Posted on by Fraser Cain

Ion Engine Shut Down After Almost Five Years

Image credit: NASA/JPL

NASA researchers finally shut down an ion engine that had been running continuously for 30,352 hours. The engine was a duplicate of the one that flew on Deep Space 1, NASA’s mission to test out a range of experimental technologies, and was originally designed to work for 8,000 hours. The engine was finally turned off so that engineers could take it apart to examine the different engine components for wear. Deep Space 1’s engine operated for 16,265 hours.

The future is here for spacecraft propulsion and the trouble-free engine performance that every vehicle operator would like, achieved by an ion engine running for a record 30,352 hours at NASA?s Jet Propulsion Laboratory, Pasadena, Calif.

The engine is a spare of the Deep Space 1 ion engine used during a successful technology demonstration mission that featured a bonus visit to comet Borrelly. It had a design life of 8,000 hours, but researchers kept it running for almost five years, from Oct. 5, 1998, to June 26, 2003, in a rare opportunity to fully observe its performance and wear at different power levels throughout the test. This information is vital to future missions that will use ion propulsion, as well as to current research efforts to develop improved ion thrusters.

“Finding new means to explore our solar system ? rapidly, safely and with the highest possible return on investment ? is a key NASA mission,” said Colleen Hartman, head of Solar System Exploration at NASA Headquarters, Washington, D.C. “Robust in-space flight technologies such as ion propulsion are critical to this effort and will pioneer a new generation of discovery among our neighboring worlds.”

While the engine had not yet reached the end of its life, the decision was made to terminate the test because near-term NASA missions using ion propulsion needed analysis data that required inspection of the different engine components. In particular, the inspection of the thruster?s discharge chamber, where xenon gas is ionized, is critical for mission designers of the upcoming Dawn mission. Dawn, part of NASA’s Discovery Program, will be launched in 2006 to orbit Vesta and Ceres, two of the largest asteroids in the solar system.

“The chamber was in good condition,” said John Brophy, JPL?s project element manager for the Dawn ion propulsion system. “Most of the components showed wear, but nothing that would have caused near-term failure.”

Marc Rayman, former Deep Space 1 project manager, said, ?There are many exciting missions into the solar system that would be unaffordable or truly impossible without ion propulsion. This remarkable test shows that the thrusters have the staying power for long duration missions.?

Ion engines use xenon, the same gas used in photo flash tubes, plasma televisions and some automobile headlights. Deep Space 1 featured the first use of an ion engine as the primary method of propulsion on a NASA spacecraft. That engine was operated for 16,265 hours, the record for operating any propulsion system in space. Ion propulsion systems can be very lightweight, since they can run on just a few grams of xenon gas a day. While the thrust exerted by the engine is quite gentle, its fuel efficiency can reduce trip times and lower launch vehicle costs. This makes it an attractive propulsion system choice for future deep space missions.

“The engine remained under vacuum for the entire test, setting a new record in ion engine endurance testing, a true testament to the tremendous effort and skill of the entire team,” said Anita Sengupta, staff engineer in JPL?s Advanced Propulsion Technology Group. “This unique scientific opportunity benefits current and potential programs.”

“The dedicated work of NASA?s Solar Electric Technology Application Readiness test team, led by JPL, continues to exemplify a commitment to engineering excellence,” said Les Johnson, who leads the In-Space Propulsion Program at NASA?s Marshall Space Flight Center, Huntsville, Ala. “This work, along with significant contributions from NASA?s Glenn Research Center in Cleveland, will take NASA?s space exploration to the next level.”

NASA?s next-generation ion propulsion efforts are led by the In-Space Propulsion Program, managed by the Office of Space Science at NASA Headquarters and implemented by the Marshall Center. The program seeks to develop advanced propulsion technologies that will help near and mid-term NASA science missions by significantly reducing cost, mass or travel times.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Leaders Renew Space Station Commitment

Image credit: NASA

Leaders from five of the world’s space agencies met in California this week and pledged to continue building the International Space Station, despite the delays and setbacks from the Columbia disaster. The five groups represented the US, Canada, Europe, Japan and Russia and they usually meet twice a year. Their next meeting is scheduled for October in Moscow to discuss the impact the Columbia accident investigation report will have on their plans.

