R-7M: TIIE *MOLNIYA5 LUNAR AND PLANETARY LAUNCH VEHICLE
In early 1958 Korolev began planning for planetary missions. His original intention w as to use the 8K73, a version of the 8K72 with a more capable third stage. During that summer OKB-1 began w ork on spacecraft for launch to Venus in June 1959 and Mars in September 1960. However, the 8K73 project and the 1959 Venus mission were abandoned w’hen Glushko’s engines for the new’ third stage had development problems. Korolev turned to Kosberg again and decided to adapt the second stage of the new’ silo-based ICBM under development, the R-9A. also know n as the 8K75. as the third stage for his planetary launcher. Kosberg fitted the stage with larger tanks to sustain the longer engine burn times. In the meantime, the R-7 w as still in its final development phases in preparation for operational deployment.
During 1958 an improved version of the basic tw o-stage R-7. the R-7A or 8K74.
was being developed for easier operational servicing and greater performance. The 8K74 had all-inertial guidance with the original radio guidance system retained only as a backup, improved engines for reliability, redesigned verniers for simpler control and increased performance, a new ignition system, and some portions of the engines were moved nearer to service hatches. The first launch of the 8K74 on December 24. 1959, was a success. The 8K74 became the basic two-stage booster for generations of launchers to the present day. The only 8K71-based vehicles used after this 8K74 test were two 8K72 Luna launches on April 12 and 18. 1960. both of which failed.
In all this rush of rocket development in 1958 59, Keldysh*s mathematicians had determined that continuous burn of all stages was an inefficient use of energy to reach interplanetary velocities. Continuous burn also required precise timing without margin for launch delays. Instead they recommended a scheme in which the booster placed an escape stage into low Earth orbit. This would be ignited when the orbital phasing was optimum for launch towards the Moon or planetary target, and once on course it would release its payload.
Abandoning the three-stage approach for lunar and planetary launches, in early 1959 Korolev began w ork on a four-stage approach. The airframe of the 8K74 core vehicle w as strengthened to support the mass of the new upper stages, modifications w ere made to the operating pressures and burn programs to increase the thrust of the core vehicle, a stronger open truss was provided between the suStainer and third stage, and new guidance and control systems were supplied for the upper stages. The К os berg third stage was modified further with an increased propellant load and an upgraded 8D715K four-chamber engine and designated Block I. The 8K74 III two – stage core vehicle w ith the new Block I third stage and a first burn by a new fourth stage. Block L. built by OKB-1. would put the Block L and spacecraft combination in Earth orbit. The Block L was made res tart able, so that its second burn would put the spacecraft on an interplanetary trajectory. It would be capable of sending 1,600 kg to the Moon or 1,200 kg to either Venus or Mars. This four-stage 8K78 is known as the ‘Molniya* launcher. A prototype with a dummy fourth stage w7as successfully tested on January 20. 1960, with a second successful test 10 days later. The Block L completed its ground tests in the summer of 1960. and Korolev rushed preparations for three Mars launches on the first tests of this new launcher. 1 he spacecraft were also built in a great rush before the launch window7 closed in mid-October. Only two rockets made it to the launch pad on time.
The first flight test of the complete 8K78 occurred on October 10, 1960, w ith a 1M Mars spacecraft at the top of the stack. The spacecraft had to be stripped down in order to provide sufficient mass for rocket test instrumentation. The launch failed when resonant vibrations in the upper stages damaged the avionics during third stage burn and the rocket veered off course. A second attempt on October 14 also failed when the third stage engine did not ignite because a LOX leak on the pad had frozen kerosene in the fuel lines. The first test of the Block L did not come until the third flight on Kebruary 4, 1961, which attempted to launch a 1 VA Venus spacecraft. The first three stages performed perfectly, but the Block L was stranded in Earth orbit by a primary powder failure.
The Block L stage was a challenging design because it had to coast unpowered for
Figure 4.3 Launch vehicles for robotic spacecraft in 1961. From left, US Viking, US Jupiter-C, US Atlas-Agena, USSR 8K-72 Luna, USSR RK-7R Molniya (from Peter Gorin in Siddiqi 2000).
almost 2 hours in Earth orbit without losing volatile propellant, orient itself to the proper firing attitude at a programmed time, and ignite its engine in a zero-G state. The engine used a more efficient ‘closed-cycle’ technology which US rocket makers deemed unworkable, and used gimbals for yaw and pitch control and a pair of small verniers for roll control. The stage used, a cold gas attitude control system and solid rockets to provide ullage control before engine ignition in zero-G. The challenges of perfecting this planetary injection stage proved difficult. The Block L succeeded on its second opportunity on February 12, I960, deploying Venera 1. But it failed many times thereafter, including the final planetary mission to use the Molniya launcher on March 31, 1972, when the Block L stage failed to put another spacecraft intended for Venus on an escape trajectory.
In 1962 an extended shroud was introduced to accommodate the next generation
Figure 4.4 R-7 vehicle on rail carrier.
2MV Mars and Venus spacecraft and the sustainer engines were upgraded. In 1964 a new version of the 8K78 was introduced, with improved versions of Glushko’s RD – 107/8 engines and an improved engine in the Block L fourth stage. This vehicle was designated 8K.78M, and was known in the West variously as SL-6 and А-2-е. Tt was first used for the test launch of a 3MV Venera spacecraft on March 19, 1964, then used consistently for Venus missions until the introduction of the Proton-launched spacecraft in 1975. Mars launches used the 8K78 until switching to the Proton in 1969. The Ye-6 Luna probes used both the 8K78 and 8K78M vehicles until Luna 9 on January 31, 1966, when the SK78M came into exclusive use. A variant of this vehicle was created for the Luna soft landing missions, in which the avionics were deleted from the upper stages to save mass and the Ye-6 spacecraft controlled the functioning of the third and fourth stages. This vehicle was designated with a / Ye-6 suffix. The 8K78 vehicle was completely replaced by the 8K78M after December 1965. ‘
The 8K78M received another upgrade in 1966-67 when the core and strap-ons were replaced by those of the three-stage LSoyuz’ version used in the manned space program. In 1965, responsibility lor the Block L stage was transferred from OKB-1 to NPO-Lavochkin, which introduced improvements in 1968 including upgraded avionics and a new third stage interface and fairing design. Lavochkin produced two versions of this new Block L, one for lunar and planetary missions and the other to place ‘Molniya’ communications satellites into highly elliptical Earth orbits. Further improvements to the 8K78M were made in 1974 and again in 1980. In its various forms the Molniya launcher was the workhorse for the lunar and planetary program in the 1960s and early 1970s, successfully deploying the Luna 4 to 14 missions from 1963-1968, Mars missions from 1960-1965 including Mars 1, and Venera 1 to 8 from 1961-1972. The versatility of the ‘Semyorka’ rocket is demonstrated by its continued
Figure 4.5 Molniya launch.
use up to the present day, particularly in its three-stage Soyuz* variant. It resumed its utility for planetary launches on June 2, 2003, with the successful launch of the Mars Express spacecraft for the European Space Agency using a Soyuz fitted with the new Fregal fourth stage.