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Friday, March 1, 2024

How to Leave Space and (Safely) Crash Back Down to Earth

This story is adapted from How to Astronaut: An Insider’s Guide to Leaving Planet Earth, by Terry Virts.

There are several key things that every spaceship has to do if it wants to leave orbit and come back to Earth. The most obvious is changing its flight path to bend down toward the atmosphere, where the air drag will capture it and bring it relentlessly down to the surface. Next is withstanding the tremendous temperatures of reentry. Changing your flight path angle in an airplane is a relatively easy thing; you push forward on the stick and the air pressure on the elevator moves the nose of the airplane down and the trees get bigger. Pull back on the stick and the trees get smaller.

However, in space we have Sir Isaac Newton to thank for a very useful trick that allows astronauts to come home. Orbital mechanics are what determine a spacecraft’s motion once in space, and to change your course to the left or right you need a tremendous amount of delta-v, or change in speed. Because of this, it’s very inefficient to change your inclination, or heading. Most human spacecraft carry only enough rocket fuel to change their heading by a few tenths of a degree to the left or right. The good news is that we don’t have to move left or right to come back to Earth, we just need to go down. Here’s where the useful trick comes in handy—if you slow down, your orbit will descend. Conversely, speeding up makes your orbit climb. The amount of delta-v required for this trick is much less than for changing your inclination.


My spaceflight career began on the space shuttle Endeavour, as the pilot of STS-130, and we delivered the final two modules of the space station assembly sequence in 2010. A few years later I returned to the ISS, this time on a Russian Soyuz. When it was time to come back to Earth in both the shuttle and Soyuz, we turned the spacecraft around backward, fired the engine for a few minutes, slowed down by a few hundred mph, and our orbital flight path trajectory was bent downward toward the planet. This put us on an inevitable collision course with the atmosphere and our eventual landing sitet. While the rocket is firing, it is a gentle ride, only a few tenths of a g, nothing at all like dramatic Hollywood movies with astronauts screaming and being smashed into their seats. (That is what happened during launch, though.) After the burn finished, we had some time to relax and enjoy our last few minutes of weightlessness. Because once we contacted the atmosphere, about 20 minutes later, at what we call EI (entry interface), there was no more relaxing.

It was at EI that the shuttle and Soyuz experience diverged. Dramatically. The space shuttle was a magnificent flying machine, roughly the size of an airliner, and once it was back in the atmosphere it could bank and turn and maneuver like a normal plane. Except it was traveling at 17,500 mph and was surrounded by a cocoon of plasma that was as hot as the sun, created by the indescribable friction of the massive shuttle smashing into unsuspecting O2 and N2 molecules of the vanishingly thin upper atmosphere.

The view from the pilot’s seat returning to Earth that night in February was spectacular. At first there was a gentle pink glow outside my window, then it began to radiate a brighter orange and then red, accompanied by a flashing white light above the overhead window, reminding me of the scene in Alien when the strobe light was flashing while the ship was getting ready to self-destruct. This final phase of my mission took place in darkness, so I was able to see every nuance of the colorful plasma. It finally turned gray, and I raised the visor on my helmet and leaned over to the window. The plasma was slowly swirling around, like eddies and currents on a pond. I reached up, pulled my hand out of my glove, and felt the window, which surprisingly wasn’t at all hot. The most bizarre thing was a very distinct yet faint sound, like tapping your fingertips gently on a counter. I guess I expected burning sounds or air rushing sounds.

Ironically, as Endeavour continued to slow from the mounting air pressure, things began to speed up in my brain. The airspeed felt by the shuttle’s wings steadily increased, and the g loading built up to roughly one and a half g’s. Because our orbital track did not take us exactly to the runway at the Kennedy Space Center, we had to make several S-turns to fly toward our destination, taking advantage of the orbiter’s big wings. Our first roll reversal—turning the shuttle from left to right—took place over Central America as I peeked out the window, trying to get a glimpse of the ground speeding by below, but I couldn’t see anything other than a few city lights in the darkness.

