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In my setting (something of a grounded take on Buck-Rogers-style space opera) militaries sometimes are unable to directly breach landmasses from orbit (due to complications similar to how anti-aircraft turrets could deny air-supplies or bombings during WWII) and are forced to depend on a sea-side approach.

To this end they have to deploy warships and other sea craft from orbit, and do so as quick as possible in a blitzkrieg effort to establish a presence in the sea before the enemy can respond to counter.

The problem is that warships are big, and heavy. Further the aquatic warships are legitimately aquatic warships and should not be capable of flight. (The setting is only pseudo scientific, but I haven't hand waved the expense and technical issues of getting massive objects into the air or into space)

To this end, establishing a:

  • Reasonably safe
  • Fast as possible
  • Reasonably cost-effective
  • Disposable

...Manner of deploying the vessels.

To this end I have the following solution:

Heat-resistant paneling would cover the bottom of the vessels. Large (removable) side panels (increasing surface area) would slow the descent to something of a fast plummet. Large partial parachutes would deploy closer to the water, perforated as to not actually bring the descent to a gentle fall, but just to reduce the speed only slightly faster than the speed of oil rig lifeboats upon deployment. As it hit the water, chemical balloons would inflate as charges would eject the side panels. The balloons would ensure the vessel wouldn't submerge too far, and would return to the surface, after which the balloons would be ejected.

The skeleton crew, meanwhile, would be strapped into padded harnesses much like rollercoaster chairs, and would have mouthguards and helmets. Upon resurface (which should only take a matter of <5 seconds, I'd reason) they would leave their harnesses, and set to work getting the ship operational, guns online, and cover incoming transports with the additional crew.

Is this feasible? What problems could be foreseen? How could these issues be corrected?

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  • $\begingroup$ What if, instead of all that, you try en.wikipedia.org/wiki/Lun-class_ekranoplan? $\endgroup$ – cobaltduck Jul 26 '16 at 16:24
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    $\begingroup$ Don't come from space. Stablish an underwater presence. Google for "supercavitation", which is a way to reach hypersonic speeds while underwater. Your vehicles would literally fly underwater, so they could go form sea to air seamlessly. $\endgroup$ – Renan Jul 26 '16 at 16:41
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    $\begingroup$ It used to be that torpedoes would hit a ship full-on, and just make a big hole in the side. But these days torpedoes explode under the ship, displace the water, and cause the ship to break in two (or otherwise suffer major structural damage) due its own weight. That is the problem with ships. They are meant to have their weight supported by the water, not hold themselves together the same way a plane does. $\endgroup$ – AndreiROM Jul 26 '16 at 17:02
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    $\begingroup$ If you can drop aircraft carrier sized drop-pods on your enemy's planet, why aren't you just dropping them on his cities? $\endgroup$ – Kys Jul 26 '16 at 18:24
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    $\begingroup$ I meant dropping a city block sized bomb rather than a landship, but if you want your army to fight "cleanly", I can see your point. $\endgroup$ – Kys Jul 26 '16 at 18:45
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First things first. You want to bomb the surface of the ocean where you're gonna be landing your ships. You're gonna wanna bomb under the surface as well, because you don't know what you're going to find in there.

You should probably be able to do so with minor ethical implications since you'll be bombing open seas, not major population centers (unless there are people living under the water where you are going).

You are going to do that from orbit. This orbital bombing will serve to take out anyone or anything that might intercept your seaships before they land.

As for the ships proper, they will be submarines. But they won't be shaped like the submarines you've just thought about. They will look like a mix between fighter planes and a spaceship.

An example of a sub-fighter from Deep Angel Supercav An example of a sub-fighter from Deep Angel Supercav

They will enter the atmosphere just like the shuttle does. That is going to be hypersonic speed. And they will do some flight, unpowered flight at that, but controlled. They will be able to steer, but they will not be able to fly like a fighter.

For an atmosphere like that of the Earth, the ships will need ablation layers. The atmosphere will slow them down and their terminal velocity will be around a couple hundred meters per second. When they get close to the sea (between 500 and 200 meters), they will need to deploy retro-rockets for the final slow down (much like the Soyuz does, but for a longer time and distance).

