IEEE Spectrum September, 2008 - 7

by the Scripps Institution of
Oceanography and the Woods
Hole Oceanographic Institution.
The Navy solicitation, part of
a larger program called Littoral
Battlespace Sensing, Fusion,
and Integration, involves
using fleets of gliders to gather
data on ocean currents and on

test kind of manufacturing to
commercial production mode,"
says Tom Curtin, chief knowledge
officer at the Association
for Unmanned Vehicle
Systems International, a trade
organization in Arlington, Va.
The Navy contract will pit the
three main glider designs against

Pressurized
chamber

Batteries
(roll control)
Pump
Flooded
chamber

Batteries
(pitch control)
Oil
reservoir

Bladder

powEr, sAns
propELLErs:
A glider rises
by inflating a
bladder with
oil and sinks by
deflating the
bladder. The fixed
wings convert
vertical motion
into horizontal,
and the glider
displaces its
batteries to
control roll
and pitch.
illustrAtioN:
JohN MacNeill

12

acoustic properties that may
affect military sonar systems.
The Navy deal "got a lot of
attention because right now
people are buying gliders in
ones and twos and threes, so
it's a big increment," says Russ
Davis, an oceanographer at
Scripps, which is part of the
University of California, San
Diego. Gliders are enticing, he
says, because of their relatively
low cost: a fully equipped unit
sells for about US $100 000 and
can go for six months; a datagathering mission using a ship
can cost over $30 000 a day.
Up to this point, however,
AUVs have been a cottage
industry. "The challenge now
is making the transition from
this very hands-on build-and-

NA * Ieee Spectrum * September 2008

one another. As it happens, they
all emerged from the same Office
of Naval Research program in the
mid-1990s. Similar in design, each
is a torpedo-shaped aluminum
hull about 1.5 to 2 meters long
crammed with sensors, batteries,
and electronics. To move, the glider
uses a pump to inject or remove
oil from a bladder located in a
flooded part of the hull. To ascend,
a robot expands the bladder,
displacing water and increasing its
buoyancy; to descend, it empties
the bladder out. A pair of fixed
wings converts part of the vertical
displacement into horizontal
motion, causing the glider to
travel in a sawtooth trajectory.
To change pitch while
climbing or sinking or to turn
left or right, the gliders change

their center of mass by shifting the position of their battery packs. "There are no
external moving parts-no propellers or jets or moving fins-
to push this thing through the
water," says Tom Frost, iRobot's
program manager for the
Seaglider. "It's really elegant."
And even though their original
designs are alike, their makers
boast of unique capabilities.
iRobot claims the Seaglider has
the longest range and battery
lifetime, being the first glider to
complete a mission of more than
3750 kilometers and lasting six
months. Bluefin, which is also
supplying an offshore oil and gas
contractor, says the Spray glider
can go about 50 percent deeper-
1500 meters-than its competitors
and has more durable sensors.
And Teledyne says the Slocum's
rudder gives it better shallowwater maneuverability and that a
new system that harvests energy
from temperature variations in the
water could allow its gliders to stay
at sea for years at a time.
For researchers like Scott
Glenn, a professor of physical
oceanography at Rutgers
University, in New Brunswick,
N.J., any extension of a glider's
time at sea is welcome news. In
the past few years, Glenn and
others have turned to gliders to
study ocean circulation, climate
events, and marine life. One of
his projects involves tracking
the flow of sediments off New
Jersey's coast during storms. He
and his colleagues can't go out on
research boats in those conditions,
but with gliders they can be
anywhere there's an Internet
connection to monitor-or "fly"-
the vehicles. "I do a lot of flying
from McDonald's or Starbucks,"
Glenn says. "Anywhere, anytime,
you can go to sea." -Erico Guizzo
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Table of Contents for the Digital Edition of IEEE Spectrum September, 2008
