-
WHOI 2/13//06
11,000 Meter HROV Development Program and itsRelation to
Oceanographic and Commercial Undersea Use
February 2006Andy Bowen, Dr. Dana Yoerger, (Woods Hole
Oceanographic Institution), Dr. Louis
Whitcomb (Johns Hopkins University), Ms. Barbara Fletcher
(SPAWAR/SSC)
The Hybrid Remotely Operated Vehicle (HROV) programhas drawn
from and incorporated cutting edge technologiesfrom across the
academic, commercial, and militarycommunities. The unique
capabilities required by theHROV system are driving the innovative
use anddevelopment of relevant technologies such as
advancedmaterials, energy storage, imaging and lighting
technology,micro-fiber communications, low power
manipulativesystems, and autonomous underwater vehicle control.
-
WHOI 2/13//06
Materials• First use of high performance ceramics for full
ocean
depth floatation.Discussion:HROV will be the first project to
exploit highstrength ceramic technology for full ocean
depthfloatation, building on over 30 years of Navy andcommercial
development. Weight savings to beachieved are approximately 40%
over the moretraditional syntactic foam material, allowing
thesystemto achieve significantly lighterweight andsmaller size.
The HROV project has significantlycontributed to the exposure of
this technologywhich is likely to have a positive impact to
manyoceanographic and commercial projects requiringfloatation. The
vendor (DeepSea Power and LightInc.) is now marketing the ceramic
spheres to theoceanographic and commercial oil and gas industryas
an alternative to syntactic foam. Lower densityfloatation has the
profound benefit of allowingsystems to achieve significantly
lighter weights andsmaller sizes. For example, an AUV that is
smallerand lighter can travel further underwater.
• First use of high performance ceramics for full oceandepth
pressure proof enclosures.
Discussion:The traditional solution for deep ocean
pressureresistant enclosures to protect electrical componentsfrom
the environment is to use titanium. Thismaterial has high specific
strength for its weight and
-
WHOI 2/13//06
is generally impervious to corrosion, yet theresultant weights
are prohibitive for full oceandepths. Here too, the HROV project
will exploithigh performance ceramic materials, with aresultant 60%
weight savings over titanium. Thelighter enclosures will reduce the
need for floatation(ROVs and AUVs require neutral buoyancy to
dotheir jobs), thus resulting in smaller and ultimatelylower cost
vehicles with enhanced performance.The development and
demonstration of thesesystems for HROV provide new resources for
boththe oceanographic and commercial ROV/AUVcommunities.
Energy StorageDiscussion:
The HROV will require a large amount of on-boardbatteries. The
batteries must be economical, easy tooperate and maintain, provide
high energy density,and must be safe for conventional shipping.
Basedon WHOI’s success with battery packs for theAutonomous Benthic
Explorer (ABE) and othersimilar projects, lithium-ion rechargeable
batterieswere selected. While these batteries are ubiquitousfor
small-scale applications such as cell phones andlaptop computers,
packs of the size we need forHROV are not commercially
available.
To solve this problem, we have chosen to use smallcells like
those found inside laptop computer batterypacks. These cells are
economical, very consistent,
-
WHOI 2/13//06
and reliable as they are produced in very largenumbers. However,
we need to combine over 2000of these small cells to provide the
energy needed forHROV.
Our packs will be built up from subpacks of12 cells connected in
parallel. Thesesubpacks can be tested extensively, allowingthe HROV
packs to be shipped byconventional means.
For both charge and discharge, the packswill be managed by
innovative WHOI-designed battery management electronics.With such a
large collection of cells, cellscan become imbalanced over
repeatedcharge and discharge cycles. Our balancingcircuit keeps all
subpacks at even levels onboth charge and discharge, maintaining
fullpack capacity automatically.
Our approach could be easily scaled tosupport either larger or
smaller vehicles.
Extensive safety analysis methodology isbeing developed and we
expect the results ofthis work to apply to future applications
forAUVs and other battery powered systems.
