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. 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.
", "instance": { "id": 467079, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a011200/a011229/Earth_Debris_Large.jpg", "filename": "Earth_Debris_Large.jpg", "media_type": "Image", "alt_text": "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. 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.", "width": 1500, "height": 2667, "pixels": 4000500 } }, { "id": 406183, "type": "details_page", "extra_data": null, "instance": { "id": 4648, "url": "https://svs.gsfc.nasa.gov/4648/", "page_type": "Visualization", "title": "Pulsar Current Sheets - All Particle Flows", "description": "This movie presents a basic tour around the simulation magnetic field including motion of the the bulk particles and high-energy electrons and positrons. This version is generated with some simple reference objects for more general use. || PulsarParticles_grid_bulk_positrons_electrons_tour_inertial.HD1080i.01001_print.jpg (1024x576) [172.3 KB] || tour-glyph (1920x1080) [0 Item(s)] || PulsarParticles_grid_bulk_positrons_electrons_tour.HD1080i_p30.webm (1920x1080) [9.4 MB] || PulsarParticles_grid_bulk_positrons_electrons_tour.HD1080i_p30.mp4 (1920x1080) [148.0 MB] || tour-glyph (3840x2160) [0 Item(s)] || PulsarParticles_grid_bulk_positrons_electrons_tour_2160p30.mp4 (3840x2160) [375.4 MB] || PulsarParticles_grid_bulk_positrons_electrons_tour.HD1080i_p30.mp4.hwshow [228 bytes] || ", "release_date": "2018-10-10T11:00:00-04:00", "update_date": "2025-01-06T00:12:55.985824-05:00", "main_image": { "id": 404666, "url": "https://svs.gsfc.nasa.gov/vis/a000000/a004600/a004648/PulsarParticles_bulk_positrons_electrons_tour_inertial.HD1080i.01000_print.jpg", "filename": "PulsarParticles_bulk_positrons_electrons_tour_inertial.HD1080i.01000_print.jpg", "media_type": "Image", "alt_text": "This movie presents a basic tour around the simulation magnetic field including motion of the bulk particles and high-energy electrons and positrons. This version is generated with no background objects and an alpha channel for custom compositing.", "width": 1024, "height": 576, "pixels": 589824 } } }, { "id": 406184, "type": "details_page", "extra_data": null, "instance": { "id": 4644, "url": "https://svs.gsfc.nasa.gov/4644/", "page_type": "Visualization", "title": "Pulsar Current Sheets - Bulk Particle Trajectories", "description": "This movie presents a basic tour around the simulation magnetic field including motion of the bulk particles. This version is generated with some simple reference objects for more general use. || PulsarParticles_grid_bulk_tour_inertial.HD1080i.01001_print.jpg (1024x576) [112.0 KB] || tour-glyph (1920x1080) [0 Item(s)] || PulsarParticles_grid_bulk_tour.HD1080i_p30.mp4 (1920x1080) [67.7 MB] || PulsarParticles_grid_bulk_tour.HD1080i_p30.webm (1920x1080) [5.3 MB] || tour-glyph (3840x2160) [0 Item(s)] || PulsarParticles_grid_bulk_tour_2160p30.mp4 (3840x2160) [129.1 MB] || PulsarParticles_grid_bulk_tour.HD1080i_p30.mp4.hwshow [208 bytes] || ", "release_date": "2018-10-10T11:00:00-04:00", "update_date": "2025-01-06T00:12:52.923992-05:00", "main_image": { "id": 404387, "url": "https://svs.gsfc.nasa.gov/vis/a000000/a004600/a004644/PulsarParticles_bulk_tour_inertial.HD1080i.01000_print.jpg", "filename": "PulsarParticles_bulk_tour_inertial.HD1080i.01000_print.jpg", "media_type": "Image", "alt_text": "This movie presents a basic tour around the simulation magnetic field including motion of the bulk particles, held fixed by co-rotating with the pulsar. This version is generated with no background objects and an alpha channel for custom compositing.", "width": 1024, "height": 576, "pixels": 589824 } } }, { "id": 406185, "type": "details_page", "extra_data": null, "instance": { "id": 10582, "url": "https://svs.gsfc.nasa.gov/10582/", "page_type": "Produced Video", "title": "Pulsar Blinking", "description": "A pulsar is a neutron star which emits beams of radiation that