Students fly in zero gravity to protect satellites from tiny meteoroids

Stanford researchers have completed the first successful tests in zero gravity of a canopy for CubeSats -- the tiny satellites that hitch rides on rockets sending larger satellites into orbit. The goal is to gather data on what happens when micrometeoroids slam into a satellite. Such impacts often knock out electronic equipment on satellites. The encounters are poorly understood, but the canopies could be a first step in eventually building "black boxes" for satellites similar to airplane flight recorders.

Orbiting the Earth is risky business for a satellite. Over a hundred billion meteoroids enter Earth's atmosphere every day, and while big, fierce, spacecraft-crushing meteoroids are rare, even the tiniest ones are a hazard.

What happens when a really tiny meteoroid (so small a stack of 500 would stand less than an inch tall) hits a satellite is not fully understood, but Stanford researchers have successfully done preliminary testing of a device that may help shed light on these collisions in space.

The testing was in zero gravity, aboard a diving airplane flying over the ocean.

Nicolas Lee, a graduate student in aeronautics and astronautics, and several colleagues have designed a canopy to pop out of a tiny satellite called a CubeSat and absorb the impacts of these micrometeoroids, sometimes referred to as "interplanetary flyspecks."

"The canopy might eventually be deployed to protect a spacecraft from meteoroids or shield it from the sun, but for now, we just want it to get hit," Lee said.

Even tiny meteoroids travel at tremendous speeds in orbit around the sun (more than 250,000 kilometers per hour) and pack a hefty punch when they strike a spacecraft.

"It is pretty much an explosion," Lee said.

Since the impact disrupts the satellite's electronics, no one knows exactly how the micrometeoroid causes the damage. But Lee's advisor, Sigrid Close, assistant professor of aeronautics and astronautics, has a theory.

She suspects the meteoroid instantly vaporizes into free electrons and ions that float around in a little ball. As that ball expands in the vacuum of space, it gives off energy at radio frequencies that interfere with the electronic equipment on the satellite, disrupting communications and other essential functions.

"We want to fly a dedicated mission that can study this effect and make sure that we can protect against it," Lee said. For that mission, the team would work with Andrew Kalman, a consulting professor of aeronautics and astronautics, to equip a CubeSat with plasma sensors and radio antennas to measure radio frequency emissions.

As a first step in field-testing their canopy, Lee and fellow graduate students Shandor Dektor and Joseph Johnson recently tested their canopies in zero gravity aboard a NASA-hire airplane flying over the Gulf of Mexico.

The plane flew a flight path any rollercoaster lover would die for: up and down in a series of parabolas, from about 22,000 to 32,000 feet. At the top of each parabola, the plane's occupants experienced weightlessness for about 20 seconds, which was when the team tested how their canopies opened. Over the course of two flights and 80 parabolas, the students did 37 successful trial runs.

Operating in zero gravity took some getting used to. "You don't realize gravity is gone so you are still pushing against it," Lee said. "And so you end up feeling like you are falling upwards."

The team tested three prototypes of the canopy, each a square meter in area. One design was thin mylar, rolled up in a spiral pattern inside the little black CubeSat box. Another design had the mylar folded to expand in a radial pattern. The third design used the spiral unfolding, but with a thicker membrane for the canopy. For all the designs, the unfolding was powered by struts made of common metal tape measures rolled up with the canopies.

The thin membrane rolled in a spiral pattern was the most successful. Lee thinks with proper folding, a thicker membrane could work well, too. Although Lee had some prior experience in origami, he said getting the proper folding was initially just trial and error.

"I folded so many prototypes," he said. But after figuring out the basic geometry of the folding, he developed a mathematical algorithm to employ.

"We are also hoping to deploy some metallic sheets, which might give us a different effect than the plastic mylar we've been using," he said. "For the purpose of a meteoroid impact screen, we would need a thicker membrane so the screen doesn't break when it gets hit by a large meteoroid."

When the CubeSat is deployed in space, in addition to zero gravity, it will have to open in a vacuum, so the researchers want to take their canopies into a vacuum chamber and shoot high velocity particles at it to supplement the zero gravity tests.

As the CubeSat canopy testing progresses, Close sees long-term potential not only in protecting satellites but also in recording what spacecraft experience in orbit.

"This could lead to devices that could be attached to satellites just like a black box in an airplane," Close said.

The zero-gravity flight was sponsored by the National Aeronautics and Space Administration.

