LotR meme: most powerful quote
Fermi’s Close Call with a Soviet Satellite -Nasa
NASA scientists don’t often learn that their spacecraft is at risk of crashing into another satellite. But when Julie McEnery, the project scientist for NASA’s Fermi Gamma-ray Space Telescope, checked her email on March 29, 2012, she found herself facing this precise situation.
While Fermi is in fine shape today, continuing its mission to map the highest-energy light in the universe, the story of how it sidestepped a potential disaster offers a glimpse at an underappreciated aspect of managing a space mission: orbital traffic control. As McEnery worked through her inbox, an automatically generated report arrived from NASA’s Robotic Conjunction Assessment Risk Analysis (CARA) team based at NASA’s Goddard Space Flight Center in Greenbelt, Md.
On scanning the document, she discovered that Fermi was just one week away from an unusually close encounter with Cosmos 1805, a dead Cold-War era spy satellite. The two objects, speeding around Earth at thousands of miles an hour in nearly perpendicular orbits, were expected to miss each other by a mere 700 feet. Although the forecast indicated a close call, satellite operators have learned the hard way that they can’t be too careful.
The uncertainties in predicting spacecraft positions a week into the future can be much larger than the distances forecast for their closest approach. With a speed relative to Fermi of 27,000 mph, a direct hit by the 3,100-pound Cosmos 1805 would release as much energy as two and a half tons of high explosives, destroying both spacecraft.
The update on Friday, March 30, indicated that the satellites would occupy the same point in space within 30 milliseconds of each other. Fermi would have to move out of the way if the threat failed to recede. Because Fermi’s thrusters were designed to de-orbit the satellite at the end of its mission, they had never before been used or tested, adding a new source of anxiety for the team.
By Tuesday, April 3, the close approach was certain, and all plans were in place for firing Fermi’s thrusters. Shortly after noon EDT, the spacecraft stopped scanning the sky and oriented itself along its direction of travel. It then parked its solar panels and tucked away its high-gain antenna to protect them from the thruster exhaust.
The maneuver was performed by the spacecraft based on previously developed procedures. Fermi fired all thrusters for one second and was back doing science within the hour. In 2012, the Goddard CARA team participated in collision-avoidance maneuvers for seven other missions.
A month before the Fermi conjunction came to light, Landsat 7 dodged pieces of Fengyun-1C, a Chinese weather satellite deliberately destroyed in 2007 as part of a military test. And in May and October, respectively, NASA’s Aura and CALIPSO Earth-observing satellites took steps to avoid fragments from Cosmos 2251, which in 2009 was involved in the first known satellite-to-satellite collision with Iridium 33.
NASA’s Fermi, Swift See ‘Shockingly Bright’ Burst
A record-setting blast of gamma rays from a dying star in a distant galaxy has wowed astronomers around the world. The eruption, which is classified as a gamma-ray burst, or GRB, and designated GRB 130427A, produced the highest-energy light ever detected from such an event.
“We have waited a long time for a gamma-ray burst this shockingly, eye-wateringly bright,” said Julie McEnery, project scientist for the Fermi Gamma-ray Space Telescope at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The GRB lasted so long that a record number of telescopes on the ground were able to catch it while space-based observations were still ongoing.”The burst subsequently was detected in optical, infrared and radio wavelengths by ground-based observatories, based on the rapid accurate position from Swift. Astronomers quickly learned that the GRB was located about 3.6 billion light-years away, which for these events is relatively close.
Gamma-ray bursts are the universe’s most luminous explosions. Astronomers think most occur when massive stars run out of nuclear fuel and collapse under their own weight. As the core collapses into a black hole, jets of material shoot outward at nearly the speed of light.
The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star and generate bright afterglows that fade with time.
If the GRB is near enough, astronomers usually discover a supernova at the site a week or so after the outburst.
“This GRB is in the closest 5 percent of bursts, so the big push now is to find an emerging supernova, which accompanies nearly all long GRBs at this distance,” said Goddard’s Neil Gehrels, principal investigator for Swift.Ground-based observatories are monitoring the location of GRB 130427A and expect to find an underlying supernova by midmonth.
