# Fregat-SB

> model of Russian rocket upper stage

**Wikidata**: [Q122974979](https://www.wikidata.org/wiki/Q122974979)  
**Source**: https://4ort.xyz/entity/fregat-sb

## Summary
Fregat-SB is a variant of the Russian Fregat upper-stage family, designed for the heaviest payloads by incorporating an additional toroidal tank and a jettisonable external tank. Developed and manufactured by NPO Lavochkin, it extends the Fregat family's capability to manage high-energy missions beyond other variants.

## Key Facts
- **Developer & Manufacturer**: NPO Lavochkin (Russia)
- **Country of Origin**: Russia
- **Variant Classification**: Part of the Fregat family; subclass of rocket upper stages
- **Distinguishing Feature**: Incorporates an additional toroidal tank and a jettisonable external tank for heaviest payloads
- **Main Engine**: S5.92 (1 unit), powered by unsymmetrical dimethylhydrazine (UDMH)
- **Reaction-Control Thrusters**: 12 × hydrazine thrusters
- **Propellants**: UDMH for main engine; hydrazine for attitude control
- **Rocket Family Members**: Fregat, Fregat-M, Fregat-MT, Fregat-SB
- **Wikipedia Sitelinks**: 19 language editions (shared with Fregat family)

## FAQs
### Q: What makes Fregat-SB unique among Fregat variants?
A: Fregat-SB integrates both an additional toroidal tank and a jettisonable external tank, enabling it to handle the heaviest payloads within the Fregat family, surpassing the capacity of Fregat-M and Fregat-MT.

### Q: How does Fregat-SB differ from Fregat-MT?
A: While Fregat-MT adds an external toroidal tank for ~3 tons of propellant, Fregat-SB combines this internal stretch with a jettisonable external tank specifically for maximum payload capacity missions.

### Q: Which launch vehicles utilize Fregat-SB stages?
A: Like other Fregat variants, Fregat-SB is compatible with Russian Soyuz and European Soyuz-ST launch vehicles, serving as the restartable final stage for payload delivery.

### Q: What specific mission profiles benefit from Fregat-SB?
A: Fregat-SB excels in high-energy missions requiring heavy payloads, such as direct injections to geostationary orbit or interplanetary trajectories, where its jettisonable tank optimizes efficiency.

## Why It Matters
Fregat-SB addresses a critical gap in launch vehicle capabilities by enabling heavy payloads to achieve complex orbits without requiring prohibitively large boosters. Its combination of internal stretch and jettisonable external tank provides unmatched flexibility within the Fregat family, reducing mission costs for scientific agencies and commercial operators. This capability directly supports ambitious programs like OneWeb constellation deployment and deep-space missions by maximizing the usable delta-v delivered to payloads, effectively extending the utility of medium-class launch vehicles.

## Notable For
- Only Fregat variant equipped with both an additional toroidal tank and jettisonable external tank
- Designed to carry the heaviest payloads in the Fregat family, though exact mass capacity is unspecified in sources
- Distinguished by its dual-tank configuration that optimizes propellant management for extreme mission profiles
- Critical for missions requiring multiple burns and high energy, such as planetary probes and heavy satellite deployments
- Maintains Fregat family core capabilities: autonomous guidance, multiple S5.92 engine restarts, and triple-axis control via 12 hydrazine thrusters

## Body
### Design Overview
Fregat-SB follows the modular Fregat architecture, comprising six spherical or toroidal aluminium alloy tanks arranged around a central structural truss. It incorporates an additional toroidal tank and a jettisonable external tank specifically to maximize propellant load. An integrated avionics bay houses the guidance computer, inertial measurement unit, and telemetry system, enclosed in a thermal-protection shroud. This design extends the baseline Fregat structure while retaining the central core.

### Propulsion System
The propulsion system mirrors other Fregat variants: a single S5.92 main engine burning UDMH and nitrogen tetroxide, generating 19.6 kN vacuum thrust with 327 s specific impulse. Twelve 50-N hydrazine thrusters provide three-axis control during coast phases and propellant settling. Fregat-SB's additional tank capacity increases total propellant mass to accommodate heavier payloads, though exact figures are not specified in sources.

### Operational Use
Fregat-SB operates autonomously post-separation from the launch vehicle, executing multiple burns for payload delivery. Typical missions include transfer orbit insertion, circularization, and escape burns. Its jettisonable external tank is deployed after additional propellant depletion to reduce dead weight, enhancing efficiency. Flight duration ranges from 45 minutes (LEO) to 9 hours (GTO), aligning with other Fregat variants despite increased propellant mass.

### Variants
- **Fregat**: Baseline version with standard propellant load
- **Fregat-M**: Stretched tanks; ~1 ton additional propellant
- **Fregat-MT**: Adds external toroidal tank; total propellant ~3 tons
- **Fregat-SB**: Combines internal stretch and jettisonable external tank for heaviest payloads, incorporating the design principles of both Fregat-M and Fregat-MT

### Heritage and Deployment
Fregat-SB traces its lineage to the Fregat family's 2000 inaugural launch (Soyuz-U/Fregat carrying IRDT). It continues the legacy of the Phobos-mission-derived propulsion module. Fregat-SB supports commercial and institutional clients including ESA, Roscosmos, and the European Commission. Its jettisonable tank design represents the pinnacle of Fregat family optimization for heavy payloads, though deployment frequency is unspecified in sources.

## 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-/)