Earths discovered by the HARPS instrument on the 3.6-metre telescope at ESO’s La Silla Observatory. This planet is about 3.6 times as massive as the Earth lis at the edge of the habitable zone around the star, where liquid water, and perhaps even life, could potentially exist.

“The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better — the new results show that the pace of discovery is accelerating,” says Mayor.

In the eight years since it started surveying stars like the Sun using the radial velocity technique HARPS has been used to discover more than 150 new planets. About two thirds of all the known exoplanets with masses less than that of Neptune [4] were discovered by HARPS. These exceptional results are the fruit of several hundred nights of HARPS observations [5].


This artist’s impression shows the planet orbiting the Sun-like star HD 85512 in the southern constellation of Vela (The Sail).

Working with HARPS observations of 376 Sun-like stars, astronomers have now also much improved the estimate of how likely it is that a star like the Sun is host to low-mass planets (as opposed to gaseous giants). They find that about 40% of such stars have at least one planet less massive than Saturn. The majority of exoplanets of Neptune mass or less appear to be in systems with multiple planets.

The habitable zone around some stars with planets

With upgrades to both hardware and software systems in progress, HARPS is being pushed to the next level of stability and sensitivity to search for rocky planets that could support life. Ten nearby stars similar to the Sun were selected for a new survey. These stars had already been observed by HARPS and are known to be suitable for extremely precise radial velocity measurements. After two years of work, the team of astronomers has discovered five new planets with masses less than five times that of Earth.

“These planets will be among the best targets for future space telescopes to look for signs of life in the planet’s atmosphere by looking for chemical signatures such as evidence of oxygen,” explains Francesco Pepe (Geneva Observatory, Switzerland), the lead author of one of the recent papers.

Wide-field view of the sky around the star HD 85512

One of the recently announced newly discovered planets, HD 85512 b, is estimated to be only 3.6 times the mass of the Earth [6] and is located at the edge of the habitable zone — a narrow zone around a star in which water may be present in liquid form if conditions are right [7].

“This is the lowest-mass confirmed planet discovered by the radial velocity method that potentially lies in the habitable zone of its star, and the second low-mass planet discovered by HARPS inside the habitable zone,” adds Lisa Kaltenegger (Max Planck Institute for Astronomy, Heidelberg, Germany and Harvard Smithsonian Center for Astrophysics, Boston, USA), who is an expert on the habitability of exoplanets.

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Animation of artist’s impression of the super-Earth planet HD 85512 b

The increasing precision of the new HARPS survey now allows the detection of planets under two Earth masses. HARPS is now so sensitive that it can detect radial velocity amplitudes of significantly less than 4 km/hour [8] — less than walking speed.

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Zooming in on HD 85521 b

"The detection of HD 85512 b is far from the limit of HARPS and demonstrates the possibility of discovering other super-Earths in the habitable zones around stars similar to the Sun," adds Mayor.

These results make astronomers confident that they are close to discovering other small rocky habitable planets around stars similar to our Sun. New instruments are planned to further this search. These include a copy of HARPS to be installed on the Telescopio Nazionale Galileo in the Canary Islands, to survey stars in the northern sky, as well as a new and more powerful planet-finder, called ESPRESSO, to be installed on ESO’s Very Large Telescope in 2016 [9]. Looking further into the future also the CODEX instrument on the European Extremely Large Telescope (E-ELT) will push this technique to a higher level.

"In the coming ten to twenty years we should have the first list of potentially habitable planets in the Sun's neighbourhood. Making such a list is essential before future experiments can search for possible spectroscopic signatures of life in the exoplanet atmospheres," concludes Michel Mayor, who discovered the first-ever exoplanet around a normal star in 1995.

Notes:

[1] HARPS measures the radial velocity of a star with extraordinary precision. A planet in orbit around a star causes the star to regularly move towards and away from a distant observer on Earth. Due to the Doppler effect, this radial velocity change induces a shift of the star’s spectrum towards longer wavelengths as it moves away (called a redshift) and a blueshift (towards shorter wavelengths) as it approaches. This tiny shift of the star’s spectrum can be measured with a high-precision spectrograph such as HARPS and used to infer the presence of a planet.

[2] Planets with a mass between one and ten times that of the Earth are called super-Earths. There are no such planets in our Solar System, but they appear to be very common around other stars. Discoveries of such planets in the habitable zones around their stars are very exciting because — if the planet were rocky and had water, like Earth — they could potentially be an abode of life.

[3] Currently the number of exoplanets stands at close to 600. In addition to exoplanets found using radial velocity techniques, more than 1200 exoplanet candidates have been found by NASA’s Kepler mission using an alternative method — searching for the slight drop in the brightness of a star as a planet passes in front of it (transits) and blocks some of the light. The majority of planets discovered by this transit method are very distant from us. But, in contrast, the planets found by HARPS are around stars close to the Sun. This makes them better targets for many kinds of additional follow-up observations.

[4] Neptune has about seventeen times the mass of Earth.

[5] This huge observing programme is led by Stéphane Udry (Geneva Observatory, Switzerland).

