Attention to details
Reportage
Objectivity
I am standing in front of the Johnson Space Center building in Houston, trying to gauge the scale of what lies inside. Before me is the Neutral Buoyancy Laboratory, the NBL. The numbers speak for themselves: 62 meters long, 31 meters wide, 12 meters deep. The water volume is 23.5 million liters. But numbers do not convey the main point: here, at the bottom of this pool, space begins right here on Earth.
I am not here by accident. For the past few months, I have been talking to astronaut instructors, simulator engineers, and the cosmonauts themselves from various countries. I asked one question: how, on a planet with constant gravity, a dense atmosphere, and familiar pressure, do you recreate orbital conditions? It turned out that the answer is not a single trick, but a whole system of engineering solutions. Each of them simulates a specific aspect of the space environment.
Today I will see the first part of this system from the inside.
The Pool as a Substitute for Orbit
An instructor named Hervé Stevenin explains the principle that lies at the heart of everything: «We cannot remove gravity. But we can counterbalance it.» He is French, works at the European Astronaut Centre (EAC) in Cologne, but has come to Houston today for joint training. He speaks with a slight accent, but pronounces every technical word clearly.
Neutral buoyancy is a state where an object in water neither floats nor sinks. Gravity pulls it down, Archimedes' buoyant force pushes it up. When they are equal, the body hovers in the water column. It is precisely this state that is used to simulate weightlessness.
«But this is not true weightlessness», Hervé clarifies immediately. «In space, when you push an object, it moves uniformly until it hits an obstacle. In water, there is resistance. Therefore, movements are slowed down. An astronaut initiates a movement easily, but stopping it is a battle against inertia.»
I descend the metal stairs to the very edge of the pool. On the bottom lies a full-scale copy of the International Space Station modules. Metal structures, panels, handrails – everything is exactly like it is in orbit. Figures in white spacesuits move slowly around them. Above each astronaut is a group of support divers. Their task is to add or remove weights to maintain perfect neutral buoyancy.
One of the trainees is David Saint-Jacques from the Canadian Space Agency. He is rehearsing a spacewalk procedure that will become reality in six months at an altitude of 400 kilometers above Earth. Every movement is slow, precisely calculated. He grabs a handrail, turns around, moves a tool.
«They spend from 6 to 10 hours per session here», says Hervé. «For every hour of work in space, there are roughly 7 hours of training in water.»
The math is simple but tough. One spacewalk lasts an average of 6–7 hours. To prepare for it, an astronaut spends about 50 hours in this pool. In a spacesuit. Underwater. Repeating procedures until they become muscle memory.
I look at my watch: the session has been going on for four hours. Saint-Jacques is still working on the same section of the module. Slowly, methodically. This is not endurance training – this is precision training.
But water does not provide everything. It simulates the lack of weight, but not the lack of air. It allows one to rehearse movements, but does not convey the temperature fluctuations of space. For that, other equipment exists.
Vacuum Chambers: Where Pressure Drops to Zero
The next day, I am in another building of the center. Located here is Thermal Vacuum Chamber B – a thermo-vacuum chamber where both spacesuits and the people inside them are tested.
Engineer Thomas Sceurs explains the design: «The chamber allows us to create a pressure of about 0.01 millimeters of mercury. For comparison: normal atmospheric pressure is 760 millimeters. We create roughly one hundred-billionth of normal. This corresponds to an altitude of 65–70 kilometers above Earth – almost space.»
Inside the chamber is an overhead monorail system. It supports the astronaut in the suit, partially relieving the weight to simulate weightlessness. At the same time, air is pumped out of the chamber. When the pressure drops, the spacesuit inflates. Inside it remains 0.4 atmospheres – pure oxygen.
Italian astronaut Luca Parmitano described the sensations to me: «When the air is pumped out, you hear the suit crackling. Soft membranes turn into rigid walls. You feel the space inside the suit expanding. Movements become harder – you are working against pressure.»
For Chinese astronauts of the «Shenzhou» missions, such training is a mandatory part of the program. The Astronaut Center of China in Beijing has its own high-vacuum chamber with low temperatures. They recreate not only the vacuum there but also temperature conditions: from minus 100°C to plus 100°C.
Why is this important? In space, there is no air to transfer heat. The sunny side of an object can heat up to 120°C, while the shaded side can cool down to minus 150°C. Spacesuit materials must withstand these fluctuations. And the human inside must understand how the thermoregulation system works.
But even a vacuum chamber does not provide one thing – a prolonged sensation of weightlessness. For that, there are airplanes.