sweep through the earth's line of sight. Like a black hole, it is an endpoint to stellar evolution. The \"pulses\" of high-energy radiation we see from a pulsar are due to a misalignment of the neutron star's rotation axis and its magnetic axis. Pulsars pulse because the rotation of the neutron star causes the radiation generated within the magnetic field to sweep in and out of our line of sight with a regular period. External viewers see pulses of radiation whenever this region above the the magnetic pole is visible. Because of the rotation of the pulsar, the pulses thus appear much as a distant observer sees a lighthouse appear to blink as its beam rotates. The pulses come at the same rate as the rotation of the neutron star, and, thus, appear periodic. || ", "release_date": "2010-03-05T00:00:00-05:00", "update_date": "2023-05-03T13:54:20.985039-04:00", "main_image": { "id": 493759, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a010500/a010582/BhSURFtv.0019.jpg", "filename": "BhSURFtv.0019.jpg", "media_type": "Image", "alt_text": "Animation of pulsar viewed from a great distance.", "width": 720, "height": 486, "pixels": 349920 } } }, { "id": 406186, "type": "details_page", "extra_data": null, "instance": { "id": 10543, "url": "https://svs.gsfc.nasa.gov/10543/", "page_type": "Produced Video", "title": "Neutron Star Merge", "description": "Binary systems containing neutron stars are born when the cores of two orbiting stars collapse in supernova explosions. Neutron stars pack the mass of our sun into the size of a city. They are so dense and packed so tightly that the boundaries atoms nuclei disappear. In such systems, Einstein's theory of general relativity predicts that neutron stars emit gravitational radiation, ripples of space-time. This causes the orbits to shrink and gradually brings the neutron stars closer together. Shown here is such a system after about 1 billion years, when two equal-mass neutron whirl around each other at 60,000 times a minute. The stars merge in a few milliseconds, sending out a burst of gravitational waves and a brief, intense gamma-ray burst. || ", "release_date": "2010-01-26T00:00:00-05:00", "update_date": "2023-05-03T13:54:23.191409-04:00", "main_image": { "id": 494494, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a010500/a010543/Merge_Horizontal.00038_print.jpg", "filename": "Merge_Horizontal.00038_print.jpg", "media_type": "Image", "alt_text": "This animation shows the merger of two neutron stars from a horizontal perspective. Theory predicts that these kinds of collisions would not produce a long afterglow because there isn't much \"fuel\" — dust and gas — from the objects and in the region to sustain an afterglow", "width": 1024, "height": 691, "pixels": 707584 } } }, { "id": 406187, "type": "details_page", "extra_data": null, "instance": { "id": 20142, "url": "https://svs.gsfc.nasa.gov/20142/", "page_type": "Animation", "title": "Electromagnetic Spectrum", "description": "This animation shows a graphical representation of the electromagnetic spectrum and includes - Radio Waves, Infrared, Visible, Ultraviolet, X-Rays and Gamma Rays || ", "release_date": "2008-07-14T00:00:00-04:00", "update_date": "2023-05-03T13:55:18.623248-04:00", "main_image": { "id": 504783, "url": "https://svs.gsfc.nasa.gov/vis/a020000/a020100/a020142/spec090001777_print.jpg", "filename": "spec090001777_print.jpg", "media_type": "Image", "alt_text": "Electromagnetic Spectrum", "width": 1024, "height": 576, "pixels": 589824 } } }, { "id": 406188, "type": "details_page", "extra_data": null, "instance": { "id": 3439, "url": "https://svs.gsfc.nasa.gov/3439/", "page_type": "Visualization", "title": "Simulations of the Gamma-Ray Sky", "description": "The Gamma-Ray Large Area Space Telescope (GLAST) will observe the sky in gamma-rays with energies between 10 million electron volts (MeV) to 300 billion electron volts (GeV) (a photon of visible light is roughly 2 electron volts). At these energies, the detectors will receive