Gravity and Extreme Magnetism Small Explorer
Gravity and Extreme Magnetism Small Explorer (GEMS or SMEX-13) mission was a NASA space observatory mission. The main scientific goal of GEMS was to be the first mission to systematically measure the polarization of 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 and never moved into the development phase.
Artist's impression of GEMS satellite | |
| Names | Explorer GEMS SMEX-13 |
|---|---|
| Mission type | X-ray astronomy |
| Operator | NASA |
| Website | https://gems.gsfc.nasa.gov/ |
| Mission duration | 9 months (planned) 15 months (possible extension) |
| Spacecraft properties | |
| Spacecraft | Explorer |
| Spacecraft type | Gravity and Extreme Magnetism Small Explorer |
| Bus | LEOStar-2/750 |
| Manufacturer | Orbital Sciences Corporation Alliant Techsystems |
| Launch mass | 289 kg (637 lb) |
| Dimensions | 7.12 × 2.73 m (23.4 × 9.0 ft) |
| Start of mission | |
| Launch date | July 2014 (planned) (cancelled) |
| Rocket | Pegasus XL |
| Launch site | Cape Canaveral, Stargazer |
| Contractor | Orbital Sciences Corporation |
| Orbital parameters | |
| Reference system | Geocentric orbit (planned) |
| Regime | Low Earth orbit |
| Perigee altitude | 575 km (357 mi) |
| Apogee altitude | 575 km (357 mi) |
| Inclination | 28.50° |
| Period | 95.00 minutes |
| Instruments | |
| X-ray Polarimeter Instrument | |
Explorer program | |
GEMS was managed by the NASA Goddard Space Flight Center (GSFC). The project was an astrophysics program reporting to NASA's Science Mission Directorate (SMD) in Washington, D.C.
Cancelled missions can be reinstated - for example, NuSTAR was cancelled in 2006, but reinstated a year later and launched in June 2012. However, NuSTAR was not cancelled due to project overruns, but rather due to changes in the overall NASA budget, so the circumstances for cancellation were very different. Small missions of the Explorer program offer much flexibility and launch opportunities, and the lessons learned can be applied to the same missions goals, but on a different mission (compare, for instance, Vanguard 1 to Explorer 1). Several years later two new X-ray polarimetry missions won a NASA award to develop X-ray polarimetry missions. NASA's IXPE X-ray polarimetry telescope was launched in 2021; its X-ray observational capabilities and mission objectives are very similar to those (proposed) of the GEMS.