Wind Monitor
Orbital Sciences Corporation (OSC), Fairfax, Virginia is a
world leader in the design and manufacture of small space systems
intended to reduce the cost of space operations and thereby broaden
the market for space products and services.
Among the company's extensive line of products is a family
of inflatable structures for the atmospheric monitoring community.
One such inflatable, known as the "Jimsphere," is of
particular interest because, although developed more than 30
years ago, it remains the standard at all U.S. missile/launch
vehicle ranges for obtaining accurate upper level wind data.
The Jimsphere wind measurement balloon is made of lightweight
radar-reflective materials.
Large missiles and launch vehicles are very sensitive to windshear,
especially as they approach the area of maximum dynamic pressure,
typically between 30,000 and 50,000 feet. Prior to every flight
today, launch teams analyze a computer-generated flight profile
that involves detailed specifications of the wind field through
which the vehicle must fly. In the early 1960s, however, no method
existed for making high resolution measurements of the wind profile.
At that time NASA was already developing the Saturn launch vehicles
for the Apollo lunar landing program and it was essential that
NASA also develop a meteorological sensor of superior aerodynamic
stability to determine the vertical gradients of the wind before
Saturn launches commenced.
The standard smooth-surface weather balloon could not do the
job. The reason: the smooth balloon was subject to zigzagging
or spiraling as it ascended, due to large air vortices that shed
off the surface at various positions; this caused sporadic horizontal
motions of the rising balloon that made accurate radar-tracking
measurement of the balloon impossible.
After several NASA-sponsored studies failed to provide a suitable
method, a NASA engineer came up with an answer. Dr. James R.
Scoggins, today director of meteorological studies at Texas A&M
University, then at Marshall Space Flight Center, took a simple
approach to a complex problem: rather than invent a new system,
change the characteristics of the existing system, the smooth
surface balloon. He bought some conical dixie cups and attached
them to a balloon to "rough up" the smooth surface.
The cones, or "roughness element," were intended to
prevent the formation of vortices and thus damp the sporadic
motions; additionally they increased drag. The combination of
reduced lift and increased drag stabilized the balloon so that,
when it entered a changing wind field, it would quickly assume
the speed of the wind without zigzagging. It worked; named the
Jimsphere in honor of its inventor, the system was assigned to
a company for refinement and production and OSC subsequently
acquired the patent rights.
The Jimsphere now being produced is a balloon two meters in
diameter, made of lightweight, flexible, radar-reflective materials.
Ground radar, navaids or theodolites track position and collect
wind data from the balloon at altitudes up to about 10 miles.
Jimsphere data was used in the design of the Saturn vehicles,
the Space Shuttle and other launch systems. The balloon has supplied
pre-launch wind data for all NASA/Air Force ground-based rocket
launches from Cape Kennedy, Kennedy Space Center and Vandenberg
Air Force Base.
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