Cosmic curiosity reveals ghostly glow of dead quasar

While sorting through hundreds of galaxy images as part of the Galaxy Zoo citizen science project two years ago, Dutch schoolteacher and volunteer astronomer Hanny van Arkel stumbled upon a strange-looking object that baffled professional astronomers. Two years later, a team led by Yale University researchers has discovered that the unique object represents a snapshot in time that reveals surprising clues about the life cycle of black holes.

In a new study, the team has confirmed that the unusual object, known as Hanny's Voorwerp (Hanny's "object" in Dutch), is a large cloud of glowing gas illuminated by the light from a quasar -- an extremely energetic galaxy with a supermassive black hole at its center. The twist, described online in the Astrophysical Journal Letters, is that the quasar lighting up the gas has since burned out almost entirely, even though the light it emitted in the past continues to travel through space, illuminating the gas cloud and producing a sort of "light echo" of the dead quasar.

"This system really is like the Rosetta Stone of quasars," said Yale astronomer Kevin Schawinski, a co-founder of Galaxy Zoo and lead author of the study. "The amazing thing is that if it wasn't for the Voorwerp being illuminated nearby, the galaxy never would have piqued anyone's interest."

The team calculated that the light from the dead quasar, which is the nearest known galaxy to have hosted a quasar, took up to 70,000 years to travel through space and illuminate the Voorwerp -- meaning the quasar must have shut down sometime within the past 70,000 years.

Until now, it was assumed that supermassive black holes took millions of years to die down after reaching their peak energy output. However, the Voorwerp suggests that the supermassive black holes that fuel quasars shut down much more quickly than previously thought. "This has huge implications for our understanding of how galaxies and black holes co-evolve," Schawinski said.

"The time scale on which quasars shut down their prodigious energy output is almost entirely unknown," said Meg Urry, director of the Yale Center for Astronomy & Astrophysics and a co-author of the paper. "That's why the Voorwerp is such an intriguing -- and potentially critical -- case study for understanding the end of black hole growth in quasars."

Although the galaxy no longer shines brightly in X-ray light as a quasar, it is still radiating at radio wavelengths. Whether this radio jet played a role in shutting down the central black hole is just one of several possibilities Schawinski and the team will investigate next.

"We've solved the mystery of the Voorwerp," he said. "But this discovery has raised a whole bunch of new questions."

Other authors of the paper include Shanil Virani, Priyamvada Natarajan, Paolo Coppi (all of Yale University); Daniel Evans (Massachusetts Institute of Technology, Harvard-Smithsonian Center for Astrophysics and Elon University); William Keel and Anna Manning (University of Alabama and Kitt Peak National Observatory); Chris Lintott (University of Oxford and Adler Planetarium); Sugata Kaviraj (University of Oxford and Imperial College London); Steven Bamford (University of Nottingham); Gyula Józsa (Netherlands Institute for Radio Astronomy and Argelander-Institut für Astronomie); Michael Garrett (Netherlands Institute for Radio Astronomy, Leiden Observatory and Swinburne University of Technology); Hanny van Arkel (Netherlands Institute for Radio Astronomy); Pamela Gay (Southern Illinois University Edwardsville); and Lucy Fortson (University of Minnesota).

Deep impact spacecraft successfully flies by comet Hartley 2

The University of Maryland-led EPOXI mission successfully flew by comet Hartley 2 at 10 a.m. EDT Nov. 3, 2010, and the spacecraft has begun returning images. Hartley 2 is the fifth comet nucleus visited by any spacecraft and the second one visited by the Deep Impact spacecraft.

Scientists and mission controllers are studying never-before-seen images of Hartley 2 appearing on their computer terminal screens. See images at: http://epoxi.umd.edu/

"We are all holding our breath to see what discoveries await us in the observations near closest approach," said University of Maryland astronomer Michael A'Hearn, one of the originators of science team leader for both the Deep Impact mission and its follow on mission EPOXI.

At approximately 10 a.m. EDT, the spacecraft passed within 700 kilometers (435 miles) of the comet. Minutes after closest approach, the spacecraft's High-Gain Antenna was pointed at Earth and began downlinking vital spacecraft health and other engineering data stored aboard the spacecraft's onboard computer during the encounter. Twenty minutes later, the first images of the encounter made the 37 million kilometer (23 million mile) trip from the spacecraft to NASA's Deep Space Network antenna, appearing moments later on the mission's computer screens.

"The mission team and scientists have worked for this day," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's good to see Hartley 2 up close."

