The 5M flight scenario: Launch and rendezvous
The extremely complex flight scenario proposed for the 5M mission was unlike anything else attempted in space exploration. The dual mission would begin with a salvo launch of two Proton rockets from adjoining launch pads in Tyuratam.
The dual 5M spacecraft in the Earth's orbit after the deployment of the TZU heat shield.
Flight scenario: Launch and rendezvous
The first UR-500K (a.k.a Proton-K) rocket of the 5M project would blast off with the 20.94-ton Passive Orbital Block, OBP, (also designated 11S824M), including the 8.7-ton spacecraft. At the conclusion of the firing of the three booster stages of the Proton and a short engine burn of the 11S824M space tug, the OBP stack would enter an initial 200-kilometer orbit around the Earth.
In the meantime, the second Proton-K rocket would follow with its blastoff just 20 seconds after the first, carrying the 20.45-ton "active" 11S86 space tug, or OBA, aiming to enter a very similar orbit around 10 kilometers away from the OBP stack.
During the first revolution of the mission around the Earth, between 50 and 60 minutes after the liftoff of the two rockets, the "active" OBA vehicle, carrying a larger fuel supply, would have to rendezvous and link up with its "passive" OBP counterpart.
Immediately after the successful docking, the 5M spacecraft would deploy its giant TZU umbrella, needed for the eventual descent in the Martian atmosphere, while the Igla rendezvous section and the orbital maneuvering section, which had been used during docking, would be discarded to save mass before the upcoming engine firing.
Also, during the first revolution, the Soviet ground stations, would have to establish the exact orbital parameters of the assembled vehicle, so that during the second orbit, they could transmit settings to the "active" vehicle with the timeline for the first maneuver. At the right moment, the "active" tug would fire its engine to turn the circular parking orbit into an ellipse extending between 3,000 and 3,700 kilometers above the Earth's surface. It would take the spacecraft between 2 and 2.2 hours to make a single revolution in this orbit. During that maneuver, the "active" space tug would also pump up to 7,300 kilograms of its extra propellant into the "passive" vehicle.
Shortly before the second maneuver, the "active" space tug and the entire docking mechanism connecting the pair would be discarded, again to save mass for the next maneuver.
Upon completion of another revolution, the "passive" vehicle would fire its engine at the pericenter of its new orbit, finally inserting the spacecraft on a journey to Mars, which would last from nine to 11 months.
Two weeks after the launch of the first 5M mission, another pair of UR-500K rockets would blast off delivering a twin version of the Mars sample return spacecraft. In the case of the 1979 launch window, the first spacecraft would depart Earth on or soon after October 30, the backup mission would lift off on November 14.
Read much more about the history of the Russian space program in a richly illustrated, large-format glossy edition:
A Soviet Proton-K/Block-D vehicle lifts off from Baikonur. Credit: Roskosmos
Architecture of the 5M mission for a two-launch scenario. Click to enlarge. Copyright © 2017 Anatoly Zak
The configuration of the 5M payload section with a passive space tug. Credit: NPO Lavochkin
The configuration of the 5M spacecraft in the Earth's orbit according to a preliminary concept. Credit: NPO Lavochkin
The OBP and OBA vehicles meet up in the low Earth's orbit at the start of the 5M Mars sample return mission. Copyright © 2017 Anatoly Zak