Soyuz MS-16 returns Space Station trio to Earth

by Mihir Neal & Chris Gebhardt

The three international crew members of the Soyuz MS-16 mission have safely returned to Earth following the undocking of their Soyuz spacecraft from the International Space Station at 19:32 EDT (23:32 UTC).

A parachute and retro-rocket assisted landing on the steppes of Kazakhstan followed at 22:55 EDT on Wednesday, 21 October (02:55 UTC on Thursday, 22 October) after a 196 day mission covering 133.5 million kilometers (83 million miles) over 3,136 orbits of Earth.

Prior to undocking, NASA astronaut and Expedition 63 Commander Chris Cassidy handed over command of the Station to Russian cosmonaut Sergey Ryzhikov, who along with Sergey Kud-Sverchkov and Kathleen Rubins arrived on the Station on 14 October on the Soyuz MS-17 flight.

The Soyuz MS-16 spacecraft’s hatch was closed at 16:24 EDT (20:24 UTC), initiating a sequence of steps to prepare the Soyuz, Station, and the two craft’s respective crews for the undocking.

Release of Soyuz MS-16 from the Station’s Poisk module came at 19:32 EDT (23:32 UTC).

The undocking process occurred when the Soyuz’s hooks between the two vehicles were opened before the separation sequence passively propelled Soyuz away from the Station at an opening rate of 0.1 meters per second.

A minute and a half after undocking, Soyuz’s onboard computer took active control of the vehicle and began preparing it for a sequence of two separation burns, the first of which occurred at 4 minutes 30 seconds after undocking and the second at 5 minutes 50 seconds after undocking.

The first burn imparted a 0.53 m/s delta v change to Soyuz and the second a 1.53 m/s delta v change — accelerating it away from the Station.

Overview of the three main parts of the Soyuz crew vehicle. (Credit: NASA)

Over the next two hours, the crew configured Soyuz for deorbit and reentry, including moving into the Descent Module and sealing the hatch between them and the Orbital Module.

The Soyuz spacecraft is composed of three modules: Orbital, Descent, and Instrumentation/Propulsion.

The Instrumentation/Propulsion Module (aft) contains the primary guidance, navigation, and computer systems as well as the propellant tanks for the thrusters and main engine.  It also houses the solar panels and power systems. 

The Descent Module (middle) carries the crew to orbit and safely back to the ground.  It is the only part of the vehicle equipment with a heat shield and recovery systems.  

A hatch provides access from the Descent Module (forward) to the Orbital Module, that houses a docking mechanism, hatch, and rendezvous antennas.  It also provides the crew with extra living space during the trip to and from the ISS. 

At 22:00:53 EDT (02:00:53 UTC on 22 October), Soyuz MS-16 began its 4 minute 40 second deorbit burn (according to NASA’s final MS-16 detailed reentry timeline — available for download on L2), slowing itself by 120 m/s and lowering its perigee (point of closest approach to Earth’s surface in an orbit) into Earth’s atmosphere.

However, NASA TV public affairs referred to a 5 minute 20 second burn that changed the velocity by 128 m/s.

This committed the craft and its trio of humans to reentry and then landing 54 minutes later. 

After the deorbit burn was complete, Soyuz maneuvered into the proper module separation orientation, which occurred at 22:28 EDT (02:28 UTC) while Soyuz was 132.9 km over Egypt.

Atmospheric reentry followed 3 minutes later at an altitude of 99.6 km.  Just 90 seconds later, the Descent Module entered the plasma phase of reentry, when air compression in front of the vehicle changes air molecules to a plasma state.

During this phase, which began at 80.1 kilometers altitude at roughly 22:32 EDT (02:32 UTC), communications were cut off with the crew.  This was a normal part of the Soyuz’s reentry.

The module exited the plasma regime at roughly the same time G-force loads peaked.  This occurred at an altitude of 34 km at 22:37 EDT (02:38 UTC), at which point communications were restored.

Initial contact with the Soyuz came by direct voice communication with Commander Ivanishin.

Just two minutes after exiting the plasma environment, Soyuz deployed its parachute; this occurred quite high for a reentering craft — at 10.4 km.  The size of the parachute slowed the Descent Module down so rapidly that it took 15 minutes to travel the 10 km to the surface.

The unusually high deployment altitude of the main chute was driven by the smaller size of the reserve chute and the longer time it would have needed to slow the Descent Module down for a harder-than-usual-but-safe landing.

For the parachute deployment sequence, the two pilot parachutes, followed by a drogue chute immediately after, slowed the capsule from 230 m/s to 80 m/s.  Shortly after, the main parachute was released, further slowing the module down to just 7.3 m/s. 

The main parachute’s harness allowed the Soyuz to descend at an angle of 30 degrees to allow for the continued expulsion of heat before shifting the vehicle to vertical descent.

Just 2 seconds before touchdown, two sets of three small engines on the bottom of the capsule fired just 0.8 meters above the ground, reducing the capsule’s rate of descent to 1.5 m/s for a “small car crash-like landing,” as crews have described it.

After landing, the crew will return by Russian helicopters to the recovery staging city in Karaganda, Kazakhstan.  From there, Cassidy will board a NASA plane for a flight back to Houston while Ivanishin and Vagner will board a Gagarin Cosmonaut Training Center aircraft and return to Star City, Russia.

With landing, Cassidy will complete his third flight for a total of 378 days in space, the fifth-highest among U.S. astronauts.  Ivanishin will finish his third flight, accumulating 476 days in space.  This was Vagner’s first spaceflight totalling 196 days.

Expedition 64 begins:

At the time of Soyuz MS-16 undocking, Expedition 64 will begin aboard the Station with a crew of three, including Station Commander Sergey Ryzhikov and Flight Engineers Sergey Kud-Sverchkov and Dr. Kate Rubins.

In mid-November, they will be joined by the four-person crew of SpaceX’s Crew-1 mission.  This will be the first regular, six-month crew rotation flight for NASA’s Commercial Crew Program, the first operational crew rotation flight conducted by the U.S. since 2009, and the first time SpaceX launches humans for a half-year long stay off world.

Expedition 64 crew portrait. (Credit: NASA)

Crew-1 will launch NASA astronauts Michael Hopkins, Victor Glover, and Shannon Walker along with Soichi Noguchi of the Japan Aerospace Exploration Agency (JAXA).  This will be the second launch of U.S. astronauts on a commercial spacecraft and rocket and the first with a partner agency crew member aboard.

Crew-1 is the first of at least six launches awarded to SpaceX to ferry U.S., Canadian, European, Japanese, and Russian astronauts to the ISS under the Commercial Crew program.

Based on current schedules, all seven members of Expedition 64 will welcome Boeing’s Starliner crew vehicle in January 2021 on its second uncrewed Orbital Flight Test (OFT-2) following last year’s aborted OFT-1 mission.

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