| The following paragraphs
provide technical data about the canister under the following headings:
Canister Weight
The following chart shows the relationship between total canister weight
and size.
The following assumptions have been used in creating the chart:
- The canister inner cylinder is made from steel 3mm thick.
- The canister's two outer cylinders are made from steel 1mm thick.
- The outermost cylinder has a diameter 1.2 times that of the inner
cylinder
- Three height/diameter (H/D) ratios are considered: 2:1,2.5:1,3:1
- Alkaline batteries with 320kWh/m3 energy & 1500kg/m3
- The battery occupies 40% of the canister volume.
- The payload occupies 40% of the canister volume and weighs 10% of
the battery weight.
- The burying mechanism is 20% of the canister volume and weighs 10%
of the battery weight.
- Battery density is 1,500kg/m3 and energy density is 321kWh/m3
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. A practical approach
to this matter follows:
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 degrees
spacing round the canister will be sufficient but four at 90 degrees spacing
will give a simpler control system. The jets would be driven by a pump
and three or four solenoid operated valves.
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Communications
Two-way communication with the payload will be through a third party package
using hydroacoustic modems. These provide reliable data transmission rates
up to 33kbits/sec are claimed over a range of 2km.
EvoLogics of Berlin offers marine systems underwater telemetry with the
revolutionary Sweep-Spread-Carrier (S2C) technology to provide optimum
underwater data transmission. S2C technology in the communications package
means unrivalled performance and reliability under virtually any underwater
data transmission scenario. It is claimed to have been proved world wide.
The S2C communication technology is now established as possibly the most
accurate and efficient method for acoustic digital data transmission in
difficult environments such as horizontal underwater (multipath) channels.
Battery requirements can be minimised by using a WakeUp type of communications
module, in which the electronics can be kept to extremely low power. Additional
reductions in power consumption can be achieved by toggling the WakeUp's
acoustic receiver 'On/Off' with a software-controllable duty cycle.
Such a system would be highly suitable for use with Checkmate.
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Batteries
The can size and the burying mechanism will depend on the specific requirements
of the application and hence the burying power and the battery life needed.
The Australian trials provided technical data regarding power consumption
during the burying process. This data has been used in projecting power
requirements and hence battery needs for any specific Checkmate canister.
The following data shows the power requirements for a canister 2.0 meters
high and 1.0 meter diameter which has a volume 1.57 cu.meters and assuming
the canister only burrows into the seabed once.
Burying energy: 300 Wh (Result from prototype trials in sand.)
Payload Power:
Collecting data:100W with On-Off factor f1
Transmitting data: 50W with On/Off factor f2.
Discussion on the "On-Off factor" of the payload.
For Checkmate when used in the data gathering role a possible operational
requirement is:
Collecting data from local sensors and from more distant sensors
via hydroacoustic modems.
Storing the collected data.
Reporting the data to a friendly receptor using an 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 an:
On/Off factor, f1 = Minutes in an hour/10 = 60/10 = 6.
Thus the average power consumption in this mode will be 100/f1 = 100/6
= 16.7W.
When transmitting data, the hydroacoustic modem will be switched on for
the time necessary to transfer all the stored data to the receiving friendly
receptor. Assume this is 15minutes once a day. This gives an:
On/Off factor f2 = Minutes in a day/15 = 1440/15 = 96.
The average power consumption in this mode will be 50/ f2 = 50/96 =0.52W.
Thus the total payload energy usage will be (16.7+0.52)tWh = 17.22tWh where
t is the battery life in hours.
Battery size and life.
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 alkaline batteries have an energy density of 320,539Wh/cum. If
the battery occupies 40% of the canister this leaves 60% for the burying
mechanism and the payload electronics. For a canister 2.0m by 1.0m diameter, the energy available
from the battery when new will be: 0.4x1.57x320,539 = 201,298Wh or about 201,000Wh
after burrowing is complete.
The battery life can be calculated from:
201,000 = 17.22t, thus t = 201,000/17.22 = 11,672hours or 1.33 years.
Due to the normal loss of capacity of the battery over time this will be
reduced to, say, 1.2 years.
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Monitoring equipment
The local sensors, i.e. those built into Checkmate, can be chosen from
a wide range of functions such as the measurement of:
Temperature,
Salinity,
CO2,
Pollution,
Current and tidal flows
Surveillance, Reconnaissance and intelligence data
Data storage and data processing modules are available from numerous
sources. The environment they operate in within Checkmate is benign, as
the temperature is stable and there is only mild vibration and shock during
the burying process.
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