page_title: Gravity and Extreme Magnetism
section_title: Mission
hierarchical_section_title: Gravity and Extreme Magnetism / Mission
caption_attribution_description: English: Public GEMS poster.
context_page_description: The Gravity and Extreme Magnetism SMEX mission was a cancelled space observatory mission. The main scientific goal of GEMS was to be the first mission to systematically measure the polarization of cosmic X-Ray sources. GEMS would have provided data to help scientists study the shape of spacetime that has been distorted by a spinning black hole's gravity and the structure and effects of the magnetic fields around neutron stars. It was cancelled by NASA in June 2012 for potential cost overruns due to delays in developing the technology.
  GEMS was managed by the National Aeronautics and Space Administration NASA, the United States space agency, at the Goddard Space Flight Center. The project was an astrophysics program reporting to NASA's Science Mission Directorate in Washington, D.C..
  The spacecraft would have been launched on in July 2014 on a nine-month mission with a possible 15-month extension for a guest observer phase; but the mission was terminated at the Confirmation Review stage on May 10, 2012 due to expected cost overruns.
  Cancelled missions can be reinstated—for example, NuSTAR was cancelled in 2006, but reinstated a year later and launched in June 2012.
context_section_description: The GEMS X-ray telescope was designed to indirectly measure the regions of distorted space around spinning black holes through a measurement of the polarization of X-rays emitted. It would have also probed the structure and effects of the magnetic fields around magnetars and other star remnants with magnetic fields trillions of times stronger than Earth's.
  GEMS could reveal:
  How spinning black holes affect space-time and matter as it is drawn in and compressed by strong gravitational fields.
  What happens in the very strong magnetic fields near pulsars and magnetars.
  How cosmic rays are accelerated by shocks in supernova remnants.
  Current missions cannot do this because the required angular resolution is limited and magnetic fields are invisible.
  The detector in GEMS would have been a small chamber filled with gas. When an X-ray is absorbed in the gas, an electron carries off most of the energy, and starts out in a direction related to the polarization direction of the X-ray. This electron loses energy by ionizing the gas; the instrument measures the direction of the ionization track, and thereby the polarization of the X-ray. The GEMS detector readout will employ a time projection chamber to image the track. The GEMS instrument is about 100 times more sensitive than previous X-ray polarization experiments.
  Mission costs were capped at US$105 million (in Fiscal Year 2008 dollars), excluding the launch vehicle, but an independent confirmation review board at NASA claimed it would grow to an estimated $150 million, leading to cancellation of the mission.
  The cancellation of GEMS marks the end of a multi-year-long binge of cancellations and attempted cancellations of current and future missions: it was at the time the last funded future U.S. space telescope besides JWST. The cancellation of GEMS may have jeopardized the  Pegasus XL launcher. (The Pegasus XL has successfully launched other small explorer missions)
caption: Mission poster for the GEMS telescope
exif: {"Image ImageWidth": "7650", "Image ImageLength": "11250", "Image BitsPerSample": "[8, 8, 8]", "Image PhotometricInterpretation": "2", "Image Orientation": "Horizontal (normal)", "Image SamplesPerPixel": "3", "Image XResolution": "200", "Image YResolution": "200", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS5 Macintosh", "Image DateTime": "2011:05:12 11:34:15", "Image ExifOffset": "232", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "382", "Thumbnail JPEGInterchangeFormatLength": "7060", "EXIF ExifVersion": "0221", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "1864", "EXIF ExifImageLength": "2800"}