Splashdown (spacecraft landing)


Splashdown (spacecraft landing)

Splashdown is the method of landing a spacecraft by parachute in a body of water. It was used by American manned spacecraft prior to the Space Shuttle program. It is also possible for the Russian Soyuz spacecraft and Chinese Shenzhou spacecraft to land in water, though this is only a contingency. The only example of an (unintentional) splashdown in Soviet history is the Soyuz 23 landing.

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 was the case with Russian and Chinese manned space capsules, which returned to Earth over land. The American practice came in part because American launch sites are on the coastline and launch primarily over waterFact|date=February 2007. Russian and Chinese launch sites are far inland and most early launch aborts are likely to descend on land.

The splashdown method of landing was utilized for Mercury, Gemini and Apollo (including Skylab, which used Apollo capsules). On one occasion a Soviet spacecraft, Soyuz 23, punched through the ice of a frozen lake (nearly killing the cosmonauts), and this was unintentional.

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. (Because of his overshoot aboard "Aurora 7," and mindful of the fate of "Liberty Bell 7," Scott Carpenter alone egressed through the nose of his capsule instead of through the hatch, waiting for recovery forces in his life raft.) 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.

The new Crew Exploration Vehicle, which will replace the Space Shuttle (which lands on a modified aircraft-style runway), will be designed to be recovered on land using a combination of parachutes and airbags, although it is also designed to make a contingency splashdown (only for an in-flight abort) if needed. Although not new, NASA and the Air Force originally wanted to place a paraglider recovery system to allow for a controlled, precise landing on land on ski-like skids (a landing system used on X-15 rocket plane), most likely on the dry lakebeds at Edwards Air Force Base in California. This idea was first proposed for the Gemini spacecraft, but was dropped in favor of the traditional parachute system.

Disadvantages

While the water the spacecraft landed on would cushion it to a degree, the impact could still be quite violent for the astronauts.

There are several disadvantages for splashdowns, foremost among them being the danger of the spacecraft flooding and sinking. This happened to Gus Grissom when the hatch of his Mercury-Redstone 4 capsule malfunctioned and blew prematurely. The capsule was lost and Grissom nearly drowned.

Another problem associated with splashdown is that if the capsule comes down far from any recovery forces the crew are exposed to greater danger. As an example, Scott Carpenter in Mercury 7 overshot the assigned landing zone by 400km. This was caused by a retroattitude misalignment caused by Carpenter's failure to turn the automatic system off during manual maneuvering (while trying to determine the cause of Glenn's "fireflies") causing excessive propellant use, misalignment of the spacecraft at the beginning of re-entry causing a shallow trajectory (thus landing long) and a three-second delay before firing the retro-rockets due to inattention. It took three hours for a recovery helicopter to reach his location. These recovery operation mishaps can be mitigated by placing several vessels on standby in several different locations, but this is quite an expensive option.

Locations of splashdowns

Manned spacecraft


"Planned recovery ship **"

Unmanned spacecraft


External links

Gallery

References

* [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880016045_1988016045.pdf NASA Historical Data Book - Volume II - Programs and Projects 1958 - 1968 - NASA SP-4012]
* [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880016046_1988016046.pdf NASA Historical Data Book - Volume III - Programs and Projects 1969 - 1978 - NASA SP-4012]


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