Power and endurance

How long will an ecoSUB mission run for?

This depends upon several variables; the type of batteries fitted, the speed of the mission, the depth of the mission, the number of dives and surfaces in a mission, the sensors being carried and their sample rates, the number of message transmissions made and the local oceanographic conditions.  Currently, we expect that the Micro (u5) will have mission times up to 8 hours and the Milli (m5/25) up to 8 hours.  This can be increased using alternative battery chemistries.

The GUI (Graphical User Interface) has a simple endurance calculator built in.  With planned enhancements, we anticipate mission times of 24 hours or 100 km being possible in the not too distant future.

​What batteries does ecoSUB use?

​Currently, ecoSUB uses standard D size Alkaline cells available almost anywhere in the world.  There are no transport issues associated with these batteries.  ecoSUB incorporates some advanced battery management  hardware and software to ensure maximum battery life and minimize effects of deep discharge; remember that low temperatures affect battery capacity.  We have undertaken extensive research on battery technology and for maximum capacity it is recommended that the brand mentioned in the operational manual are used.  ecoSUB can also use Lithium cells; these offer extended endurance but less capacity to supply high currents and so may not be suitable for all missions.  Battery technology is constantly under review and because of the manufacturing process selected we can adapt the design to quickly take advantage of changes in battery technology.

​Can ecoSUB use rechargeable batteries?

Announcement pending...

​How fast will the vehicles go?

​Assuming a zero current environment, then speeds of around 1 to 1.5 m/s or 3 kts should be achievable at full power.  This can be affected by increased drag due to some sensor fits.  Of course the faster the ecoSUB goes, the shorter the battery life.

What happens if the batteries expire or if there is a fault?

​ecoSUB has several watchdog systems running simultaneously, these monitor battery health, and various electronics and firmware sub systems.  There are multiple levels emergency behaviours built into ecoSUB, to maintain vital systems in the event of failures or low battery levels.  The final level of protection is “survival mode” if the battery level falls below that which can maintain a full system, then everything shuts down with just the bare minimum over watch enabled.  ecoSUB is naturally positively buoyant, and it will always float to the surface, where it will send its position every hour via Iridium.  Motors, sensors and other non-essential services are turned off.  When the user is in the general area of the ecoSUB for recovery, a command can be sent to the vehicle, to increase the transmission rate to 5 minutes, and/or activate the strobe to assist recovery.  

Communications

​HOW DO ECOSUBS COMMUNICATE?

ecoSUBs carry Wi-Fi for short range high bandwidth communications used mainly for data transfer, initial set up and testing.  With a beam antenna at the base station, ranges of up to 300m are attainable.  For long distance, over the horizon, the Iridium satellite short burst data (SBD) system is used and an Iridium modem and antenna are provided as standard.  An Iridium airtime agreement is required.  Iridium is mainly used to send status data and sensor snapshots due to reduced bandwidth and to locate the vehicle when on the surface, an important consideration at recovery time.  Vehicles can be re-tasked over the Iridium channel.  Both subs also carry GPS for position information.
 
ecoSUBs can carry acoustic nano-modems for vehicle to vehicle, and vehicle to surface communications.  This is a low power, short range (~2-3km) system for low bandwidth data.  It can be used for enhanced navigation, by using a surface GPS reference to inform ecoSUBs of their precise location using novel, but sophisticated LBL techniques. The acoustic communications can also be used for data harvesting from seabed nodes using compatible equipment.
 
The specially designed Wi-Fi, Iridium and GPS antenna also incorporates visible and infra-red strobes which are activated on the surface.  These are particularly useful for recovery even in daylight.
 
We have developed a specialist command, control and communications box “HERMES-C3” to enable Iridium, Wi-Fi, 3G/4G and Acoustic Communications in internet denied environments.  This useful tool allows monitoring of submerged subs fitted with acoustics, as well as long and short range communications.  A variant of HERMES-C3 can be fitted to ASVs or other surface assets to act as an LBL surface node or communications gateway in force multiplier scenarios
​

​ARE ECOSUB DATA ENCRYPTED?

