Returning Home in Soyuz – a Wild, Wild Ride

A second edition of the book ‘The Farthest Shore: A 21st Century Guide to Space’ has just been published by Apogee Books (a Canadian publisher). http://www.cgpublishing.com/ The original book was a paperback that served as a textbook for the students of International Space University. It covered all aspects of space exploration and development.

The new edition is being published online, making it accessible to a wider readership. It includes updates to recognize the astounding innovations and interdisciplinary collaborations that have emerged in the space program over the last decade.

The book was edited by Joseph Pelton and Angie Bukley. Joe and Angie asked me to contribute to the third chapter. This chapter includes stories from former astronauts and space pioneers who tell what it was like to fly in space or work in the program. I was pleased to help. I thought it would be fun to describe my wild ride home from space in a Soyuz vehicle:

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Simply stated, the goal of Soyuz reentry is to safely return the spacecraft and its crew from space back to Earth. In practice, however, reentry is a daunting and complex operational undertaking. The Soyuz vehicle returns from an altitude of 350 kilometers and with an orbital velocity of 28,000 kilometers per hour. This enormous amount of potential and kinetic energy must be completely dissipated before the vehicle touches down at a designated landing site with near-zero velocity.

In December 2009, I had the opportunity to return to Earth in a Russian Soyuz spacecraft. Nothing that I have experienced in life can compare to that memorable flight. It was action-packed. This is the story of my voyage home from space …

Following completion of our expedition aboard the International Space Station (ISS), my two crewmates and I entered our Soyuz TMA spacecraft and closed the hatches between our vehicle and the Station. Roman Romanenko (from Russia), Frank De Winne (from Belgium) and I (from Canada) donned our Sokol suits and ingressed our seats. As our Soyuz commander, Roman took the center seat. Frank (flight engineer one) sat in the left seat and I (flight engineer two) sat in the right. The crew compartment of the Soyuz vehicle is only two meters in diameter so three pressure-suited crew members lying shoulder-to-shoulder (along with 100 kilograms of returning cargo) is a tight fit. Once strapped in, we activated the vehicle systems and initiated the undocking process.

The Soyuz vehicle is a cozy spacecraft. Courtesy of NASA.

Undocking occurred precisely on time. The recoiling springs of the docking mechanism provided the impulse that backed us off the berthing port. Frank and I had window seats. Through the porthole at my right shoulder, I saw the trusswork, solar arrays and habitation modules slowly pass by. This was my wistful last view of the remarkable Station that had been our home and workplace for the past half year.

Since we didn’t wish to “plume” the Station’s solar arrays and other structures with exhaust gasses, we waited a few minutes before firing our thrusters. The short separation burn increased our relative velocity and backed us a safe distance above and away from the Station.

Throughout the first orbit, we verified proper functioning of the spacecraft systems and loaded the deorbit burn parameters into the onboard computer. Descent is a critical phase of flight. All crew actions must be executed correctly and on time to ensure that our capsule intercepts the atmosphere at the right location and with the right velocity and orientation. Vigilance and accurate performance are paramount.

At the start of the second orbit, the automated descent timeline was initiated. We had been flying around the Earth in “airplane mode”, i.e. with the vehicle’s fuselage and solar arrays parallel to the Earth’s surface below. As we approached the southern tip of South America and while on the dark side of the orbit, we spun our vehicle around so that its aft end was facing the direction of flight. We then fired the main engine for four-and-a-half minutes. Any anomalies with this important burn could seriously impact our return to Earth. Accordingly, we closely monitored the progress of the burn and were ready to take corrective action if it stopped prematurely or if the engine did not shut down on time.

Happily, the burn was completely nominal. There was now no turning back – we were committed to a descent trajectory and would be on the ground in less than an hour.

The deorbit burn decreased our velocity by 115 meters per second – a small ΔV compared to our total orbital velocity of 8,000 meters per second. The more important effect of the burn was to change the shape of our orbit from circular to elliptical. The low point (perigee) of our new orbit was to occur in about 45 minutes and would intercept the dense layers of the atmosphere below. When it did, aerodynamic drag forces on our vehicle would dramatically increase, decelerate us and allow gravity to pull us toward the ground.

Entering daylight, I noticed that we were flying over the south Atlantic. The ocean surface seemed closer – we were already losing altitude. We crossed the equator over Africa and sped northeast toward our targeted landing zone in central Asia.

