THE RD-191 ENGINE

Another offshoot of the Energiya propulsion system is the RD-191, a single-chamber version of the RD-170/171 designed to power Russia’s new Angara family of launch vehicles.

Originally, Angara (named after a Siberian river) was conceived as a heavy launch vehicle to replace the Proton. Its history began with a government decree (nr. 716-53) issued on 15 September 1992 calling for the development of a launch vehicle capable of lifting 24 tons to low orbit and 3.5 tons to geostationary orbit from the Plesetsk cosmodrome in northern Russia. Proton could only fly from Baykonur in Kazakhstan, the future of which was uncertain after the collapse of the USSR. The new launch vehicle was to be built exclusively by Russian enterprises and make maximum use of Energiya-Zenit technology.

Responding to the decree, the Russian Space Agency and the Ministry of Defense, the two organizations that had ordered the vehicle, launched a tender between three design bureaus: NPO Energiya, the Khrunichev Center, and the Makeyev bureau, the latter having specialized for years in sea-launched inter­continental ballistic missiles. Rather than proposing separate projects, NPO Energiya and Makeyev joined forces in January 1994 to design a launch vehicle provisionally called Energiya-3. This had a first stage comprised of three modules each powered by an RD-180 engine, and a second stage with an RD-146 engine, a re-ignitable version of the Zenit second stage’s RD-120.

The Khrunichev vehicle had a first stage employing the RD-174, yet another modification of the RD-170/171, and a second stage using one of the Energiya core stage’s RD-0120 LOX/LH2 engines. Both the first and second stages had suspended propellant tanks, giving the rocket an odd external appearance. For geostationary missions the rocket would have used a LOX/LH2 upper stage. Other plans were to turn the first stage into a reusable flyback booster and eventually to launch the vehicle

Khrunichev’s original Angara configuration (source: Khrunichev).

from the Svobodnyy cosmodrome in the Russian Far East. Both proposed launch vehicles would have been able to fly from modified Zenit pads.

In September 1994 the Russian Space Agency and the Ministry of Defense selected Khrunichev as the winner of the competition, although development of the second stage was subcontracted to RKK Energiya. The decision was consolidated by another government decree on 26 August 1995, which set the maiden flight of Angara for 2005. However, during the following two years it became apparent that Khrunichev’s design was basically flawed. Among the problems were the rocket’s very low thrust-to-weight ratio (1.09) and the challenges associated with igniting the RD-0120 at altitude, not to mention the fact that the engine’s production line at KBKhA in Voronezh had been closed [74].

Another problem with Khrunichev’s design was that it was primarily geared to replacing the Proton and left little room for building derived launch vehicles. The best Khrunichev had come up with were two rockets called Yenisey and Neva. Yenisey basically was an Angara first stage topped by a Zenit second stage, giving an 18-ton capacity to low orbit, and a 2.5-ton capacity to geostationary orbit with a KVRB cryogenic upper stage. Neva was an all-cryogenic vehicle, using Angara’s second stage as its first stage and the KVRB as second stage, optimized to place 4.1-ton payloads into polar orbit [75]. However, the range of payloads that could be orbited by these boosters was minimal and, moreover, Neva required a dedicated launch pad.

All this was at a time when the Russians realized that they needed a replacement not only for Proton, but also for other venerable 1960s launch vehicles such as the Tsiklon and Kosmos-3M, whose production lines were expected to be closed. The problem could at least temporarily be solved by switching to converted ballistic missiles such as Rokot and Dnepr, declared excess in accordance with international disarmament agreements. However, under those agreements all redundant Russian ICBMs had to be destroyed by 2007.

In 1997 several Russian companies devised strategies to modernize the Russian rocket fleet, aiming to lower costs by relying on modular designs and allay environ­mental concerns by using ecologically clean propellants rather than the toxic storable propellants employed by the old ICBM-derived rockets. In many ways this was a return to the plans for standardized launch vehicles in the early 1970s that had given rise to the Energiya and Zenit families. Ironically, the Energiya family was now dead because of a lack of affordable payloads and the Zenit family had remained restricted to the 11K77 because its design bureau was now situated in independent Ukraine.

