American astronaut Gus Grissom felt like he was on top of the world for about 15 minutes on July 21, 1961, and indeed he was.
Grissom crewed on the Liberty Bell 7 mission, a ballistic test flight that launched him into the atmosphere on a rocket. During testing, it sat in a small capsule and reached a peak of over 160 kilometers before splashing down into the Atlantic Ocean.
The Navy ship USS Randolph watched the successful end of the mission from a safe distance. Everything had gone as planned, controllers at Cape Canaveral were jubilant, and Grissom knew he had entered a VIP club as the second American astronaut in history.
Grissom remained inside his capsule and bobbed on gentle ocean waves. She finished recording some flight data while waiting for the helicopter to take her to the dry deck of the USS Randolph. But then things took an unexpected turn.
An incorrect command in the capsule’s explosive system caused the hatch to pop out, which allowed water to flow into the small gap. Grissom had also forgotten to turn off a valve in his spacesuit, so water began to leak into his suit as he fought to stay afloat.
After a dramatic escape from the capsule, he struggled to keep his head above the surface while signaling to the helicopter pilot that something was wrong. The helicopter managed to save him at the last minute.
Grissom’s near-death escape remains one of the most dramatic events in history. But splashing into water remains one of the most common ways for astronauts to return to Earth. I am an aerospace engineering professor who studies the mechanisms involved in these events. Luckily, most jumps aren’t that frustrating, at least on paper.
Splashdown announced
Before a safe landing can be achieved, a spacecraft returning to Earth must slow down. A spacecraft has a lot of kinetic energy as it returns to Earth. Friction with the atmosphere creates friction, which slows the spacecraft down. Friction converts the spacecraft’s kinetic energy into thermal energy, or heat.
All that heat is released into the surrounding air, and it gets really hot. Since re-entry speeds can be several times the speed of sound, the force of the air pushing against the vehicle turns the vehicle’s surroundings into a scorching flow of about 2,700 degrees Fahrenheit (1,500 degrees Celsius). In the case of SpaceX’s massive Starship rocket, that temperature even reaches 3,000 degrees Fahrenheit (about 1,700 degrees Celsius).
Unfortunately, no matter how quickly this transfer occurs, there is not enough time during re-entry for the vehicle to slow down to a speed safe enough to avoid an accident. Therefore, engineers are resorting to other methods that can slow down the spacecraft during the jump.
Parachutes are the first option. NASA often uses designs with bright colors like orange, which make them easier to spot. They are also very large, over 100 feet in diameter, and each reentry vehicle often uses more than one vehicle for best stability.
The first parachutes, called drag parachutes, are launched when the vehicle’s speed drops below 2,300 feet per second (700 meters per second).
However, the rocket cannot hit a hard surface. It needs to land somewhere to soften the blow. Researchers realized early on that water is an excellent shock absorber. Thus the leap was born.
Why water?
Water has a relatively low viscosity, meaning it deforms quickly under stress, and its density is much lower than that of hard rock. These two features make it ideal for landing spacecraft. But another main reason why water works so well is that it covers 70% of the planet’s surface, so there’s a good chance it will hit it when falling from space.
The science behind water landing is complex, as evidenced by a long history.
In 1961, the United States conducted the first crewed landing in history. These used Mercury reentry capsules.
These capsules had a roughly conical shape and fell with their base toward the water. The astronaut inside was sitting face up. The base absorbed most of the heat, so the researchers designed a heat shield that boiled over as the capsule blasted into the atmosphere.
As the capsule slowed down and friction decreased, the air cooled, allowing excess heat to be absorbed from the vehicle, thus cooling the vehicle as well. At a sufficiently low speed, parachutes open.
Jumping occurs at approximately 80 feet per second (24 meters per second). While it’s not exactly a smooth collision, it’s slow enough for the capsule to hit the ocean and absorb the shock from the impact without damaging its structure, its payload, or the astronauts inside.
Following the Challenger loss in 1986, when the space shuttle Challenger broke up shortly after liftoff, engineers began focusing vehicle designs on what is called the crashworthiness phenomenon, or the degree of damage a vehicle sustains after striking the surface.
All vehicles now need to prove that they can offer a chance of survival in water after returning from space. Researchers build complex models, then test them in laboratory experiments to prove that the structure is strong enough to meet this requirement.
to the future
Between 2021 and June 2024, seven of SpaceX’s Dragon capsules performed a perfect jump on their return from the International Space Station.
On June 6, SpaceX’s Starship, the most powerful rocket to date, made a spectacular vertical splashdown into the Indian Ocean. The rocket’s thrusters continued to fire as it approached the surface, creating a spectacular hissing cloud of steam surrounding the nozzles.
SpaceX uses splashdowns to recover its boosters after launch so it can recycle them for future missions without causing significant damage to critical parts. Unlocking this reusability will allow private companies to save millions of dollars in infrastructure and reduce mission costs.
Splashdown remains the most common spacecraft re-entry tactic, and with more space agencies and private companies shooting for the stars, we’ll likely see many more of them happen in the future.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by: Marcos Fernandez Tous, University of North Dakota.
Read more:
Marcos Fernandez Tous does not work for, consult, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic duties.