Space agency leaders from the United States, Europe, Canada, Japan and Russia met today in Monterey California, to review the status of cooperation on the International Space Station (ISS) Program.

The meeting participants noted the significant milestone of the 1,000th day of permanent human presence aboard the ISS in a live telephone conversation with Expedition Seven Commander, Yuri Malenchenko, and NASA ISS Science Officer, Ed Lu, the cosmonaut and astronaut members of Expedition Seven. The Heads of Agency were briefed on the preliminary recommendations of the Columbia Accident Investigation Board and NASA’s plans for the return to flight of the U.S. Space Shuttle. They agreed to review and update the ISS Program Action Plan, adopted in December 2002, in order to realize the objectives of the ISS Program as soon as possible. The HOA agreed that the ISS Program Action Plan should remain the basis for proceeding with selection of an ISS configuration. The HOA also agreed to meet again in Moscow in mid-October to discuss specific ISS implementation plans taking into account NASA’s Return to Flight activities.

Appreciation was expressed for the strong support for the ISS Program by all Partner agencies, and in particular by the Russian Aviation and Space Agency, for resolutely providing for continuing human presence on the ISS after the tragic loss of the Space Shuttle Columbia and her courageous crew. The ISS partnership looks forward to continuing critical Russian support for general ISS operations, logistics and crew transportation and rescue capability until the Space Shuttle returns to flight and beyond. The Partners expressed great enthusiasm for NASA’s Return to Flight and the timely resumption of ISS assembly and opportunities for enhanced utilization of this world-class research facility.

Original Source: NASA News Release

Posted on by Fraser Cain

NASA Needs Better Shuttle Pictures

Image credit: CAIB

The Columbia Accident Investigation Board released its fifth major finding today, which recommends that NASA improve the way it takes photographs of the shuttle launch. During the launch of Columbia, NASA cameras provided poor images from a critical point of view which would have showed foam falling from the external fuel tank more clearly. NASA is considering additional ground, aircraft, and even shuttle-mounted cameras to better document future launches. The final report is expected within a month.

The Columbia Accident Investigation Board today issued its fifth preliminary finding and recommendation to the National Aeronautics and Space Administration, in advance of its appearance in the final report.

Recommendation Five:

  • Provide a capability to obtain and downlink high-resolution images of the External Tank (ET) after ET separation. Modifying one of the two umbilical cameras to meet this requirement is acceptable.
  • Provide a capability to obtain and downlink high-resolution images of the underside of the orbiter leading edge system and forward section of both wings? Thermal Protection System (TPS).

Facts:

  • Imaging the Space Shuttle System during launch and ascent provides necessary engineering data including the ability to examine the Space Shuttle System for any unexpected debris or other anomalies during ascent.
  • The Shuttle has two on-board cameras that image the ET after separation, but the images from these cameras are available only post-flight.
  • Very little engineering quality, on-board imaging of the ET was available for STS-107.

Findings:

  • There is a requirement to obtain and downlink on-board engineering quality imaging from the vehicle during launch and ascent.

Background:

  • The Space Shuttle is still a developmental vehicle, and engineering data from each launch is essential to further understand the vehicle.
  • An ability to provide engineering quality imaging data of the ET after separation is important to determine if any debris from the ET was shed during ascent.
  • Since the total elimination of all sources of debris has not yet been achieved, a much better understanding of all the potential sources of debris is required.
  • Since the total elimination of all sources of debris has not yet been achieved, early detection of debris strikes against the forward underwing TPS of both wings will increase safety margins.
  • The CAIB is aware of the excellent preliminary work already in progress at NASA in this area.

