The URM-2 rocket module for the Angara family
The second stage of the Angara launch vehicle is known as URM-2, which stands for Universal (or common) Rocket Module No. 2.
Cutaway view of the URM-2 rocket stage configured for the first launch of the Angara rocket. Copyright © 2014 Anatoly Zak
Angara owes its unusual appearance to the URM-2 upper stage whose diameter of 3.6 meters makes it wider than the 2.9-meter first-stage booster below it. Like the first stage, the URM-2 uses liquid oxygen oxidizer and kerosene fuel. However, on the URM-2, the kerosene tank is installed in the upper position, with the liquid oxygen tank below it. The stage is powered by the four-chamber RD-0124A engine, adapted from the third stage of the Soyuz-2 rocket.
The aft bulkhead of the oxidizer tank also carries spherical vessels containing pressurization gas. Front bulkheads have access hatches and drainage valves. Because oxidizer tank contains cryogenic liquid oxygen, both of its bulkheads are covered with thermal blankets to reduce heating.
All electric connections, fueling and thermal conditioning of the URM-2 stage on the launch pad is accomplished via quick-disconnect umbilicals, BRS, of the stationary service tower.
In the course of development, there was also an alternative proposal to use a pair of one-chamber RD-0125A engines with a total thrust of 59 tons on URM-2. The new engine would lower the cost of the stage and increase its payload, but it had never been developed.
According to the original plans, the URM-2 stage was supposed to be used on both types of the Angara launch vehicles approved for development -- the Angara-1 and the Angara-5. Ultimately, the decision was made to develop a custom-built upper stage for the Angara-1 and use the URM-2 on the Angara-5 only. (The Angara-3, if ever built, could also use URM-2.) Still, during the first inaugural launch of the new rocket family, the URM-2 stage flew as the second stage of the first Angara-1 rocket. It was not intended to reach orbit, but was programmed to fire its RD-0124A engine, testing flight performance of the entire stage. As a result, by the time the Angara-5 rocket is ready to fly, the flight-tested URM-2 would be ready to serve as the third stage.
Still, a live firing of a fully integrated URM-2 stage was planned at the RKTs test center as late as 2019.
Known specifications of the URM-2 module:
URM-2 mass specifications:
A prototype of Angara's upper stage known as the A5A2S article No. A13 is being towed to a test stand at the Remmash facility at the NITs RKP test center in Peresvet for endurance tests in cryogenic environment in the fall of 2012. Credit: GKNPTs Khrunichev
Tanks for the URM-2 booster during production in Omsk. Credit: PO Polyot
Assembly of the URM-2 rocket module for the Angara-5 rocket. Its fuel tank can be seen on the background on the left. Credit: GKNPTs Khrunichev
Propulsion system and oxidizer tank of the URM-2 stage.
A prototype of the URM-2 module for the Angara-1.2PP rocket in Plesetsk in July 2012. Credit: Zvezda TV channel
Final processing of the URM-2 booster for the Angara-1.2PP rocket in Plesetsk. Credit: Rossiya TV channel