For incoming spacecraft from a very high orbit (think Mercury, Gemini, Apollo) they have always landed these crafts in the ocean (or perhaps there is an exception I am missing). I have heard people say that landing on land and landing on water has the same impact/devastation as landing on land with such a velocity.
Is this true? Why or why not?
I don’t know the answer, but it occurs to me that Russia has a lot more unpopulated open space for a dry landing. Almost certainly the guidance systems were good enough for a safe dry landing of U.S. capsules within the U.S., but there’s a lot more unpopulated water in the world’s oceans than there is unpopulated land in the U.S.
The exception is the space capsules from the former Soviet Union’s space program, which AFAIK always landed on land.
I think Johnny L.A.'s explanation is probably pretty close to the reason the two major space programs did things differently…the USSR had a lot of unpopulated land and it was easier for them not to have to send out a bunch of ships to retrieve a capsule that had landed in the ocean.
The space capsules you mention didn’t land with all that high a velocity being slowed by parachutes. It’s a matter of acceleration. Say the parachutes slow the capsule to a landing speed of 10 mph (15 ft/sec). When hitting the water the water does yield and permit the velocity to be lost over some span of time. The ground doesn’t yield and would stop the craft in a much shorter time which increases the acceleration experienced by the occupants significantly. Alternatively, the spacecraft could be made crumple like modern autombile front ends, reducing the velocity more slowly to lower the acceleration but seriously damaging the craft.
And, by the way, the Soviets did land their capsules on land.
An object moving through water experiences much more drag than an object moving through air. If the object is moving at high speed through water, the drag and negative acceleration is enormous.
Thank you all for pointing out the Soviet landings on land. I thought I was forgetting something (damn my ethnocentrism).
However, I am wondering about the statement I’ve heard that at these velocities landing on water is as bad as landing on land. I understand we all (U.S., Soviet) used parachutes. But was the velocity with parachutes still fast enough to make the impact on water as bad as the impact on land?
What about non-parachute landing (e.g. Genesis). Would the instantaneous velocity when hitting water be the same as on land? Would it have made a difference to the damage to the craft. (And no need to talk about the fact that there was supposed to be a parachute, or that the science would have been much harder to recover from the water - that is not my question).
I am asking about the truth of the statement “landing on water is as bad as landing on land when coming in at X velocity.”
The statements that it is as bad to land on water as on land are wild exaggerations, to say the least. Landing on water or landing on land from an altitude of 500 ft. are both close to 100% fatal. However, I’d like to see some one do a swan dive from the high board into an empty swimming pool. Well, no I wouldn’t really but you get my drift?
The impact velocity would be the same, but not the negative acceleration rate immediately afterward (force, which is what causes damage, is proportional to acceleration, not velocity). Water is a lot more compressible than dirt, and can flow out of the way much more easily, so a spacecraft hitting it will decelerate more gradually. If you get a chance, look at footage of an Apollo CM splashing down - it would sink into the water a good 5 feet or more over a full second or so. The same impact on dirt would have involved some loud crunching noises.
The best answer would be “No, but close”.
Further comments: The Soviets did not have aircraft carriers suitable for retrieval operations, and landing in their own territory was good for security. In the Vostok program, the cosmonauts actually bailed out and parachuted down separately once the capsule chutes were open. They did have to make the spacecraft stronger and heavier because of that.
“Instantaneous velocity” was a bad phrase. I have a terrible habit of not editing my posts before posting. Of course the velocity is the same as landing on land or water.
I am a loss for the correct term. I mean is there such a veolcity that hitting the water is as bad as hitting a brick wall?
Can someone give me a figure? Like what velocity would you have to be coming in to make the deceleration from the water as low as the decelration from a brick wall? Or what mass must the object be to make this difference negligible? Or are you folks trying to tell me the statement is just plain not true in any case?
I apologize in advance for being obtuse, if I am. That is not my intention.
Poking around a bit, I found one reference that the Mercury capsules slowed to 30 ft/sec, about 20 mph, and equivalent to about 1 second of freefall (32 ft/sec), or a 16 foot drop. The high board on a swimming pool would indeed be a pretty good analogy. Hitting the water would be OK, but I wouldn’t want to hit a hard surface at that speed. I’m presuming the Soviets slowed their capsules down a bit more to come down on land.
I’m going to take a stab in the dark (gosh, I like that phrase!) about where the idea that “landing on land and landing on water has the same impact/devastation as landing on land with such a velocity.”