Original Source: CAIB News Release

Posted on by Fraser Cain

Neutron Star Binaries are More Common in Clusters

Image credit: Chandra

Many of the stars that we see in globular star clusters are actually binary stars, formed when two stars get caught in each other’s gravity. But new research from the Chandra X-Ray Observatory shows that there are many more binary objects which are stars orbiting a neutron star or white dwarf. Chandra can detect the unique x-ray signature that a neutron star gives off, which is invisible in an optical telescope. The research seems to indicate that these neutron star binaries form much more commonly found in globular clusters than in other parts of a galaxy.

NASA’s Chandra X-ray Observatory has confirmed that close encounters between stars form X-ray emitting, double-star systems in dense globular star clusters. These X-ray binaries have a different birth process than their cousins outside globular clusters, and should have a profound influence on the cluster’s evolution.

A team of scientists led by David Pooley of the Massachusetts Institute of Technology in Cambridge took advantage of Chandra’s unique ability to precisely locate and resolve individual sources to determine the number of X-ray sources in 12 globular clusters in our Galaxy. Most of the sources are binary systems containing a collapsed star such as a neutron star or a white dwarf star that is pulling matter off a normal, Sun-like companion star.

“We found that the number of X-ray binaries is closely correlated with the rate of encounters between stars in the clusters,” said Pooley. “Our conclusion is that the binaries are formed as a consequence of these encounters. It is a case of nurture not nature.”

A similar study led by Craig Heinke of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. confirmed this conclusion, and showed that roughly 10 percent of these X-ray binary systems contain neutron stars. Most of these neutron stars are usually quiet, spending less than 10% of their time actively feeding from their companion.

A globular cluster is a spherical collection of hundreds of thousands or even millions of stars buzzing around each other in a gravitationally-bound stellar beehive that is about a hundred light years in diameter. The stars in a globular cluster are often only about a tenth of a light year apart. For comparison, the nearest star to the Sun, Proxima Centauri, is 4.2 light years away.

With so many stars moving so close together, interactions between stars occur frequently in globular clusters. The stars, while rarely colliding, do get close enough to form binary star systems or cause binary stars to exchange partners in intricate dances. The data suggest that X-ray binary systems are formed in dense clusters known as globular clusters about once a day somewhere in the universe.

Observations by NASA’s Uhuru X-ray satellite in the 1970’s showed that globular clusters seemed to contain a disproportionately large number of X-ray binary sources compared to the Galaxy as a whole. Normally only one in a billion stars is a member of an X-ray binary system containing a neutron star, whereas in globular clusters, the fraction is more like one in a million.

The present research confirms earlier suggestions that the chance of forming an X-ray binary system is dramatically increased by the congestion in a globular cluster. Under these conditions two processes, known as three-star exchange collisions, and tidal captures, can lead to a thousandfold increase in the number of X-ray sources in globular clusters.

In an exchange collision, a lone neutron star encounters a pair of ordinary stars. The intense gravity of the neutron star can induce the most massive ordinary star to “change partners,” and pair up with the neutron star while ejecting the lighter star.

A neutron star could also make a grazing collision with a single normal star, and the intense gravity of the neutron star could distort the gravity of the normal star in the process. The energy lost in the distortion, could prevent the normal star from escaping from the neutron star, leading to what is called tidal capture.

“In addition to solving a long-standing mystery, Chandra data offer an opportunity for a deeper understanding of globular cluster evolution,” said Heinke. “For example, the energy released in the formation of close binary systems could keep the central parts of the cluster from collapsing to form a massive black hole.”

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Original Source: Chandra News Release

Posted on by Fraser Cain

Ion Drive Powered Spacecraft

Image credit: ESA

The European Space Agency’s SMART-1 mission will use a revolutionary ion engine to help it search for evidence that the Moon was formed after a violent collision of a smaller planet with the Earth. An ion engine works by accelerating ionized particles of gas in a constant stream for months or even years. Although the thrust is very low, it’s very efficient and requires a fraction of fuel that traditional rockets use.