Explanation:
The 1st animation: The maps in the animation show how the sky looks at gamma-ray energies above 100 million electron volts (MeV) with a view centered on the north galactic pole. The first frame shows the sky during a three-hour interval prior to GRB 130427A. The second frame shows a three-hour interval starting 2.5 hours before the burst, and ending 30 minutes into the event. The Fermi team chose this interval to demonstrate how bright the burst was relative to the rest of the gamma-ray sky. This burst was bright enough that Fermi autonomously left its normal surveying mode to give the LAT instrument a better view, so the three-hour exposure following the burst does not cover the whole sky in the usual way.
The 2nd animation: This animation shows a more detailed Fermi LAT view of GRB 130427A. The sequence shows high-energy (100 Mev to 100 GeV) gamma rays from a 20-degree-wide region of the sky starting three minutes before the burst to 14 hours after. Following an initial one-second spike, the LAT emission remained relatively quiet for the next 15 seconds while Fermi’s GBM instrument showed bright, variable lower-energy emission. Then the burst re-brightened in the LAT over the next few minutes and remained bright for nearly half a day.
Credit: NASA/Swift/Stefan Immler
att:
No Text is worth Dying For. It Can Wait.
Please join us, Verizon, Sprint, T-Mobile US, Inc. and more than 200 other organizations to stop texting while driving. Encourage everyone in your community to join the movement and take the pledge today to never text and drive at www.itcanwait.com.
I’m trying to stop too.
How to Measure the Spin of a Black Hole
Black holes are tremendous objects whose immense gravity can distort and twist space-time, the fabric that shapes our universe. These effects, consequences of Einstein’s general theory of relativity, result in the bending of light as it travels through space-time. By looking for these light distortions in X-rays streaming off material near black holes, researchers can gain information about their spin rates.
This chart illustrates the basic model for determining the spin rates of black holes. The three artist’s concepts represent the different types of spin: retrograde rotation, where the disk of matter falling onto the hole, called an accretion disk, moves in the opposite direction of the black hole; no spin; and prograde rotation, where the disk spins in the same direction as the black hole.
The faster a black hole spins, the closer its accretion disk can lie to it — another consequence of Einstein’s theory of relativity.
Scientists assess how close the inner edge of an accretion disk comes to a black hole by breaking the X-ray light up into a spectrum of different colors, or energies. The resulting spectra for the three spin scenarios are shown at right. The sharp peak is X-ray radiation from iron atoms circulating in the accretion disk. If the accretion disk is close to the black hole, as is the case in the final row, the X-ray colors from the iron will be spread out by the immense gravity of the black hole. The degree to which the iron feature is spread out, a phenomenon referred to as the “red wing,” reveals how close the accretion disk is to the black hole. Because this distance depends on the black hole’s spin, the spin rate can then be determined.
Prior to observations with NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), which captures X-ray radiation with energy from the 3 to 79 kiloelectron volt (keV) range, this model remained uncertain. Together with the European Space Agency’s XMM-Newton telescope, which sees X-ray light in the 0.1 to 10 keV range, the observatories were able to show that the model is correct. Their data ruled out the possibility that the iron feature only appears to be distorted as a result of intervening absorbing clouds, and not gravitational effects.
Black Holes - And You Thought You Had Too Much Mass
Imagine travelling months, or even years, into the future within a matter of days or even mere minutes. Scientists and science fiction enthusiasts have fantasized for ages about the possibility of time travel or travelling great distance…
Black Hole-Powered Jets Plow Into Galaxy
This composite image of a galaxy illustrates how the intense gravity of a supermassive black hole can be tapped to generate immense power. The image contains X-ray data from NASA’s Chandra X-ray Observatory (blue), optical light obtained with the Hubble Space Telescope (gold) and radio waves from the NSF’s Very Large Array (pink).
Image Credit: NASA