When using Wi-Fi, normal WPA-2 protection is employed.  A further level of protection is that the vehicle can only connect to the ecoSUB control router, and cannot be accessed by another generic router, each router being setup differently for each user.  Furthermore the range of the Wi-Fi connection is limited to a few hundred meters.  When using Iridium, data are transferred in binary, using a format and compression technique known only to ecoSUB.  The Iridium gateway also employs its own privacy protocols for its users.  In addition, we utilise some proprietary techniques to add a further layer of security to the channel.
 
Should end users wish to deploy their own data encryption protocols, this can be achieved using the front seat / back seat facility.  Iridium has no restrictions on the sending of encrypted data so long as it conforms to their SBD general requirements.  An example of this, would be where a user’s, confidential sensor produces confidential data; this can be encrypted in the back seat, passed to the front seat for transmission without ecoSUB or any other link in the chain having access to the decryption key.  Conversely, encrypted messages can be received in the front seat and passed though the barrier to the back seat for decryption by the end users installed technology.

HOW MUCH DATA CAN I SEND THROUGH IRIDIUM?

We use the Iridium Short Burst Data service (SBD) this is limited to 270 bytes in a single message and so large data sets cannot be sent via this channel.  We do use a binary format, with additional compression where possible to maximize the available bandwidth.  It is possible to send data over several SBD messages and reconstruct at the receiving end but this can be expensive and unreliable.

​​CAN ECOSUB CARRY OPTICAL MODEMS?

Not currently.  Available blue light ultra-high bandwidth underwater optical modems, are large and very power hungry, two attributes not aligned with the ecoSUB concept.

​​WHY DO I RECEIVE SOME IRIDIUM EMAILS WITH NO ATTACHMENT?

​This means the vehicle is checking the iridium ‘mail box’ and is not sending a message containing any data, this allows the vehicle to receive missions or commands.

​How do I recover my data?

​Subsets of data as well as system status are delivered by Iridium when on the surface.  Complete data sets including vehicle control data are transferred via Wi-Fi when within range.  Data are stored internally on an SD card which may be removed for download.

​How can I protect my data if I cannot recover the vehicle?

​We have included an “erase data” command that can be sent to the vehicle which totally erases all recorded data for security reasons.  A “Wipe Data” command is also provided to totally erase the system firmware as well as all the data.  Wipe data means that there is no longer any chance of communicating with the vehicle without a return to factory refit.

 

Missions

​HOW DEEP CAN THE VEHICLES GO?

The ecoSUBµ5 is designed for operation to 500m, whilst the ecoSUBm25 can be used to 2,500m.  A shallow version of the ecoSUBm is available to 500m (ecoSUBm5).

​HOW STEEP CAN THEY DIVE?

Because of the way that the pitch control is arranged using the internal battery pack as a moving mass, the vehicles can dive very steeply.  In fact the micro (µ) can spiral down almost vertically, a great attribute when obtaining water column profile data. 
​
As standard, ecoSUBµ comes to the surface, un powered and tail first.  This saves energy; however this means that sensors located in the nosecone may not be flushed with new water samples on the way up, providing misleading data.  To mitigate this, missions can be constructed such that the ecoSUB surfaces nose first with thrusters on or off.

​CAN ECOSUB FOLLOW A FEATURE?

​Yes, ecoSUB can follow a “layer” say, depth/pressure, salinity, temperature etc in the vertical or bottom track if the altimeter is available

​How do I program a mission into my ecoSUB?

​We provide a free and simple to use GUI (Graphical User Interface) mission planner which allows missions to be constructed simply on a map or chart overlay and sent to the vehicle using the Wi-Fi or Iridium connection.  Missions are checked for errors and impossible scenarios before being uploaded to vehicles.  The GUI also provides special tools to aid recovery at the end of a mission as well as performing pre and post launch checks.  Alternatively, users can construct missions at a “code” level using our pseudo open source interface.  An enhanced version of the GUI with additional features is available as a paid for upgrade.

How do I know if my vehicle is operating properly before launch?

Pre-launch checks are carried out using the Wi-Fi connection, the GUI provides a graphical view of the major vehicle sub systems health.  We monitor internal pressure, temperature and humidity as well as battery status, motor and actuator activity; this provides early warnings of leaks and other issues.  We also use the visible strobe light to signal both AOK and ERROR conditions so that the basic status can be checked without Wi-Fi and upon removal of the start magnet. ​ The vehicle also sends status messages via Iridium, to provide advance warning of potential issues.