Once they splash down, at a speed of around 5 to 10 meters per second, the fighter-jet plane shape of theirs comes to use. They will eject their shuttle-like nose, revealling a nose much like that of the Shkval torpedo (which makes them a little different from the picture I used above). The ships sink, then kick in their engines. The nose, and the high speed they will soon attain, will cause water to vaporize around them. They will be enveloped by water vapor that has as much drag as air, so that they will literally fly underwater due to supercavitation.

By these means they can move awesomely faster than a seaship would, while also making detection much harder (your enemies know where you splashed down, but not where you are going from there!). They will be moving faster than sound in water so they will be hard to track on sonar, and since they are underwater radar will be quite useless to detect them as well. If they do get detected somehow, the water outside their bubbles will deter most kinds of attacks.

As you approach your target, you should be able to take out any submarines and ships stationed there with a lightning strike, then stablish naval superiority.

Once they reach a city, the ships can surface and either bomb the city from the sea, or run into it if you give them wheels.

Since they do fly underwater, they could have limited flight abilities for a little while outside the water (remember they are more hydrodynamic than aerodynamic though), so they can probably hover for a while (think of a modifierd VTOL system) over water and on the shore. Yes, I am bending your no-flight rule a little... You can ignore this last paragraph if you want to keep them strictly naval.

Good luck, commander.

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  • $\begingroup$ Excellent answer, Renan; I was typing much the same thing when your answer was posted! One thing I would like to add for OP's benefit, if you don't mind, is that much of this process requires massive amounts of power. Retrorockets, for example, are much less efficient than parachutes and use a lot of energy. At first glance this is a problem, but the energy used to get these ships into space in the first place will be even greater, so getting them down to the surface will be cheap in comparison. You needn't worry about saving power in this scenario! $\endgroup$ – MozerShmozer Jul 26 '16 at 17:36
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    $\begingroup$ @MozerShmozer retrorockets would be cheap in this scenario. You'd be only be using them in the very last few meters of the descent, using them to go from 200m/s to 5m/s. Any fighter in our real world does that nowadays in a matter of seconds with their regular engines, and they fly for hours. To the pilot it should feel like taking off, but in reverse. $\endgroup$ – Renan Jul 26 '16 at 17:39
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    $\begingroup$ I might point out that supercavitating submarines are actually going to be the loudest things in the ocean. As well, supercavitating bullets designed to be fired at underwater targets (like mines) don't benefit at all from slowing down before entry, the rapid entry creates the bubble. A human crew might not survive, though. $\endgroup$ – Thucydides Jul 26 '16 at 23:27
  • $\begingroup$ @Thucydides I put the slow down phase there to make sure the vrew does survive. As for being loud, any sonar will either detect a hypersonic object when it gets hit by it, or it will detect the shockwave without being able to track it. In order to track hypersonic objects you'd need a sonar array with each microphone separated from each other by many miles and interconnected by radio so that you can triangulate the signals, and it wouldn't be accurate. $\endgroup$ – Renan Jul 26 '16 at 23:39
  • $\begingroup$ Sorry, sonar does not work that way. A towed array from a single ship would suffice to get a track, and two ships in formation would make accurate triangulation. Any weapon that causes the bubble to collapse would also destroy the supercavitating sub as it slammed into a wall of water. $\endgroup$ – Thucydides Jul 27 '16 at 2:19
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While landing a spaceship at sea is perfectly possible (All American manned capsules outside of the Space Shuttle landed at sea), the solution isn't very efficient for the invaders.

First off, spacecraft carrying ships will be far larger and have much more inertia than spacecraft which are not carrying them. These spacecraft will be easy targets for the enemy space fleet and space defences, since they will be large targets with very limited maneuverability. Most of your wet navy ships will never make it to the planet.

The second issue is that the carrier spacecraft are not just going to hover over the oceans, but need to come into orbit around the planet in order to make the drop. If ground based defences are so effective that they can deny a landing zone on any of the continents, they can most certainly shoot down any spacecraft passing overhead as it attempts to go into orbit. This is just amplified when the spacecraft in question is already the size of an aircraft carrier or larger.

