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The following paragraphs describe the canister under the following headings:
Technical details about the canister are provided on the Technical data page. Click
HERE
to go to the this page.
General
Checkmate is a canister capable of self-burying in any sand/silt-based seabed.
It has a payload compartment for the monitoring equipment appropriate
to its role. It has its own internal battery power source to power the
burying mechanism as well as for the payload systems and the two-way communications
package.
The payload compartment dimensions will be dependent on the role assigned
to Checkmate and can be tailor made to suit this role. The battery requirements
and hence size of battery compartment will also depend on the payload
role and will be tailored to the package.
At the end of the useful life of the package the canister can be left
to decay, destroyed with an internal explosive device or recovered by
use of the external lifting lugs with air bags.
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Burying mechanism
The canister consists of three concentric tubes forming an inner and outer
annulus with the space inside the innermost tube forming a space divided
into compartments to carry the payload. At the bottom of the lowest compartment is the impeller
with drive motor. The impeller draws water down the outer annulus from
the sea at the top of the canister, and forces this out of the base of
the canister to agitate the sea bed and form a slurry. This slurry is
forced up the inner annulus and expelled into the sea at the top of the
canister. This action produces a cavity the same size as the canister
and the weight of the canister makes it drop into the cavity as it is
formed. The result is that the canister is held firmly in the orientation
of burying and remains static on the sea bed.
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Communications
If two-way communications are required between the with the payload and a host these will be through a
third party package. Systems are available from companies such as EvoLogics of Berlin. They offer underwater
telemetry with Sweep-Spread-Carrier (S2C) technology. This communication
technology. This provides optimum underwater data transmission and is now established
as possibly the most accurate and efficient method for acoustic digital
data transmission. This system would be suitable for use with Checkmate.
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Burying position stabilisation
The principle of Checkmate burrowing into the seabed has been well demonstrated
by the prototypes. Some refinement of this aspect will be required when
a specific operational requirement has been identified by an end user.
However, the method of positional stabilisation of Checkmate during the
burying process has still to be tested in practice. No new technology
is involved, as positional stabilization is already well proven in applications
such as rocketry and remotely operated submersibles. The following paragraphs
set out how this will be achieved:
Checkmate may be launched into the water from a surface vessel, a submarine
or an aircraft. However it enters the water, it must be moved to, and
held in, a vertical position until it reaches the seabed. Once there,
it must be maintained upright as it burrows into the seabed. In addition,
the depth to which it buries must be controlled so that the sensors
carried in the upper part of the unit are able to function correctly.
Checkmate would be held upright as it sinks to the seabed from the
deployment of a small airbag attached to the top of the canister. This
would be activated by Checkmate's entry into the water.
During the descent a two axis, roll and pitch, angular rate gyro would be switched on and
would establish a vertical reference from the vertical position of Checkmate
in this phase of the operation. On arrival at the seabed the airbag
would be released to prevent its lift inhibiting burying.
The gyro's outputs would then be connected to a position control microprocessor
which operates horizontal water jets located near the top of the canister.
Three jets at 120 degree spacing round the canister will be sufficient
but four at 90 degree spacing will give a simpler control system. The
jets would be driven by a pump and three or four solenoid operated valves.
Provision of gyro stabilisation is a well proven technology and available
in the UK from a number of companies.
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Batteries
The calculations for power requirements and hence battery specification
are based on the UK and Australian trials where power usage recordings
have been made.
Checkmate requires power for both burying and then to operate the payload.
The burying power is a one off requirement whereas the payload needs are
continuous. To minimise this payload power demand an "On-Off" procedure
will be utilised. For Checkmate used in the data gathering role the operational
requirement is:
- Collecting data from local sensors and from more distant sensors via
hydroacoustic modems;
- Storing the collected data; and
- Reporting the data to a friendly vessel using a hydroacoustic modem.
When collecting data the local sensors, hydroacoustic modem and data
storage do not need to be continually switched on as data readings usually
change slowly. If they are switched on for, say, 10 seconds every minute
then the average power required will be reduced by a factor of six.
When transmitting data, the hydroacoustic modem will be switched on for the time necessary
to transfer all the stored data to the receiving station.
Alkaline batteries have a long shelf life and lose only a few percent of their capacity over a
year. They are also well suited to a high current load which is needed for the burying mechanism
and, to a lesser extent, for the hydroacoustic modems. Primary Lithium batteries have a slightly
higher energy density but are not yet available for high current applications.
Primary alkaline batteries have an energy density of 320,000Wh/cu.meter
hence enabling battery capacity and size to be calculated.
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Monitoring equipment
The payload monitoring instrumentation will be custom designed to suit the role of the package. Typical
monitoring equipment will include:
- Measuring sub sea oil field depletions:
- Providing navigational aid;
- Surveillance in harbours and anchorages
- Measuring current and tidal flows;
- Measuring pollution;
- Measuring radioactivity;
- Recording fish shoals;
- Identifying sea traffic from acoustic signatures;
- Coastal surveillance for unauthorised movements associated with people and other smuggling;
- Intelligence gathering; and
- Vessel recognition for military purposes, both defensive or offensive. Please see the Militarey site for
these applications.
There are many companies manufacturing the equipment required for these tasks.
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