The second stage of Proton rocket

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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

stage2

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 8D84-00 solid-propellant motors firing against the direction of the flight at T+327.2 seconds (on the Proton-M variant). 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

APPENDIX

Technical specifications of the second stage of the original Proton-K rocket:

Dry mass	11,730 kilograms
Fueled mass	236,590 kilograms
Liftoff mass	236,400 kilograms
Oxidizer mass	112,230 kilograms
Fuel mass	43,280 kilograms
The end mass	82,780 kilograms
Liftoff to end mass ratio	2.86
Propulsion system thrust to liftoff mass ratio	0.99
Burn time	213.3 seconds

Technical specifications of the second stage of the original UR-500, Proton-K and Proton-M rockets:

-	UR-500	Proton-K	Proton-M
Diameter	4.1 meters	4.1 meters	4.1 meters
A total length of the second stage	14.56 meters	17.5 meters	17.5 meters
Propulsion system	Four RD-0208/0209	Four RD-0210/0211	-
A total thrust of the second stage in vacuum	- meganewtons	2.3 meganewtons	2.4 meganewtons
A total dry mass of the second stage	12,100 kilograms	11,715 kilograms	11,400 kilograms
A total mass of propellant in the second stage	- kilograms	156,113 kilograms	157,300 kilograms
Separation time	T+210-230 seconds*	T+327.3 - 331.3 seconds*	T+- seconds*
Separation speed	?	4,399.0 meters per second*	4,380.8 meters per second
Separation altitude	?	121.7 kilometers*	126.4 kilometers*

*Varies depending on a particular mission

Page author: Anatoly Zak;

Last update: May 31, 2019

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Engines

A second stage of the proton rocket during its assembly in Moscow. Credit: GKNPTs Khrunichev

Stage 2

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

stage