Finally, assuming the landing goes as planned, your wet navy is going to be far away from the actual target zones you wish to deal with, so unless you are dropping supercavitating submarines capable of travelling at supersonic speeds under water, you will be vulnerable for a period of hours to days against conventional weapons designed to attack ships and submarines.

Far better to use military shuttlecraft which can manoeuvre in the atmosphere and give your troops the ability to control the time and place of the landing. Instead of trying to come ashore like the Marines, you will essentially be coming in like an airmobile force.

In other words, you want this.

Aliens dropship

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  • $\begingroup$ So a couple of issues I have with this answer that'd I'd appreciate you addressing before I upvote: A) Earth's atmosphere is only about 10 miles high, give or take, while the ISS is about 250 miles high. Defenses could reasonably guard the atmosphere but not orbit, nor against medium-distance ships, save airforce deployment (which the questions is aiming to outrun). B) Assuming the wet ship deployment is successful, the ships (and their complements) should, reasonably, be able to defend themselves. $\endgroup$ – Nex Terren Jul 26 '16 at 17:21
  • $\begingroup$ C) The question is focused on getting an established foothold, so I wouldn't say extended travel to land is out of the question. $\endgroup$ – Nex Terren Jul 26 '16 at 17:21
  • $\begingroup$ @NexTerren Earth's atmos is 62mi high. en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line $\endgroup$ – dpdt Jul 26 '16 at 21:25
  • $\begingroup$ @dpdt Technically that depends on what you define as the atmosphere, as the final layer is well above 62 miles (100 km) high: nasa.gov/mission_pages/sunearth/science/atmosphere-layers2.html I was using the portion that typically an 'air force' would be limited to. $\endgroup$ – Nex Terren Jul 26 '16 at 21:31
  • $\begingroup$ Attacking spacecraft in orbit is well with the capabilities of today's military forces. and interceptors have been demonstrated launching from land, sea and even aircraft, so it is quite possible to defend against objects in LEO. The number of wet navy ships which can be deployed would be tiny compared to the wet navy of the defending planet, and will be overwhelmed; attackers from space will always be on the wrong end of the logistics equation. Realistically, SF war should bypass spacecraft altogether and use a wormhole to bring troops and supplies directly to the target. $\endgroup$ – Thucydides Jul 26 '16 at 23:17
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Just taking your scenario and working off what you have so far.

A ship designed for space, is a lot different than a ship designed water. See this question and answer/S from SpaceExploration SE. A 'spaceship' is designed to withstand internal atmosphere pressure of 1 bar pressure to the outside and can be designed with no cross beam support and have very thin walls. While submarines have to withstand several to dozens of bars of external atmospheric pressure. They have much thicker walls and need some sort of structure support.

Now from what I can understand, these military 'water units' of yours don't have to be designed for space but it has to get from space down to the water! May I suggest a MIRV style re-entry method.

This was described as a Cyclon MIRV This was described as a Cyclon MIRV

What I'm envisioning is a hollow outer shell that is designed for space and more importantly the heat of re-entry. This could be tube shaped, cone shaped, whatever works best. Once through atmospheric re-entry, this outer shell can fall away revealing several of your water units. This 'thinner' outer shell would be no use to any explosive bombardment and any fragments might get caught in critical ship parts so I reckon best to lose the fake walls.

Your panelling and parachutes should still work. However, as I mentioned in my previous edit land based defenders would target your parachutes, panelling and balloons. You could possibly use the release of your fake walls as red herrings for any guided weapons coming your way, like chaff. Invest in Chaff!

You would aim to either land in the middle of the ocean with some distance from any land based defensive systems or have multiple, self deploying panelling and parachute replacements in case they do manage to destroy your already deployed equipment (I would recommend both alternatives). I believe you would have several to hundreds of these MIRV styled units deploying at the same time, simultaneously releasing your 'smaller' water units at calculated stages to reduce the risk of all of them getting hit by each other and by the defenders.

You can then have each individual 'water unit' split off from your MIRV increasing the chances of a ship getting through. More chaff would be necessary if under fire from the planet's defenders. These are the war ships built for atmosphere and water pressure. So they will be thicker hauled and capable of surviving hits from missiles and explosives (I hope!).