​What happens if I cannot recover my ecoSUB right away or I want it to be dormant for a while?

​ecoSUB can be sent a command to enter survival mode, whereby everything shuts down with just the bare minimum over watch enabled.  ecoSUB is naturally positively buoyant, and it will always float to the surface, where it will send a position every hour via Iridium.  Motors, sensors and other non-essential services are turned off.  If the user wishes to re-activate the vehicle, a new mission can be sent to exit survival mode and resume normal operation, If sufficient battery power remains.  The messages will be received once every hour, the reactivation command can take time before it is processed by the vehicle.

​Does ecoSUB have bottom avoidance?

ecoSUB AUVs can carry an altimeter which can be used for bottom avoidance or bottom tracking or for basic bathymetry.  We pre-set the bottom avoidance to 1m, although this can be altered, for example when using side scan sonar.  Remember that the hard bottom may be at say, 100m, but there could be 10m of weed!!

Can ecoSUB hibernate for long periods on the bottom?

​No, ecoSUB is slightly positively buoyant and so would need continual thrust from its motor to remain on the seabed thus depleting batteries in a short period of time.  ecoSUB does have a “loiter” behaviour whereby it will circle around a fixed waypoint for a fixed period of time.  ecoSUB also has a “stay in circle” behaviour which will power the ecoSUB back to a fixed Lat/Long should it drift out of a pre-set circle on the surface.

​How accurate is the underwater navigation?

​The small size and low cost of ecoSUB precludes the use of large, expensive Inertial Measurement Units (IMU), we currently use a system of dead reckoning with low cost IMU which yields and accuracy better than +/- 10% of distance travelled.  This can be improved by more frequent surfacing to get GPS correction, or by use of our network localisation which can achieve +/- 5m accuracy independent of distance travelled.
 
ecoSUBm can now carry a DVL for enhanced navigation and georeferencing of data.  DVL provides +/- 0.1% accuracy over distance travelled whilst bottom lock is active.

​How is ecoSUB affected by currents?

​ecoSUBs are small and lightweight, they are almost neutrally buoyant in water.  Nuclear submarines are also neutrally buoyant, but they have significant mass and so are not influenced greatly by currents.  ecoSUB has very small mass and is easily blown off course by currents.  Using our LBL navigation system, DVL and enhanced IMU A.I algorithms allows individual vehicles to compensate in real-time for effects of currents.  In the absence of acoustic LBL or DVL, careful attention to tidal currents during mission planning can mitigate for this.  ecoSUBs are no worse than submarine gliders in this respect.

Can ecoSUB be launched from an aircraft?

Yes, ecoSUB has been integrated into the University of Southampton “Spotter” UAV and is dropped using a parachute.  ecoSUBu5 can be accommodated within an A size Sonobuoy package.  ecoSUB has no CAA or other air launch related approvals.

​ecoSUB has no control surfaces how does it surface and dive?

ecoSUB uses an internal moving mass system.  The battery pack moves forwards and backwards under processor control to raise or lower the nose.  The ecoSUBu5 can stand almost vertically when the battery pack is pushed fully forward to lift the antennas and strobes are clear of the water.

​How do I launch & recover my ecoSUB?

​Because of their size and weight ecoSUBs can easily be hand launched by one person.  The ecoSUBµ can be dropped into the water from 1-2m whilst the ecoSUBm is normally lowered using a sacrificial rope or boat hook.  We do offer a launch harness accessory for the ecoSUBm. 
 
Recovery is best effected by hand from a small boat with a low freeboard such as a RIB.  Alternatively, a large salmon net or boat hook can be used.  

​Can ecoSUB operate as an autonomous surface vehicle (ASV)?

​ecoSUBm has “a traditional” antenna mast, which allows Wi-Fi, Iridium communication and GPS navigation on the surface.  Some sensors are below the water line when surfaced which means that surface measurements can be acquired, for example Chlorophyll, turbidity or Hydrocarbons.  ecoSUBu5, needs to pitch fully forward to expose the antenna and whilst it can travel on the surface, it cannot communicate or get reliable GPS whilst doing this.

Payload

What sensors can ecoSUB carry?