Science fiction movie fans know that, if you want to travel short distances from your home planet, you would use a sublight ‘ion drive’. However, is such an ion drive science fiction, or science fact?

The answer lies somewhere in between. Ion engines date back to at least 1959. Two ion engines were even tested in 1964 on the American SERT 1 satellite – one was successful, the other was not.

The principle is simply conventional physics – you take a gas and you ionise it, which means that you give it an electrical charge. This creates positively charged ions of gas, along with electrons. The ionised gas passes through an electric field or screen at the back of the engine and the ions leave the engine, producing a thrust in the opposite direction.

Very fuel-efficient
Operating in the near vacuum of space, ion engines shoot out the propellant gas much faster than the jet of a chemical rocket. They therefore deliver about ten times as much thrust per kilogram of propellant used, making them very ‘fuel-efficient’.

Although they are efficient, ion engines are very low-thrust devices. The amount of push you get for the amount of propellant used is very good, but they do not push very strongly. For example, astronauts could never use them for taking off the surface of a planet. However, once in space, they could use them for manoeuvring around, if they are not in a hurry to accelerate quickly. Why? Ion drives can get up to high speeds in space, but they need a very long distance to build up to such speeds over time.

Leisurely advantage
Ion engines work their magic in a leisurely way. Electric guns accelerate the ions. If the power for this acceleration comes from the spacecraft’s solar panels, scientists call it ‘solar-electric propulsion’. Solar panels of the size typically used on current spacecraft can supply only a few kilowatts of power.

A solar-powered ion engine could therefore not compete with the large thrust of a chemical rocket. However, a typical chemical rocket burns for only a few minutes, whereas an ion engine can go on pushing gently for months or even years – as long as the Sun shines and the supply of propellant lasts.

Another advantage of gentle thrust is that it allows very accurate spacecraft control, very useful for scientific missions that require highly precise target pointing.

Ensuring ESA’s place in space
Engineers tested an ion engine as a main propulsion system for the first time using NASA’s Deep Space 1 mission between 1998 and 2001. ESA’s SMART-1 mission, due for launch in late August 2003, will go to the Moon and demonstrate more subtle operations of the kind needed in future long-distance missions. These will combine solar-electric propulsion with manoeuvres using the gravity of planets and moons for the first time.

SMART-1 will ensure Europe’s independence in the use of ion propulsion. Other space science missions are expected to use ion engines for complex manoeuvres close to Earth’s orbit. For example, ESA’s mission LISA will detect gravitational waves coming from the distant Universe. ESA’s future missions to the planets will also use ion engines to send them on their way.

Now science fact
The present-day realities of solar-electric propulsion might not match the movie magic of sci-fi films with spacecraft flying around on our cinema screens. However, ESA’s work on SMART-1 and future missions is ensuring that ion drives are now more science fact than science fiction.

Original Source: ESA News Release

Posted on by Fraser Cain

Satellite Confirms Ozone Recovery

Image credit: NASA

Observations from three NASA satellites have confirmed that the rate of ozone depletion in the Earth’s upper atmosphere is decreasing. The observations were made by SAGE I, SAGE II, and HALOE satellites which scanned the upper stratosphere since 1997. Their observations are consistent with the decline of man-made chemicals in the atmosphere which contribute to ozone depletion. The ozone layer protects the Earth’s surface from sun’s harmful ultraviolet radiation.

NASA satellite observations have provided the first evidence the rate of ozone depletion in the Earth’s upper atmosphere is decreasing. This may indicate the first stage of ozone layer recovery.

From an analysis of ozone observations from NASA’s first and second Stratospheric Aerosol and Gas Experiment (SAGE) and the Halogen Occultation Experiment (HALOE) satellite instruments, scientists have found less ozone depletion in the upper stratosphere (22-28 miles altitude) after 1997. The American Geophysical Union Journal of Geophysical Research has accepted a paper for publication on these results.

