Under the command of Russian cosmonaut Anatoly Ivanishin, Soyuz MS-01 undocked from the ISS on Saturday. With NASA astronaut Kate Rubins and Japanese astronaut Takuya Onishi onboard, the trio successfully landed on the steppes of Kazakhstan at 11:59 p.m Eastern.
The End Of Mission (EOM) events marked the conclusion to the debut use of the newly upgraded Soyuz MS series vehicle.
The MS variant is the last in a series of planned upgrades for the veteran Soyuz vehicle of the Russian Federal Space Agency (Roscosmos).
The new MS series sports more efficient solar panels, a new Kurs NA approach and docking system weighing less than half that of its predecessor, additional micro-meteoroid debris shielding, and a modified docking and attitude control engine – which will add redundancy during docking and deorbit burns.
It successfully docked with the ISS in July, marking the start of a somewhat shorter mission for the trio, when compared to the standard six month tours of the ISS during expeditions.
Despite the shorter mission, numerous achievements were made for the crew that will soon be back on terra firma. This included the first-ever successful in-space DNA sequencer experiment, conducted by Rubins.
Preparations for departure began several days ago. This included a checkout on the crew’s ride home.
The Soyuz packed with a few late stow items to take advantage of its limited downmass cargo capability, notably the Radiation Area Monitor (RAM).
The crew then participated in a nominal Soyuz Decent Drill, during which they reviewed preliminary undocking and descent data and worked through the descent timeline from Soyuz activation through post-landing activities. They also conducted routine spacesuit checks.
The crew then parted ways with their colleagues, with farewell speeches and hatch closures between the Station and the Soyuz.
With the crew completing the translation from the Orbital Module (BO) and Descent Module (SA) to strap themselves into their Kazbek couches inside the SA, Soyuz TMA-20M undocking took place at 8:37pm Eastern.
At the time of undocking, Expedition 50 began aboard the station under the command of NASA astronaut Shane Kimbrough. Along with his crewmates Sergey Ryzhikov and Andrey Borisenko of Roscosmos, the three-person crew will operate the station for three weeks until the arrival of three new crew members.
Peggy Whitson of NASA, Thomas Pesquet of ESA (European Space Agency) and Oleg Novitsky of Roscosmos are scheduled to launch in November from Baikonur, Kazakhstan.
Following undocking – which included an impressive manual test via Ivanishin – Soyuz enjoyed a few hours of free flight as it departed from the Station’s neighborhood via two separation burns while the onboard crew prepared for the final aspect of their mission.
The deorbit burn occurred at 11:06 Eastern, reducing the Soyuz’s velocity just enough for it to begin the plunge back to Earth.
The Soyuz then entered a critical part of its mission as the spacecraft has no other option but to re-enter.
The first milestone was the module separation as the three major elements of the Soyuz spacecraft – the OM, DM and Instrumentation/Propulsion Module (IPM) – were pushed apart via the use of pyrotechnics.
All three modules separated simultaneously – shortly after the deorbit burn was completed – at around 140 km altitude.
Two “off nominal” re-entries occurred in 2007 and 2008 and were the cause of separation failures on the modules, thus initiating a very stressful return for their three-person crews.
Known as “ballistic entry” – the crew have to endure much higher G-forces and land at an alternative site.
An investigation (L2 Russian Section) noted issues with the long-term exposure to electromagnetic emissions on-orbit, and the potential to cause issues with the pyro bolts, came after an extensive investigation that included the removal and return of one pyro bolt from Soyuz TMA-12.
Mitigation against this issue has resulted in no further issues with the module separation milestone in any of the following missions.
Once through the plasma of entry interface, the capsule was prepared for the deployment of its drogue chute. This prepared the spacecraft for the deployment of its main parachute.
This is one of the hardest parts of the return for the crew, which has been described as being inside a washing machine by some returning astronauts.
The Soyuz craft then completed the return to terra firma, landing on the steppes of Kazakhstan at around 23:58 Eastern.
The exact timing of touchdown, under a “soft” thruster engine firing, is always dependent on a number of factors – such as the impact of winds on the Soyuz chutes – and can vary by several minutes.
With the vehicle safely back on Earth, ground and air crews converged on the Soyuz to extract the crew from the SA.
The crew underwent immediate and preliminary health checks once outside their Soyuz spacecraft. All three were then transferred to a medical tent to prepare them for transit away from the landing site.
Eventually, they will part ways for their respective countries and space agencies.
(Images: NASA, Roscosmos, ESA and L2.
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