In RKK Energiya’s vision the light payload range (1-5 tons) would be covered by rockets known as Kvant and Diana, medium-size payloads (7-15 tons) would con­tinue to be launched by Soyuz-derived rockets and Zenit rockets, and heavy payloads (20-25 tons) would go up on RKK Energiya’s originally planned Angara version. For geostationary missions the Angara would carry a Blok-DM-SL upper stage of the Sea Launch program with an increased propellant load. The company also proposed to launch the same Angara vehicle from Baykonur’s UKSS pad under the name Sodruzhestvo (“Commonwealth”) with equal financial input from Russia, Kazakhstan, and Ukraine. The Kvant rocket would be redesigned to have a first stage with an RD-180 engine and a Blok-DM-SL second stage, thereby paving the way to Angara, much like Zenit had served as a pathfinder for Energiya. Other contenders were the Makeyev design bureau with a family of both land and sea-launched lightweight boosters (Riksha) burning liquid oxygen and methane, the Kompomash corporation, TsNIIMash, the Keldysh Center, and TsNII-50 [76].

Khrunichev also changed its strategy in accordance with the new requirements. In March 1997 the company scrapped plans for its original heavy-lift Angara and decided to turn Angara into a family of launch vehicles accommodating a broad range of payloads. The core element of the Angara family became a so-called Universal Rocket Module (URM) acting as the first stage. Powered by the RD-191, the URM could fly as a single unit or in clusters of three to six. Mounted above it would be one or two stages, depending on the mass of the payload. Propellant combinations considered for these upper stages were nitric acid/UDMH, LOX/kerosene, LOX/methane, and LOX/LH2. Khrunichev retained its earlier idea of turning the first stage into a reusable flyback booster, now called Baykal, in cooperation with NPO Molniya.

Baykal flyback booster (source: Timofey Prygichev).

The Khrunichev plan seems to have been given the nod in late 1997/early 1998 without much consideration for the other proposals, which was possibly a result of the fact that Khrunichev became subordinate to the Russian Space Agency in 1998. This sparked off angry reactions from RKK Energiya, whose Angara proposal had been turned down in 1994 largely on the basis of the fact that the RD-180 was an unflown engine. However, by now the RD-180 was undergoing successful (US-sponsored) test firings in support of the Atlas program, and it was the RD-191 that was the untested engine.

By late 1998 Khrunichev had more than 10 Angara configurations on the drawing boards, some looking more exotic than others. Payload capacity would have been between 2 to 4 tons to low orbit on the lower end of the payload scale, and between 13 and 24 tons on the heavier end of the payload spectrum, leaving the 7-10 ton niche to the Soyuz family. Geostationary orbit capability would have been between about 1 and 5 tons [77]. However, economic realities soon forced Khruni­chev to scale down its ambitions to just four rockets, two light versions (Angara 1.1 and 1.2) with a single URM and two heavier versions (Angara-A3 and Angara-A5) with three and five URM modules, respectively. Payload mass to low orbit for the first two rockets is 2.0 and 3.7 tons and 14.6 and 24.5 tons for the latter two.

Although the RD-191 is an unflown engine, the idea to build a single-chamber version of the RD-170/171 is not at all new. In the late 1970s/early 1980s Energomash had already done detailed design work on such an engine (the MD-185) for the

first stage of Zenit and Energiya’s strap-ons to safeguard against problems with the RD-170/171 (see Chapter 6). A similar engine (the RD-141) had been considered for the second stage of the 11K37. The RD-191 delivers 196 tons of thrust at sea level and has a specific impulse of 310 s. It features a new turbopump unit driven by a single gas generator and a new system of mixture ratio control. Control of the thrust vector is provided through gimbaling of the engine about two axes.

On 31 December 1998 Khrunichev signed a deal with Energomash for the design, manufacture, and delivery of RD-191 engines for the Angara family. Mock-up versions of the engine were built for full-scale models of Angara 1.1 and

The RD-191 engine (source: NPO Energomash).

the Baykal flyback booster shown at the Paris Air Show in 1999 and 2001, respec­tively. The RD-191 test-firing program began with a short 5 s test at Energomash’s Khimki facilities on 27 July 2001. About 70 test firings are required to certify the engine for flight [78].

Launch dates for the Angara rockets have continued to slip, partly due to slow progress in the construction of launch facilities at Plesetsk. Although these are located on the same site once intended to support launches of Zenit rockets, they essentially had to be built from scratch. In a plan reminiscent of RKK Energiya’s 1997 Sodruzhestvo proposal, Angara is also expected to be launched from a modified Proton complex at Baykonur called Bayterek (“Poplar”) under a joint venture between Khrunichev and the Kazakh Finance Ministry’s State Property and Privatization Committee. In addition to that, Khrunichev is developing a modified version of Angara’s URM (also carrying the RD-191) that will act as the first stage of a South Korean launch vehicle called KSLV-1. The first Angara is now not expected to fly until after 2010, but whenever it goes up, it will carry with it the legacy of the Energiya-Buran program.