This decrease in the rate of ozone depletion is consistent with the decline in the atmospheric abundance of man-made chorine and bromine-containing chemicals that have been documented by satellite, balloon, aircraft and ground based measurements.

Concerns about ozone depletion in the upper atmosphere or stratosphere led to ratification of the Montreal Protocol on Substances that Deplete the Ozone Layer by the international community in 1987. The protocol restricts the manufacture and use of human-made, ozone-depleting compounds, such as chlorofluorocarbons and halons.

“Ozone is still decreasing but just not as fast,” said Mike Newchurch, associate professor at the University of Alabama, Huntsville, Ala., and lead scientist on the study. “We are still decades away from total ozone recovery. There are a number of remaining uncertainties such as the effect of climate change on ozone recovery. Hence, there is a need to continue this precise long-term ozone data record,” he said.

“This finding would have been impossible had either SAGE II or HALOE not lasted so long past their normal mission lifetime,” said Joe Zawodny, scientist on the SAGE II satellite instrument science team at NASA’s Langley Research Center, Hampton, Va.

SAGE II is approaching the 19th anniversary of its launch, and HALOE has been returning data for 11 years. Scientists also used international ground networks to confirm these data from satellite results.

SAGE I was launched on the Applications Explorer Mission-B spacecraft in 1979; the Earth Radiation Budget Satellite carried SAGE II into orbit in 1984. The Space Shuttle Discovery carried HALOE into space on the Upper Atmosphere Research Satellite in 1991.

NASA’s Earth Science Enterprise funded this research in an effort to better understand and protect our home planet. The ozone layer protects the Earth’s surface from the sun’s harmful ultraviolet rays. Ultraviolet radiation can contribute to skin cancer and cataracts in humans and harm other animals and plants. Ozone depletion in the stratosphere also causes the ozone hole that occurs each spring over Antarctica.

Original Source: NASA News Release

Posted on by Fraser Cain

Mars is Close and Getting Closer

Image credit: Hubble

On August 27, 2003 the Planet Mars will be a mere 55.76 million kilometres away from the Earth – the closest it’s been in 50,000 years. Visible in the early morning, Mars is the brightest object in the sky, after the Moon and Venus, and almost any small telescope will be able to show details on the planet’s surface. Make sure you enjoy Mars’ close approach this summer, as it won’t make another visit this close for nearly 300 years.

Living too close to a neighbor may not be very appealing, but when Earth?s neighboring red planet moves closer than it?s been in 60,000 years, observers expect nothing but acclaim.

This August, scientists and amateur astronomers will benefit from the spectacular view of Mars as it appears bigger and brighter than ever before, revealing its reflective south polar cap and whirling dust clouds.

On August 27, 2003, the fourth rock from the sun will be less than 55.76 million kilometers (34.65 million miles) away from the Earth. In comparison to the space between your house and your neighbor?s yard, that may seem like a large distance, but Mars was about five times that distance from Earth only six months ago.

“Think of Earth and Mars as two race cars going around a track,” said Dr. Myles Standish, an astronomer from NASA?s Jet Propulsion Laboratory, Pasadena, Calif. “Earth is on a race track that is inside the track that Mars goes around, and neither track is perfectly circular. There is one place where the two race tracks are closest together. When Earth and Mars are at that place simultaneously, it is an unusually close approach, referred to as a ‘perihelic opposition’.”

Opposition is a term used when Earth and another planet are lined up in the same direction from the Sun. The term perihelic comes from perihelion, the point of orbit in which a celestial body is closest to the Sun. This August, Mars will reach its perihelion and be in line with Earth and the Sun at the same time.

The average opposition occurs about every two years, when Earth laps Mars on its orbit around the Sun. In 1995, the opposition brought Mars 101.1 million kilometers (62.8 million miles) from the Earth, twice as far as this most recent approach.

“It gets more complicated as the race tracks are changing shape and size and are rotating, changing their orientation,” Standish explains. “So this place where the two tracks are closest together constantly changes, changing the opposition closeness as well. This is why a ‘great’ approach, like the one this month, hasn?t happened in 60,000 years. But with the tracks closer together now, there will be even closer approaches in the relatively near future.”

