# LRE

> Japanese passive satellite

**Wikidata**: [Q5413096](https://www.wikidata.org/wiki/Q5413096)  
**Source**: https://4ort.xyz/entity/lre

## Summary
LRE (Laser Ranging Experiment) is a Japanese passive satellite designed for precise orbital laser ranging experiments. Launched on 29 August 2001 aboard the maiden flight of the H-IIA rocket, the 87 kg, 51 cm-diameter sphere serves as a high-visibility target for ground-based laser tracking stations worldwide.

## Key Facts
- Launch date: 29 August 2001 at 07:00 UTC from Yoshinobu Launch Complex Pad 1, Japan
- Launch vehicle: H-IIA-1F (first flight of the H-IIA medium-lift rocket)
- Satellite catalogue number: 26898; COSPAR ID: 2001-038A
- Mass: 87 kg; Diameter: 51 cm
- Type: passive laser ranging satellite (no onboard propulsion or electronics)
- Country of origin: Japan
- Primary purpose: provide a stable orbital target for laser ranging experiments
- Also known as: Laser Ranging Experiment

## FAQs
### Q: What does LRE stand for?
A: LRE stands for "Laser Ranging Experiment," describing its role as a passive target for ground-based laser tracking systems.

### Q: Why is LRE called a "passive" satellite?
A: LRE is passive because it carries no active electronics, power systems, or propulsion; it simply reflects laser pulses back to Earth, allowing precise distance measurements.

### Q: How is LRE tracked from Earth?
A: Ground stations fire short laser pulses at the satellite and measure the round-trip time of the reflected light, calculating the satellite's position to within millimetres.

## Why It Matters
LRE plays a quiet but foundational role in geodesy and orbital mechanics. By offering a precisely machined, high-reflectivity target of known dimensions and mass, it enables calibration of global laser ranging networks that underpin GPS accuracy, sea-level monitoring, and studies of Earth's gravitational field. Data collected via LRE and similar passive satellites feed directly into international terrestrial reference frames used by scientists, surveyors, and navigation systems. As one of the first payloads launched on Japan's H-IIA rocket, LRE also marked a milestone in the country's shift toward more reliable, domestically developed launch vehicles, helping to secure independent access to space for future scientific and commercial missions.

## Notable For
- First payload launched on the inaugural H-IIA rocket (flight H-IIA-1F)
- One of the few dedicated Japanese laser ranging satellites, complementing international targets such as LAGEOS and Etalon
- Extremely simple design—an unpowered 51 cm sphere—yet supports millimetre-level orbital determination
- Continues to be tracked by the global International Laser Ranging Service (ILRS) network more than two decades after launch

## Body
### Mission Overview
LRE was conceived as a calibration and technology demonstration satellite for Japan's expanding space-based geodesy program. Its sole function is to reflect laser pulses from ground stations, enabling precise orbit determination and contributing to Earth-orientation and reference-frame science.

### Physical Characteristics
The satellite is a solid sphere 51 cm in diameter and 87 kg in mass, giving it a mean density of roughly 1.3 g cm⁻³. The exterior is studded with retro-reflectors—small corner-cube prisms that return incoming light in the direction of its source, allowing laser ranging even when the satellite is thousands of kilometres away.

### Launch and Orbit
LRE rode piggyback on the first H-IIA launch, lifting off at 07:00 UTC on 29 August 2001 from Pad 1 of the Yoshinobu Launch Complex at Tanegashima Space Center. The H-IIA-1F vehicle placed the satellite into a mid-inclination low-Earth orbit, where atmospheric drag is low enough for a multi-decade operational lifetime.

### Operational Status
More than 20 years after deployment, LRE remains a regularly tracked target of the International Laser Ranging Service. Its simple, passive design ensures longevity: with no batteries or moving parts, the satellite will continue to serve as a reference object until orbital decay eventually brings it back into the atmosphere.

## References

1. Jonathan's Space Report