roughly 2 photons every second. At these energies, the objects visible will be active galaxies, quasars, pulsars, and gamma-ray bursts. This visualization is generated from one year of simulated photon event-lists using known sources. These event lists are used for testing the various data analysis software being developed for the project. Due to the extremely low event rate, it takes about one week of event accumulation to see structure in the sky. To generate the 600+ frames of this visualization, the event lists were box-car averaged for a duration of one week for each frame, and each frame shifted 50,000 seconds in time from the previous frame. The low angular resolution of gamma-ray detectors makes point sources appear spread out in the sky. In these maps, the color of each pixel represents the number of photons accumulated in that pixel (over an energy range of 10MeV-300GeV). Horizontally, across the center of the map, is the diffuse emission from the plane of our own Milky Way galaxy. The images are projected in galactic coordinates with a plate carrée projection so there is significant distortion with increasing latitude above the galactic disk. This emission in the galactic plane is created by pulsars and supernova remnants. Located away from this plane is emission from active galaxies and high-velocity pulsars. Occasionally, a bright spot appears which can be a gamma-ray burst or quasar in an active state. || ", "release_date": "2007-09-13T00:00:00-04:00", "update_date": "2023-05-03T13:55:35.619222-04:00", "main_image": { "id": 507582, "url": "https://svs.gsfc.nasa.gov/vis/a000000/a003400/a003439/GLAST.0272.jpg", "filename": "GLAST.0272.jpg", "media_type": "Image", "alt_text": "A frame from the movie. Notice that some sources visible in the first frame are no longer visible and some new sources have appeared.", "width": 2880, "height": 1440, "pixels": 4147200 } } }, { "id": 406189, "type": "details_page", "extra_data": null, "instance": { "id": 10143, "url": "https://svs.gsfc.nasa.gov/10143/", "page_type": "Produced Video", "title": "Millisecond Pulsar with Gravitational Waves", "description": "A pulsar is generally believed to be a rapidly rotating neutron star that emits pulses of radiation (such as x-rays and radio waves) at known regular intervals. A millisecond pulsar is one with a rotational period in the range of 1-10 milliseconds. As the pulsar picks up speed through accretion, it distorts due to subtle changes in the crust. Such slight distortion is enough to produce gravitational waves. Material flowing onto the pulsar surface from its companion star tends to quicken the spin, but the loss of energy to gravitational waves tends to slow the spin. This competition between forces may reach an equilibrium, setting a natural speed limit for millisecond pulsars beyond which they cannot spin faster. || ", "release_date": "2007-07-03T00:00:00-04:00", "update_date": "2023-05-03T13:55:40.408593-04:00", "main_image": { "id": 508297, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a010100/a010143/PulsarWide065.jpg", "filename": "PulsarWide065.jpg", "media_type": "Image", "alt_text": "This animation shows a wide shot of a millisecond pulsar.", "width": 1280, "height": 720, "pixels": 921600 } } }, { "id": 406190, "type": "details_page", "extra_data": null, "instance": { "id": 10144, "url": "https://svs.gsfc.nasa.gov/10144/", "page_type": "Produced Video", "title": "Millisecond Pulsar with Magnetic Field Structure", "description": "A pulsar is a rapidly rotating neutron star that emits pulses of radiation (such as X-rays and radio waves) at regular intervals. A millisecond pulsar is one with a rotational period between 1 and 10 milliseconds, or from 60,000 to 6,000 revolutions per minute. Pulsars form in supernova explosions, but even newborn pulsars don’t spin at millisecond speeds, and they gradually slow down with age. If, however, a pulsar is a member of a binary system with a normal star, gas transferred from the companion