Conference 7.286::space

772.0. "Laser-based system may replace KSC wind weather ballons" by PRAGMA::GRIFFIN (Dave Griffin) Mon Dec 16 1991 17:58

Ed Campion
Headquarters, Washington, D.C.                             December 13, 1991

Jean Clough
Langley Research Center, Hampton, Va.

Mike Finneran
Langley Research Center, Hampton, Va.


RELEASE:  91-206

        Researchers at NASA's Langley Research Center, Hampton, Va., have
developed a laser-based system for measuring winds above launch sites that
eventually may replace weather balloons as a means of gathering data aloft.

        The system is called CLAWS for Coherent Launch Site Atmospheric
Wind Sounder and was created by the Spacecraft Controls Branch, Flight
Systems Directorate, and Lockheed.

        The system underwent its first full-system test at the Sept. 12
launch of the Space Shuttle Discovery. Researchers were wrapping up final
testing earlier this month in which detailed comparisons were made of
CLAWS, weather balloons and a Doppler radar wind profiler.

        Dr.  Daniel D. Moerder, of Langley's Spacecraft Controls Branch,
said CLAWS has the potential for providing better wind information more
quickly than weather balloons.

        "This is really a huge step forward," he said. "It will provide us
with a level of detail that will permit increased availability for
launches, an added measure of safety in launches and will make it possible
to design more efficient vehicle trajectories that will enable us to launch
more payload into orbit per vehicle."

        Moerder said CLAWS has several advantages over balloon systems long
used to gather wind data. "That process takes about an hour as several of
these balloons are released as the time of launch approaches," he said.
"The balloons have a number of disadvantages, one of which is that when
they encounter strong winds, they get blown away from the launch site."

        With CLAWS, Moerder said, "we are able to get a vertical wind
profile in about a minute instead of in about an hour.  Also, because light
propagates in a straight line, we are actually measuring along the line of
sight.  We're actually looking up through a cone of atmosphere.

        "And finally, and this is extremely important, CLAWS is capable of
a 75-meter vertical range resolution, which lets us see fine-grained
phenomena that balloons miss, such as sharp wind shears."

        The system uses high energy, short wavelength, solid-state laser
light to measure, over a series of altitudes, the Doppler shift of very
fine aerosol particles as they pass overhead.  Measurements are taken from
a series of back-reflected laser pulses.

        "In recent testing," Moerder said, "the system has been able to
measure winds with a 0.1 meter-per-second accuracy up to an altitude in
excess of 16 miles."

        Development of CLAWS "is part of a several year effort that will
culminate in fully demonstrating the technological maturity that would
justify procurement of an operational system for launch support," Moerder
said.

        The current system does have several drawbacks, he said.  It cannot
penetrate solid cloud cover.  In addition, the laser is not eye-safe and
requires that air space be cleared before the laser can be used.  Plans are
to upgrade to an eye-safe laser.

        Moerder said the cloud-cover problem may be skirted by using the
CLAWS system in conjunction with wind radar, another method being developed
for measuring winds aloft.