After the under ice submarine Autosub 3 was officially retired in 2017 the National Marine Equipment Pool was left with just one ship-deployed, high-power imaging submarine, Autosub6000.
Autoub6000 specializes in deep water imaging operations including sidescan, multibeam and camera surveys; it has however been in service for 12 years and although revolutionary for its time the vehicle will shortly come to the end of its serviceable life. When we set about starting the Oceanids Autosub2000 Under Ice (A2KUI) project we were keenly aware that what we had to design was not a single submarine but a submarine architecture, which can be used for multiple vehicles.
We currently have three submarines in the pipeline which will use the architecture we have created under the A2KUI project.
 Autosub2000 Under Ice (A2KUI)
The main focus of the current project is to deliver a 2000m depth-rated submarine capable of multi-day under ice operations equipped with a default scientific payload of upwards and downwards facing multibeams and Acoustic Doppler Current Profilers (ADCP), side scan sonar, sub-bottom profiler and Seabird 9+.
Autosub6000 Mk2
The replacement submarine for the existing Autosub6000 will be a 6000m rated vehicle of almost identical design to A2KUI, but fitted with the required 6000m rated syntactic foam and a different suite of default sensors including EM2040 multibeam, sidescan sonar, sub-bottom profiler, downward facing and forward facing camera systems, Seabird 9+ and down facing ADCP.
Autosub Hover One
The NOC's first foray into hover-capable vehicles, this small inspection-class vehicle will become our engineering development platform for future research and development activity.
Vehicle architecture
The submarine architecture was developed with two major design considerations:
- Reliability – Sending a submarine under an ice cap for multiple day missions is still a major technical challenge. The lack of remote communications, the stand-alone navigation and the difficulty in detecting and then avoiding obstacles still make these under ice missions hugely challenging.
- Flexibility – The key reason for building our own submarines rather than procuring off-the-shelf vehicles is so we can modify them to accommodate the latest sensors. An example being the latest Oceanids Biocam deployment where a large proportion of the submarine was reconfigured to fit the sensor package.
We decided upon an architecture designed around a dual redundant system, which means that if any one system in the submarine were to fail there would be a back-up to get the vehicle home. The central piece of this architecture is the payload tube (pictured below).
 One of the first submarine payload tubes undergoing temperature cycling in our oven. All testing is being done between -40°C and 70° to ensure it continues to operate in all conditions.
Onboard Autosub2KUI there are two payload tubes - one forward and one to the rear which connect every vehicle sensor. The 14 new PCB’s required for this system have all arrived and are undergoing rigorous testing of temperature and load. These payload tubes are designed to handle more power and communications than we have ever needed before, with a total of 1.2kW available (400W x 12v, 400W x24V, 400W x 48V) per tube.
Batteries
For the battery power, we have completely re-designed our re-chargeable pressure tolerant batteries. Autosub6000 currently supports 22.86 kWHrs whereas the new submarines will have 50kWhrs of onboard capacity. The first batch of 40 battery modules equalling 50kWhrs of capacity is now being manufactured to this new NOC design. The 50kWhrs will give an initial science range of 300-400km with the ability to increase this as we make power efficiency savings in the future.
 One of the first battery modules received for testing on the vibration jig. Once complete the submarine will contain 40 of these modules.
Vehicle Mechanics
As most are aware, getting equipment in the water is far easier than retrieving it, and our submarines are no exception. There are two main types of submarine launch recovery system (LARS). The most common is the sled type where a sled is lowered down from the stern of a ship and the submarine is pulled up the sled. It is a more generic system and allows the submarine to not experience such high lifting forces, allowing less of the overall submarine weight to be dedicated to structure. The downside is in a higher sea state you are trying to mate your submarine with a solid sled off the back of the ship and thus damage to the vehicle or the inability to recover it in rough seas is more common.
Autosub6000 in the NOC LARS after a deployment
The Autosub LARS uses the less common system which is closer in design to a regular crane with dual lifting cables. This system allows operators to remove the submarine from the water before mating it with the ship.
The downside is you require a much stronger - and therefore heavier - submarine structure to withstand all the forces involved. We have previously used this system to recover Autosub6000 in sea states as high as 6. The mechanical design team have been hard at work designing the new submarine structure, which is now complete, and currently in manufacture with the core pieces being made from titanium.
 One of many stress analyses completed by the mechanical design team, ensuring the structure can withstand all the loads of a recovery. At the top of the image you can see one of the two 'donuts' used to lift the submarine. The bottom of the image is the centre section where the batteries will be stored.
Next steps
Due to the impact of COVID-19 all on-site work on the hardware had to stop for three months. However, the team has now been back in the workshop for over a month and are progressing with the assembly. All of the main electrical systems, including the navigation, will shortly be connected to enable full systems testing to begin. Initial in-water trials had originally been planned for before the end of the year. These have been pushed back to March 2021, with two more trial dates scheduled for June and a sea trial later in 2021.
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