can spin up an old, slow pulsar to the millisecond range. || ", "release_date": "2007-07-03T00:00:00-04:00", "update_date": "2023-05-03T13:55:40.565321-04:00", "main_image": { "id": 508319, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a010100/a010144/PulsarCU1300.jpg", "filename": "PulsarCU1300.jpg", "media_type": "Image", "alt_text": "This animation zooms into a neutron star and its accretion disk to show a millisecond pulsar in close-up.", "width": 1280, "height": 720, "pixels": 921600 } } }, { "id": 406191, "type": "details_page", "extra_data": null, "instance": { "id": 11437, "url": "https://svs.gsfc.nasa.gov/11437/", "page_type": "Produced Video", "title": "First Gamma-ray Measurement of a Gravitational Lens", "description": "Astronomers using NASA's Fermi observatory have made the first gamma-ray measurements of a gravitational lens, a kind of natural telescope formed when a rare cosmic alignment allows the gravity of a massive object to bend and amplify light from a more distant source.The opportunity arose in September 2012, when Fermi's Large Area Telescope (LAT) detected a series of bright gamma-ray flares from a source known as B0218+357, located 4.35 billion light-years away in the constellation Triangulum. These powerful outbursts in a known gravitational lens provided the key to making the measurement. Astronomers classify B0218+357 as a blazar, a type of active galaxy noted for intense outbursts. At the blazar's heart is a supersized black hole with a mass millions to billions of times that of the sun. As matter spirals toward this black hole, some of it blasts outward as jets of particles traveling near the speed of light in opposite directions.Long before light from B0218+357 reaches us, it passes directly through a spiral galaxy – one much like our own – located 4.03 billion light-years away. The galaxy's gravity bends the light into different paths, so astronomers see the background blazar as dual images. But these paths aren't the same length, which means that when one image flares, there's a delay of many days before the other does.While radio and optical telescopes can resolve and monitor the individual blazar images, Fermi's LAT cannot. Instead, the Fermi team exploited the playback delay between the images. In September 2012, when the blazar's flaring activity made it the brightest gamma-ray source outside of our own galaxy, Fermi scientists took advantage of the opportunity by using a week of dedicated LAT time to hunt for delayed flares. Three episodes of flares showing playback delays of 11.46 days were found, with the strongest evidence in a sequence of flares captured during the week-long LAT observations. || ", "release_date": "2014-01-06T10:00:00-05:00", "update_date": "2023-05-03T13:51:19.955910-04:00", "main_image": { "id": 459769, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a011400/a011437/Lensed_Blazar_Still.jpg", "filename": "Lensed_Blazar_Still.jpg", "media_type": "Image", "alt_text": "This movie illustrates the components of a gravitational lens system known as B0218+357. Different sight lines to a background blazar result in two images that show outbursts at slightly different times. NASA's Fermi made the first gamma-ray measurements of this delay in a lens system. Credit: NASA's Goddard Space Flight Center", "width": 1920, "height": 1080, "pixels": 2073600 } } }, { "id": 406192, "type": "media_group", "extra_data": null, "title": "Neutron Star Scale", "caption": null, "instance": { "id": 482484, "url": "https://svs.gsfc.nasa.gov/vis/a010000/a010800/a010858/Neutron_Star_Manhattan_Update.jpg", "filename": "Neutron_Star_Manhattan_Update.jpg", "media_type": "Image", "alt_text": "A pulsar is a neutron star, the crushed core of a star that has exploded. Neutron stars crush half a million times more mass than Earth into a sphere no larger than Manhattan. Some of these objects spin at 43,000 revolutions per minute. ", "width": 1080, "height": 1920, "pixels": 2073600 } } ], "extra_data": {} } ] }