[6] Using the radial velocity method, astronomers can only estimate a minimum mass for a planet as the mass estimate also depends on the tilt of the orbital plane relative to the line of sight, which is unknown. From a statistical point of view, this minimum mass is however often close to the real mass of the planet.

[7] So far, HARPS has found two super-Earths that may lie within the habitable zone. The first one, Gliese 581 d, was discovered in 2007 (eso0722). HARPS was also recently used to demonstrate that the other candidate super-Earth in the habitable zone around the star Gliese 581 (Gliese 581 g) does not exist.

[8] With large numbers of measurements, the detection sensitivity of HARPS is close to 100% for super-Earths of ten Earth-masses with orbital periods of up to one year, and even when considering planets of three Earth masses with a one-year orbit, the probability of detection remains close to 20%.

[9] ESPRESSO, the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, is to be installed on the ESO Very Large Telescope. Currently undergoing preliminary design, it is scheduled to start operating in 2016. ESPRESSO will feature radial velocity precision of 0.35 km/h or less. For comparison, Earth induces a 0.32 km/h radial velocity on the Sun. This resolution should thus enable ESPRESSO to discover Earth-mass planets in the habitable zone of low-mass stars.

More information:

The results are being presented on 12 September 2011 at the conference on Extreme Solar Systems held at the Grand Teton National Park, Wyoming, USA.

A summary is presented in the following paper (in preparation): “The HARPS search for southern extra-solar planets, XXXIV — Occurrence, mass distribution and orbital properties of super-Earths and Neptune-type planets” to appear in the journal Astronomy & Astrophysics.

The team is composed of M. Mayor (Observatoire de Genève [OAUG], Switzerland), M. Marmier (OAUG), C. Lovis (OAUG), S. Udry (OAUG), D. Ségransan (OAUG), F. Pepe (OAUG), W. Benz (Physikalisches Institut Universität Bern, Switzerland), J. L. Bertaux (Service d’Aéronomie, Paris, France), F. Bouchy (Institut d’Astrophysique de Paris, Université Pierre & Marie Curie, France and Observatoire de Haute-Provence/CNRS, France), X. Dumusque (OAUG), G. LoCurto (ESO, Germany), C. Mordasini (Max Planck Institute for Astronomy, Germany), D. Queloz (OAUG), N. C. Santos (Centro de Astrofísica da Universidade do Porto, Portugal and Departamento de Física de Astronomia, Faculdade de Ciências da Universidade do Porto, Portugal), D. Queloz (OAUG).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

ESOcast 35: Fifty New Exoplanets: http://www.eso.org/public/videos/eso1134a/

Science papers in Astronomy & Astrophysics:
“The HARPS search for Earth-like planets in the habitable zone, I — Very low-mass planets around HD20794, HD85512, HD192310” (Pepe et al., 2011): http://www.eso.org/public/archives/releases/sciencepapers/eso1134/eso1134a.pdf

"The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets" (Mayor et al., 2011): http://www.eso.org/public/archives/releases/sciencepapers/eso1134/eso1134b.pdf

HARPS: http://www.eso.org/sci/facilities/lasilla/instruments/harps/overview.html

ESPRESSO: http://www.eso.org/sci/facilities/develop/instruments/espresso/

Gliese 581: http://www.eso.org/public/news/eso0722/

Photos of La Silla Observatory: http://www.eso.org/public/images/archive/category/lasilla/

Images, Text, Credits: ESO / M. Kornmesser / Observatoire de l’Université de Genève Switzerland / Stéphane Udry / Francesco Pepe / Max Planck Institute / Lisa Kaltenegger / La Silla, Paranal, E-ELT & Survey Telescopes / Richard Hook / Videos: ESO / A. Fujii / Digitized Sky Survey 2. Music: John Dyson (from the album Moonwind) / Video "Fifty New Exoplanets": Visual design and editing: Martin Kornmesser and Luis Calçada / Editing: Herbert Zodet / Web and technical support: Lars Holm Nielsen and Raquel Yumi Shida / Written by: Mathieu Isidro and Richard Hook / Narration: Gaitee Hussain / Music: Movetwo / Footage and photos: ESO, Serge Brunier and H.H. Heyer / Directed by: Herbert Zodet / Executive producer: Lars Lindberg Christensen.

Best regards, Orbiter.ch

ERS satellite missions complete after 20 years

ESA - ERS-2 Satellite Mission logo.

12 September 2011

After a final thruster firing last week to deplete its remaining fuel, ESA's venerable ERS-2 observation satellite has been safely taken out of service. Ground controllers also ensured the space environment was protected for future missions.

The mission ended on 5 September, after the satellite's average altitude had already been lowered from 785 km to about 573 km. At this height, the risk of collision with other satellites or space debris is greatly reduced.

ERS-2

The final critical step was to 'passivate' ERS-2, ensuring that all batteries and pressurised systems were emptied or rendered safe in order to avoid any future explosion that could create new space debris.

This primarily consisted of burning off the fuel, disconnecting the batteries and switching off the transmitters.

"As soon as we saw fuel depletion occurring, a series of commands was sent to complete passivation, before shutting the satellite down for good. The last command was sent at 13:16 GMT on 5 September," said Frank Diekmann, ERS-2 Operations Manager.