Parabolic Flights: 25 Seconds of Free Fall
Three days later, I am at Ellington Field, an airbase near Houston. Before me is a modified Boeing C-9, which NASA calls the «Weightless Wonder». Commonly, it has another name: the «Vomit Comet». The reason is simple – about a third of the passengers experience nausea.
The pilot explains the trajectory: «We fly horizontally at an altitude of 7,300 meters. Then we climb at an angle of about 45 degrees to an altitude of 9,750 meters. At this moment, passengers experience 1.8 G – meaning their weight almost doubles. Then we go over the top of the parabola and begin the descent. For 20–25 seconds, everything inside the cabin is in a state of free fall. True weightlessness.»
The physics is simple. The plane does not «create» weightlessness – it simply falls at the same speed as everything inside it. Passengers, equipment, dust particles – everyone falls simultaneously. Therefore, relative to the cabin, they are motionless. This is the exact state astronauts experience in orbit.
«But there is a difference», the pilot adds. «In orbit, weightlessness is constant. Here, it is 25 seconds. Then we pull out of the dive, and the G-force returns – again 1.8 G. Passengers are pressed to the floor. Then another climb, another parabola. We do 30–40 such maneuvers in a single flight».
The European Space Agency uses an Airbus A310 Zero-G for training – the procedure is the same, but the plane is larger. NASA used to use a KC-135: one of them performed over 58,000 parabolas between 1973 and 1995 before being retired. Now it stands as a museum exhibit next to Ellington Field.
Steven Ghiste, an instructor from the European Centre, told me about the first experience of astronaut candidates: «They learn not just to float in the air. They learn to control their body without support: how to push off, how to stop, how to turn. In weightlessness, inertia is your enemy. Initiating movement is easy, stopping is hard.»
These 25 seconds are used in different ways. Rookies learn to move. Experienced astronauts rehearse operations with tools. Scientists conduct experiments that require microgravity but do not require orbit.
Former astronaut Chris Hadfield told me: «A parabolic flight is the first introduction to weightlessness. After it, you realize: the brain is not ready for this. The vestibular system is confused. The stomach protests. But this is normal. The first time should be here, on Earth, and not in orbit.»
Centrifuges: When Gravity Intensifies
Weightlessness is one side of preparation. But there is the opposite side – G-forces during launch and reentry. For this, centrifuges exist.
I arrived in San Antonio, Texas, where the company KBRwyle operates one of the most powerful active centrifuges in the US. It is a massive structure: a 7.6-meter arm with a gondola attached to the end. Inside is an astronaut's seat. The entire system rotates, creating centrifugal force.
Sean Scully, a senior aerospace physiologist, points to the control panel: «The centrifuge can create up to 30 G. But for astronauts, we usually use 3–6 G. These are the loads they experience during rocket launch and landing.»
Six G is when your weight increases sixfold. If you weigh 80 kilograms, then under a 6 G load, your body presses against the seat with a force of 480 kilograms. Blood drains from the head to the feet. Vision narrows: first colors disappear, then only tunnel vision remains. If you do not apply special breathing techniques and muscle tension, you can lose consciousness.
Astronauts learn the Anti-G Straining Maneuver. The essence is tensing the muscles of the legs and abs, accompanied by short, sharp exhales. This helps keep blood in the upper body and maintain consciousness.
Historically, the most famous centrifuge was located in Johnsville, Pennsylvania. Astronauts of the Mercury, Gemini, and Apollo programs trained there. John Glenn recalled: «At 16 G, every bit of strength and technique was required not to blackout. Skin flattened, blood vessels burst.»
The centrifuge in Johnsville could create up to 30 G and operated from the 1950s until 1996. One of the records was set by Scott Carpenter, who withstood 18 G using the explosive breathing technique.
The Chinese program has its own centrifuge at the Astronaut Center of China in Beijing. It creates up to 9 G and is used at all stages – from selection to pre-flight training.
The European Space Agency sends candidates to Cologne, where there is a centrifuge capable of creating 6 G with a «chest-to-back» load direction – exactly how it acts during a rocket launch. The new ESA class, including Sophie Adenot and Raphaël Liégeois, underwent training there in 2024: they lay in the gondola, connected to biomonitors, and described their sensations over the radio.
But even a centrifuge does not provide a complete set of conditions. It creates G-force but does not provide a visual picture, nor does it simulate procedures. For this, virtual reality exists.
Virtual Reality: Space in Glasses
At the Johnson Space Center, on the third floor, is the Virtual Reality Laboratory. This is a place where astronauts «go out into open space» without leaving a room of 50 square meters.
