Soyuz MS-08 lands as Station crew to reduce to five people

by Chris Gebhardt

The Soyuz MS-08 spacecraft, launched earlier this year in March, has departed the International Space Station with three of the Station’s six crew members – returning them to Earth after a 6-month tour of duty on the international outpost.  Soyuz MS-08 landed on the steppes of Kazakhstan on Thursday, 4 October at 07:45 EDT (1145 UTC) or 17:45 local time at the landing site.

The departure of three crewmembers from the ISS would normally signal the pending arrival of three new crew; however, this is not the case.  Launching next week, Soyuz MS-10 will only bring up two new crew for the Station as part of Russia’s continued decision to keep their total crew complement at two until their main research module, Nauka, can be launched late next year at the earliest.

Soyuz MS-08 landing:

The Soyuz MS-08 commander, Oleg Artemyev of Roscosmos, and his two NASA crewmates (Drew Feustel and Ricky Arnold) launched from Baikonur Cosmodrome, Kazakhstan, on 21 March 2018 at 1744 UTC to begin their six-month mission to the ISS as members of the Expedition 55 and 56 increments.

On 1 June, Expedition 56 officially began, and Drew Feustel took Command of the Space Station.

While a vast majority of the mission focused on ISS maintenance and science operations, one major event occurred on 29 August when a leak of the Station’s atmosphere led to the discovery of a small hole in the MS-09 spacecraft (not the spacecraft returning the three crewmembers today).

An investigation into that leak is ongoing, but Russian media outlets recently claimed that the hole was not a manufacturing defect.  This prompted NASA to release a statement on Wednesday, 3 October.

Per NASA, “On Aug. 29, 2018 a small hole was discovered on the International Space Station.   This resulted in a pressure leak. The hole has been identified and fixed by space station crew.   Russian media recently reported that General Director Rogozin said the hole was not a manufacturing defect.  Ruling out a manufacturing defect indicates that this is an isolated issue which does not categorically affect future production.

“This conclusion does not necessarily mean the hole was created intentionally or with mal-intent.  NASA and Roscosmos are both investigating the incident to determine the cause. The International Space Station Program is tentatively planning a spacewalk in November to gather more information.

“On October 11, American Astronaut Nick Hague and Russian Cosmonaut Alexey Ovchinin will launch to the International Space Station on a Russian Soyuz MS-10 spacecraft from the Baikonur Cosmodrome in Kazakhstan.  Administrator Bridenstine is scheduled to attend the launch and plans to meet with Mr. Rogozin.”

The hole discovered in the Soyuz MS-09 crew vehicle’s Orbital Module in August 2018. (Credit: NASA)

The hole was first temporarily and then permanently sealed in rapid sequence by the Russian crew – much to Commander Feustel’s consternation, who requested additional time for ground crews to examine the hole before proceeding with a permanent fix.

Nonetheless, the Soyuz MS-08 crew’s time on Station was relatively uneventful, with the crew helping with the SpaceX CRS-14 and CRS-15 missions, the Orbital ATK/then Northrop Grumman Innovation Systems OA-9/NG-9 mission of Cygnus, Progress MS-09, and the opening days of the HTV-7 resupply missions to the Station.

On Wednesday, 3 October, the formal Change of Command ceremony took place, at which time Feustel handed off Command of the ISS to his European counterpart Alexander Gerst.

A farewell ceremony occurred at 00:30 EDT (0430 UTC) on 4 October before Artemyev, Feustel, and Arnold climbed into the Soyuz MS-08 and closed the hatches between Soyuz and the Station at 00:55 EDT (0455 UTC).

After vestibule depressurization and system checkouts, the Soyuz MS-08 undocked from the ISS at 03:57 EDT (0757 UTC) to begin the two and a half orbit process of bringing Artemyev, Feustel, and Arnold home.

Soyuz MS-08 approaches the ISS for docking on 23 March 2018. (Credit: NASA)

After leaving the ISS, following a flyaround to take photos of the orbital outpost, the trio closed the hatch between the Soyuz MS-08’s Orbital Module (where the docking systems and hatch to the Station are located) and the Descent Module (where the crew sits for launch, reentry, and landing).

Two orbits after undocking, the Soyuz MS-08’s computers performed the craft’s deorbit burn at 06:51 EDT (1051 UTC) using an engine on the back of the Instrumentation and Service Module.  Shortly thereafter, the Soyuz separated into its three constituent parts – the Orbital Module, the Descent Module, and the Instrumentation and Service Module – with only the Descent Module surviving atmospheric reentry.

Once safely through the plasma stage of reentry, a period during which communications becomes ratty and unreliable, the Descent Module released its parachutes and eased down toward the Kazakh steppes.

In the final second before contact with the ground, the Descent Module fired a breaking thruster – essentially putting the crew through a minor car accident as the module decelerates rapidly for touchdown.

Landing occurred around 07:45 EDT (1145 UTC) on Wednesday, 4 October, though prevailing winds and atmospheric flight impacts the accuracy of this anticipated time.

Comparison of a nominal v. ballistic reentry profile for Soyuz. (Credit: NASA)

This landing time was based on an assumed nominal reentry trajectory and profile.  Soyuz also has a backup trajectory available to it – known as a Ballistic Reentry – in the event an emergency is detected after the deorbit burn occurs.

This type of emergency reentry profile last occurred on back-to-back Soyuz TMA landings on the TMA-10 and -11 missions when the Instrumentation and Service Module failed to separate from the Descent Module.  When this occurred, the Descent Module’s computers triggered a ballistic reentry on both flights – a trajectory designed to get the crew through reentry as quickly as possible to maintain their safety.

The trajectory on ballistic reentries is much steeper, exerts higher G-force loads on the crew, and results in a landing hundreds of kilometers from the intended recovery zone.  In both the Soyuz TMA-10 and -11 cases, the ballistic reentry worked as designed, protected the crew, and got them to the ground safely, where they were then recovered.

At the moment Soyuz MS-08 undocked, Expedition 57 formally began, with Alexander Gerst (ESA), Serena Aunon-Chancellor (NASA), and Sergey Prokopyev (Roscosmos) comprising a three-person crew for one week until the launch of the next group of residents on 11 October when Alexey Ovchinin of Roscosmos and Nick Hague of NASA will launch aboard the Soyuz MS-10 spacecraft.

This will bring the Station’s crew complement to just five – a number that will be maintained (except for periods of Soyuz crew rotations) for over a year until the Soyuz MS-14 mission launches in November 2019 to return the Station’s crew number to six.

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