Final design of the 5M Mars sample-return project
When the three-launch scenario considered for the Mars sample return mission proved to be too complicated in the mid-1970s, the 5M mission was re-designed once again to rely on just two Proton rockets. The resulting two-launch 5M complex consisted of the "passive" 11S824M space tug carrying the sample-return vehicle and the 11S86 "active" space tug designed to help push the mission away from Earth.
Final design of the 5M vehicle.
5M Mars sample return mission at a glance (the final design circa 1976):
Proton-based spacecraft design
Upon taking charge of the 5M project after the resignation of his predecessor, Panteleev decided that the first order of business would be to try to simplify its flight scenario by reducing the number of dockings that would be required in the course of the mission. Obviously, the most significant shortcut would be eliminating the need for a super-complex rendezvous in the orbit of Mars. To do that, some extra capabilities to accomodate a heavier spacecraft would have to be found. The first step in achieving that goal was the introduction of refueling of the passive Block-D space tug after it had been intercepted and docked with the "active" space tug in the Earth's orbit. That measure alone enabled an increase of the badly needed mass of the 5M spacecraft from 8,500 kilograms to 9,135 kilograms. (633)
Additional savings for the payload were obtained by abandoning aerodynamic descent in the Martian atmosphere in favor of a simple ballistic entry.
Also, the headlight shape of the lander was changed to an umbrella-like vehicle with a diameter of 11.35 meters. The solid center had a diameter of three meters surrounded by heat-resistant berillium spokes with fiberglass shields. (633)
A custom-built payload fairing with a diameter of 4.7 meters to accomodate the probe's massive folded heat shield was developed specificaly for the Proton rocket launching the 5M mission. (67)
The cruise stage of the vehicle was to have a mass of 1,680 kilograms and a lander would weigh 7,455 kilograms.
During the second phase of development, the mass of the spacecraft was apparently reduced by another four percent. (633)
Preliminary design is ready
Kryukov approved the preliminary design of the 5M vehicle in January 1976. The spacecraft was to use an umbrella-like braking device expanding to a diameter of almost 12 meters to slow itself in the Martian atmosphere. According to its technical requirements, the mass of the return rocket should not exceed two percent of the mass of the overall vehicle in order to make the whole scheme feasible.
In the meantime, A.P. Vinogradov, a Member of the Soviet Academy of Sciences, proposed a method for the thermal sterilization of Martian soil samples during their stay in the orbit of Mars. The proposal was finally seen as a solution to the issue of interplanetary cross-contamination. In turn, this proposal opened the door to further mass reductions of the Earth return vehicle. The developers now felt comfortable doing away with the parachute system during the landing on Earth of the sample return capsule. The associated landing radar, a battery and the automated control unit were also eliminated, bringing down the mass of the ballistic capsule to just 7.8 kilograms.
These mass savings were especially effective, because every kilogram shaved from the Mars return vehicle would eliminate 10 kilograms from the Martian lander. (633)
The final design
The resulting two-spacecraft 5M complex consisted of the "passive" 11S824M space tug carrying the Martian vehicle and the 11S86 "active" space tug. The flight control system, SAU, aboard the Martian landing vehicle would be fully responsible for the operation of the "passive" space tug at all stages of the flight until their separation.
Most likely, the 5M spacecraft would rely on the Igla-M radio system, borrowed from the Soyuz 7K-OK complex, to dock to parts of the complex in the low Earth's orbit. However, the Kontakt-M rendezvous system, which was developed for the L3 lunar expeditionary complex, was also considered as an alternative.
The 5M spacecraft itself consisted of the Lander Section known as PB (from Russian "posadochny blok" or landing block) and the Trajectory Section, TB (from Russian "trayektorny blok" or trajectory module). In turn, the PB lander contained the Return Rocket, VR (from Russian "vzletnaya raketa").
Proton-based mission design
The 5M project targeted the 1979 launch window to Mars. It would use the most mass effective, but relatively slow, Mars approach trajectory, making 1.5 orbits around the Sun.
In case of launches of two pairs of spacecraft during a two-week interval starting on October 30 and ending on November 14, 1979, a pair of probes would spend 337 and 329 days respectively on their way to Mars.
Between five and 10 days into the flight, each spacecraft would conduct its first trajectory correction maneuver, followed by another firing between 10 and 15 days prior to reaching the Red Planet.
Depending on the year of the launch, the lander would enter the Martian atmosphere with a speed ranging from 5.7 to 6.35 kilometers per second, at an angle of around 11.5 degrees, with a possible variation one way or another of about 2.5 degrees. The descent would be conducted on a ballistic trajectory and initial deceleration would be achieved with the Braking Umbrella Device, TZU.
The landing time was to be selected from 1.5 to 4.5 hours from the onset of the Martian night, depending on the local season at the time of the arrival. The spacecraft was also expected to have no less than two hours for direct radio contact with the Earth.
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Architecture of the 5M mission for a two-launch scenario. Click to enlarge. Copyright © 2017 Anatoly Zak
Preliminary design of the 5M vehicle. Credit: NPO Lavochkin
The configuration of the 5M mission after docking in the low Earth's orbit. Credit: NPO Lavochkin
Berrilium bars designed to deploy the umbrella shield of the 5M lander. Credit: NPO Lavochkin