Imaging and Lighting Technology• Development of LED based
lighting
Discussion: HROV will rely upon newlydeveloped LED lighting in
order to meet severalsystem requirements, including strobing
-
WHOI 2/13//06
capability, pressure tolerance, and low relativepower
consumption. While these capabilities arerequirements for HROV,
they will also be highlyadvantageous in other
oceanographicapplications. All remote and human operatedvehicles
will benefit from the availability of lowprofile pressure tolerant
lighting. The ability tostrobe lighting at the duty rate of imaging
sensorsshould offer energy savings in many applications,and the
monochromatic ability of LED's, whencoupled with appropriate
sensors, should extendthe imaging ability of autonomous vehicles
andsubsea installations.
• Advanced ImagingDiscussion:The pursuit of an imaging sensor
that can fillboth still and motion imaging needs forunderwater
applications has been ongoing foryears. HROV has strong needs for
such a sensor,given its power and space constraints. Whenintegrated
with advanced LED lighting, theavailability of a single
multi-purpose sensor willbe of great benefit to any space or
powerconstrained subsea system
Micro-Fiber TetherDiscussion:One of the most innovative
technologies for theHROV project is use of a very small diameter
fiberoptic tether. Use of this tether is critical to achievingthe
goal of a lightweightand inexpensive system for
-
WHOI 2/13//06
use at extreme depths, yet with real-timecommunications.
Adapting a system developed forthe Mk 48 ADCAP torpedo (ARL Penn
State), theHROV is pioneering the use of small diameter
micro-fiber. This capability lends itself well to
otherapplications, where real time communication isrequired, but
space and weight are limited. It is likelythat such micro-fiber
tethers will be adapted to otherapplications. For example, a
micro-fiber tether couldbe a critical technology enabling real-time
explorationof under ice environments, rapid deployment of
smalllightweight vehicles, and a “strap-on” means toprovide
real-time communication with autonomous orhuman occupied
vehicles.
Low Power Manipulative SystemsDiscussion:HROV will emphasize
efficient use of power in allareas, including manipulation of
instrumentation andsamples. For this project a hydraulic
manipulator hasbeen chosen as a reasonable compromise
betweendevelopment risk, weight, cost and performance. Akey to this
system will be the development of ahydraulic power unit, coupled
with a suitable controlsystem, intended to minimize electrical
powerconsumption. While it is quite possible such a systemmay not
be suitable for a fully autonomous samplingvehicle, it is likely
that certain parts of the HROVmanipulation system will provide
valuable lessons forfuture vehicle developments.
-
WHOI 2/13//06
Hybrid Vehicle ControlDiscussion:From a control systems
perspective, the HROV projectwill require a combination of the
characteristics of anROV such as Jason II and an autonomous vehicle
suchas ABE. When in ROV mode, the vehicle will becontrolled by a
human pilot using joystick control aswell as a variety of
supervisory control modes likethose demonstrated in Jason II
(closed-loop hover,automatic trackline following, automatic
bottom-following) while allowing the pilot to observe andmanage
on-board sensors, sampling equipment, andmanipulators. In AUV mode,
the control system willenable preprogrammed surveys as well as
adaptivesurvey schemes. Also, when in ROV mode, thevehicle will
automatically branch to a pre-plannedAUV mission should the
micro-fiber cable loseconnectivity.
The Jason II control system has already been ported toseveral
other scientific ROVs (URI’s Hercules andSOC’s ISIS), where it has
proven to be effective,reliable, and extensible. The Jason2 control
systemwill serve as the base for the HROV control system,which will
be extended to include the autonomousfeatures required for AUV mode
and for recoveryfrom the loss of the micro-fiber cable. Many of
theseautonomous processes will be based on successfulresults from
ABE. It is further expected that theHROV control system will prove
to be an incremental
-
WHOI 2/13//06
step forward to AUV mission planning and thusreduce the
dependence on highly.
Light Weight Deployable VehiclesDiscussion:System operating cost
is often driven size and weight.HROV will introduce new
technologies thatdramatically reduce weight of a subsea vehicle
(e.g.lighting and ceramics). Such vehicles will be lessexpensive to
ship and mobilize and although they maynot be ultimately as capable
as either a humanoccupied submersible or remotely operated
vehicle(such as Jason II), the reduced staffing requirementswill
drive operating costs down for certain operations.The reduce size
of both the vehicle and surfacehandling system will enable
deployment of HROVand its derivatives to take place from smaller
vessels.