# Array of Low-Energy X-ray Imaging Sensors

> decommissioned American X-ray telescope

**Wikidata**: [Q18539](https://www.wikidata.org/wiki/Q18539)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Array_of_Low_Energy_X-ray_Imaging_Sensors)  
**Source**: https://4ort.xyz/entity/array-of-low-energy-x-ray-imaging-sensors

## Summary
The Array of Low-Energy X-ray Imaging Sensors (ALEXIS) was a decommissioned American X-ray telescope launched in 1993 to demonstrate experimental space technologies and conduct astronomical observations. Operated by Los Alamos National Laboratory, it operated in low Earth orbit until its decommissioning in 2005. The mission focused on detecting soft X-ray emissions from celestial objects.

## Key Facts
- **Launch Date**: April 25, 1993, at 13:56 UTC, aboard a Pegasus rocket (F4 configuration) from Edwards Air Force Base.
- **Cost**: $17 million (1993 USD).
- **Mass**: 115 kg (launch weight), with a 45 kg spacecraft bus.
- **Orbit**: Low Earth orbit with 70° inclination, 749 km periapsis, 844 km apoapsis, and 0.00662 eccentricity.
- **Power**: 50-watt photovoltaic system.
- **Decommissioning**: April 29, 2005.
- **Operators**: Los Alamos National Laboratory (funded by the U.S. Department of Energy).

## FAQs
### Q: When was ALEXIS launched and how long did it operate?
A: ALEXIS launched on April 25, 1993, and operated for 12 years until its decommissioning on April 29, 2005.

### Q: What was the primary purpose of the ALEXIS mission?
A: ALEXIS served as a technology demonstration spacecraft to test low-energy X-ray imaging sensors and conduct astronomical observations in soft X-ray wavelengths.

### Q: What type of rocket deployed ALEXIS into orbit?
A: ALEXIS was launched using a Pegasus air-launched rocket (F4 configuration) from a Lockheed L-1011 TriStar aircraft.

## Why It Matters
ALEXIS played a significant role as a technology demonstrator for low-cost, small-satellite missions, paving the way for future space-based X-ray astronomy projects. Its sensors tested the feasibility of detecting soft X-ray emissions, contributing to studies of stellar coronae, supernova remnants, and other high-energy astrophysical phenomena. As a collaborative effort between the U.S. Department of Energy and Los Alamos National Laboratory, ALEXIS highlighted the potential for compact, focused science missions in low Earth orbit. Its 12-year operational lifespan demonstrated the durability of its design, informing later spacecraft development.

## Notable For
- First U.S. X-ray telescope launched via an air-launched Pegasus rocket.
- Operated as both a technology demonstrator and a functional space telescope.
- Utilized a photovoltaic power system to support its X-ray imaging sensors.
- Conducted observations in the soft X-ray spectrum (0.1–10 keV range).

## Body
### Launch and Deployment
ALEXIS launched on April 25, 1993, at 13:56 UTC from Edwards Air Force Base. The spacecraft was deployed using a Pegasus rocket (F4 configuration) dropped from a Lockheed L-1011 TriStar aircraft ("Balls 8"). The launch cost $17 million (1993 USD) and was funded by the U.S. Department of Energy and Los Alamos National Laboratory.

### Mission and Operations
The mission aimed to test experimental X-ray imaging sensors and observe celestial X-ray sources. ALEXIS operated in a low Earth orbit with a semi-major axis of 7,167.5 km, 70° inclination, and an orbital period of approximately 100 minutes. Its sensors focused on detecting soft X-rays (0.1–10 keV) from stellar coronae, supernova remnants, and other astrophysical objects.

### Technical Specifications
- **Mass**: 115 kg (launch weight), 45 kg (spacecraft bus).
- **Power**: 50-watt photovoltaic system.
- **Orbit**: 749 km periapsis, 844 km apoapsis, 0.00662 eccentricity.
- **Sensors**: Array of low-energy X-ray imaging detectors.

### Decommissioning
ALEXIS ceased operations on April 29, 2005, after 12 years in service. The mission concluded due to natural orbital decay and the completion of its primary scientific objectives.

## References

1. Jonathan's Space Report
2. [Source](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1993-026A)
3. [Source](http://web.archive.org/web/20100806154541/http://www.aeroastro.com/index.php/program-heritage/alexis)
4. Freebase Data Dumps. 2013
5. [Source](https://space.skyrocket.de/doc_sdat/alexis.htm)
6. [Source](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1993-026A)
7. [Source](http://web.archive.org/web/20041216055957/http://www.lanl.gov/external/news/releases/archive/98-062.html)