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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, view 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 would end its firing five and a half minutes after liftoff and separate in the stratosphere at an altitude of more than 120 kilometers, with the help of six small solid-propellant motors firing in the direction of the flight. Its total burn time normally lasts around three and a half minutes.
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: October 30, 2016
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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
A scale model of the RD-0210 engine. Click to enlarge. Copyright © 2008 Anatoly Zak