Valuable data archive

The end of flight operations does not mean the end of the mission's usefulness, though.

Final ERS-2 image showing Rome, Italy

"We will continue exploiting data gathered by ERS-2, especially the radar imagery," said Volker Liebig, ESA's Director for Earth Observation Programmes.

"Combining this rich scientific store with new data delivered by improved radar instruments on the GMES Sentinel-1 mission will generate strong synergies as we work to understand our planet's climate."

Atmospheric burn up

With the effects of natural atmospheric drag, ERS-2 is predicted to enter and largely burn up in the atmosphere in about 15 years. This is well within the 25-year-limit that is imposed to minimise the risk of collision before re-entry.

"ERS-2 deorbiting is being conducted in compliance with ESA's space debris mitigation requirements," said Heiner Klinkrad, Head of ESA’s Space Debris Office.

"This indicates the strong commitment by the Agency to reducing space debris, which can threaten current and future robotic and human missions."

End of 16-year mission

ERS-2 was launched in 1995, four years after ERS-1, the first European Remote Sensing satellite. The missions paved the way for the development of many new Earth observation techniques.

Part of the ESA team at ESOC for deorbiting

"ERS-1 and -2 delivered 20 years of continuous high-quality data covering the oceans, land, ice and atmosphere," said Wolfgang Lengert, ERS-2 Mission Manager.

"Throughout these two decades, the emphasis has been on quantifying measurement accuracy and documenting results, ensuring the data will serve as a heritage for future generations."

ERS-2 travelled 3.5 billion km during its lifetime, providing data for thousands of scientists and projects.

Operations team prepares for deorbiting

Mission controllers, flight dynamics specialists and technical experts prepared for many months prior to starting the deorbit procedure in July 2011.

Some of Operations team discussing deorbiting procedures

Lowering the satellite's orbit to 573 km came after a set of 66 carefully controlled manoeuvres commanded by the mission control team at ESA's European Space Operations Centre (ESOC) in Germany during July and August 2011.

"At this targeted altitude, the satellite orbits Earth exactly 15 times a day, and we could monitor ERS-2 shut-down activities via a chain of ground stations," says Xavier Marc, the mission’s lead flight dynamics engineer.

"Now, its orbit will slowly decay due to natural atmospheric drag."

Three of ERS-2's six gyroscopes failed in the early years of the mission, and the data storage system ceased functioning in 2003, making deorbiting a particular challenge for the ESOC team.

“ERS-2 deorbiting demonstrates excellent team work at ESA, directly fed by the unique expertise gained by the flight dynamics and flight control teams at ESOC during 20 years.”

Depleting fuel avoids creating future debris

On 26 August, controllers began the last series of thruster firings that alternately raised then lowered the spacecraft altitude, using up substantially all remaining fuel. The firings took place several times per week, running up to 40 minutes each.

The firings occurred during mid-afternoon while the satellite was nearly continuously tracked by the Agency’s 15 m ground stations in Kiruna (Sweden), Maspalomas (Canary Islands) and Kourou (French Guiana).

Additional tracking support was provided by the Japan Aerospace Exploration Agency station at Katsuura, near Tokyo, and the Svalbard station in Norway, operated by KSAT.

Keeping an eye on the gas

"The orbit and the selected ground stations offered a nearly uninterrupted spacecraft visibility slot of approximately 50 minutes each day where fuel depletion could be conducted and closely monitored," said Marc.

Mission complete: ERS-2 deorbiting team at ESOC

"The challenge was to burn up as much fuel as possible right up until it was substantially all gone, then quickly shut down the satellite’s subsystems while we were still tracking it in ground station visibility."

Unlike a car, ERS-2 had no convenient fuel gauge showing when it was, say, nine-tenths empty. Instead, engineers had to monitor a set of parameters carefully that indicated thruster activity and the fuel system's pressure and temperature, and use these to estimate the mass of remaining fuel.

Controllers could also monitor parameters that indicated when thrust had become uneven or intermittent, which also showed whether fuel had been depleted.

In recent days, Diekmann and the ESOC team monitored each depletion firing minute-by-minute from the mission’s Dedicated Control Room, watching intently for the signs that fuel was nearing exhaustion.

"ERS-2 deorbiting demonstrates excellent team work at ESA, directly fed by the unique expertise gained by the flight dynamics and flight control teams at ESOC during 20 years of demanding ground control for ESA Earth observation missions, including ERS-1 and ERS-2," said Manfred Warhaut, ESA’s Head of Mission Operations.

Related missions:

ERS overview: http://www.esa.int/esaEO/SEMGWH2VQUD_index_0_m.html

Related links:

Malindi station: http://www.esa.int/SPECIALS/Operations/SEMIIDUL05F_0.html

Svalbard station: http://www.esa.int/SPECIALS/Operations/SEM8P1SVYVE_0.html

JAXA Katsuura Station: http://www.jaxa.jp/about/centers/ktcs/index_e.html

Images, Text, Credit: ESA.

Greetings, Orbiter.ch