As we descended, Endeavour’s indicated airspeed (essentially air pressure) steadily increased while her altitude and Mach number decreased (Mach 1 is the speed of sound, Mach 5 is five times the speed of sound, etc.). Because we were still supersonic until a few minutes before landing, people in Florida below us heard a very distinctive, double sonic boom from the shock wave the shuttle created as it smashed into air molecules faster than they were able to get out of the way. Once we began our final turn to line up with the runway, Zambo (George Zamka, our commander) let me fly Endeavour for a few minutes. As a test pilot, this was one of the highlights of my career.

The flying qualities of our rocket-turned-spaceship-turned-airplane were not great. It had what is called a harmony problem. It was very sluggish in roll, but very sensitive in pitch. It also had a quirky feature common to any delta wing airplane—if you pull back on the stick to climb, it first drops a bit in altitude, and then as the wing catches more air it finally climbs. This isn’t a big deal up at high altitudes, but in the final few feet before touchdown on the runway it was a serious trap that shuttle pilots trained extensively to avoid, because a sudden command to pitch up would lead to an abrupt touchdown. My job during those few minutes of stick time was to keep us centered and on the path that computer guidance was commanding. After those brief minutes of fame, Zambo took back control of Endeavour for final approach and landing.

My next job as PLT (pilot) was to be a cheerleader—calling out altitudes and airspeeds as we performed what amounted to a 20-degree dive-bombing flight path on the outer glideslope to the runway. When we were 2,000 feet above touchdown, Zambo slowly pulled up to aim down the runway on a 1.5-degree inner glideslope. At 300 feet I put down the landing gear, my most important task of the whole mission. Zambo greased the landing, it was perfect, and I occasionally remind him that it was the best shuttle landing I had ever experienced. Of course, it was also the only one. There was still quite a bit of piloting to do, though, as he flew the nose gear precisely down to the runway at the proper speed; getting that maneuver wrong could have led to a violent slap-down that would have cracked the fuselage. He kept our 220,000-pound vehicle on the centerline as it hurtled down the runway at nearly 200 mph, and I deployed the drag chute to slow us down. All the while a continuous stream of fire spewed from the back of the orbiter, where our rocket-fuel-powered hydraulic pumps vented their exhaust. Videos of the STS-130 landing looked like a scene from a Mad Max movie. As we slowed to less than 50 mph I jettisoned the chute, and shortly after that Zambo made the radio call, “Houston, Endeavour, wheels stop.” We could finally breathe again.

I liken the experience of landing in a space shuttle to a nice, smooth Air Force landing. But let’s go back to EI (400,000 feet above Earth’s surface) and switch our narrative over to the Soyuz, because there are other adjectives to describe that experience. If coming back to Earth in the shuttle is like riding an airliner, being in the Soyuz is like riding a bowling ball.

The first noticeable difference was shortly after EI as we reentered the atmosphere. This time it occurred in daylight. Capsules like the Soyuz, Apollo, SpaceX Dragon, and Boeing CST-100 all use bank angle just like an airplane does to turn, though much less effectively. While the shuttle had a cross-range of more than 1,000 miles, a capsule returning from orbit can typically turn only 50 miles to the left or right. As we were zooming over Africa, we banked to the right, and when I looked out the hatch at the ground below, we were moving fast! You don’t notice your speed up in orbit, 250 miles above the planet, but by this time we were only about 50 miles above the deserts and mountains, and still zooming by at several miles per second. It was so impressive that I scribbled a few unintelligible notes to myself on my kneeboard, trying to draw my fleeting view while scrunched up in that tiny capsule and bulky spacesuit.

