Humans are the most curious animals on earth. Their quest for knowledge and to explore the world around them and beyond has led them on innumerable explorations. Man reached the moon (literally) on 20 July 1969. Thereafter man has sent several probes into deep space reaching and crossing the expanse of the solar system. However, ironically there are places on the earth which remain a mystery. One of these are the deep oceans that cover 75% of our mother planet’s surface. Exploring the oceans is a difficult task. Firstly water is not our natural habitat, and we need support to breathe in water. But that, may be the least of our problems. The main issue is the water pressure. Every 10 meter column of water exerts a pressure equal to the pressure exerted by the atmosphere on us. The pressure at depths of 400 to 600 meters is enough to squeeze a cylinder made from steel around 32 mm (1.23″) thick like a can of beer. And the deepest oceans are 9,937 m (32,600 ft) deep. That means, if we put Mt Everest at this point, we will still have more than a kilometer of water above it. This location is called the “Challenger Deep” and lies at the southern end of the Mariana Trench in the Pacific Ocean. It is impossible for humans to survive such pressures and there are very few materials which can sustain such pressures.
However, the ever curious human has found ways and means of exploring these deeps also. The main requirements for exploration of the deep sea are: –
- Building a vehicles which can sustain the pressure exerted by the ocean and keep the humans inside it safe.
- The vehicle should be able to dive to the requisite depth and return back.
- It should be able to manoeuvre some distances.
- The vehicle should have a life support system like sufficient air/ oxygen for the crew to breathe.
- It should have means to collect samples from the areas being explored.
- It should have means to see outside, some kinds of portholes or windows.
- It should have external lights to allow people to see, as light cannot penetrate to the depths of the ocean.
- It should be able to communicate with the people on the surface.
Hence building a Human Occupied Vehicle which can dive deep is a tough task and this is evident from the fact that only five countries in the world – USA, Russia, France, Japan and China have operational HOVs which can dive to 6,000 m (19,685 feet) or more. In fact only USA and Japan have vehicles which can dive to 6,500 m (21,325 feet) and only China has a vehicle which can dive to 7,000 m (22,966 feet). But the oceans are such that with a 6,000 m (19,685 feet) diving vehicle, you can explore 98% of the world oceans, with a vehicle diving 6,500 m (21,325 feet) you can explore 99% of the world oceans and with a HOV diving up to 7,000 m (22,966 feet), you can explore 99.9% of the oceans.
An HOV system comprises the HOV itself, a mother ship which carries the HOV to the designated location. A launch and recovery system which is used to lift the HOV off the mother ship and place it in water and also to retrieve it onto the mother ship when the mission is completed.
A typical HOV comprises a pressure sphere, most frequently made from Titanium which can accommodate three people. It has life support systems, navigation and control systems and viewing ports to explore the outside world. The dark world outside is illuminated using high intensity lights. The HOV has ballast and trim systems to allow the vehicle to dive and maintain its attitude. It also has a buoyancy system made from syntactic foam to allow it to surface once the mission is over. A battery power pack provides the energy needed to operate the onboard systems as well as the external robotic arms and baskets for collecting samples. They communicate using either underwater telephone, which is a sonar based system with a very low bandwidth or they may have a tethered optic-fibre cable to relay live feed to the mother ship. Every HOV also has several sets of thrusters which are used to manoeuvre it in vertical as well as horizontal planes.
The typical endurance of these vehicles is between eight and ten dived hours per mission. Unlike submarines, HOVs do not use propulsion for diving but dive under gravity. Hence the process is slow and diving to 6,000 m (19,685 feet) can take up to two and a half hours one way. They flood their ballast tanks to dive and pump them out to make the vehicle light for surfacing. The ascend is also supported by the buoyant syntactic foam. The viewing portholes are made from perspex which are a few inches thick. There is hardly any space inside the Titanium pressure hull where the pilot sits on a box and the scientists sit on the floor on thin mats. There are no toilets and limited food for the 10 hour mission.
Modern HOVs carry high definition cameras for recording the underworld as the portholes have limited width of vision. However, some companies are experimenting with plexi-glass bubbles to replace the Titanium hull. This would allow for a panoramic 360 degree view of the ocean. Plexi-glass has limitations, but an American company claims that its Plexi-glass HOV can dive up to 11,400 m (37,402 feet). These vehicle look like the vehicle show in the underwater Hollywood thriller “The Meg”.