Russia charts new path to super rocket
After essentially losing the venerable Zenit rocket to the conflict with Ukraine in 2014, the Russian space industry began gearing up for building a replacement launcher. In addition to carrying commercial satellites, the new booster was conceived as a stepping stone toward a super-heavy rocket, even if decades after the Zenit was available for the same role in the Energia and Sodruzhestvo projects.
The Sunkar launcher concept.
The loss of Zenit left a gap in the payload range of the Russian rocket fleet, in particular its ability to deliver mid-size communications satellites with a mass of under five tons into the geostationary transfer orbit, GTO. The death of Zenit also further stalled a decade-long Russian-Kazakh venture known as Baiterek, aiming to bring a new-generation commercial launcher to the Baikonur Cosmodrome.
On January 26-27, 2016, representatives of Roskosmos met with their Kazakh counterparts to discuss the fate of the Baiterek project and directed the industry to consider various alternatives to Zenit. By the middle of the year, the industry came up with a concept dubbed Sunkar, or "falcon" in Kazakh.
At the heart of the new design was the idea to enlarge the diameter of the Zenit rocket from 3.9 to 4.1 meters, so it could match the "caliber" of the Proton rocket. As a result, the Proton's production machinery could be re-used with relatively few upgrades to manufacture the new-generation launcher, after its predecessor's planned retirement in mid-2020s.
Unlike Proton, all stages on Sunkar would burn non-toxic kerosene and liquid oxygen, as it had long been insisted upon by the Kazakh government.
The Sunkar could utilize the existing launch and processing infrastructure for the Zenit rocket in Baikonur, which could be funded by Kazakhstan. According to the Izvestiya daily, by September 2016, Roskosmos made plans to transfer the launch facility under control of the Kazakh company Baiterek in 2020.
In the commercial launch market, the Sunkar should replace the yet-to-be-built Proton-Light variant, delivering mid-size satellites, while Angara-5 would take over duties of the Proton-M version carrying the heaviest payloads.
Ironically, the proposal to develop yet another type of space launcher essentially reverses the previous strategy at GKNPTs Khrunichev of relying on a modular architecture of the Angara family to cover the entire spectrum of space payloads. However, unlike Angara's standard booster, URM-1, the first stage of the Sunkar rocket will be large enough to serve as a building block for a future super-heavy rocket, reaching payloads of at least 80 tons, so it could serve as the main vehicle for the deep-space exploration program. Therefore, the Sunkar proposal can be considered as the first step in building a more powerful family of space rockets in Russia.
Both stages of the Sunkar rocket were to feature a diameter of 4.1 meters, allowing their shipment to Baikonur by rail. However that economic method of delivery would not be an option for the new Russian launch site in Vostochny due to various bottlenecks at tunnels and bridges.
The first stage of the Sunkar booster was to be propelled by a modified four-chamber RD-171 engine, inherited from Zenit and generating a thrust of around 740 tons at sea level. Alternatively, a pair of two-chamber RD-180 engines could be employed to generate an equal amount of thrust. At the MAKS-2017 air show, Chief Designer at NPO Energomash Petr Levochkin announced that the rocket could also be equipped with a new engine developing thrust of 1,000 tons. It would differ from RD-171 by the in-line placement of pumps (for fuel and oxidizer) and parallel arrangement of turbines, which according to Levochkin would reduce loads on the turbopump.
The first stage was to be equipped with an aft section with a diameter of 3.68 meters, matching the dimensions of the Zenit rocket and housing the similar propulsion system, in order to make the Sunkar compatible with the most of Zenit's ground infrastructure.
The second stage of the Sunkar launch vehicle was to be propelled by a pair of modified four-chamber RD-0124A engines, renamed RD-0124M or RD-0124AP, which would be inherited from the URM-2 booster in the Angara family. Although this newly improvised propulsion system wielding eight combustion chambers is not an example of simplicity, it allows to keep the length of the second stage to an absolute minimum, while still providing an unmatched efficiency. Not to mention, the RD-0124 engine is already available and was thoroughly flight tested on the Soyuz-2-1b and Angara rockets.
In preparation for the manufacturing of both RD-171MV and RD-0124M engines, NPO Energomash in Moscow announced in June 2017 a major renovation of its production facilities at a price tag of nearly seven billion rubles and lasting until the end of 2019.
Unfortunately, the new rocket could not take advantage of Angara's URM-2 stage itself, because it would be too small for a vehicle of that size.
The existing variant of the Block-D space tug, such as Block DM-03, which employs the same propellant as the lower booster stages, is expected to serve as the third stage on the Sunkar booster. It will have the task of completing the orbital insertion into the initial parking orbit and then pushing its cargo to the geostationary transfer orbit or to the proper geostationary orbit.
Chances for implementation
The development of the Sunkar rocket could be folded into the Feniks project, which was to be funded within the Russian Federal Space Program extending from 2016 to 2025 and aimed at developing a new-generation rocket to replace the Soyuz family. Another contender for federal funds within the Feniks program was the Soyuz-5 proposal from RKTs Progress, which builds all Soyuz rockets. However after the conflict with Ukraine had began in 2014, the Feniks was steered toward building an equivalent of the Zenit rocket inside Russia.
The authors of the Sunkar proposal believed that if approved in the near future, the new rocket could be ready for launch from an upgraded launch facility at Site 45 at the beginning of 2024 and start commercial missions from Baikonur a year and a half later, right around the time of the Proton's retirement.
The manufacturing of the rocket could be distributed between various industrial centers in Russia, with RKTs Progress in Samara likely taking the leading role, possibly relying on available manufacturing base inherited from the Energia program.
Also during 2017, NPO Lavochkin proposed heavy versions of the Fregat upper stage for the Soyuz-5 rocket, which would enable it to fully replace the Proton in missions to the geostationary orbit. The upgraded Fregat could carry from 14 to 17 tons of propellant delivering from 3,600 to 3,800 kilograms to the geostationary orbit or 6,400 kilograms to the geostationary transfer orbit.
Sunkar/Soyuz gets a role in human space flight
In April 2017, head of RKK Energia Vladimir Solntsev told the official TASS news agency that the of the Sunkar rocket would be preferable launch vehicle for the PTK Federatsiya new-generation spacecraft to the Angara-5P rocket due to a lower cost of the former vehicle.
On August 11, 2017, RKK Energia officially confirmed that it had been working on the preliminary design of the Soyuz-5 launch vehicle (formerly Sunkar) including its man-rated version in cooperation with RKTs Progress and the TsENKI launch infrastructure organization, among other subcontractors.
Known specifications of the Sunkar launch vehicle as compared to the Zenit:
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Zenit (left) and Sunkar launchers shown to the same scale. Copyright © 2016 Anatoly Zak
Alternatively, two RD-180 engines could be used to propel the first stage of Sunkar. Click to enlarge. Copyright © 2013 Anatoly Zak
A possible depiction of the RD-171MV engine.