# Cluster 4

> one of four identical magnetospheric research satellites in the Cluster II constellation

**Wikidata**: [Q111658950](https://www.wikidata.org/wiki/Q111658950)  
**Source**: https://4ort.xyz/entity/cluster-4

## Summary
Cluster 4 is one of four identical magnetospheric research satellites in the European Space Agency's Cluster II constellation, launched to study Earth's magnetosphere and its interaction with solar wind. It operates alongside three sister satellites to provide 3D observations of space plasma. Launched in 2000, it remains operational far beyond its planned 5-year mission.

## Key Facts
- **Launch Date**: August 9, 2000, at 11:13:35 UTC from Baikonur Cosmodrome Site 31.
- **Mission**: Part of the Cluster II constellation to investigate Earth's magnetosphere and plasma interactions.
- **Operator**: European Space Operations Centre (ESOC).
- **Manufacturer**: Astrium (now Airbus Defence and Space).
- **Mass**: 1,200 kg (launch weight) and 550 kg (dry weight).
- **Dimensions**: 1.3 m height, 2.9 m diameter.
- **Power**: 224 solar cell panels and S400 batteries.
- **Launch Vehicle**: Soyuz-U rocket with Fregat upper stage (serial A 15000-070).
- **Identifiers**: COSPAR ID 2000-045B, NSSDCA ID 2000-045B, NAIF ID -196.

## FAQs
### Q: What is the primary mission of Cluster 4?
A: Cluster 4 studies Earth's magnetosphere and its interaction with solar wind as part of the Cluster II constellation, providing 3D plasma observations.

### Q: How long was Cluster 4 designed to operate?
A: It was designed for a 5-year mission but has far exceeded this, remaining operational for over two decades.

### Q: What makes Cluster 4 unique compared to other satellites?
A: It is one of four identical satellites in the Cluster II mission, enabling simultaneous, multi-point observations of space plasma dynamics.

## Why It Matters
Cluster 4 plays a critical role in advancing our understanding of Earth's magnetosphere and space weather. As part of the Cluster II constellation, it revolutionized space plasma research by enabling 3D observations of magnetic reconnection, plasma turbulence, and solar wind interactions. Initially planned for a 5-year mission, its extended operation has provided unprecedented long-term datasets, supporting over 2,000 scientific publications. The mission's success highlights international collaboration in space science, involving ESA, NASA, and other partners. By addressing gaps in magnetospheric research, Cluster 4 helps improve predictive models for space weather, which impacts satellite operations, communications, and planetary protection.

## Notable For
- First mission to conduct 3D magnetospheric observations using four synchronized satellites.
- Operated far beyond its 5-year design life, with ongoing scientific contributions.
- Utilized a Fregat upper stage for precise deployment into a highly elliptical polar orbit.
- Carried identical payloads to its sister satellites, ensuring data consistency across the constellation.

## Body
### Mission Overview
Cluster 4 (aliases: Tango, Cluster C4, FM8) is a geomagnetic satellite launched to investigate Earth's magnetosphere, magnetotail, and polar regions. Its instruments analyze plasma density, magnetic fields, and electric fields to study solar wind interactions and space weather phenomena.

### Launch Details
- **Date/Time**: August 9, 2000, 11:13:35 UTC.
- **Site**: Baikonur Cosmodrome Site 31/6.
- **Rocket**: Soyuz-U (serial A 15000-070) with Fregat upper stage (P2598: 1004).

### Design and Specifications
- **Structure**: Cylindrical body with 1.3 m height and 2.9 m diameter.
- **Power**: 224 solar cells generating 1,100 W (peak) and S400 batteries.
- **Propulsion**: Used for orbital adjustments; dry mass 550 kg.

### Operational History
- **Orbit**: Highly elliptical polar orbit (perigee ~4,000 km, apogee ~19,000 km).
- **Constellation**: Maintains formation with Cluster 1, 2, and 3 for multi-point observations.
- **Extended Mission**: Operated for over 20 years, surpassing its 5-year design life.

### Legacy
Cluster 4's data has been instrumental in studying magnetic reconnection, auroral acceleration, and plasma waves. Its longevity and collaborative science framework set a precedent for future magnetospheric missions like Magnetospheric Multiscale (MMS).

## References

1. [Source](https://space.skyrocket.de/doc_sdat/cluster.htm)
2. [Source](https://sci.esa.int/web/cluster/-/47348-fact-sheet)
3. Jonathan's Space Report