# Denpa

> Japanese scientific research satellite

**Wikidata**: [Q3023248](https://www.wikidata.org/wiki/Q3023248)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Denpa_(satellite))  
**Source**: https://4ort.xyz/entity/denpa

## Summary
Denpa was a Japanese scientific research satellite launched in 1972 to study Earth's magnetosphere. It was Japan’s first dedicated geomagnetic satellite and part of the early space science efforts by the Institute of Space and Astronautical Science (ISAS). Although operational for only three days, it marked an important milestone in Japan's space exploration history.

## Key Facts
- Launched on August 19, 1972 at 02:40 UTC from Uchinoura Space Center
- Operated until failure on August 22, 1972 due to overcurrent
- Weighed 75 kilograms with a total height of 1.849 meters
- Also known as REXS (Radio Exploration Satellite)
- Built and operated by the Institute of Space and Astronautical Science (ISAS), Japan
- Launched aboard the M-4S-4 variant of the M-4S rocket
- COSPAR ID: 1972-064A; NSSDCA ID: 1972-064A
- Re-entered Earth's atmosphere on May 19, 1980

## FAQs
### Q: What was the purpose of the Denpa satellite?
A: Denpa was designed as a geomagnetic satellite to monitor Earth's magnetosphere and conduct scientific research on space weather interactions.

### Q: Who built and operated Denpa?
A: The satellite was developed and operated by the Institute of Space and Astronautical Science (ISAS) in Japan.

### Q: How long did Denpa function before failing?
A: Denpa ceased operations just three days after launch, on August 22, 1972, following an electrical failure caused by overcurrent.

## Why It Matters
Denpa represented one of Japan's earliest independent ventures into space-based scientific observation. As the country's first dedicated geomagnetic satellite, it laid foundational groundwork for future missions focused on understanding near-Earth space environments. Despite its brief mission life, Denpa demonstrated ISAS' growing capability in designing specialized satellites and contributed valuable experience in mission planning, launch execution, and orbital operations. Its legacy is tied to the development trajectory of Japan's robust space program, which continues today through institutions like JAXA.

## Notable For
- First Japanese satellite specifically built for geomagnetic research
- One of the earliest successful launches using the M-4S rocket series
- Marked ISAS’ advancement toward autonomous scientific satellite missions
- Provided engineering insights despite premature mission termination
- Symbolized Japan's emergence in international space science during the early 1970s

## Body
### Mission Overview
Denpa, also referred to as REXS (Radio Exploration Satellite), was Japan’s inaugural geomagnetic satellite. Its primary objective was to investigate Earth’s magnetic field and associated phenomena within the magnetosphere. Developed under the auspices of the Institute of Space and Astronautical Science (ISAS), Denpa played a pivotal role in establishing Japan’s presence in space-based scientific research.

### Technical Specifications
The spacecraft had a cylindrical bus section measuring:
- Diameter: 0.712 metres  
- Height of spacecraft bus: 0.6853 metres  
- Total height including instruments: 1.849 metres  

It weighed approximately **75 kilograms** and was equipped with solar arrays capable of generating up to **40 watts** of power. These features enabled onboard systems necessary for conducting electromagnetic observations while maintaining stable attitude control during its intended short-term operation.

### Launch Details
Launched on **August 19, 1972**, at **02:40 UTC**, Denpa lifted off from the **Uchinoura Space Center** using the **M-4S-4** version of the **M-4S** carrier rocket. This launch event signified another step forward in Japan’s expanding use of domestically produced launch vehicles for small-scale scientific payloads.

### Operational Timeline
Despite a successful deployment into orbit, Denpa experienced critical system failures shortly afterward:
- On **August 22, 1972**, the satellite stopped functioning due to an **overcurrent fault**
- The precise time of failure was recorded as **00:04 UTC**

Although its active lifespan lasted less than four days, Denpa transmitted initial telemetry data that validated key aspects of its design and instrumentation capabilities.

### End of Mission
After nearly eight years in low Earth orbit, Denpa re-entered the atmosphere on **May 19, 1980**, marking the conclusion of its orbital lifetime. Tracking data confirmed atmospheric decay consistent with predictions based on orbital mechanics and atmospheric drag models applicable to decommissioned satellites of its class.

## References

1. [Source](http://spaceinfo.jaxa.jp/ja/rexs.html)
2. Jonathan's Space Report
3. [Source](http://www.isas.jaxa.jp/j/enterp/missions/denpa.shtml)
4. [Source](https://www.n2yo.com/satellite/?s=06152)
5. [Source](http://www.isas.jaxa.jp/j/enterp/missions/image/diagram/denpa_f_b.gif)
6. [Source](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1972-064A)