By Marcos Fernandez Tous, University of North Dakota
For about 15 minutes on July 21, 1961, American astronaut Gus Grissom felt on top of the world — and in a very real sense, he was.
Grissom crewed the Liberty Bell 7 mission, a ballistic test flight that launched him through the atmosphere atop a rocket. During the flight, he sat inside a small capsule and reached a peak altitude of more than 100 miles before splashing down in the Atlantic Ocean.
A Navy ship, the USS Randolph, watched the successful end of the mission from a safe distance. Everything had gone according to plan. Controllers at Cape Canaveral were exultant, and Grissom knew he had just entered a very exclusive club as the second American astronaut in history.
Then things took an unexpected turn.
Grissom remained inside his capsule, swaying on the ocean waves while waiting for a helicopter to carry him to the dry deck of the USS Randolph. As he finished recording flight data, an incorrect command in the capsule’s explosives system caused the hatch to pop open, allowing water to pour into the tiny spacecraft.
Grissom had also forgotten to close a valve in his spacesuit, so water began seeping into the suit as he fought to stay afloat. After escaping the capsule, he struggled to keep his head above the surface while signaling to the helicopter pilot that something had gone wrong. The helicopter managed to save him at the last instant.
Grissom’s near-death escape remains one of the most dramatic splashdowns in spaceflight history. But despite the danger of that early mission, splashing down in water remains one of the most common ways astronauts return to Earth.
I am a professor of aerospace engineering who studies the mechanisms involved in these events. Fortunately, most splashdowns are not quite that nerve-racking — at least on paper.
Splashdown Explained
Before a spacecraft can land safely, it has to slow down.
A spacecraft returning to Earth carries tremendous kinetic energy. As it tears back through the atmosphere, friction creates drag, slowing the vehicle. That friction converts the spacecraft’s kinetic energy into thermal energy, or heat. The heat radiates into the surrounding air, which becomes extremely hot.
Because reentry speeds can be several times the speed of sound, the force of the air pushing back against the vehicle creates a scorching flow around it. Temperatures can reach about 2,700 degrees Fahrenheit, or 1,500 degrees Celsius. In the case of SpaceX’s massive Starship rocket, that temperature can climb to nearly 3,000 degrees Fahrenheit, or about 1,700 degrees Celsius.
Even with all that atmospheric drag, a returning spacecraft still cannot slow down enough on its own to avoid a crash. Engineers need additional methods to reduce speed before landing.
Parachutes are the first major tool.
NASA typically uses bright-colored parachutes, such as orange, to make them easier to spot. They are also enormous, often with diameters of more than 100 feet. Reentry vehicles usually deploy multiple parachutes to improve stability. The first parachutes, called drag parachutes, deploy when the vehicle’s speed drops below about 2,300 feet per second, or 700 meters per second.
Even then, the spacecraft cannot land safely on a hard surface. It needs something that can cushion the impact.
Researchers learned early on that water makes an excellent shock absorber.
That is how splashdown became a standard part of human spaceflight.
Why Water Works
Water has a relatively low viscosity, meaning it deforms quickly under stress. It also has a much lower density than hard rock. These two qualities make it ideal for absorbing the impact of a returning spacecraft.
The other major advantage is simple: water covers about 70% of Earth’s surface. If you are falling from space, your odds of hitting ocean are pretty good.
The science behind splashdown is complex, and its history goes back to the earliest years of human spaceflight. In 1961, the United States conducted its first crewed splashdowns using Mercury reentry capsules.
Those capsules had a roughly conical shape and fell with the base facing the water. The astronaut inside sat facing upward. The base absorbed most of the reentry heat, so engineers designed a heat shield that would boil away as the capsule shot through the atmosphere.
As the capsule slowed and atmospheric friction decreased, the surrounding air cooled enough to absorb excess heat from the vehicle. At a low enough speed, the parachutes deployed.
A typical splashdown occurs at about 80 feet per second, or 24 meters per second. That is not exactly a gentle landing, but it is slow enough for the capsule to hit the ocean and absorb the shock without destroying the structure, damaging the payload, or injuring the astronauts inside.
Designing for Survival
After the loss of the space shuttle Challenger in 1986, engineers placed increased emphasis on what is known as crashworthiness — the degree to which a vehicle can protect its occupants and structure after impact.
Today, spacecraft must prove they can offer a chance of survival after returning from space, including in water landing scenarios. Researchers build complex models and test them through laboratory experiments to show that the structure is strong enough to meet these requirements.
Splashdown may look simple from the outside, but it requires careful engineering. The spacecraft must survive reentry heat, parachute deployment, ocean impact and recovery operations. Each stage has to work properly for the mission to end safely.
Splashdown in Modern Spaceflight
Splashdown remains central to modern spacecraft recovery.
Between 2021 and June 2024, seven SpaceX Dragon capsules performed successful splashdowns after returning from the International Space Station. SpaceX uses splashdowns to recover Dragon capsules after launch and return, with no significant damage to critical parts, allowing the company to refurbish and reuse them for future missions.
On June 6, 2024, SpaceX’s Starship, the most powerful rocket to date, made a vertical splashdown in the Indian Ocean. Its rocket boosters continued firing as it approached the surface, creating a dramatic cloud of steam around the nozzles.
Reusability is one of the major goals of modern spaceflight. Recovering capsules and spacecraft components allows private companies to reduce costs, reuse hardware and make future missions more affordable.
The Future of Splashdown
Splashdown continues to be one of the most common tactics for spacecraft reentry, and that is unlikely to change soon.
As more space agencies and private companies send vehicles into orbit and beyond, we are likely to see many more spacecraft return to Earth by landing in water. The method may be old, but it remains practical, reliable and deeply connected to the history of human spaceflight.
From Gus Grissom’s terrifying escape to modern reusable capsules, splashdown represents one of space exploration’s great paradoxes: after traveling beyond Earth, crossing the edge of space and surviving the fire of reentry, the journey often ends with a hard slap into the ocean.
Marcos Fernandez Tous is an Assistant Professor of Space Studies at the University of North Dakota.
Editor’s Note: This article is republished from The Conversation under a Creative Commons license. The original article noted that it had been updated to clarify that SpaceX has been recovering Dragon capsules during splashdown.
