# Gravity and Extreme Magnetism Small Explorer

> cancelled NASA mission

**Wikidata**: [Q1544005](https://www.wikidata.org/wiki/Q1544005)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Gravity_and_Extreme_Magnetism_Small_Explorer)  
**Source**: https://4ort.xyz/entity/gravity-and-extreme-magnetism-small-explorer

## Summary
Gravity and Extreme Magnetism Small Explorer (GEMS) was a NASA mission to study X-ray polarization from cosmic sources, developed by Goddard Space Flight Center and Orbital Sciences Corporation. The project was cancelled in 2012 before launch, despite being selected in 2008 as part of NASA's Small Explorer program.

## Key Facts
- Cancelled NASA mission to study X-ray polarization from cosmic sources
- Selected by NASA in May 2008 as part of the Small Explorer program
- Cancelled on May 10, 2012, before launch
- Mass: 267 kg (589 lbs)
- Length: 7.12 meters (23.4 feet)
- Planned launch vehicle: Pegasus air-launched rocket
- Principal Investigator: Jean Swank
- Operated by Goddard Space Flight Center with Orbital Sciences Corporation as contractor
- Powered by 637-watt photovoltaic system
- Spacecraft bus: Star Bus design

## FAQs
### Q: What was the purpose of the GEMS mission?
A: GEMS was designed to study X-ray polarization from cosmic sources like black holes and neutron stars to understand extreme magnetic fields and gravity in space.

### Q: Why was the GEMS mission cancelled?
A: NASA cancelled GEMS in May 2012 due to cost overruns and technical challenges, despite having already invested significant development resources.

### Q: What happened to GEMS after cancellation?
A: After cancellation, NASA continued the Small Explorer program with subsequent missions like the Imaging X-ray Polarimetry Explorer (IXPE), which launched in 2021 to fulfill similar scientific objectives.

## Why It Matters
GEMS represented an ambitious attempt to pioneer X-ray polarimetry in space, a technique that could reveal unprecedented details about extreme cosmic environments. The mission aimed to study phenomena like black holes, neutron stars, and supernova remnants by measuring the polarization of X-rays they emit, providing insights into magnetic fields and spacetime geometry near these objects. Though cancelled, GEMS pushed forward the technology and scientific understanding needed for future X-ray polarimetry missions. Its cancellation highlighted the challenges of managing innovative space science projects within budget constraints, leading to improved planning for subsequent missions. The scientific goals of GEMS were eventually realized through the IXPE mission, demonstrating how cancelled projects can inform and enable future successes in space exploration.

## Notable For
- First NASA mission specifically designed for X-ray polarimetry
- Advanced X-ray telescope technology developed at Goddard Space Flight Center
- Part of NASA's cost-capped Small Explorer program for focused scientific missions
- Cancelled after significant development investment, providing lessons for future missions
- Scientific objectives carried forward to successful IXPE mission in 2021

## Body
### Mission Overview
GEMS was conceived as a Small Explorer (SMEX) mission to study X-ray polarization from cosmic sources. The mission would have used innovative X-ray polarimetry techniques to probe extreme environments like black holes and neutron stars, measuring how X-rays from these objects become polarized as they travel through intense magnetic fields and curved spacetime.

### Technical Specifications
The spacecraft had a mass of 267 kg and measured 7.12 meters in length. It was powered by a 637-watt photovoltaic system and built on the Star Bus platform by Orbital Sciences Corporation. The X-ray telescope instrumentation was developed by Goddard Space Flight Center, with Alliant Techsystems serving as a subcontractor.

### Development Timeline
NASA selected GEMS in May 2008 as part of its Small Explorer program. The project progressed through initial development phases but encountered technical challenges and cost growth. On May 10, 2012, NASA formally cancelled the mission, citing the need to manage resources across its portfolio of space science projects.

### Scientific Objectives
The mission aimed to measure X-ray polarization from sources including black holes, neutron stars, and supernova remnants. This would have provided unique insights into the geometry of spacetime near compact objects, the strength and structure of magnetic fields in extreme environments, and the physics of matter under conditions impossible to replicate on Earth.

### Legacy
Although GEMS never flew, its scientific goals and technological developments informed subsequent missions. The Imaging X-ray Polarimetry Explorer (IXPE), launched in December 2021, successfully carried out X-ray polarimetry observations, achieving many of the objectives originally planned for GEMS. The experience gained from GEMS contributed to improved project management and technical approaches in later missions.

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## References

1. [Source](http://web.archive.org/web/20130213232854/http://gems.gsfc.nasa.gov/)
2. [Source](https://www.nasa.gov/centers/goddard/news/topstory/2008/gems.html)
3. [Source](https://www.spacemart.com/reports/Orbital_To_Build_New_Space_Science_Satellite_To_Study_X_Ray_Polarization_999.html)
4. [Source](https://spacenews.com/review-finds-nasa-acted-properly-gems-cancellation/)
5. [Source](http://web.archive.org/web/20130214175056/http://gems.gsfc.nasa.gov/sc_inst.html)
6. [Source](https://www.nasa.gov/home/hqnews/2008/may/HQ_C08029_SMEX_Awards.html)
7. [Source](https://spacenews.com/nasa-cancel-gems-x-ray-telescope/)
8. [Source](http://web.archive.org/web/20120806162701/http://www.orbital.com:80/SatellitesSpace/ScienceTechnology/GEMS/)