James Tinch, head of the laboratory since the 2000s, shows the equipment: «The core of the system is the DOUG program, Dynamic Onboard Ubiquitous Graphics. It creates a three-dimensional model of the ISS accurate to the centimeter. The astronaut puts on a VR helmet, takes controllers, and sees the station. They can move along it, pick up tools, perform operations».
In the center of the room is the robot Charlotte. It is a mechanical arm linked to the virtual environment. When an astronaut in VR grabs a virtual object – for example, a panel with a mass of 200 kilograms – the robot creates the corresponding resistance. The astronaut feels the mass.
«This is critically important», says Tinch. «In space, there is no weight, but there is mass. A large object is easy to lift, but hard to accelerate or stop. The robot simulates exactly this.»
VR is used to train for SAFER – Simplified Aid for EVA Rescue, an emergency jetpack on the spacesuit. If an astronaut accidentally detaches from the station, SAFER allows them to return using 24 nitrogen micro-thrusters. Control is via a small joystick on the chest.
Training in VR allows one to practice the rescue repeatedly: the astronaut «detaches», activates SAFER, orients themselves, chooses a direction, returns. All this happens in a virtual environment, but the sensations are as close to real as possible.
Angelica Garcia, a simulation engineer, told me: «One astronaut said after a spacewalk: 'It was exactly like in the VR lab.' For us, that is the best assessment».
ESA also actively uses VR. In Cologne, the XR Lab operates, where several simulators have been created. The EVA Spacewalk Training Tool allows for studying external components of the ISS before exit. LUNA XR simulates the lunar surface for Artemis preparation.
Florian Saling, an engineer at the ESA XR Lab, explained: «VR does not replace the pool or the centrifuge. It complements them. VR allows you to repeat a procedure 50 times a day. In the pool, that is impossible – too long and expensive. VR brings the action to automaticity.»
Astronauts, according to instructors, love VR training. It is engaging, interactive, and gives instant feedback. Made a mistake? Start again. Lost orientation? Try differently. All without risk and the limitations of the physical world.
But there is a nuance: VR does not provide physical load. It does not convey the weight of the spacesuit, the resistance of water, or G-forces. Therefore, VR is part of the system, not a replacement.
How It Works Together
By the end of the trip, I understood the main point: no single technology recreates space completely. But together, they provide everything necessary.
The neutral buoyancy pool gives the sensation of weightlessness and the ability to practice multi-hour operations. Parabolic flights give true weightlessness – but only for 25 seconds. Centrifuges prepare for launch and landing G-forces. Vacuum chambers show how the spacesuit works in conditions close to cosmic ones. VR allows for repeating procedures many times.
Each method simulates one or two aspects of the space environment. But none simulates everything: «everything» is a combination of conditions that is impossible to create on Earth. One can only get close.
Before flying to the ISS, Thomas Pesquet told journalists: «I spent hundreds of hours in water, dozens of hours in the weightlessness plane, went through all the simulators. But when the rocket launched and I felt the real 3 G, I realized: you cannot prepare for this fully. Training gives skills. But space is always a first time».
Therefore, preparation lasts for years. The Basic Training program at NASA is two years. Advanced Training is another year and a half to two. Mission-Specific Training is from 10 months to two years. In total – up to five years before the first flight.
For missions to the ISS, the average astronaut spends about 300 hours in various simulators before the first flight. For Artemis lunar missions, the preparation time is shorter – about a year, but the intensity is higher.
The Chinese «Shenzhou» program uses a three-phase system: a year of basic training, three years of advanced training including full-scale ship simulators, and about ten months of mission-specific preparation.
All these programs are built on one idea: you cannot remove gravity on Earth, you cannot create a total vacuum at sea level, you cannot keep a human in continuous weightlessness longer than a minute without orbit. But you can divide the space environment into components – weightlessness, vacuum, G-forces, isolation, temperature fluctuations – and recreate each one separately.
Hervé Stevenin, who spent three days with me, put it this way: «Space is a puzzle of conditions. We cannot assemble it on Earth. But we can show every detail. And then the astronaut's brain and body will assemble the picture themselves.»
I am standing again by the NBL pool, where I started a week ago. Inside is a new group. Some of them will be in orbit in a year. Some will be on the Moon in five years. They move slowly along the bottom, in white spacesuits, under the supervision of divers. Around them is water, the light of lamps, concrete walls. Nothing resembles space. But every movement of theirs is a rehearsal of what will happen 400 kilometers above Earth, in the silence of the vacuum.
Space cannot be brought to Earth. But it can be taken apart, each part studied, and reassembled – in the memory, in the muscles, in the reactions of the person preparing to go there.
This is what preparation looks like. This is how Earth teaches humans to live without it.