Aside from visiting a local observatory, peering through a telescope is the best way to take advantage of this unique opportunity. Since June, Mars has been noticeably bright in the night?s sky, only outshined by Venus and the Moon. Observers in the Northern Hemisphere will see it glowing remarkably in the southern sky in the constellation Aquarius, best seen just before dawn.

“You’re not going to go outside and see some big red ball in the sky. It will look like a bright red star,” said Standish.

The word ‘planet’ is derived from the Greek expression for ?wanderer.? At such a close distance, Mars remains true to this expectation as it consistently wanders across the night?s sky. Tracking the “red star?s” movement from week to week is yet another way to appreciate the opposition as Mars appears to dart across the sky in comparison to more distant planets, such as Jupiter.

Although Mars will be closest on August 27, astronomers suggest viewing the planet earlier, as dust storm season is just beginning on the red planet and can obstruct a more detailed view.

Whether you are viewing through a telescope, glancing through a pair of binoculars, or star-gazing outside the city, be sure to take advantage of this once-in-a-lifetime opportunity, for Mars will not make another neighborly visit this close until 2287.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

New Satellite Image of the Aral Sea

Image credit: ESA

A new image taken by the European Space Agency’s Envisat satellite shows how much the Aral Sea has evaporated. Located in Central Asia, the Aral Sea used to be the fourth largest lake in the world, but rivers that feed the lake were diverted for cotton agriculture. It’s now half its former surface area and one-quarter its original volume and continuing to shrink. The picture was taken using the Medium Resolution Imaging Spectrometer (MERIS) instrument which has a resolution of 300 metres.

Earth?s youngest desert is shown in this July MERIS satellite image of the Aral Sea in Central Asia. Once the fourth largest lake in the world, over the last 40 years the Aral Sea has evaporated back to half its original surface area and a quarter its initial volume, leaving a 40,000 square kilometre zone of dry white-coloured salt terrain now called the Aralkum Desert.

As its water level has dropped 13 metres since the 1960s the Sea has actually split into two ? the larger horseshoe-shaped body of water and a smaller almost unconnected lake a little to its north. This Small Aral Sea is the focus of international preservation efforts, but the Large Aral Sea has been judged beyond saving (the shallowness of its eastern section is clear in the image). It is expected to dry out completely by 2020.

Towards the bottom right can be seen the sands of the Qyzylqum Desert. Already stretching across an area greater than Italy, this desert is set to extend further west in future, eventually merging with its younger Aralkum sibling. The distinctive darker area to the south of the Large Aral Sea is the delta of the Amu Darya river. Its waters support environmentally-unique tugai forests found only in Central Asia, along with land used for rice and cotton cultivation.

The grey area seen in the otherwise whitish zone between the two arms of the Large Aral Sea was once Vozrozhdeniye (‘Rebirth’) Island, the isolated site of biological warfare experimentation during the Cold War, now joined to the mainland and freely accessible by foot. In reaction to this development, a US-led international team last year moved in to destroy remaining anthrax stocks.

Located on the border between Uzbekistan and Kazakhstan, the Aral Sea shows what happens when the concept of sustainable development is disregarded. Starting in the 1960s, the waters of the two rivers feeding the Sea ? the Amu Darya, seen south, and the Syr Darya to the northwest ? were diverted by Soviet planners to irrigate thirsty cotton fields across the region. By the 1980s there was little water reaching the lake and it began to shrink.

For local people the results have been disastrous. The Aral Sea’s retreating shoreline has left ports landlocked and boats stranded on dry sand. Commercial fishing was forced to halt twenty years ago. The few remaining fishermen commute by car to the water’s edge. The waters that remain grow increasingly saline so only salt-resistant fish imported from elsewhere can endure them. Wildlife habitats have been destroyed and communities find themselves without clean water supplies.

