Briz-M: Russia's workhorse space tug

First introduced in 1999, the Briz-M space tug replaced the veteran Block-D series as the fourth stage of Russia's workhorse Proton rocket in the 21st century. In 2016, Briz-M got its first opportunity to fly a deep-space mission aimed at sending the ExoMars-2016 spacecraft on a path to the Red Planet.

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General architecture of the Briz-M stage.

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Briz-M history

The Briz-M (breeze) stage derived from the smaller Briz-K and Briz-KM variants, which previously flew on the lightweight Rockot launcher. To match the capabilities of the larger Proton rockets, Briz-K was upgraded with a torus-shaped external propellant tank to form the 22.9-ton Briz-M under the industrial designation 14S43. In addition, all the avionics on the upgraded stage were re-designed to work in the vacuum of space, unlike the previous-generation systems on Briz-K, which required pressurized containers.

The full-scale development of the Briz-M started after its proposed design had been declared the winner in a tender which the Russian government conducted in 1993 and 1994 for the new upper stage of the Proton rocket. The project was funded by the Ministry of Defense for prospective military missions.

Moscow-based GKNPTs Khrunichev, which also built the Proton rocket, advertised such advantages of Briz-M as its very compact size and its capability to function in space for prolonged periods of time. Briz-M stood just 2.6 meters high, compared to the 6.5 meters of Proton's older upper stage Block D. As a result, the new stage would leave much more volume available for potential payloads onboard the launch vehicle. Briz-M's main engine was promised to be able to fire up to eight times during its mission, while the stage was to survive in orbit up to 24 hours. In combination with a cluster of smaller engines onboard, the stage could perform carefully choreographed maneuvers when delivering single or multiple payloads.

The design arm of GKNPTs Khrunichev -- KB Salyut -- completed the preliminary design for Briz-M in 1996. A year later, a set of blueprints for the first flight vehicle and for as many as 10 development prototypes of the stage was issued.

According to Khrunichev, the introduction of Briz-M would enable Proton to carry between 3.2 and 3.5 tons of payload directly into geostationary orbit (instead of previous 2.5 tons with Block D) or to deliver from 5.5 to more than 6 tons into geostationary transfer orbit. Proton/Briz-M combination could place around 15 tons into low Earth orbit, the company's documents said.

Briz-M was also designed to be compatible with the next-generation Angara family of launch vehicles including Angara-A3 and Angara-A5. During the 1990s, the stage was also proposed for the European Ariane-5 rocket, the Ukrainian-built Zenit and, even possibly, for the Russian Soyuz-2 launcher.

Briz-M's architecture

The Briz-M stage is composed of a central core and an auxiliary propellant tank. The external tank is depleted first during the flight, after which all its fuel and electric links to the core stage are severed with pyrotechnics, and springs push the empty tank away from the core stage along two guides. A special cone structure inside the external tank helps to distribute loads from the payload to the rest of the stage during the launch.

A special transfer ring with a diameter of 4.1 meters, also known as spacer, serves as an interface between the third stage of the Proton, its payload fairing and the external tank of Briz-M. The transfer ring remains on the third stage when it separates from Briz-M around nine minutes after launch.

Briz-M is powered by a pump-fed S5.98 main engine developed at the Isaev KB Khimmash design bureau in Korolev, Russia. Capable of producing around 20 kilonewtons of thrust, the engine has a special gimbal suspension system, which allows it to steer the vehicle in flight under commands from an onboard computer. To protect the engine from the harsh environment of space during prolonged periods of unpowered flight, its exposed nozzle is closed with a special movable thermal cover.

In addition, Briz-M is equipped with four 11D458M settling thrusters, which are used to give the stage an initial acceleration, in order to cause the propellants to shift toward the bottom and thus ensure that the main engine has an uninterrupted flow of propellant at the time of its ignition. The same engines can also be used to fine tune the maneuvers performed by the main engine. Finally, the stage also sports twelve 17D58E thrusters used for attitude control. All auxiliary thrusters are mounted in four clusters on the dome-shaped aft bulkhead of the core stage: one propellant settling thruster and three attitude-control thrusters in each cluster. The entire propulsion system burns a self-igniting mix of nitrogen tetroxide and unsymmetrical dimethyl hydrazine.

Along with the engines, the dome-shaped aft bulkhead of the core stage is used to attach a pair of tanks containing helium for pressurization of the propellant tanks, as well as some pneumatic and hydraulic hardware. Two other ball-shaped high-pressure tanks on the aft bulkhead are used to store propellant components for the ignition of the main engine and for feeding orientation and stabilization thrusters, SOiS. Other components for pneumatic and hydraulic systems are located inside the propellant tanks. The "waist" of the core stage is enveloped in the lines of the thermal control system. The external tank has four helium pressurization vessels of its own.

The Briz-M's flight control system includes an on-board computer, a three-axis gyro stabilized platform, and a navigation system. Most of the space tug's avionics and its power batteries are housed in the unpressurized equipment section at the top. A series of antennas for telemetry transmission, trajectory tracking, and satellite navigation extend from the core stage.

