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Proton's second stage
The second stage of the Proton rocket has a traditional shape of a cylinder. After four test launches of Proton's original version in 1965 and 1966, the second stage was stretched and it has kept its new dimensions ever since.
Previous chapter: Stage I of the Proton rocket
Proton's second stage as seen from the front.
In first four missions of the Proton rocket, its second stage was equipped with three RD-0208 engines and one RD-0209 engine, all suspended in a special gymbal system designed to steer the rocket in flight. However beginning in 1967, Proton-K's second stage was upgraded to RD-0210 and RD-0211 engines, respectively.
Over the years, modifications to Proton second stage, currently designated 8S811KM, included structural reinforcement of the forward portion of the stage, in order to carry greater payload and to withstand higher aerodynamic loads. Minor structural weight reductions were also implemented.
During a typical mission of the Proton-K rocket, the second stage ignited slightly more than two minutes after launch, while still connected to the first stage. The separation between the first and second stage takes place around four seconds later with the help of 20 pyro-bolts.
The second stage ends its firing five and a half minutes after liftoff and separates in the stratosphere at an altitude of more than 120 kilometers, with the help of six small solid-propellant motors thrusting against the direction of the flight. The total burn time of the second stage normally lasts around three and a half minutes.
Following the separation and the ballistic descent, the second-stage booster falls at the impact site No. 310 on the border between Eastern Kazakhstan and the Altai Republic in Southern Russia, some 1,620 kilometers from its launch site.
Next chapter: Stage III of the Proton rocket
Technical specifications of the second stage of the original Proton-K rocket:
Technical specifications of the second stage of the original UR-500, Proton-K and Proton-M rockets:
*Varies depending on a particular mission
Read much more about the history of the Russian space program in a richly illustrated, large-format glossy edition:
Page author: Anatoly Zak;
Last update: March 14, 2017
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A second stage of the proton rocket during its assembly in Moscow. Credit: GKNPTs Khrunichev
The second stage of the Proton rocket on its railway trailer in Baikonur. Credit: GKNPTs Khrunichev
Front section of the second stage serving as an interface with the third stage. Click to enlarge. Credit: Roskosmos
A scale model of the RD-0210 engine. Click to enlarge. Copyright © 2008 Anatoly Zak