The first stage of the Proton rocket

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Proton's first stage: this is all one thing!

The design of the first stage had forever defined Proton's unique architecture. No other launch vehicle before or after it had the same design and when this architecture started emerging from behind the Iron Curtain, it became a great source of mystery and confusion.

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front

Designated 8S810KM, the first stage of the Proton-M rocket is comprised of a central (core) oxidizer tank, surrounded by six strap-on fuel tanks. Each of stage's six engines are attached to the one of the strap-on tanks, however the entire cluster of tanks remains connected during the flight. Sectioning of the first stage was dictated by the transportation restrictions, not by flight dynamics. The core tank of the stage has a diameter of 4.1 meters, which is an absolute maximum still allowing its delivery by rail.

The first stage is connected to the second stage with a lattice structure manufactured from the aluminum alloy V95. It is designed to let exhaust gas from the engines on the second stage to escape as they fire shortly before the separation of two stages around two minutes after liftoff.

With the introduction of the Proton-M version of the rocket in 2001, the first stage was slightly lightened thanks to improved manufacturing techniques and the reduction in the mass of onboard avionics. In addition, RD-253 engines used on the first stage had been upgraded and, from 1993, they were designated RD-275. Yet another upgrade of the engine became known as RD-276.

Another upgrade on the first stage involved its propellant feed system. It was simplified and redesigned in order to reduce by as much as 50 percent the amount of propellant remaining inside the stage by the time it finishes firing close to two minutes into the flight. A special propellant purge system was added to dump all residuals from the spent first and second stages before they fall back to earth. Although the main purpose of this change was to reduce controversial spills of toxic propellants at the impact sites downrange from Baikonur, the rocket's performance was also improved as a result.

Proton

The core tank of Proton's first stage (left) before the installation of strapon tanks (right). Credit: GKNPTs Khrunichev

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

Dry mass	34,000 kilograms
Fueled mass	685,280 kilograms
Liftoff mass	683,680 kilograms
Oxidizer mass	300,870 kilograms
Fuel mass	113,710 kilograms
The end mass	280,110 kilograms
Liftoff to end mass ratio	2.44
Propulsion system thrust to liftoff mass ratio	1.33
Burn time	126.6 seconds

Technical specifications of the first stage of the Proton-K and Proton-M rocket:

-	Proton-K	Proton-M
Maximum diameter (a cluster of core and strap-on tanks)	7.4 meters	7.4 meters
Diameter of core (oxidizer) tank	4.1 meters	4.1 meters
Diameter of strap-on fuel tanks (each of six)	1.6 meters	1.6 meters
A total length of the first stage	20.2 meters	21.18 meters
Propulsion system	Six RD-253, later RD-275 engines	Six RD-275/276 engines
A total thrust of the first stage at sea level (all six engines combined)	9.5 meganewtons	10.0 meganewtons
A total dry mass of the first stage	approximately 31,000 kilograms	approximately 30,600 kilograms
A total mass of propellant in the first stage	approximately 419,410 kilograms	?
Separation time	T+126.7 seconds*	T+119.7 - 123.3 seconds*
Separation speed	1,649 meters per second*	1,680.4 - 1,796 meters per second
Separation altitude	43.5 kilometers*	42.4 - 42.48 kilometers*
Latitude of impact location	-	47 degrees 18 minutes 23 seconds North
Longitude of impact location	-	66 degrees 33 minutes 27 seconds East
Distance of impact location from the launch site	-	306 kilometers

*Varies depending on a particular mission

Next chapter: RD-253 / RD-275 engine

Page author: Anatoly Zak

Last update: April 3, 2023

The first stage of the Proton rocket during the assembly. Credit: GKNPTs Khrunichev

Stage 1

A launch pad view of Proton's first stage. Credit: GKNPTs Khrunichev

separation

Separation of the Proton's first stage during the launch of the Eutelsat-9B satellite as seen by ground cameras. Credit: ILS

stage1

First stage of the Proton rocket separates during the launch of Elektro-L No. 4 satellite in 2023.