# Fregat

> family of Russian rocket upper stages

**Wikidata**: [Q1453740](https://www.wikidata.org/wiki/Q1453740)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Fregat)  
**Source**: https://4ort.xyz/entity/fregat

## Summary
Fregat is a family of Russian-built upper-stage rocket modules designed to carry satellites from a parking orbit to their final mission orbit or interplanetary trajectory. Developed and manufactured by NPO Lavochkin, the Fregat stage is powered by a single S5.92 main engine and multiple hydrazine-fuelled attitude-control thrusters.

## Key Facts
- **Developer & Manufacturer**: NPO Lavochkin (Russia)
- **Propellants**: Unsymmetrical dimethylhydrazine (UDMH) for the main engine; hydrazine for the 12 reaction-control thrusters
- **Main Engine**: S5.92 (1 unit)
- **Reaction-Control Thrusters**: 12 × hydrazine thrusters
- **Rocket Family Members**: Fregat, Fregat-M, Fregat-MT, Fregat-SB
- **Classification**: Space tug; subclass of rocket upper stages
- **Country of Origin**: Russia
- **Wikipedia Sitelinks**: 19 language editions
- **Commons Image**: Model of the Fregat upper stage (Phobos-Grunt base section)

## FAQs
### Q: What launch vehicles use Fregat upper stages?
A: Fregat stages are routinely flown atop Russian Soyuz and, in export configurations, European Soyuz-ST launch vehicles. They serve as the final, restartable stage that injects payloads into precise orbits.

### Q: How many times can a Fregat engine restart?
A: The S5.92 main engine is restartable multiple times (exact on-orbit restart count is mission-specific), allowing Fregat to perform complex multi-satellite deployments or interplanetary injection burns.

### Q: What distinguishes Fregat-M, ‑MT, and ‑SB variants?
A: Fregat-M carries additional propellant for higher-energy missions; Fregat-MT adds a toroidal tank for still more propellant; Fregat-SB incorporates an additional toroidal tank plus a jettisonable external tank for the heaviest payloads.

## Why It Matters
Fregat is Russia’s workhorse space tug, bridging the gap between the lift capacity of medium-class launch vehicles and the exact orbital or escape-energy needs of modern satellites and interplanetary probes. By providing up to several kilometres per second of additional delta-v after the booster has finished its burn, Fregat enables:

- Multi-satellite rideshares to different orbital planes
- Direct-injection deliveries to geostationary orbit without the satellite needing its own apogee motor
- High-energy escape trajectories for lunar and planetary missions such as Phobos-Grunt

Because it is restartable and carries its own autonomous guidance system, Fregat reduces mission risk and cost for commercial customers and scientific agencies alike, extending the operational life of existing launch vehicles without requiring new rockets.

## Notable For
- First flown in 2000, Fregat has logged more than 60 successful missions with a reliability record above 95%
- Only Russian upper stage qualified for both low-Earth-orbit satellite constellations and interplanetary injection burns
- Modular tank design allows propellant load to be tailored, giving the same stage a span of payload capacities from 1 t to 3 t depending on mission profile
- Exported to Europe; served as the upper stage for Soyuz-ST launches from Kourou, marking one of the few Russian propulsion systems integrated into Western launch campaigns

## Body
### Design Overview
Fregat consists of six spherical or toroidal aluminium alloy tanks arranged around a central structural truss. An integrated avionics bay houses the guidance computer, inertial measurement unit, and telemetry system. The entire assembly is enclosed in a thermal-protection shroud.

### Propulsion
The S5.92 engine, developed by the Kosberg Bureau, burns UDMMH and nitrogen tetroxide in a gas-generator cycle. Vacuum thrust is rated at 19.6 kN; specific impulse is 327 s. Twelve 50-N hydrazine thrusters provide three-axis control during coast phases and settle propellant prior to main-engine restarts.

### Operational Use
Fregat operates autonomously once separated from the launch vehicle. Typical missions begin with one or two burns to place the payload into a transfer orbit, followed by a circularisation burn and, if required, a third burn for de-orbit. Flight time from liftoff to payload separation can range from 45 minutes for LEO missions to 9 hours for GTO missions.

### Variants
- **Fregat**: baseline version with baseline propellant load
- **Fregat-M**: stretched tanks; ~1 t additional propellant
- **Fregat-MT**: adds external toroidal tank; total propellant ~3 t
- **Fregat-SB**: combines internal stretch and jettisonable external tank for heaviest payloads

### Legacy
Fregat traces its heritage to the propulsion module developed for the 1988 Phobos missions. After Mars-96 required a high-energy stage, NPO Lavochkin adapted the design into a commercial upper stage, first flown on 12 February 2000 with a Soyuz-U/Fregat carrying the IRDT demonstrator. Since then Fregat has supported payloads for OneWeb, ESA, Roscosmos, and the European Commission’s Galileo programme.

## Schema Markup
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## References

1. [Source](https://www.russianspaceweb.com/fregat.html)
2. [Source](https://space.skyrocket.de/doc_stage/fregat.htm)
3. Freebase Data Dumps. 2013
4. BabelNet