As previously mentioned, everything will have to be strapped in for a vertical entry. I think a roller-coaster styled harness which is fixed in place may be a death dealer for your troops. Rather have the harness on a 'elasticated' system, almost like bungy rope (but not that stretchy). IE a suspension system. This would lessen the effects of the sudden impact into the ocean while still keeping them secure. You could have several critical ship systems on a suspension system as well.

If you wish, you can design a secondary MIRV-like capsule that could encompass your 'water units' that would act as the suspension unit to the entire 'water unit' rather than just the troops - almost like a ship on an internal track system. But that is a lot of debris to take into account.

I know you mentioned that your panelling and parachutes would slow your speed down to that of lifeboats launching off oil rigs. You could combine this with this previous worldbuilding SE question regarding breaking the surface tension of the water.

I initially suggested that you consider shooting something 'large' into the ocean before you crash into it to break up the surface. Apparently mythbusters has disproven this on a human scale. However, you will be in a ship with a thicker skin than that of a human body. Seeing as you may be coming in under heavy fire, maybe some of your airbraking techniques failed to work to maximum effect so you would still be coming in too hot. The answer, to the previous linked question, by ckersch suggested that it is not so much breaking the surface tension but aerating the nearby water.

creates a localized downward current and aerates the water. The downward moving water reduces the velocity differential between the faller and the water, which in turn reduces the force exerted by the water on the faller. Aeration reduces the effective density of the fluid, which also reduces the force of the water on the faller. (In essence, the faller has to move less water out of the way per unit distance travelled if some of the water is replaced by air.)

You could design a 'cannon' in the 'bow' (front?) of the falling ships. These could shoot an explosive device into the water that would release a large concussive force aerating the water before the ships hit. Make sure that the ships aren't too close behind the explosive as you don't want to weaken your own ship's defences before you even start fighting your enemies!

You can then use the water dynamics of the water returning to normal effective density, along with your balloons to help propel your ships into your horizontal position. If there are defenders in close proximity to your water landings, your balloons are especially vulnerable. So, maybe consider a kevlar based material or again multiple balloons in reserve. You could consider using a substance similar to the spray filler for tyre punctures as a balloon's 'self healing' technique but I don't know how that would affect the landing qualities of the balloon.

Take a few minutes to take stock, see that all your troops survived and then you can decide how it is you wish to attack your land and possibly naval based enemies.

References:

Mirv image from a osnetdaily http://osnetdaily.com/2014/12/china-tests-icbm-multiple-warheads-thanks-clinton-era-tech-transfer/

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  • $\begingroup$ What do you mean by 'break up the surface?' Do you mean create waves? How would waves help lessen the impact? $\endgroup$ – Nex Terren Jul 26 '16 at 16:33
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    $\begingroup$ If yo were to jump from more than 30ft or 30metres above the surface of water, it will bee like landing on concrete. You need to shoot or throw something at the water or break up the surface somehow. When people jump from high up, you often see them throw the equipment bag first. Consider haveing a big cannon on the bow (front?) of the ship facing straight down at the water. Shoot an explosive or similar device shortly before you hit. This isn't to make 'waves' :) $\endgroup$ – EveryBitHelps Jul 26 '16 at 16:37
  • $\begingroup$ Each individual ship will be very tiny, and not have much room for crew, supplies or weapons. Attacking a planet with a fleet of motorboats is an interesting concept, but might not be very practical.... $\endgroup$ – Thucydides Jul 26 '16 at 23:21
  • $\begingroup$ Haha. It would be something to see! No, I'm thinking MIRV styled but larger. Much larger. Don't know how that would affect the delivery system but that is something to be looked into. Maybe another SE question. Can MIRV delivery system be upscaled?! $\endgroup$ – EveryBitHelps Jul 27 '16 at 6:07
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You asked for problems:

  • The defenders could try to secure oceans with air defense cruisers, or possibly even hidden submarine batteries. The dropped ships won't be able to maneuver much.
  • The square-cube law. Large vehicles will find it difficult to aerobrake or use parachutes because their drag area is small compared to their mass.
  • All fittings will need shock-proof mountings. That increases the weight of the warship and makes it less effective compared to a planet-bound defensive warship.
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