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When Fermi Dodged a 1.5-ton Bullet

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.

Watch this video on YouTube.

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Another multimedia item related to this story:
     Fermi Collision Avoidance Animations (id 11228)
More information on this topic available at:
http://www.nasa.gov/mission_pages/GLAST/news/bullet-dodge.html

Fermi Collision Avoidance Short video    Fermi Collision Avoidance Short video

For complete transcript, click here.
Duration: 4.3 minutes
Available formats:
  1280x720 (59.94 fps) QT         4 GB
  1280x720 (59.94 fps) QT         2 GB
  1280x720 (29.97 fps) QT         204 MB
  1280x720 (29.97 fps) QT         157 MB
  1280x720 (29.97 fps) WMV         142 MB
  1280x720 (29.97 fps) MPEG-4   93 MB
  960x540 (29.97 fps) MPEG-4   123 MB
  640x360 (29.97 fps) QT         116 MB
  640x360 (29.97 fps) MPEG-4   49 MB
  320x240 (29.97 fps) MPEG-4   26 MB
  1280x720   JPEG         659 KB
  960x540 (29.97 fps) WEBM         56 MB
  320x180     JPEG         67 KB
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Animation of Earth with near-Earth orbital debris.  The debris field is real data from the NASA Orbital Debris Program Office. Credit: NASA's Goddard Space Flight Center/JSC    Animation of Earth with near-Earth orbital debris. The debris field is real data from the NASA Orbital Debris Program Office.

Credit: NASA's Goddard Space Flight Center/JSC
Duration: 20.0 seconds
Available formats:
  1280x720 (59.94 fps) QT         345 MB
  1280x720 (59.94 fps) QT         253 MB
  1280x720 (29.97 fps) QT         24 MB
  1280x720 (29.97 fps) QT         12 MB
  1280x720 (29.97 fps) WMV         12 MB
  1280x720 (29.97 fps) MPEG-4   11 MB
  2667x1500 TIFF         7 MB
  2667x1500 JPEG         1 MB
  960x540 (59.94 fps) WEBM         3 MB
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Shorter version of animation showing Earth with near-Earth orbital debris.  The debris field is real data from the NASA Orbital Debris Program Office. Credit: NASA's Goddard Space Flight Center/JSC    Shorter version of animation showing Earth with near-Earth orbital debris. The debris field is real data from the NASA Orbital Debris Program Office.

Credit: NASA's Goddard Space Flight Center/JSC
Duration: 10.0 seconds
Available formats:
  1280x720 (59.94 fps) QT         171 MB
  1280x720 (59.94 fps) QT         147 MB
  1280x720 (29.97 fps) QT         13 MB
  1280x720 (29.97 fps) WMV         7 MB
  1280x720 (29.97 fps) QT         6 MB
  1280x720 (29.97 fps) MPEG-4   6 MB
  1280x720   TIFF         2 MB
  1280x720   JPEG         473 KB
  960x540 (29.97 fps) WEBM         2 MB
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Short URL to This Page:http://svs.gsfc.nasa.gov/goto?11229
Animation Number:11229
Completed:2013-03-25
Animators:Chris Meaney (HTSI)
 Walt Feimer (HTSI)
 Scott Wiessinger (USRA)
Video Editor:Scott Wiessinger (USRA)
Interviewees:Julie McEnery (NASA/GSFC)
 Eric Stoneking (NASA/GSFC)
Producer:Scott Wiessinger (USRA)
Videographers:Rob Andreoli (AIMM)
 John Caldwell (AIMM)
Writers:Francis Reddy (Syneren Technologies)
 Scott Wiessinger (USRA)
Series:Narrated Movies
 Astrophysics Animations
 Astrophysics Features
Goddard TV Tape:G2012-083 -- Fermi Collision Avoidance
Please give credit for this item to:
NASA's Goddard Space Flight Center
 
Keywords:
SVS >> HDTV
SVS >> Music
SVS >> Satellite
SVS >> Edited Feature
SVS >> Gamma Ray Observatory
SVS >> Fermi
SVS >> Interview
NASA Science >> Universe
 
 


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Many of our multimedia items use the GCMD keywords. These keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 8.0.0.0.0

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