|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.
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.
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.
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 would fly 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.
Propulsion system and oxidizer tank of the URM-2 stage.
Known specifications of the URM-2 module:
URM-2 mass specifications:
*includes the 100-kilogram lower transfer ring.
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
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