The URM-1 rocket module for the Angara family
The first stage of the Angara launch vehicle is known as URM-1, which stands for the Universal (or common) Rocket Module.
The first-stage booster, URM-1, of the Angara family, configured for the inaugural flight of the Angara-1PP test vehicle.
The URM-1 standard module serves as the first-stage booster for all versions of the Angara family of space launchers. The Angara-1 would feature one URM-1, the Angara-3 would be made of three URMs and the Angara-5 would sport five URMs. Finally, the Angara-7, if ever approved for development, would feature six URM-1 boosters.
All URM-1 boosters are equipped with the RD-191 engine which burns relatively non-toxic kerosene as a fuel and cryogenically cooled liquid oxygen as an oxidizer. The liquid oxygen is stored in the top tank of the booster and kerosene is loaded in the tank below it. An intertank compartment (located between propellant tanks) contains flight control electronics, telemetry systems and power batteries.
The tail compartment houses the RD-191 main engine. The engine's suspension system enables to rotate it up to eight degrees in order to steer the rocket along the pitch and yaw axis. The roll of the vehicle can be controlled with two aerodynamic stabilizers and four thrusters, also installed in the tail of the rocket and propelled by the hot gas generated in the main engine.
The tail section also has an outlet with multiple interfaces for pneumatic and hydraulic lines coming from the launch pad. Four minutes before liftoff, a special movable arm of the service tower retracts from the rocket. At liftoff, as the rocket rises just 20 millimeters, pyrotechnics cut all pneumatic connections with ground equipment and the vehicle flies free.
During the flight, the central URM-1 module separates from the upper stage along with a top transfer section, which serves as an interface between two parts of the vehicle. Two small solid propellant motors attached to exterior of the transfer section fire against the direction of the flight pushing the empty URM-1 away from the upper stage.
Engineers at NII Parashutostroenia, Russia's main parachute development company, studied the possibility of soft landing of the URM-1 stages so they could be reused on subsequent flights, however, currently, there are no signs that the idea had been implemented.
After their free fall, URM-1 boosters would impact the ground around 2,860 kilometers from the launch site. (702) During Angara-5 missions to the geostationary orbit originating from Plesetsk, four URM-1 boosters fall within a 150 by 50-kilometer drop zone in the Vuktylsk District of Komi Republic.
The URM-1 core stage, probably for the third Angara-5 rocket, during assembly in Omsk
Known specifications of the URM-1 module:
Mass specifications of the URM-1 modules:
Aft (propulsion) section of the URM-1 stage for the Angara-1.2 rocket. Credit: GKNPTs Khrunichev
A fuel tank of the URM-1 module during the assembly. Credit: GKNPTs Khrunichev
The final assembly of the URM-1 booster for the first Angara mission. Credit: GKNPTs Khrunichev