A cone-shaped adapter for the spacecraft is attached to the top of the equipment section via a 2.49-meter ring. The payload then can be attached to an adapter with a special release mechanism which is designed to gently separate the satellite at the conclusion of its orbital insertion.

Upgrades

In the course of its operational life, various components of the Briz-M underwent upgrades. Phase IV upgrade of the Proton-M rocket inaugurated in June 2016, also marked the introduction of the new Pirit-RBs multi-functional radio-telemetry system employing a modular architecture. According to AO RKS, which developed Pirit-RBs, its mass was reduced to eight kilograms, compared to the previous 14-kilogram version, while relying on domestically built avionics. The five-unit system also used pocket telemetry principles compatible with the international standard CCSDS. Pirit-RBs also has a unique capability to simultaneously downlink real-time data and pre-recorded telemetry stored in its memory, AO RKS said.

Phase IV also saw the removal of two high-pressure tanks from the instrument compartment.

As of 2020, a total of five variations of the Briz-M were known for the Proton rocket and three variants were being developed for the Angara family.

Briz-M space tug gets new fueling system

At the end of 2019, Roskosmos began testing new mobile fueling hardware for the low-pressure propellant tanks of the Briz-M upper stage.

Developed at the KBTKhM design bureau, the new fueling hardware was delivered to Baikonur Cosmodrome and deployed at Briz-M's outdoor fueling site near Proton's 92A-50 processing facility, along with a mockup of the Briz-M stage. According to Roskosmos, tests with loading and draining of fuel were conducted from November 25 to November 29, 2019, and similar tests with oxidizer were started on December 2. The entire test program was scheduled to be completed by January 24, 2020.

Roskosmos said the new weight-based method for propellant dosage used by the new equipment provided better reliability and safety of fueling operations, but the State Corporation did not explain the need for a mobile element in Briz-M preparations.

One industry source familiar with the subject told RussianSpaceWeb.com that the old fueling equipment for Briz-M had also had mobile vehicles, which would bring propellant tanks to the Briz fueling area from their main base at the KAZ propellant production facility in Baikonur. With the latest upgrade, the fueling team received heavy duty Volvo trucks and other equipment which replaced the fueling hardware exceeding its service life. At the time, GKNPTs Khrunichev reportedly considered an option of flying the Briz-M space tug on the Angara-5 rocket based in Vostochny, even though until recently Roskosmos had only planned to use the Block DM-03 upper stage with the variant of the vehicle launched from the rocket's future new pad, the source said. If plans for Briz-M in Vostochny were approved, the new fueling equipment could be re-deployed at the new spaceport after the retirement of the Proton.

According to Roskosmos, the new fueling equipment would be operationally used in Baikonur for the first time during the preparation of the Proton/Briz-M rocket slated to launch Ekspress-80 and Ekspress-103 communications satellites in the first quarter of 2020.

Known specifications of Briz-M stage:

Liftoff mass 22.5 - 22.9 tons Dry mass 2.39 - 2.665 tons Total propellant mass 19.8 - 19.92 tons Total oxidizer mass 13.26 tons Total fuel mass 6.66 tons Propellant mass in the core stage 5.2 tons Propellant mass in the external tank 14.6 tons Height 2.65 meters Diameter 4.0 meters Maximum number of engine firings during the mission up to 8 (5 during a typical mission) Maximum autonomous flight duration up to 24 hours according to original technical assignment* Propulsion system designation S5.98M (14D30) First launch 1999 June 5

Briz development team:

GKNPTs Khrunichev (Moscow) Prime contractor and system integrator KB Khimmash (Korolev) Propulsion system MOKB Mars Inertial flight control system NII KP (St. Petersburg) Gyroscopic stabilization platform AO Radiophisika and RNII KP Telemetry systems AO Savma Hardware

14D30 engine specifications:

Thrust in vacuum 2,000 kilograms (19.62 kN) Specific impulse 328 seconds A total firing duration 3,200 seconds Number of ignitions in flight 8 Dry mass 95 kilograms Dimensions 1,150 by 948 millimeters

Flight history

The Briz-M lifted off for the first time on June 5, 1999, but it never had a chance to fire during that mission due to the second-stage failure of its Proton-K rocket. The second attempt to test the stage was made on June 6, 2000, when the rocket successfully delivered the Gorizont-45 satellite into its planned orbit. On April 7, 2001, the Briz-M flew for the first time on the modified Proton-M rocket. Finally, at the end of 2002, the space tug was employed for the first time to deliver a commercial payload, which became its main job.

By mid 2000s, as its production expanded, Briz-M mainly replaced the Block DM upper stage on the Proton rocket. In 2008, KB Khimmash manufactured 10 engines for Briz.

By March 2016, Briz-M logged 91 flights, during which the stage failed or experienced serious technical problems seven times. This number includes seemingly anomalous performance of Briz-M during the first test launch of the Angara-5 rocket in December 2014, even though official Russian sources have not yet disclosed any problems during this flight.

Prior to the launch of the TGO orbiter and the Schiaparelli lander for the ExoMars-2016 mission in March 2016, Briz-M completed eight increasingly accurate satellite deliveries, demonstrating the maturity of its flight control and navigation systems.

A complete list of Briz-M missions: