Medium variant to expand Proton family

The Proton-Medium would be the first of the two new variants aimed at expanding the capability of Russia's commercial workhorse toward a lighter payload range.

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Key design features of the Proton-Medium launcher.

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Proton Medium concept

GKNPTs Khrunichev, the prime developer of the Proton rocket, officially unveiled the Proton-Medium architecture on Sept. 13, 2016. The modifications centered around the removal of the second stage from the standard Proton-M configuration. To compensate for the absence of the second-stage booster, the first stage of the rocket, including its core tank and six strap-on tanks would be stretched to accommodate 35 tons of extra propellant. At the same time, the former third stage of the standard Proton would be also stretched to play the role of the second stage in the Proton-Medium. This modified stage would be able to carry 22 tons of additional propellant.

A new interstage adapter will have to be developed to serve as an interface between the first and the second stage. The new structure will have openings to enable the ignition of four vernier thrusters of the RD-0214 steering engine, shortly before the separation of the first stage. At separation, solid motors mounted on the exterior of the adapter will fire against the direction of the flight to ensure clean jettisoning of the first stage along with the adapter.

Using the standard Briz-M space tug as its third stage, the Proton-Medium could deliver from 5.0 to 5.7 tons to the geostationary transfer orbit, GTO, on the condition that the satellite would use its own propulsion system to add from 1,500 to 1,800 meters per second in velocity. The same rocket will also be able to insert 2.4 tons of payload directly into the proper geostationary orbit, GSO, without additional maneuvers.

Development schedule

According to plans announced in September 2016, the design of the Proton-Medium rocket will be under review for the rest of the year, anticipating the full-scale development during 2017. The production of first components for the rocket was penciled for the middle of the same year. If the developer can sustain this very optimistic schedule, Proton-Medium will be ready for the first flight in the fourth quarter of 2018.

The rocket will be launched from Baikonur's Pad 24 at Site 81, which will likely need its own upgrades to accommodate boosters with different dimensions. It is not immediately clear whether existing railway trailers for transporting components of the Proton rocket to Baikonur could be easily modified to fit longer propellant tanks of the first stage.

If ever built, the Proton-Medium might remain operational until at least the mid-2020s, when it could be replaced by a new-generation launcher, such as Sunkar or Angara-3. Given current uncertainty around the production rate and the capabilities of the Angara, all new members of the Proton family should be available to operate for as long as necessary to provide smooth transition between the two generations of rockets and to enable the Russian rocket fleet to stay competitive on the international commercial market.

Proton-Medium gets its first customer

On October 12, 2016, just a month after the design of the Proton-Medium had been unveiled, the International Launch Services, ILS, announced an agreement with the European communications consortium Eutelsat to "baseline" its unidentified payload with the Proton-Medium variant launching in 2019 or 2020. The deal was a part of a wider multi-launch agreement between the two companies, which was made public in October of 2015.

(To be continued)

Official payload capabilities of the Proton-Medium variant as of 2016:

Geostationary orbit, GSO
2.4 tons
Geostationary orbit, GTO with delta V of 1,500 meters per second provided by a payload
5.0 tons
Geostationary orbit, GTO with delta V of 1,800 meters per second provided by a payload
5.7 tons


Next chapter: Proton-M-Plus


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The article and illustrations by Anatoly Zak; Last update: October 12, 2016

Page editor: Alain Chabot; Last edit: September 19, 2016

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Both, core and strap-on tanks of the Proton's first stage, would have to be stretched in order to build Proton-Medium and Proton-Light rockets. Click to enlarge. Credit: Roskosmos


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