The Soyuz vehicle is composed of three segments attached end-to-end. Frank, Roman and I were seated in the center segment called the Descent Module. The other two segments (the Orbital Module and the Instrumentation/Propulsion Module) contained flight systems that had performed vital functions during our ascent, rendezvous and undocking. We no longer needed these systems. Fifteen minutes after the Instrumentation/Propulsion Module powered the deorbit burn, we closed the visors on our helmets and fired the pyrotechnics that severed the connections between the three modules. The Descent Module, now flying alone, had secondary flight systems (computer, life support, electrical power) that allowed it to operate independently. It also had a thermal protection system designed to withstand the intense heat loads that we were about to encounter. The two jettisoned modules, on the other hand, were not thermally protected. They began to tumble and would soon burn up in the atmosphere.

A few minutes after module separation, the Descent Module reached Entry Interface – a point 100 kilometers above the Earth’s surface where the atmosphere begins to thicken. My first indication of atmospheric reentry was the motion of the dust particles floating in the air. They no longer flew randomly about the cabin but now trended downward. The g-force indication displayed on our computer monitor no longer read 0.00, but ticked up slowly to 0.01 … then 0.02 …

An envelope of vapour-like plasma (i.e. charged glowing air particles) soon appeared around our capsule. Looking outward through my porthole was like looking through orange-tinted sunglasses. As the surrounding air became more and more heated, the orange tint darkened to a deep red. Minutes later I noted molten slag streaming by the window. Astonishing!

Our capsule’s kinetic energy was quickly being converted to thermal energy and being dissipated into the surrounding atmosphere. Viewed from the ground, our spacecraft resembled a fireball with a long plasma tail streaking through the sky.

Returning home in a Soyuz vehicle is like going over Niagara Falls in a barrel … a barrel that is on fire! Courtesy of NASA.

Some of the thermal energy was also heating up the Descent Module. Facing the direction of flight, the bottom of the capsule underwent the most intense heating and encountered high temperatures (1650oC – hot enough to melt iron). As protection, a heat shield covered the rounded bottom of the Module. The composition of the heat shield includes special materials that change from solid to gas upon extreme heating. This change of phase as well as the convecting away of the superheated gas cooled our spacecraft (a process known as ablation).

Our fiery descent through the upper atmosphere was also associated with rapidly increasing g-loads. Lying on our backs (the most comfortable way to return), the g-load vector passed through our chests from front to back and pushed us deeper into our seats. We sustained loads up to 4G’s for several minutes. Breathing became laboured. I performed the anti-G straining maneuver (contracting my leg and abdominal muscles) to retain blood volume and pressure in my chest and head.

Believe it or not but the ungainly Descent Module has maneuvering capability – it does not simply fall like a rock toward Earth. As we descended, the entry control system slowly rolled the capsule alternately to the left and right. This rolling action increased and decreased the aerodynamic lift force acting on the vehicle and modified our down-range and cross-range distances. If this entry system should malfunction, then Roman was prepared to take manual control. Using a hand controller, he would operate thruster jets on the outside of the capsule and steer the vehicle to the targeted landing site. A landing within 10 kilometers of the designated site (where the search-and-rescue crew await us) and while subjecting the crew to no more than 4G’s of loading would be considered a good landing.

With the g-load subsiding, we continued our fall toward Earth. It was now time to activate the parachute system. At 11 km altitude, the parachute cover on the outside of our capsule blew off with a loud bang and a shudder. A drogue chute was deployed and slowed our descent rate from 230 to 80 meters per second. The buffeting noise under chute was impressive. Sixteen seconds later, the drogue extracted the main parachute. This chute is large (1,000 m²) and slowed our rate of descent to seven meters per second. The sequence of chute deployments created some unusual vehicle dynamics. I had the impression that our capsule was bouncing side-to-side like a yo-yo on the end of an enormous cord and had the disturbing sensation that I was tumbling head over heels.

Two days earlier, aboard the ISS, my crewmates and I had participated in a procedure review with the reentry specialists at the Moscow Mission Control Centre. As the review session ended, Soyuz veteran Frank De Winne took me aside and said, “Bob, there will be a moment during descent when you will think that we are about to die. The motion dynamics of Soyuz entry can be extreme. But rest assured, all will be okay.” What a curious remark! I had no idea what Frank was talking about but made a mental note to be on the lookout for something unusual that might happen.

Now aboard a yo-yo’ing Soyuz, I turned my head to the left to look at Frank. The motion associated with chute deployment certainly felt extreme. Frank was looking at me with a big grin on his face and giving me the thumbs-up sign. This evidently was that moment of terror that he had pre-briefed a couple days earlier.

Deployment of the main parachute was a major flight milestone signaling that the nail-biting part of descent had passed. We would be on the ground in 15 minutes. Relieved, we all enjoyed the rest of the ride. Roman, particularly, was yeehawing like a cowboy.

An overview of the Soyuz flight plan. Courtesy of NASA.

