# Explorer 21

> American satellite of Explorers program

**Wikidata**: [Q3736074](https://www.wikidata.org/wiki/Q3736074)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Explorer_21)  
**Source**: https://4ort.xyz/entity/explorer-21

## Summary
Explorer 21 was an American satellite launched as part of NASA's Explorers program on October 4, 1964. It was launched from Cape Canaveral Space Launch Complex 17 aboard a Delta C rocket, marking a continuation of ionospheric research following the Beacon Explorer-B missions.

## Key Facts
- **Launch Date**: October 4, 1964
- **Launch Vehicle**: Delta C
- **Launch Site**: Cape Canaveral Space Launch Complex 17
- **Program**: NASA's Explorers program
- **Classification**: Spacecraft
- **COSPAR ID**: 1964-060A
- **Predecessor**: Beacon Explorer-B (launched in 1964)
- **Image Available**: [Explorer 21 image](https://commons.wikimedia.org/wiki/Special:FilePath/Explorer-21_image.jpg)
- **Wikipedia Languages**: Arabic, English, Galician, Italian, Polish, Portuguese

## FAQs
### Q: What was the purpose of Explorer 21?
A: Explorer 21 was part of NASA's ionospheric research program, continuing studies initiated by the Beacon Explorer-B missions.

### Q: Which rocket launched Explorer 21?
A: Explorer 21 was launched aboard a Delta C rocket from Cape Canaveral Space Launch Complex 17 on October 4, 1964.

### Q: What was the relationship between Explorer 21 and Beacon Explorer-B?
A: Explorer 21 followed the Beacon Explorer-B missions, both of which were NASA ionospheric research satellites.

### Q: Where can I find images of Explorer 21?
A: An image of Explorer 21 is available on Wikimedia Commons: [Explorer 21 image](https://commons.wikimedia.org/wiki/Special:FilePath/Explorer-21_image.jpg).

### Q: What was the significance of Explorer 21's launch date?
A: Explorer 21 was launched on October 4, 1964, as part of ongoing research into the ionosphere, building on earlier missions like Beacon Explorer-B.

## Why It Matters
Explorer 21 played a role in NASA's broader efforts to study the ionosphere, a critical layer of Earth's atmosphere that influences radio communications and space weather. As part of the Explorers program, it contributed to the agency's long-term mission of advancing scientific understanding of Earth's atmosphere and space environment. The satellite's launch and operation helped expand knowledge of ionospheric dynamics, supporting both civilian and military applications. While not as widely documented as some other missions, Explorer 21 represents a key data point in NASA's ionospheric research, continuing the legacy of earlier Beacon Explorer missions.

## Notable For
- **Continuation of Ionospheric Research**: Explorer 21 followed the Beacon Explorer-B missions, maintaining NASA's focus on atmospheric studies.
- **Delta C Launch**: It was launched using the Delta C rocket, a key vehicle in early U.S. space exploration.
- **Cape Canaveral Launch Site**: The mission originated from Space Launch Complex 17, a significant site in NASA's early satellite deployments.
- **COSPAR Identification**: Its COSPAR ID (1964-060A) provides a unique reference in spaceflight records.
- **Multilingual Documentation**: Explorer 21 has Wikipedia entries in multiple languages, reflecting its broader scientific impact.

## Body
### Mission Overview
Explorer 21 was launched on October 4, 1964, as part of NASA's Explorers program, which focused on small, low-cost satellites for scientific research. The mission continued ionospheric studies initiated by the Beacon Explorer-B satellites, contributing to understanding atmospheric dynamics and their effects on radio communications.

### Launch Details
- **Launch Vehicle**: The satellite was launched aboard a Delta C rocket, a U.S. expendable launch vehicle used in early space missions.
- **Launch Site**: Cape Canaveral Space Launch Complex 17 served as the departure point for Explorer 21.
- **COSPAR ID**: The satellite's COSPAR ID is 1964-060A, a standard identifier in spaceflight records.

### Scientific Contributions
Explorer 21 supported NASA's broader goals of atmospheric research, particularly in the ionosphere—a region critical for radio wave propagation and space weather. The mission helped refine models of ionospheric behavior, aiding both scientific and practical applications.

### Documentation and Legacy
- **Wikipedia Presence**: Explorer 21 has Wikipedia entries in Arabic, English, Galician, Italian, Polish, and Portuguese, indicating its broader scientific relevance.
- **Image Archive**: An image of Explorer 21 is available on Wikimedia Commons, providing visual documentation of the satellite.
- **Predecessor Missions**: The satellite followed the Beacon Explorer-B missions, maintaining continuity in NASA's ionospheric research efforts.

Explorer 21 remains a relatively underdocumented entry in NASA's satellite history, but its role in atmospheric studies underscores the agency's commitment to advancing space science.

## References

1. Jonathan's Space Report