“Ditching” an airplane – that is, alighting in water – is a hazardous maneuver. There have been many successful ditchings, examples of which can be seen in WWII newsreels. The problem with a water landing is that there are often swells. If an airplane is landed into a swell, it may well be destroyed. I’ve often heard “hitting a swell is like hitting concrete”. Water doesn’t compress, but it can move out of the way when it is uncontained. But airplanes are pretty fragile structures; they’re more likely to be shredded by hitting a swell than the swell is likely to be moved out of the way in a significant manner.
Another problem with water landings is that aircraft often have dangly bits. A Cessna 180 has conventional landing gear that will hit the water first and probably flip the aircraft on its back. A Grumman F6F Hellcat is a retractable-gear mid-wing design. (I believe that, since it was a warplane, it’s a bit stronger than your typical modern “spam can”, too.) If it hits the water with the gear retracted, the fuselage would tend to skim a bit and slow down before it dragged a wing. I’ve heard that a low-wing retractable is more likely to “groundloop” in a ditching, but the cockpit will be above the water. A high-wing retractable is likely to skim better upon alighting, but that the cockpit will be underwater. Non-retractables will hit wheels-first (which will decrease velocity) but may be more likely to flip. And so on…
U.S. capsules have a rounded bottom, which creates less friction on re-entry. They would also aid in discplacing water. This is how they were designed. Most aircraft were not designed to land in water, so this may be where the “landing in water is like landing on concrete” comes from.
PussyCow,
At all speeds below the speed of sound in water, water is ALWAYS softer than dirt or rock. So any impact at any given speed will always result in lower accelerations, versus hitting rock or dirt at the same speed. That’s just Physics 101.
But Engineering 101 also tells us that if your machine will be destroyed by, say, a 20G deceleration, then hitting the water or the land at, say, 30 mph will have the same practical effect: the 50G acceleration at water impact and the 300G acceleration at land impact both produce a pile of junk. The peices will be larger & less bent in the water than on the land, but beyond a certain point, junk is junk.
So you have to decide if you’re interested in looking at this issue from a physics or an engineering perspective.
I suppose I was looking for the engineering perspective.
Thank you, LSLGuy. You totaly answered my question with example numbers and everything.
Another note for all, the US capsules which landed on water simply splashed into the water under the slowing effect of the parachutes. To counter the lack of water the Soviet (and now russian) capsules, used a rocket pack on the bottom of the capsule that fired just before impact to slow the craft even further.
Not sure of what the actual impact velocity was on the Soviet/Russian capsules was, but I’m sure I’d prefer the nice wide open water to land in myself.
-Butler
In the Soviet ones, at least you wouldn’t get seasick. A lot of the US astronauts, who had managed zero g okay, got seasick waiting to be picked up after splashdown. The space capsules made terrible vessels, and rolled something fierce.
I’ve just recently been reading “This New Ocean” by William Burrows and he talks about the sea/land landing decision a bit. He suggests that the decision to land American spacecraft in water primarily had to do with the relatively small area of suitable landing area to be found in the US as opposed to the larger spaces available to the soviets. Apparently the thinking was that if the capsule actually came down on target there wouln’t have been a problem, but a capsule off target could end up in rough terrain. On the other hand, missing the middle of the ocean landing zone would still result in a water landing.
Burrows also suggests that, at least for the early Soviet landings, the Russians were concerned to obscure the fact that their cosmonauts actually parachuted from their capsules before landing. It was easier to do this when the capusule came down in the middle of nowhere.
As far as American landings on dry land are concerned, I remember building plastic models of Gemini capsules in the late sixties with some sort of landing skids that extended from the bottom. Maybe there was some sort of contingency early on that made it into the design of the model.
Technically that meant they didn’t have the first official manned mission into space, their craft carried a Cosmonaut up but didn’t carry him back down to the planet’s surface because he bailed out on the way. Its why the landing of the craft was so secretive IIRC.
And Soviet crew were equipped with a camoflaged suit for landing in as well as a gun in their survival gear incase of wild animals 
I make it equivalent to a 14 ft. drop. If the acceleration on splashdown is limited to 3 g’s (WAG) then the capsule needs to come to a stop in a little more that 4-1/2 ft. which would take just under 1 second assuming constant acceleration.
OOPS. Make that just under 1/3 second.
1 second would be 32 ft/sec, pretty close to 30, and a 1 second drop is 16 feet. I didn’t want to figure it exactly.