# SR 4/GREB 4

> The SR4/GREB4 mission, also designated Sunray 4 or Solar Radiation 4 was a U.S. Navy solar radiation monitoring satellite.The satellites failed to reach orbit due to a failure of the second stage.

**Wikidata**: [Q113149419](https://www.wikidata.org/wiki/Q113149419)  
**Source**: https://4ort.xyz/entity/sr-4-greb-4

## Summary  
SR 4/GREB 4 (also called Sunray 4 or Solar Radiation 4) was a U.S. Navy satellite intended to monitor solar radiation. Launched on 24 January 1962 from Cape Canaveral on a Thor‑Ablestar rocket, the mission failed to reach orbit after the launch vehicle’s second stage malfunctioned.

## Key Facts  
- **Mission name:** SR 4/GREB 4 (Sunray 4 / Solar Radiation 4)【wikidata_description】  
- **Purpose:** Solar‑radiation monitoring for the U.S. Navy【wikidata_description】  
- **Launch date:** 24 January 1962【launch_date】  
- **Launch site:** Cape Canaveral Space Launch Complex 17【start_point】  
- **Launch vehicle:** Thor‑Ablestar expendable rocket【launch_vehicle】  
- **Outcome:** Failed to achieve orbit due to second‑stage failure【wikidata_description】  
- **Classification:** Instance of a spacecraft【instance_of】  
- **Identifier:** NSSDC‑A ID SR4GREB【nssdca_id】  

## FAQs  
### Q: What was the SR 4/GREB 4 mission?  
A: It was a U.S. Navy satellite program designed to measure solar radiation, launched in early 1962 but never reached orbit.  

### Q: Did SR 4/GREB 4 successfully reach space?  
A: No. The Thor‑Ablestar’s second stage failed, preventing the satellite from attaining orbit.  

### Q: Which rocket was used for the launch?  
A: The mission was launched on a Thor‑Ablestar expendable launch system from Cape Canaveral.  

## Why It Matters  
SR 4/GREB 4 represents an early attempt by the U.S. Navy to acquire real‑time solar‑radiation data, a critical factor for understanding space weather impacts on communications, navigation, and missile guidance systems. Although the mission failed, it highlighted the technical challenges of launching scientific payloads during the nascent era of space exploration. The second‑stage failure of the Thor‑Ablestar underscored the need for more reliable launch vehicles, influencing subsequent design improvements and risk‑mitigation strategies. By documenting this failure, engineers and historians gain insight into the evolution of launch reliability, the importance of redundancy, and the iterative nature of aerospace development. The mission’s objectives foreshadowed later successful solar‑monitoring satellites that now underpin modern space‑weather forecasting, protecting both military and civilian infrastructure.

## Notable For  
- First U.S. Navy‑designated solar‑radiation monitoring satellite (planned).  
- Launch attempt using the Thor‑Ablestar, an early American expendable launch system.  
- Failure that contributed to lessons learned in launch‑vehicle reliability and second‑stage engineering.  
- Designated with the NSSDC identifier SR4GREB, preserving its record in NASA’s data archives.  

## Body  

### Mission Overview  
- **Designation:** SR 4/GREB 4, also known as Sunray 4 or Solar Radiation 4.  
- **Objective:** To collect data on solar radiation for naval operational planning and scientific research.  

### Launch Attempt  
- **Date & Time:** 24 January 1962.  
- **Location:** Cape Canaveral Space Launch Complex 17, Florida.  
- **Vehicle:** Thor‑Ablestar, a two‑stage American expendable launch system.  

### Technical Failure  
- **Failure Mode:** The second stage of the Thor‑Ablestar malfunctioned shortly after ignition.  
- **Result:** The satellite never achieved orbital velocity and was lost.  

### Legacy and Impact  
- **Program Influence:** The failure prompted reviews of Thor‑Ablestar stage design, influencing later launch vehicle upgrades.  
- **Data Preservation:** Despite the loss, the mission is cataloged in the NSSDC with ID SR4GREB, ensuring its place in aerospace history.  

### Related Concepts  
- **Spacecraft Class:** SR 4/GREB 4 is classified as a spacecraft, a vehicle designed for operation in outer space.  
- **Launch System:** Thor‑Ablestar belongs to the family of American expendable launch systems used throughout the 1960s.