The retreat of the waters has also altered the regional microclimate. Winters are colder and the summers hotter. Each year violent sandstorms pick up at least 150,000 tonnes of salt and sand from the dried-up lakebed and transport it across hundreds of kilometres.

The sandstorms are tainted with pesticide residue and have been linked to high regional rates of respiratory illnesses and certain types of cancer. The salty dust does harm to livestock pastures and has even been linked with melting glaciers up in the distant Pamir Mountains, on the Afghanistan border.

Back in the days of the USSR, planners spoke casually of diverting Siberian rivers to save the Aral Sea. Today that certainly will not happen. Instead Central Asian governments have come together to establish the International Fund for Saving the Aral Sea. But their economies are too dependent on cotton exports to end all irrigation.

The Small Aral Sea is still thought to be saveable, and several dikes have been constructed to cut it off from the Large Aral Sea ? preventing water loss and salt contamination – but shifting water levels have so far defeated these efforts. The channel connecting the two should soon dry up anyway, preserving the Small Aral Sea at least. Meanwhile researchers are studying the salty Aralkum Desert ? effectively the newest land surface on Earth ? to see how best to promote plant growth and stabilise the dusty dry lakebed.

Original Source: ESA News Release

Posted on by Fraser Cain

South African Observatory Nearing Completion

Image credit: SALT

The observatory that will house the largest optical telescope in the Southern hemisphere is nearing completion. The Southern African Large Telescope (SALT) is being built by a consortium of six countries at the southern edge of the Kalahari Desert in Africa. The 11-by-10 metre telescope is 18 months away from being done, but the structure of the observatory is nearly complete. The entire project will cost $18 million and be fully operational in late 2004.

A new observatory that promises to give Wisconsin astronomers unique access to the southern sky is now a prominent feature on a remote South African plateau.

The observatory that will house the largest optical telescope in the Southern Hemisphere, known as the Southern African Large Telescope (SALT), is now nearly complete, according to astronomers at UW-Madison. Although the telescope itself is still 18 months from completion, the mirror segments that will make up the 11-by-10-meter hexagonal primary mirror are starting to come together, says Matthew Bershady a UW-Madison professor of astronomy who is helping to oversee planning and construction of the new observatory.

“We are at a point where we have a structure that is nearly completed,” says Bershady of the observatory situated 220 miles from Cape Town on a mountain plateau at the southern end of the Kalahari Desert. “Now, we are starting to populate the (telescope) truss with glass.”

The $18 million SALT Observatory is being built by a consortium of government and academic institutions from six countries. In addition to UW-Madison, Rutgers and Carnegie Mellon universities, Germany’s University of Gottingen, the University of Canterbury in New Zealand, the United Kingdom Consortium, and the governments of Poland and South Africa are partners in the SALT consortium.

UW-Madison’s contribution is a $3 million imaging spectrograph that is being built under the direction of astronomy Professor Kenneth H. Nordsieck. A spectrograph is a device that breaks light down into its constituent wavelengths, each of which has a different story to tell about the star or galaxy from which the light is gathered.

“We’re past the design stage now,” says Nordsieck of the 500-kilogram instrument that will be at the heart of the new observatory. “We’re cutting metal and polishing glass.”

The Wisconsin spectrograph will be the telescope’s primary scientific instrument. Positioned high above the huge segmented mirror at the prime focus of the telescope, the device will be capable of capturing spectra at a rate of 10 times a second.

To explain the importance of spectroscopy to astronomy, one spectrum – in the words of one astronomer – is worth a thousand pictures.

The device, says Nordsieck, will sample light in the near ultraviolet part of the electromagnetic spectrum: “This is light that our eyes can’t see, but it still gets through the atmosphere. It’s the same kind of light that causes sunburn.”

In addition, the spectrograph will be capable of doing polarimetry, measuring how light waves are scattered as they bounce off objects in space and are pushed and pulled by the immense magnetic fields of interstellar space. Polarimetry, Nordsieck says, helps reveal geometric information, giving astronomers insight into how starlight interacts with the objects it encounters.