A Deeper Impact on Planetary Science

With the latest EPOXI mission data on Hartley 2, the Deep Impact spacecraft is adding to an already extensive scientific legacy. Launched in January 2005, the spacecraft made scientific history and world-wide headlines when it smashed a probe into comet Tempel 1 on July 4th of that year. Following the conclusion of that mission, a Maryland-led team of scientists won approval from NASA to fly the Deep Impact spacecraft to a second comet.

The name EPOXI itself is a combination of the names for the two extended mission components: the extrasolar planet observations, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). During the EPOCh phase of EPOXI, the Deep Impact spacecraft provided information on possible extrasolar planets and was one of three spacecraft to find for the first time clear evidence of water on Moon. A study accepted for publication in The Astrophysical Journal and just released by NASA, provides "colorful" findings on Earth and other planets in our solar system that someday may help identify earthlike worlds around other stars.

The overall objective of the flyby of Hartley 2 is the same as that for the Deep Impact mission's trip to Tempel 1: to learn more about the origin and history of our solar system by learning more about the composition and diversity of comets. Comets contain material from the early days of the solar system before the planets formed. "If we understand the comets really well it will tell us how the planets got made," explained A'Hearn. "That's why we choose comets to study."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the EPOXI mission for NASA's Science Mission Directorate, Washington. The University of Maryland, College Park, is home to the mission's principal investigator, Michael A'Hearn and eight other members of the EPOXI science team. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md., is the science lead for the mission's extrasolar planet observations. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

NASA's Chandra finds youngest nearby black hole

Astronomers using NASA's Chandra X-ray Observatory have found evidence of the youngest black hole known to exist in our cosmic neighborhood. The 30-year-old black hole provides a unique opportunity to watch this type of object develop from infancy.

The black hole could help scientists better understand how massive stars explode, which ones leave behind black holes or neutron stars, and the number of black holes in our galaxy and others.

The 30-year-old object is a remnant of SN 1979C, a supernova in the galaxy M100 approximately 50 million light years from Earth. Data from Chandra, NASA's Swift satellite, the European Space Agency's XMM-Newton and the German ROSAT observatory revealed a bright source of X-rays that has remained steady during observation from 1995 to 2007. This suggests the object is a black hole being fed either by material falling into it from the supernova or a binary companion.

"If our interpretation is correct, this is the nearest example where the birth of a black hole has been observed," said Daniel Patnaude of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. who led the study.

The scientists think SN 1979C, first discovered by an amateur astronomer in 1979, formed when a star about 20 times more massive than the sun collapsed. Many new black holes in the distant universe previously have been detected in the form of gamma-ray bursts (GRBs).

However, SN 1979C is different because it is much closer and belongs to a class of supernovas unlikely to be associated with a GRB. Theory predicts most black holes in the universe should form when the core of a star collapses and a GRB is not produced.

"This may be the first time the common way of making a black hole has been observed," said co-author Abraham Loeb, also of the Harvard-Smithsonian Center for Astrophysics. "However, it is very difficult to detect this type of black hole birth because decades of X-ray observations are needed to make the case."

The idea of a black hole with an observed age of only about 30 years is consistent with recent theoretical work. In 2005, a theory was presented that the bright optical light of this supernova was powered by a jet from a black hole that was unable to penetrate the hydrogen envelope of the star to form a GRB. The results seen in the observations of SN 1979C fit this theory very well.

Although the evidence points to a newly formed black hole in SN 1979C, another intriguing possibility is that a young, rapidly spinning neutron star with a powerful wind of high energy particles could be responsible for the X-ray emission. This would make the object in SN 1979C the youngest and brightest example of such a "pulsar wind nebula" and the youngest known neutron star. The Crab pulsar, the best-known example of a bright pulsar wind nebula, is about 950 years old.

"It's very rewarding to see how the commitment of some of the most advanced telescopes in space, like Chandra, can help complete the story," said Jon Morse, head of the Astrophysics Division at NASA's Science Mission Directorate.

The results will appear in the New Astronomy journal in a paper by Patnaude, Loeb, and Christine Jones of the Harvard-Smithsonian Center for Astrophysics. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge.

For more information about Chandra, including images and other multimedia, visit: http://chandra.nasa.gov and http://chandra.harvard.edu

Primordial dry ice fuels comet jets

One of the biggest comet findings coming out of the amazing images and data taken by the University of Maryland-led EPOXI mission as it zipped past comet Hartley 2 last week is that dry ice is the 'jet' fuel for this comet and perhaps many others.

