# Fregat-M > model of Russian rocket upper stage **Wikidata**: [Q122974868](https://www.wikidata.org/wiki/Q122974868) **Source**: https://4ort.xyz/entity/fregat-m ## Summary Fregat-M is a model of Russian rocket upper stage developed by NPO Lavochkin, functioning as a variant within the broader Fregat family of space tugs. It is distinguished from the baseline model by the inclusion of stretched tanks, which allow it to carry approximately 1 tonne of additional propellant to support higher-energy missions. Like other Fregat modules, it is designed to operate autonomously to inject payloads into precise orbits using a restartable main engine. ## Key Facts * **Classification**: Model of Russian rocket upper stage (Space tug). * **Parent Family**: Fregat. * **Developer & Manufacturer**: NPO Lavochkin (Russia). * **Distinguishing Feature**: Stretched tanks providing ~1 tonne of additional propellant compared to the baseline Fregat. * **Main Engine**: S5.92 (1 unit), developed by the Kosberg Bureau. * **Engine Thrust**: 19.6 kN (vacuum). * **Specific Impulse**: 327 s. * **Propellants**: Unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (main engine); Hydrazine (reaction control). * **Attitude Control**: 12 × hydrazine-fuelled thrusters (50 N each). * **Dimensions (Parent Class)**: 1.55 metres in height and 3.35 metres in diameter. * **Mass (Parent Class)**: 980 kg (dry weight); 6,580 kg (launch weight). * **Operational Range**: Capable of flight durations ranging from 45 minutes to 9 hours depending on the mission profile (LEO to GTO). ## FAQs ### How does the Fregat-M differ from the baseline Fregat and other variants? The Fregat-M is an upgraded version of the baseline Fregat featuring stretched tanks that hold approximately 1 tonne of additional propellant for higher-energy missions. In comparison, the Fregat-MT adds a toroidal tank for even greater capacity (~3 t total additional), while the Fregat-SB utilizes a jettisonable external tank for the heaviest payloads. ### What launch vehicles is the Fregat-M compatible with? Fregat upper stages, including the Fregat-M, are routinely flown atop Russian Soyuz rockets and European Soyuz-ST launch vehicles in export configurations. They serve as the final, restartable stage responsible for injecting payloads into precise orbits. ### What propulsion capabilities does the Fregat-M possess? The stage is powered by a single S5.92 main engine which burns UDMH and nitrogen tetroxide in a gas-generator cycle. It is restartable multiple times, allowing for complex multi-satellite deployments, and utilizes 12 hydrazine-fuelled thrusters for three-axis control during coast phases. ## Why It Matters The Fregat-M represents a critical enhancement to Russia’s primary space tug capability, bridging the gap between the lift capacity of medium-class launch vehicles and the specific energy requirements of modern satellites. By carrying approximately 1 tonne of additional propellant, the Fregat-M enables "higher-energy missions" that the baseline model cannot support as efficiently. This variant allows for direct-injection deliveries to geostationary orbit and high-energy escape trajectories for lunar and planetary missions without requiring the satellite to expend its own fuel for apogee burns. This capability reduces mission risk and cost for commercial customers (such as OneWeb and Galileo) and scientific agencies, effectively extending the operational utility of the Soyuz launch vehicle family. ## Notable For * **Enhanced Capacity**: Being the specific Fregat variant identified as carrying "additional propellant" via stretched tanks for higher-energy requirements. * **Heritage**: Tracing its lineage to the propulsion module developed for the 1988 Phobos missions and adapted for the Mars-96 high-energy stage. * **Modularity**: Utilizing a tank design that allows propellant load to be tailored, spanning payload capacities from 1 t to 3 t depending on the mission profile. * **Commercial Integration**: Serving as part of a Russian propulsion system integrated into Western launch campaigns via the Soyuz-ST exports. * **Reliability**: Belonging to a family (Fregat) with a reliability record above 95% and over 60 successful missions since 2000. ## Body ### Design and Development The Fregat-M is a product of **NPO Lavochkin**, the Russian developer and manufacturer of the Fregat upper stage family. It is subclassed under the general Fregat rocket model. The design 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, while the entire assembly is enclosed in a thermal-protection shroud. The Fregat-M specifically improves upon the baseline design through the use of **stretched tanks**, which provide approximately **1 tonne of additional propellant**. This structural modification allows the stage to support missions requiring greater delta-v than the standard configuration. ### Propulsion System The stage is powered by a single **S5.92 main engine** developed by the Kosberg Bureau. * **Cycle**: Gas-generator. * **Propellants**: Unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide. * **Performance**: Vacuum thrust is rated at **19.6 kN** with a specific impulse of **327 s**. * **Restart Capability**: The engine is restartable multiple times (mission-specific), allowing for complex orbital maneuvers. Three-axis control and propellant settling prior to main-engine restarts are managed by **12 hydrazine-fuelled reaction-control thrusters**, each providing 50 N of thrust. ### Operational Profile Once separated from the launch vehicle, the Fregat-M operates autonomously. A typical mission profile involves one or two burns to reach a transfer orbit, followed by a circularization burn. If required, a third burn may be executed for de-orbit. Flight times can range from **45 minutes** for Low Earth Orbit (LEO) missions to **9 hours** for Geostationary Transfer Orbit (GTO) missions. ### Context within the Fregat Family The Fregat-M sits between the baseline Fregat and the Fregat-MT/SB variants in terms of capability: * **Fregat**: Baseline version with standard propellant load. * **Fregat-M**: Stretched tanks; ~1 t additional propellant. * **Fregat-MT**: Adds an external toroidal tank; total propellant increased by ~3 t. * **Fregat-SB**: Combines internal stretch with a jettisonable external tank. The family is routinely flown atop **Soyuz** and **Soyuz-ST** (export) launch vehicles, supporting major programs such as **OneWeb**, **ESA**, **Roscosmos**, and the European Commission’s **Galileo programme**. The Fregat family legacy began with the propulsion module for the 1988 Phobos missions, with the first commercial upper stage flight occurring on February 12, 2000. ## References 1. [Source](https://www.russianspaceweb.com/fregat.html) 2. [Source](https://space.skyrocket.de/doc_stage/fregat.htm) 3. [Source](http://www.laspace.ru/rus/fregat_construction.php)