R-7 Semyorka Vostok-K (8K72K)

The Vostok-K, GRAU index 8K72K, was the expendable three-stage carrier rocket the Soviet Union used for thirteen launches between 1960 and 1964, six of them crewed. Derived from the R-7 missile and a member of the Vostok family, it was the refined version of the Vostok-L and the one actually used for human spaceflight: every crewed mission of the Vostok programme lifted off on an 8K72K, beginning with Yuri Gagarin's Vostok 1 on 12 April 1961.

To man-rate it, several modifications were made to the core and the strap-on boosters. The third stage, the Blok E, also received the improved RD-0109 engine, intended to correct shortcomings of the RD-0105 used earlier. The Blok E engines were designed and built by the KBKhA works in Voronezh; Gunter's Space Page identifies this stage's engine by the index 8D719.

The first two stages keep the R-7's cluster layout. The first is made up of four strap-ons (Blok B, V, G and D), each with an RD-107-8D74-1959 rated at 970.86 kN in vacuum (99,000 kgf), a specific impulse of 313 s in vacuum and 256 s at sea level, a 118 s burn, 43,300 kg gross and 3,710 kg empty mass, 19 m long and 2.68 m in diameter. The second is the core, the Blok A, with an RD-108-8D75-1959 of 912 kN in vacuum, a specific impulse of 315 s in vacuum and 248 s at sea level, a 301 s burn, 100,400 kg gross and 6,800 kg empty mass, 28 m long and 2.99 m in diameter. On top sits the Blok E: 7,775 kg gross and 1,440 kg empty, 54.5 kN of vacuum thrust, a specific impulse of 326 s and a 365 s burn, 2.84 m long and 2.56 m in diameter. All stages burn liquid oxygen and kerosene.

The Vostok-K's own Wikipedia page gives the full stack as 30.84 m tall, 2.99 m in diameter, 281,375 kg at lift-off and 4,730 kg to low Earth orbit; the Vostok family page puts that capacity at 4,725 kg and the mass between 280,000 and 290,000 kg.

The maiden flight, on 22 December 1960, came three weeks after the Vostok-L was retired. The third-stage engine failed 425 seconds after launch and the payload, a Korabl-Sputnik spacecraft with two dogs aboard, did not reach orbit; the spacecraft was recovered after landing and both animals survived. Gunter's Space Page lists that vehicle as serial L1-13A and its payload as Vostok-1K No. 4. The next two launches, on 9 and 25 March 1961, put Korabl-Sputnik 4 and Korabl-Sputnik 5 (Vostok-3KA No. 1 and 2) into orbit as test flights of the Vostok programme.

On 12 April 1961 a Vostok-K launched Vostok 1, making Yuri Gagarin the first human to fly in space. It was followed by Vostok 2 (6 August 1961), Vostok 3 and Vostok 4, launched on consecutive days (11 and 12 August 1962), and Vostok 5 and Vostok 6 (14 and 16 June 1963). All of them left from pad 1/5 at Baikonur, Gagarin's Start. According to Gunter, each mission used a vehicle with its own serial number in the E103 series (E103-16 for Vostok 1) and a Vostok-3KA spacecraft, No. 3 to No. 8.

Between the crewed missions the 8K72K also launched the first two Zenit reconnaissance satellites. The first, on 11 December 1961, was lost to a launcher failure (Zenit-2 No. 1, serial E103-21); the second, on 26 April 1962, reached orbit as Kosmos 4 (Zenit-2 No. 2). In that role it was soon replaced by the uprated Vostok-2, which was derived from it.

When the Vostok programme ended two 8K72Ks were left, and they were used to launch four Elektron scientific satellites in pairs: Elektron 1 and Elektron 2 on 30 January 1964, and Elektron 3 and Elektron 4 on 10 July 1964, the type's last flight. There had been plans for further Vostok missions after Vostok 6; had they flown, they would have used a booster based on the newer 8K74 core.

Thirteen launches, eleven successes and two failures, all from Baikonur. A Vostok 8K72K rocket is on display in Moscow at the Exhibition of Achievements of National Economy (VDNKh).