Images from the flyby show spectacular jets of gas and particles bursting from many distinct spots on the surface of the comet. This is the first time images of a comet have been sharp enough to allow scientists to link jets of dust and gas with specific surface features. Analysis of the spectral signatures of the materials coming from the jets shows primarily CO2 gas (carbon dioxide) and particles of dust and ice.

"Previously it was thought that water vapor from water ice was the propulsive force behind jets of material coming off of the body, or nucleus, of the comet," said University of Maryland Astronomy Professor Jessica Sunshine, who is deputy principal investigator for the EPOXI mission. "We now have unambiguous evidence that solar heating of subsurface frozen carbon dioxide (dry ice), directly to a gas, a process known as sublimation, is powering the many jets of material coming from the comet. This is a finding that only could have been made by traveling to a comet, because ground based telescopes can't detect CO2 and current space telescopes aren't tuned to look for this gas," Sunshine said.

Sunshine and other members of the EPOXI science team are meeting all this week at the University of Maryland to analyze the very large amount of data from the closest approach, and new data continues to come down at a rate of some 2000 images a day.

The Deep Impact spacecraft that flew past comet Hartley 2 has three instruments -- two telescopes with digital color cameras and an infrared spectrometer. The spectrometer measures the absorption, emission and reflection of light (spectroscopic signature) that is unique to each molecular compound. This allows Maryland scientists to determine the composition of the material on the comet's surface, in the jets, and in the coma, or cloud of particles around it. They have found that water and carbon dioxide dominate the infrared spectrum of comet Hartley 2's environment and that organics, including methanol, are present at lower levels.

This is no surprise to scientists. But what is surprising is that there is a lot more carbon dioxide escaping this comet than expected. "The distribution of carbon dioxide and dust around the nucleus is much different than the water distribution, and that tells us that the carbon dioxide rather than water takes dust grains with it into the coma as it leaves the nucleus, said Assistant Research Scientist Lori Feaga. "The dry ice that is producing the CO2 jets on this comet has probably been frozen inside it since the formation of the solar system."

From Deep Impact to Hartley 2

According to University of Maryland Research Scientist Tony Farnham, findings from the team's 2005 Deep Impact mission to comet Tempel 1, though less conclusive, nonetheless indicate that the Hartley 2 findings that super-volatiles (CO2) and not water drive the activity, probably are a common characteristic of comets. "Tempel 1 was most active before perihelion when its southern hemisphere, the hemisphere that appeared to be enhanced in CO2, was exposed to sunlight," said Farnham, a member of both the Deep Impact and EPOXI science teams. "Unlike our Hartley encounter, during the flyby with Tempel 1, we were unable to directly trace the CO2 to the surface, because the pole was in darkness during encounter."

The Maryland scientists devised the plan to reuse the Deep Impact spacecraft and travel to a second comet in order to learn more about the diversity of comets and the processes that govern them. This became the EPOXI mission on which the spacecraft has flown to comet Hartley 2.

The spacecraft's images show that Hartley 2 has an elongated nucleus, 2 kilometers in length and 0.4 kilometers wide at the narrow neck. Hartley 2 is only the 5th cometary nucleus ever seen and exhibits similarities and differences to the bodies or nuclei of other comets. Mission Principal Investigator and science team leader Michael A'Hearn, a University of Maryland professor of astronomy, said the mission has provided, and continues to provide, a tremendous wealth of data about Hartley 2 and the team expects to announce more science findings in the coming weeks.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Maryland.

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Neutron stars may be too weak to power some gamma-ray bursts; Black holes may be power source

A gamma-ray burst is an immensely powerful blast of high-energy light thought to be generated by a collapsing star in a distant galaxy, but what this collapse leaves behind has been a matter of debate.

A new analysis of four extremely bright bursts observed by NASA's Fermi satellite suggests that the remnant from a long-duration gamma-ray burst is most likely a black hole -- not a rapidly spinning, highly magnetized neutron star, or magnetar since such a burst emits more energy than is theoretically possible from a magnetar.

"Some of the events we have been finding seem to be pushing right up against this total limit for a neutron star progenitor system," said S. Bradley Cenko, a post-doctoral fellow from the University of California, Berkeley.

Cenko is presenting these findings Nov. 3 at the Nov. 1-4 Gamma Ray Bursts 2010 conference in Annapolis, Md. Cenko is a member of an international team that includes astronomers from UC Berkeley and the National Radio Astronomy Observatory (NRAO) in New Mexico.

The group has submitted a paper detailing its analysis to The Astrophysical Journal.

