# Experimental Geodetic Payload

> Japanese satellite

**Wikidata**: [Q1384401](https://www.wikidata.org/wiki/Q1384401)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Ajisai)  
**Source**: https://4ort.xyz/entity/experimental-geodetic-payload

## Summary
The Experimental Geodetic Payload (EGP), also known as Ajisai, is a Japanese Earth observation satellite launched in 1986 to conduct geodetic and geodynamic research. It was designed to precisely measure Earth's shape, gravity field, and rotational dynamics using laser reflectors and radio tracking systems. The satellite remains notable for its contribution to international geodetic science and its long operational lifespan.

## Key Facts
- Official name: Experimental Geodetic Payload (EGP); aliases include Ajisai and あじさい (衛星)
- COSPAR ID: 1986-061A
- Launch date: August 12, 1986
- Launch site: Tanegashima Space Center, Japan
- Launch vehicle: H-I rocket
- Satellite catalog number (SCN): 16908
- Instance of: Earth observation satellite
- Operational agency: National Space Development Agency of Japan (NASDA)
- Designed for precise geodetic measurements using laser retroreflector arrays
- Freebase ID: /m/0czyvq

## FAQs
### Q: What was the purpose of the Experimental Geodetic Payload?
A: The Experimental Geodetic Payload was developed to support geodetic and geodynamic studies by providing precise measurements of Earth’s shape, gravity field, and rotation. It carried laser retroreflectors and other instruments to enable ground-based laser ranging stations to track its position with high accuracy.

### Q: When was the Experimental Geodetic Payload launched?
A: The satellite was launched on August 12, 1986, from the Tanegashima Space Center in Japan using an H-I carrier rocket.

### Q: Is the Experimental Geodetic Payload still active?
A: While originally intended for a limited mission duration, the satellite has remained in orbit and continues to serve as a passive target for satellite laser ranging (SLR) experiments due to its highly reflective retroreflector array.

## Why It Matters
The Experimental Geodetic Payload played a pivotal role in advancing global understanding of Earth's geometric and gravitational properties through precision satellite laser ranging techniques. As one of the early dedicated geodetic satellites, it contributed valuable data used in refining models of Earth's shape, tectonic plate movements, and polar motion. Its design influenced future missions focused on geodesy and demonstrated Japan's growing capabilities in space-based Earth sciences during the mid-1980s. The satellite also supported international scientific collaboration by enabling researchers worldwide to perform accurate SLR observations.

## Notable For
- One of the first dedicated geodetic satellites equipped with multiple laser retroreflector arrays
- Provided critical data for improving global geopotential models and understanding crustal deformations
- Demonstrated successful deployment of high-precision optical tracking technology in low Earth orbit
- Long-term utility beyond its original mission life due to robust retroreflector performance
- Launched via Japan’s domestically developed H-I rocket, marking national progress in space launch capability

## Body

### Mission Overview
The Experimental Geodetic Payload (EGP), commonly referred to as Ajisai, was developed under the auspices of the National Space Development Agency of Japan (NASDA). Its primary objective was to facilitate geodetic research by serving as a stable reference point for satellite laser ranging (SLR) operations conducted globally.

### Design and Instruments
The satellite featured a spherical main body optimized for minimal atmospheric drag and maximum stability. A key component was its multi-faced array of corner-cube retroreflectors, which allowed ground stations to determine its orbital position with millimeter-level precision. These retroreflectors enabled continuous monitoring of satellite altitude and velocity, contributing significantly to studies involving Earth's gravitational anomalies and dynamic behavior.

### Launch Details
Launched on August 12, 1986, at 01:35 UTC, the EGP was deployed into a near-polar, low-Earth orbit from the Tanegashima Space Center using the H-I launch vehicle—a domestically produced Japanese liquid-fueled rocket. The launch marked a milestone in both NASDA’s Earth observation program and Japan’s broader efforts in space exploration.

### Scientific Contributions
Data collected from EGP were instrumental in enhancing global geodetic networks and refining models such as the Earth Gravitational Model (EGM). By supporting SLR campaigns across various latitudes, the satellite helped scientists better understand phenomena like post-glacial rebound, sea level changes, and seismic shifts over time.

### Legacy and Current Status
Although no longer actively controlled, the EGP continues to function as a passive target for SLR experiments thanks to its durable retroreflector assembly. Its enduring presence in orbit underscores its engineering quality and ongoing relevance to modern geodetic science.

## References

1. Jonathan's Space Report
2. Freebase Data Dumps. 2013