The drama continued. Another loud bang announced separation of the heat shield. The shield had served its purpose. Its jettisoning exposed the altimeter, soft landing engines and a radio antenna – systems that were all located on the bottom of the capsule and would be needed for landing.

The outer window panes also fell away. During reentry, the hull of our spaceship, including the window covers, had become charred. Jettisoning the opaque panes allowed Frank and me to once again see outside. Our landing zone on the flat steppes of Kazakhstan was now in sight.

Opening of the BARD (Automatic Pressure Control Unit) depress valve was associated with yet another loud bang. This pyrovalve equalizes the interior cabin pressure with the outside pressure. Ambient pressure at an altitude of 5.5 kilometers is only half that at sea level so our pressure suits immediately inflated in compensation. With the sudden drop in pressure and temperature, a water vapour mist formed and momentarily obscured our view of the cabin interior. This cabin venting is necessary to prevent overstressing of the capsule’s pressure hull and to reduce the risk of fire. Throughout descent, my crewmates and I had been exhaling oxygen-enriched air from our Sokol suits into the cabin. Venting reduces the oxygen saturation and flammability hazard.

Suspended under parachute, our Soyuz capsule had been angled downward at 30 degrees for heat dissipation reasons. Prior to landing, our capsule needed to be repositioned so that it hung straight. “Rehooking” the main chute harnesses re-oriented the capsule to a vertical position but also kicked off another wild yo-yo ride.

Below each of the crew seats, there was a shock absorber. These shock absorbers dampen the landing impact with the ground. Until this moment, the shock absorbers had been compressed, i.e. stowed in a retracted position. To be ready for landing, they must now be extended to their operational position. Accordingly, our three seats moved forward automatically in unison. Following this movement, the glass visors of our helmets were only centimeters away from the control panel. It was a bit comical – I always considered the Soyuz cockpit to be cramped, but now it was ridiculously so.

Even the inner seat liners played a role. Each crewmember had a custom-made seat liner that ensured a tight, form-fit around our bodies to cushion the impact of landing.

Soyuz seat liners are individually molded prior to flight to custom-fit each crewmember’s body shape. Courtesy of NASA.

The sequencing of these last events seemed surprisingly rapid for a first-time Soyuz flyer like me. Jettisoning of the heat shield, blowing the BARD valve, rehooking the chute and the forward cocking of our seats all happened within seconds of each other. Quite eventful!

10 minutes before landing, we stowed unnecessary procedure books, tightened our restraint harnesses and powered on the gamma ray altimeter. We had regained air-to-ground communication following a period of radio blackout. For the last few minutes Roman had been talking with the search-and-rescue crew on the ground. The team had spotted our capsule under parachute and were reporting our altitude: 900 meters … 800 meters … 700 meters … As we neared the ground, I tugged one last time on my shoulder and waist straps, positioned my head back in my helmet with my mouth closed and teeth together, and crossed my arms over my chest.

Less than a meter above the ground, six small rockets on the bottom of our capsule fired and slowed us to a final landing speed of three meters per second. Although these rockets somewhat softened the landing, we still hit the ground with a jarring thump – akin to a small car crash.

Roman immediately toggled a switch to detach one of the two parachute risers. This must be done quickly (but not prematurely – ha!) to deflate the parachute. If the wind caught our billowing parachute canopy, it could topple us over and drag us sideways across the steppe. Roman’s timing was perfect – our capsule bobbled a bit after landing but remained upright. Style points for Roman!

Our charred Descent Module rests upright on the steppes of Kazakhstan following a job well done. Courtesy of NASA.

I was relieved that my crew had landed safely. But what a wild and busy trip! We removed our gloves, opened our helmet visors and turned on a ventilation fan. Unneeded systems were powered off and a radio locator beacon was turned on. Quite fatigued, the three of us decided to await the help of the ground team rather than egress the capsule on our own.

We had been aware that a low cloud ceiling in the recovery area might not permit the rescue helicopters to fly that day. This meant that we were not being met by the primary search-and-rescue crew, but by backup personnel. The backup crew had to drive overland for several hours on ATVs to reach us.

In retrospect, it was a privilege – and a bit surreal – to have been a Soyuz crewmember. The Soyuz vehicle has been flying to and from space regularly and rather reliably since the late 1960s. In fact, my Soyuz TMA-15 flight experiences during ascent, rendezvous and reentry were probably not much different than those for the earliest cosmonauts.

I envision that in a couple of centuries, the space program will have developed teleportation capability. Returning to Earth from space will then be a civilized affair – simply a matter of “beaming down”. Until that future date, reentry will continue to be a rollicking ride.