The actual EI phase was also quite a bit different. Although I saw the same red/orange/pink glow out my window, the Soyuz was much more violent. First of all, the Soyuz separated into three parts with a giant bang minutes before EI: an empty orbital module, the descent module where we were, and an unmanned service module. After hitting the atmosphere, the external Soyuz heat blanket burned off. I had never been in a flying vehicle that was literally ripping apart while I was flying it, but thankfully this was per design. The thought 'I hope this disintegration eventually stops' did cross my mind, but there was nothing I could do in either case. There were constant banging and ripping noises as I watched pieces of the blanket (and who knows what else) fly by my window. Then came the parachute. We had had a briefing by crewmates who had done this before, and they basically said, “You’re going to think you’re going to die, but don’t worry, you won’t.” And you know what? It felt like we were going to die. But, thanks to the briefing, Samantha Cristoforetti, my Italian crewmate, Anton Shkaplerov, my Russian crewmate and Soyuz commander, and I had a blast when the drogue chute came out. We were hooting and hollering and yelling in Russian, “Rooskiy gorkiy!” Which means “crazy roller coaster!” In the F-16 community, we would have called this phase of flight “Mr. Toad’s wild ride.” The tumbling lasted a few minutes until the main parachute finally deployed and we were stable and calm, back at one g.


Next came the waiting, as we slowly descended the remaining few thousand feet to the Kazakh Steppe. Just when things seemed to be smoothing out, the seat violently raised itself lifting about a foot up from the bottom of the spacecraft. This allowed a shock-absorber device to cushion the impact a bit. Each crewmember has his own couch, form-fitted to his body; mine had been cast about two years prior, at the Energia factory near Moscow. During that procedure, you put on white long underwear to cover all of your skin and get lowered by a crane down into wet plaster. When it finally sets they pull you out, and voilà, you have a seat liner that is molded for your body. As the Russian technicians finish this seat, they manually carve out extra room above the top of your helmet area, and I used every bit of it. On Earth I fit without a problem, but after 200 days in space I had grown a few inches and the top of my head was butted up against the top of the seat liner.

Before the seat lifted up, I didn’t have much room in the cockpit. We were all in our bulky and uncomfortable spacesuits, wedged into a volume that was roughly the volume of the front seat of your car, with small pieces of equipment wedged into every inch of free space. After, I was moved up so that there was probably a foot between the control panel and my face. My right arm was smashed against the capsule wall. My knees were in my chest—no stretching your legs, there’s a capsule wall in your way. I was strapped down very tightly so I couldn’t move. I had in my right hand a control stick that doesn’t control anything, but gives the crew some primal comfort from the idea that they have some semblance of control, and a checklist in my lap. I thought to myself, “OK, I’m not claustrophobic, but if there was ever a reason in my life to panic it would be now.” I figured I had two choices: a) panic, in which case I’d be strapped in, unable to move, with absolutely nothing to do about it, or b) not panic, in which case I’d be strapped in, unable to move, with absolutely nothing to do about it. I chose option b.

Everything happened at once. A loud tone, explosion, violent crash, seemingly bouncing out of my seat, being thrown sideways. The Soyuz has “soft-landing” rockets on the bottom of the capsule, designed to fire a split second before impact, but my suggestion is to rename them “less-of-a-crash-landing” rockets, because a crash is exactly what it felt like. I imagine driving into a telephone pole in your neighborhood would feel roughly like a Soyuz landing. But the combination of form-fitted seats, soft landing rockets, and shock absorbers in the seats made the landing entirely safe, with the exception of a few minor bruises. Shortly after we landed and rolled 360 degrees, back to an upright position, someone on our crew said, “Are we alive?” The three of us put our hands together—we had survived and were back on our home planet!

Launching into space, accelerating from 0 to 17,500 mph, riding a rocket trailing flames, shaking and roaring and smashing you into your seat for the eight-and-a-half-minute ride to orbit is a kick-ass experience unlike anything you’ll find on Earth. But the ride back to Earth, slowly decelerating from 17,500 to 0 mph, is even more amazing. Many countries have launched rockets, but only a handful have successfully brought people back home from space, and there’s a reason for that. Reentry is hard. It’s an incredible experience, but a dangerous one. And if you ever get a chance to do it, you’ll feel like you’re going to die, but trust me, you’ll be OK.

Excerpted from How to Astronaut: An Insider’s Guide to Leaving Planet Earth, by Terry Virts (Workman). © 2020.

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