“We will also have one of the first large Fabry-Perot devices,” he adds. “It is basically a tunable filter” capable of imaging a large part of the sky.

Fittingly, among the system of lenses to be included in the spectrograph will be a set made of sodium chloride – or salt.

Together, the large, segmented primary mirror and the novel scientific instrumentation will position SALT to break plenty of new ground in the southern skies.

“One of the big things this telescope will be tuned for are the Magellanic Clouds,” says Bershady. “They are important because they are the galaxies nearest to our own, and they offer the best opportunity to study stars and galaxies outside of the Milky Way. It’s always a good thing to look outside of your own immediate environment to find out how unique you are, if at all.”

The SALT construction schedule is right on time, Bershady adds. “That we haven’t slipped at all is amazing,” he says. “Our hope is to stay on track for first light in late 2004.”

Original Source: SALT News Release

Posted on by Fraser Cain

Neutron Star Has Twin Tails

Image credit: ESA

Astronomers using the European Space Agency’s XMM-Newton space observatory have discovered a neutron star with two mysterious x-ray tails, stretching out almost a third of a light year. The neutron star is named Geminga, and it’s one of the closest known neutron stars, at a distance of only 500 light-years away. Unlike most neutron stars, Geminga is strangely quiet in the radio spectrum, but pulsates huge quantities of gamma radiation.

Astronomers using ESA?s X-ray observatory, XMM-Newton, have discovered a pair of X-ray tails, stretching 3 million million kilometres across the sky. They emanate from the mysterious neutron star known as Geminga. The discovery gives astronomers new insight into the extraordinary conditions around the neutron star.

A neutron star measures only 20-30 kilometres across and is the dense remnant of an exploded star. Geminga is one of the closest to Earth, at a distance of about 500 light-years. Most neutron stars emit radio emissions, appearing to pulsate like a lighthouse, but Geminga is ‘radio-quiet’. It does, however, emit huge quantities of pulsating gamma rays making it one of the brightest gamma-ray sources in the sky. Geminga is the only example of a successfully identified gamma-ray source from which astronomers have gained significant knowledge.

It is 350 000 years old and ploughs through space at 120 kilometres per second. Its route creates a shockwave that compresses the gas of the interstellar medium and its naturally embedded magnetic field by a factor of four.

Patrizia Caraveo, Instituto di Astrofisica Spaziale e Fisica Cosmica, Milano, Italy, and her colleagues (at CESR, France, ESO and MPE, Germany) have calculated that the tails are produced because highly energetic electrons become trapped in this enhanced magnetic field. As the electrons spiral inside the magnetic field, they emit the X-rays seen by XMM-Newton.

The electrons themselves are created close to the neutron star. Geminga?s breathless rotation rate ? once every quarter of a second ? creates an extraordinary environment in which electrons and positrons, their antimatter counterparts, can be accelerated to extraordinarily high energies. At such energies, they become powerful high-energy gamma-ray producers. Astronomers had assumed that all the electrons would be converted into gamma rays. However, the discovery of the tails proves that some do find escape routes from the maelstrom.

?It is astonishing that such energetic electrons succeed in escaping to create these tails,? says Caraveo, ?The tail electrons have an energy very near to the maximum energy achievable in the environment of Geminga.?

The tails themselves are the bright edges of the three-dimensional shockwave sculpted by Geminga. Such shockwaves are a bit like the wake of a ship travelling across the ocean. Using a computer model, the team has estimated that Geminga is travelling almost directly across our line of sight.

Studies of Geminga could not be more important. The majority of known gamma-ray sources in the Universe have yet to be identified with known classes of celestial objects. Some astronomers believe that a sizeable fraction of them may be Geminga-like radio-quiet neutron stars. Certainly, the family of radio-quiet neutron stars, discovered through their X-ray emission, is continuously growing. Currently, about a dozen objects are known but only Geminga has a pair of tails!

Original Source: ESA News Release