# Fregat

> model of Russian rocket upper stage

**Wikidata**: [Q122974977](https://www.wikidata.org/wiki/Q122974977)  
**Source**: https://4ort.xyz/entity/fregat-q122974977

## Summary
Fregat is a family of Russian rocket upper stages developed and manufactured by NPO Lavochkin. It functions as a space tug, designed to carry satellites from a parking orbit to their final mission orbit or interplanetary trajectory using a restartable S5.92 main engine.

## Key Facts
- **Classification**: Family of rocket upper stages; specifically a space tug.
- **Developer & Manufacturer**: NPO Lavochkin (Russia).
- **Country of Origin**: Russia.
- **Propulsion**: Powered by a single S5.92 main engine using Unsymmetrical dimethylhydrazine (UDMH) / Nitrogen Tetroxide, and 12 hydrazine-fueled reaction-control thrusters.
- **Dimensions**: Height 1.875 meters; Diameter 3.440 meters.
- **Mass**: Dry weight 945 kg; Launch weight 6,235 kg.
- **Performance**: Main engine vacuum thrust is 19.6 kN with a specific impulse of 327 s.
- **Variants**: Fregat (baseline), Fregat-M, Fregat-MT, Fregat-SB.
- **First Flight**: 12 February 2000.
- **Operational Use**: Used on Russian Soyuz and European Soyuz-ST launch vehicles.

## FAQs
### Q: What launch vehicles are compatible with Fregat?
Fregat upper stages are routinely integrated with Russian Soyuz rockets and, for export missions, the European Soyuz-ST launch vehicle.

### Q: How many times can the Fregat main engine restart?
The S5.92 main engine is restartable multiple times (mission-specific), which allows it to perform complex operations like multi-satellite deployments or interplanetary injection burns.

### Q: What are the differences between the Fregat variants?
The Fregat-M features stretched tanks for additional propellant; Fregat-MT adds an external toroidal tank for even greater capacity; and Fregat-SB includes both internal modifications and a jettisonable external tank for the heaviest payloads.

### Q: What specific missions has Fregat supported?
Fregat has supported a wide range of missions including the OneWeb constellation, ESA projects, Roscosmos missions, and the European Commission’s Galileo programme.

## Why It Matters
Fregat serves as Russia’s primary space tug, bridging the gap between the lift capacity of medium-class launch vehicles and the precise orbital or escape-energy needs of modern satellites and interplanetary probes. By providing up to several kilometers per second of additional delta-v, it enables multi-satellite rideshares to different orbital planes, direct-injection to geostationary orbit, and high-energy escape trajectories for lunar and planetary missions. Its restartable capability and autonomous guidance system reduce mission risk and cost for commercial and scientific customers, extending the utility of existing launch vehicles without requiring entirely new rocket designs.

## Notable For
- **Reliability**: First flown in 2000, Fregat has logged more than 60 successful missions with a reliability record above 95%.
- **Versatility**: It is the only Russian upper stage qualified for both low-Earth-orbit satellite constellations and interplanetary injection burns.
- **Modularity**: Its modular tank design allows propellant load to be tailored for specific missions, resulting in a payload capacity range of 1 t to 3 t.
- **Western Integration**: It serves as the upper stage for Soyuz-ST launches from Kourou, marking a rare instance of Russian propulsion systems being integrated into Western launch campaigns.

## Body

### Design Overview
Fregat is a space tug subclass of rocket upper stages developed by NPO Lavochkin. The structure consists of six spherical or toroidal aluminium alloy tanks arranged around a central structural truss. An integrated avionics bay contains the guidance computer, inertial measurement unit, and telemetry system. The entire assembly is enclosed in a thermal-protection shroud.

Physical specifications include a height of 1.875 meters, a diameter of 3.440 meters, a dry weight of 945 kilograms, and a launch weight of 6,235 kilograms.

### Propulsion Systems
The stage is powered by a single S5.92 engine developed by the Kosberg Bureau. This engine burns Unsymmetrical dimethylhydrazine (UDMH) and Nitrogen Tetroxide in a gas-generator cycle. It is rated for a vacuum thrust of 19.6 kN and a specific impulse of 327 s. Additionally, twelve 50-N hydrazine thrusters provide three-axis control during coast phases and settle propellant prior to main-engine restarts.

### Operational Use and Missions
Fregat operates autonomously once separated from the launch vehicle. Typical missions involve one or two burns to reach a transfer orbit, a circularization burn, and potentially a third burn for de-orbit. Flight times vary from 45 minutes for Low Earth Orbit (LEO) missions to 9 hours for Geostationary Transfer Orbit (GTO) missions.

Fregat traces its heritage to the propulsion module developed for the 1988 Phobos missions. Following the need for a high-energy stage for Mars-96, NPO Lavochkin adapted the design into a commercial upper stage. It first flew on 12 February 2000 aboard a Soyuz-U/Fregat carrying the IRDT demonstrator. It has since supported major payloads for OneWeb, ESA, Roscosmos, and the European Commission’s Galileo programme.

### Variants
The Fregat family includes several distinct models designed for different mission profiles:
- **Fregat**: The baseline version with standard propellant load.
- **Fregat-M**: Features stretched tanks holding approximately 1 t of additional propellant.
- **Fregat-MT**: Adds an external toroidal tank, bringing total propellant to approximately 3 t.
- **Fregat-SB**: Combines an internal stretch with a jettisonable external tank for the heaviest payloads.

### Legacy
Fregat is a workhorse in the Russian space program, used atop Soyuz and Soyuz-ST rockets. Its ability to restart multiple times and its autonomous guidance systems allow it to deliver payloads to precise orbits, reducing the need for satellites to carry their own apogee motors. This capability extends the operational life of existing launch vehicles and supports a wide range of commercial and scientific missions.

## References

1. [Source](https://www.russianspaceweb.com/fregat.html)
2. [Source](https://space.skyrocket.de/doc_stage/fregat.htm)
3. [Source](https://www.laspace.ru/en/activities/products/sredstva-vyvedeniya/razgonnye-bloki-fregat-/)