Can we agree that water is much more dense than air and that moving thru water requires much more energy and effort ? Yes, we can agree.
By itself, launching a missile from
UNDER water surface is no technically easy task, then add in the depth of water that the missile must travel through before breaking the surface and the technical issues are considerable.
First...There is the sea state...
Douglas Sea Scale - Wikipedia, the free encyclopedia
Whatever the surface does, there are effects under the surface. A Cat 4 hurricane produced surface waves can affect underwater motions as deep as 100 meters. Obviously, no one is going to be launching subsurface missiles under these conditions. But even on the Douglas sea state of 0, there are underwater currents that
WILL produce lateral course deviations of any body that travels perpendicular to those currents. An underwater missile launch will not be travelling with the current flow but quite vertically or with some angular path before breaking surface, correct ? So it appears the stability issues are quite resolved by the Iranians. We do not know up to what sea scale can this Iranian missile be launched but we can be generous with the kudos to the Iranians for resolving this.
Next...Breaking the surface...
Technically speaking, a torpedo is a missile -- an underwater missile -- of sorts. This is not semantics or wordplays to denigrate the Iranians. A torpedo is a technical sub-category of the missile family, and it is designed to operate underwater. Anyone who have been underwater, even in a bath tub, know how sensory deadened underwater can be. A torpedo is designed specifically for this environment. A missile, and let us use this word to denote an air traveling vehicle, is -- not so designed. This mean the missile must temporarily be a torpedo, and no matter how short that duration maybe, the entire contraption must have some awareness of the environments (plural) and when the contraption changes from a being a torpedo living underwater to an air traveling missile. It seems the Iranians have resolved this issue as well.
Next...The avionics...
The word 'avionics' is a portmanteau of 'aviation' and 'electronics'. A missile is an aircraft. Its avionics are designed for atmospheric flights. Its sensors are designed for effects that are produced by air, not effects produced by water. The avionics that depends on those sensors are engineered specifically for those effects from air, not effects from water. It means there cannot be a mismatch between sensors and the processors that work on those effects. It means the missile's avionics are essentially blind. The word 'blind' is important. It does not mean the avionics are not powered. It mean the entire avionics system is physically isolated from everything when it is underwater. Not only isolated but also protected because if the avionics are active, just waiting for those air produced effects, and somehow water produced effects are available, flight controls systems maybe activated underwater and disasters ensues.
If I look at this from a control system designer's perspective, there are several options available. The missile can have a physical switch that senses pressure differential between water pressure and air pressure. Now the question is the quality of this switch such as response time when the missile changes environment -- water to air. Assume the switch is top tier. Now the question is where to place the switch. If I place the switch at the missile's top section, the section that is the first to break surface, I must have a time delay based upon the missile's physical dimension, as from when the missile's lower section finally cleared the water's surface. Or I can place the switch at the missile's lowest part so there is no mistaking when the missile is no longer a torpedo.
This begs the question of: Are there advantages, disadvantages, and flaws on the location of this switch ? Absolutely.
If I place the switch at the missile's top section, the section that is the first to break surface, I can design in a pre-conditioning system that alerts the main avionics that the missile is about to break surface and these are the immediate air environment such as temperature, wind speed, baro, etc. If I place the switch at the lowest section, the section that is the last to clear water surface, the avionics would be shocked into service and sensors are at greatest risk for overload and require time to readjust. Or instead of just one switch, there can be several switches at strategic locations on the missile's body.
Depending on the missile's type, is it a pure ballistic or a cruise, I can design a control system with several switches to pre-condition the avionics' sub-systems to precision sequentially activate to maximize stability at environmental changes and finally -- stable flight. A ballistic missile does not have wings for aerodynamic exploitation but a cruise missile does, so I need to know when is the best time to deploy those wings. Going back to the Douglas sea scale. Since I may not have complete freedom to find stable location to launch, I should not have the missile in horizontal flight until X time have passed. I want the missile to continue vertical flight for at least two reasons:
1- To clear any potential higher than 0 sea state.
2- To allow the avionics time to assess the environment.
The longer this vertical flight, the better. But the downside is if the missile is a cruise type, the longer this vertical flight time, the higher the altitude, and the greater the risk of detection by the enemy. Remember, this is a subsurface launch, implying the launch mechanism -- the submarine -- want to get as close to the target as possible.
Summary...The technical issues presented are in no way comprehensive. The more sophisticate the base technology that supports the missile, no matter what type is it, the more sophisticate the weapon will be and the greater the flexibility of environment it can operate from. The US Navy is not going to tell you under what sea state it can subsurface launch its missiles, ballistic or cruise. For all you guys know, and I said 'you' without me in that group, the US Navy can subsurface launch under the cover of a Cat 4 hurricane and no one would know it.
Going back to the Iranians...What they did was technically impressive, and even if all they did was under sea state 0, they would be able to compensate for higher sea states. Kudos to them.