# Far Ultraviolet Spectroscopic Explorer

> decommissioned NASA space observatory

**Wikidata**: [Q49909](https://www.wikidata.org/wiki/Q49909)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Far_Ultraviolet_Spectroscopic_Explorer)  
**Source**: https://4ort.xyz/entity/far-ultraviolet-spectroscopic-explorer

## Summary
The Far Ultraviolet Spectroscopic Explorer (FUSE) was a NASA space observatory launched in 1999 to study ultraviolet light from astronomical objects. It operated until its decommissioning in 2007, providing critical data on the interstellar medium, galaxy evolution, and star formation. FUSE was part of NASA's Explorer program and conducted high-resolution spectroscopy in the far ultraviolet range.

## Key Facts
- **Launch Date**: June 24, 1999, at 15:44:00 UTC aboard a Delta II rocket (D271) from Cape Canaveral Space Launch Complex 17A.
- **Operator**: Johns Hopkins University Applied Physics Laboratory.
- **Mission Duration**: Over 8 years (1999–2007), exceeding its planned 5-year lifespan.
- **Primary Instrument**: Two ultraviolet spectrographs with a resolving power of 15,000–20,000.
- **Cost**: Approximately $200 million (as part of the Medium Explorer program).
- **Classification**: Space telescope, artificial satellite of Earth, and derelict satellite (post-decommissioning).
- **Decommissioning Date**: October 18, 2007, due to declining instrument performance and fuel depletion.

## FAQs
### Q: When was the Far Ultraviolet Spectroscopic Explorer launched?
A: FUSE launched on June 24, 1999, aboard a Delta II rocket from Cape Canaveral, Florida.

### Q: What was the main purpose of FUSE?
A: Its primary mission was to study the far ultraviolet spectra of astronomical objects to investigate the interstellar medium, galaxy evolution, and the formation of stars and planetary systems.

### Q: Why was FUSE decommissioned?
A: It was decommissioned on October 18, 2007, after nearly 8 years of operation due to degraded instrument performance and insufficient fuel for further operations.

## Why It Matters
FUSE significantly advanced astrophysics by providing unprecedented high-resolution spectra in the far ultraviolet range, a wavelength regime inaccessible from Earth due to atmospheric absorption. Its data enabled breakthroughs in understanding the composition and dynamics of the interstellar medium, the evolution of galaxies, and the processes of star and planetary system formation. Operating far beyond its intended 5-year mission, FUSE contributed to over 1,200 scientific papers and created a legacy dataset still used by researchers. Its success demonstrated the scientific value of focused, cost-effective space missions under NASA's Explorer program.

## Notable For
- First mission in NASA's Medium-Class Explorers (MIDEX) program, setting a precedent for cost-capped orbital observatories.
- Achieved spectral resolution 10–20 times greater than previous ultraviolet telescopes, enabling detailed studies of atomic and molecular processes.
- Operated for 8 years despite a 3-year design life, extending its mission through adaptive operations and fuel optimization.
- Collected over 100,000 observations of more than 7,000 celestial targets, including comets, stars, galaxies, and the intergalactic medium.

## Body
### Mission Overview
FUSE was designed to explore the far ultraviolet spectrum (90.5–119.5 nm) using two identical spectrographs with Rowland-grating optics. Its primary science objectives included measuring the abundance of deuterium in the universe, studying the interstellar medium's composition, and observing hot gas in galaxies and quasars.

### Instrumentation
- **Spectrographs**: Two lithium fluoride-channel-plate detectors with a spectral resolution of 15,000–20,000.
- **Aperture**: 30 cm (12-inch) diameter primary mirror.
- **Design**: Modular structure with a sunshade to maintain cryogenic temperatures for the detectors.

### Launch and Operations
- **Launch Vehicle**: Delta II 7920-10C (D271), a retired expendable rocket in the Delta family.
- **Orbit**: 746 km (463-mile) circular orbit inclined at 20° to avoid South Atlantic Anomaly radiation interference.
- **Data Archive**: Over 100,000 observations stored at the Mikulski Archive for Space Telescopes (MAST).

### Decommissioning
- **Cause**: Gradual degradation of the spectrographs' detectors and insufficient fuel for attitude control.
- **Legacy**: Final commands were sent on October 18, 2007, concluding a mission that exceeded performance expectations and expanded humanity's understanding of ultraviolet astrophysics.

### Post-Mission Status
FUSE remains in orbit as a derelict satellite, tracked by NASA and the U.S. Space Surveillance Network. Its orbital decay is projected to result in re-entry by 2070, though this timeline may vary due to atmospheric density changes.

## References

1. Virtual International Authority File
2. Jonathan's Space Report
3. Freebase Data Dumps. 2013
4. [Source](https://archive.stsci.edu/missions-and-data/fuse)