Long-duration gamma-ray bursts (GRBs) are presumed to be created by the explosive collapse in distant galaxies of massive stars. The explosion is visible from Earth because the light is emitted in a narrow cone, like a beam from a lighthouse. First discovered in 1967 by satellites looking for nuclear blasts on Earth, gamma-ray bursts have been the focus of several satellite missions, most recently NASA's Fermi gamma-ray space telescope, launched in 2008, and NASA's Swift satellite, launched in 2004.

With accumulating observations, astronomers have been able to create models of how the collapse of a rapidly rotating, massive star can accelerate matter to nearly the speed of light and collimate it into two oppositely directed, tightly focused beams along the spin axis. They have also studied how these particles generate gamma rays and other emissions.

The two leading candidates for powering these long-duration bursts are a magnetar and a black hole, sometimes referred to as a collapsar. In both cases, material from the star falls inward and is catapulted out by the spinning neutron star or black hole. What distinguishes these models is that magnetar-powered bursts cannot be as powerful as black hole-powered bursts.

"The question we have been trying to answer is: What is the true energy release from these events?" Cenko said. "We can measure all the light emitted -- very high energy gamma rays, and, at later times, X-ray, optical and radio afterglow emissions -- but that doesn't provide a very good estimate, because GRBs emit in relatively narrow jets. We have to get an idea of the geometry of this outflow, that is, how collimated the jets are."

Previous studies have shown that light measured in the afterglow begins to drop steeply at a certain point, and the sooner this drop-off, called a jet break, the narrower the jet. Typically, the gamma-ray burst itself lasts from a few seconds to as long as 100 seconds, but the afterglow, produced when the jets interact with gas and dust surrounding the star, emits visible light for a couple of weeks and radio radiation for several months.

While Swift has observed hundreds of bursts in the past five years and notified astronomers within seconds of detection, the instruments aboard the satellite detect mostly medium-sized bursts that are not as highly collimated and that have a jet break many days or weeks after the burst.

Fermi's Large Area Telescope, however, is sensitive to very bright bursts with jet breaks within several days of the burst, making follow-up observations easier with Swift's X-ray and ultraviolet-optical telescopes and the ground-based Very Large Array, a radio telescope operated by NRAO.

Fermi detects few extremely bright bursts, however -- only four in 2009, Cenko said -- and does not notify astronomers for nearly a day afterward. Once alerted, however, Cenko's team was able to observe the optical, X-ray and radio afterglow of these four events, find the jet break and use this information, along with the star's distance calculated from its redshift, to estimate the total energy output.

If the energy from these bright bursts were emitted in all directions, it would be equivalent to the mass of the sun being converted instantaneously into pure energy. Because the gamma-ray burst was focused in a cone only a few degrees wide, however, the energies for all four bursts were about 100-1,000 times less than this.

Theoretical models of how these beams are produced place a limit on how much energy a magnetar can generate in one of these explosive bursts: about 100 times less than if one converted the sun entirely into energy. Several of these bright bursts exceed this limit.

"The magnetar model is in serious trouble for such incredibly powerful events," noted coauthor Alex Filippenko, UC Berkeley professor of astronomy. "Even if the magnetar energy limit is not strictly violated, the tremendous efficiency required by this process strains credulity."

"In the future, we will be trying to make more precise measurements and be looking for more events to rule out a neutron star model," Cenko said.

Cenko and Filippenko's colleagues are post-doctoral fellows Nat R. Butler and Bethany E. Cobb, astronomy professor Joshua S. Bloom and graduate students Daniel A. Perley and Adam N. Morgan of UC Berkeley; Dale A. Frail of NRAO; Fiona A. Harrison, Mansi M. Kasliwal, Shrinivas R. Kulkarni and Vikram R. Rana of the California Institute of Technology; Joshua B. Haislip, Daniel E. Reichart, Aaron P. LaCluyze and Kevin M. Ivarsen of the University of North Carolina, Chapel Hill; Antonio Cucchiara and Derek B. Fox of Pennsylvania State University in University Park; Edo Berger of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; Poonam Chandra of the Royal Military College of Canada in Kingston, Ontario; Jason X. Prochaska of the UCO/Lick Observatory at UC Santa Cruz; Karl Glazebrook of the Swinburne University of Technology in Victoria, Australia; Sebastian Lopez of the Universidad de Chile in Santiago; and Max Pettini of the University of Western Australia in Crawley.

The work of Cenko and Filippenko is supported by Gary and Cynthia Bengier, the Richard and Rhoda Goldman Fund, NASA and the National Science Foundation.