The range of sensors available to ecoSUB users is growing all the time.  Currently, we can offer CTD, Fluorimeter, oil in water, pH DO, altimeter, sound velocity, turbidity, passive acoustics, side scan sonar, wave height and direction etc. For an up-to-date list of the possible sensors contact the ecoSUB sales team or alternatively go on www.ecosub.u

Can I fit my own sensors?

Yes, if they comply with the power demand, weight, size & communication constraints of ecoSUB.  

​Can I change sensors in the field?

​Swapping out factory fitted sensors in the field is simple, they are essentially plug & play.  Most ecoSUB sensors are designed to be pressure tolerant and installed within the free flooding nose cone of the vehicle, connected to the vehicle electronics via an underwater connector mounted on the forward bulkhead.  It is possible to replace, say a CTD sensor with a Fluorimeter or sound velocity sensor.  In some circumstances the nose cone will also need to be changed to accommodate the alternative sensor.

Can ecoSUB have a camera?

​Currently we have an optional GoPro nose cone mount which provides excellent performance in shallow well lit, clear waters.  We also provide deep rated GoPro housing (300m) to increase the capability of the vehicle.  We are developing a camera capable of tolerating the 2500m of the ecoSUBm25 but there are no plans to offer a matched lighting system for operating below the euphotic zone.  The power required by lighting is not currently available from ecoSUB.  There are solutions to this, which we have plans to adopt.  

HOW ACCURATELY DOES ECOSUB DETERMINE DEPTH?

​We use a very accurate pressure sensor installed in the rear bulkhead of the ecoSUB.  Standard specification is
 
Accuracy (Linearity (best straight line), hysteresis and repeatability) typ.  0.02 %FS
Total Error Band (10...40 °C) 0.05 %
Total Error Band (-10...80 °C) 0.10 %
 
We take a reading of atmospheric pressure at boot up to “zero” the depth measurement, and we take into account the density of the water.
 
The calculation for depth is:
(pressure – surface pressure)/(water density*acc gravity)
 
We use constants for density and gravity, but these could be altered if required.

​Is the speed of water passage enough to flush any conductivity cell chosen?

​We take great care to position the sensors to provide maximum exposure whilst mainlining an adequate level of mechanical protection and low drag.  Most sensors are located within the nose cone at the front of the vehicle and maximum flushing is achieve when the vehicle is moving forward.  To save power, we generally rise to the surface using only the vehicles natural positive buoyancy, and tail first to expose the antennas as early as possible upon reaching the surface.  If an “up cast” is required, the vehicles can be programmed to surface nose first with or without thrust.

Software / Firmware

Is ecoSUB “Open Source”?

Not exactly.  We believe it is important for the fundamental operation of the vehicles that the major systems and behaviours that have been designed and tested by us are maintained, and available to users to implement in the way that they choose.   To enable this, we have provided a firewall, split between front seat and back seat facilities.  All the essential attributes of the vehicles reside in the front seat behind a firewall through which commands developed by users in the back seat are passed.  Once received by the front seat, commands are sanity checked and passed on to be carried out.  Any resulting feedback from front seat services are passed back through the firewall to the back seat for use as seen fit.  Users can use ROS or software running on Raspberry pi, Arduino, etc. to perform their exclusive protocols independent of the vehicle.

​What operating System does ecoSUB use?

​We use LINUX, with ROS, Python and C++

Maintenance

​How easy is it to replace parts in the field?

​ecoSUB is constructed around a central tubular pressure case with removable end caps.  The nose and tail sections are 3D printed along with the rudder and propeller and are easily replaced in the field.  Many of the internal parts are also 3D printed and can be readily replaced in the field should they become damaged.  Several commonly required spare parts are provided with each vehicle and larger spares kits can be purchased.

​Do I need to purge ecoSUB with nitrogen?

No, both ecoSUB AUVs have a partial vacuum (typically 500 hPa) established using a low-cost hand vacuum pump and valve system.  This not only keeps the pressure vessel end caps in place without the use of bolts but confirm that there are no leaks prior to deployment as internal pressure is reported as part of the status data and GUI checks.  The internal pressure can be equalized to ambient using the valve which makes opening the pressure case easy.  ecoSUBs are sealed with double O ring piston seals for maximum pressure integrity.

Have more questions?  Please get in touch via [email protected].