As the name suggests, the capsule
parachutes into an
ocean or other large body of water. The properties of water cushion the spacecraft enough that there is no need for a
braking rocket to slow the final descent as is the case with Russian and Chinese crewed space capsules (while Shenzhou designed a raft and balanced capsule in case of splashdown), which return to Earth over land. The American practice came in part because American launch sites are on the coastline and launch primarily over water.[1] Russian launch sites are far inland and most early launch aborts were likely to descend on land.[citation needed]
Missions
The splashdown method of landing was used for
Mercury,
Gemini and
Apollo (including
Skylab, which used Apollo capsules).
Soyuz 23 unintentionally landed on a freezing lake with slushy patches of ice during a snowstorm.[2][3]
On early Mercury flights, a helicopter attached a cable to the capsule, lifted it from the water and delivered it to a nearby ship. This was changed after the sinking of Liberty Bell 7. All later Mercury, Gemini and Apollo capsules had a flotation collar (similar to a rubber life raft) attached to the spacecraft to increase their buoyancy. The spacecraft would then be brought alongside a ship and lifted onto deck by crane.
After the flotation collar is attached, a hatch on the spacecraft is usually opened. At that time, some astronauts decide to be hoisted aboard a helicopter for a ride to the recovery ship and some decided to stay with the spacecraft and be lifted aboard ship via crane. All Gemini and Apollo flights (Apollos 7 to 17) used the former, while Mercury missions from Mercury 6 to Mercury 9, as well as all Skylab missions and Apollo-Soyuz used the latter, especially the Skylab flights as to preserve all medical data. During the Gemini and Apollo programs, NASA used
MV Retriever for the astronauts to practice water egress.
Apollo 11 was America's first Moon landing mission and marked the first time that humans walked on the surface of another planetary body. The possibility of the astronauts bringing "Moon germs" back to Earth was remote, but not impossible. To contain any possible contaminants at the scene of the splashdown, the astronauts donned special Biological Isolation Garments and the outside of the suits were scrubbed prior to the astronauts being hoisted aboard
USS Hornet and escorted safely inside a
Mobile Quarantine Facility.[4]
Both the
SpaceX Dragon 1 and
Dragon 2 capsules were designed to use the splashdown method of landing. The original cargo Dragon splashed down in the Pacific Ocean off the coast of
Baja California. At the request of NASA, both the crew and cargo variations of the Dragon 2 capsule splashes down off the coast of
Florida, either in the
Atlantic Ocean or the
Gulf of Mexico.[5][6]
The early design concept for the Orion Spacecraft (then known as the
Crew Exploration Vehicle) featured recovery on land using a combination of parachutes and airbags, although it was also designed to make a contingency splashdown (only for an in-flight abort) if needed. Due to weight considerations, the airbag design concept was dropped. The present design concept features landings via splashdown in the Pacific Ocean off the coast of California.[7]
Disadvantages
The most dangerous aspect is the possibility of the spacecraft flooding and sinking. For example, when the hatch of
Gus Grissom's Liberty Bell 7 capsule blew prematurely, the capsule sank and Grissom almost drowned.
Since the spacecraft's flooding will occur from a location in its hull where it ruptures first, it is important to determine the location on the hull that experiences the highest loading.[8] This location along the impacting side is determined by the surrounding `air cushion' layer, which deforms the water surface before the moment of impact, and results in a non-trivial geometry of the liquid surface during first touch-down.[9][10][11]
If the capsule comes down far from any recovery forces, the crew are exposed to greater danger. As an example, Scott Carpenter in Aurora 7 overshot the assigned landing zone by 400 kilometers (250 mi). These recovery operation mishaps can be mitigated by placing several vessels on standby in several different locations, but this is quite an expensive option.
^Jain, U.; et al. (2021). "Air entrapment and its effect on pressure impulses in the slamming of a flat disc on water". Journal of Fluid Mechanics. 938 (4): A31.
arXiv:2012.10137.
doi:
10.1017/jfm.2021.846.
^Jain, U.; et al. (2021). "Air-cushioning effect and Kelvin-Helmholtz instability before the slamming of a disk on water". Physical Review Fluids. 6 (4): L042001.
arXiv:2106.09551.
doi:
10.1103/PhysRevFluids.6.L042001.
Ezell, Linda Neumann (1988),
NASA Historical Data Book(PDF), vol. II Programs and Projects 1958 - 1968 (NASA SP-4012),
archived(PDF) from the original on October 9, 2022
Ezell, Linda Neumann (1988),
NASA Historical Data Book(PDF), vol. III - Programs and Projects 1969 - 1978 (SP-4012),
archived(PDF) from the original on October 9, 2022