UCAR Communications' Robert Henson paid a visit to the National Scientific Balloon Facility in January while attending the American Meteorological Society's annual meeting in Dallas.
In the midst of the piney woods of east Texas lies one of the landmarks of high-altitude atmospheric research. The National Scientific Balloon Facility, operated by NCAR and UCAR from 1963 through 1986, is now run by New Mexico State University for NASA. Despite the advent of ever more-powerful satellite-borne instruments, the giant balloons launched at NSBF remain a key tool in the exploration of the upper atmosphere.
From 30 to 40 balloons are launched by NSBF crews each year, most between April and November. The polyethylene balloons each weigh around two tons and span 200 to 600 meters before inflation. Their payloads are created and brought to Palestine, Texas, or remote launch sites by scientists worldwide, who typically stay for one or two months to carry out their experiments.
As NCAR's first facility, NSBF began full-scale operations in August 1963. One of its first major accomplishments was the successful deployment in 1964, at an altitude of 25 kilometers, of the white-light coronal camera designed by NCAR's Gordon Newkirk. This expedition produced the first white-light coronal photos taken without the help of an eclipse. Other flights have addressed such questions as the origins of the universe, the evolution of stars, and the creation and propagation of cosmic rays. Atmospheric chemistry, particularly stratospheric ozone, has been the focus of an increasing number of flights in recent years.
Palestine was chosen by NSF as the NSBF site for several reasons:
* Average surface winds are relatively light.
* The population density is low.
* The most-used airline flight paths bypass the region.
* It is fairly close to the Texas Panhandle, source of 95% of the world's helium.
* The site lies just outside the tornado-prone belt from north Texas to Minnesota (although Palestine itself was hit by a significant tornado in 1987).
The relative lack of air travel over Palestine is a major benefit, says Harry Morris, an NSBF pilot since 1979. "A lot of people mistake our balloons for UFOs, and a lot of pilots mistake them for a collision hazard, even with the balloon at 40 kilometers and the pilot at 10 kilometers."
The NSBF complex includes payload integration areas, office and fabrication space, a storage shed for balloons, and a meteorological center staffed by three full-time forecasters. One of the profilers in the National Weather Service's demonstration network is based on site; it has proven useful in monitoring winds for launches. Two aircraft, a Cessna Conquest turboprop and a Cessna 414 twin-engine craft, are housed on site and used in conjunction with launches. A circular, kilometer-wide clearing in the woods, with a concrete pad at its center, serves as the main NSBF launch pad. The clearing is large enough to allow a significant crop of hay (which also serves to deter erosion) to be harvested twice each year from the outer rim.
On a typical launch, the balloon and payload are carted to the launch pad by Tiny Tim, a giant vehicle that resembles a double-sized tractor. The balloon is inflated for around 45 minutes, and the spectacle of the launch begins. Though winds are most conducive to launches in the early morning, many night launches are held to accommodate experiments studying stars and other celestial bodies. Most launches occur in the summer, taking advantage of easterlies in the stratosphere that push balloons west toward unpopulated parts of Texas. Eastward-bound flights have been prohibited by NASA for several years due to the risk of descending into population centers or the Gulf of Mexico.
NCAR archivist Diane Rabson and education coordinator Rene Munoz demonstrate that Tiny Tim, the vehicle that carts the balloon and payload to the launch pad, is not so tiny. (Photo by Robert Henson.)
A typical flight takes around three hours to ascend to 30-40 kilometers, the most common altitude range. Telemetry systems and onboard data storage are used to take ozone readings as well as cosmic- and gamma-ray measurements using various infrared and ultraviolet telescopes.
Descents used to be triggered by tiny explosives sewn into the balloon fabric. They're now initiated by an explosive cable cutter or explosive bolt that separates the parachute and instrument package from the balloon. It takes around 50 minutes for a payload to descend via parachute. Meanwhile, the balloon free-falls on a separate course in about 15 minutes. NSBF staff follow the descent from the ground and pick up the balloon and payload once landed. (Damage to private property is rare, but landowners are promptly compensated if any problems occur.)
Along with flights from Palestine, the NSBF sends members of its 75-person staff to launch balloons from other sites around the globe. This year, NSBF teams are heading to the vicinity of Alice Springs, Australia, for gamma-ray measurements and Lynn Lake, Manitoba, Canada, for cosmic-ray studies. One of the year's biggest projects is an around-the-world flight that will head westward from Canada's Northwest Territories across Asia and Europe to Greenland during June and July. It will be NSBF's first circumpolar flight in the Northern Hemisphere after several around-the-world ventures in the Southern Hemisphere. The flight will carry two experiments measuring cosmic-ray spectra for James Adams (Naval Research Laboratories).
Scientists interested in conducting balloon-based experiments through NSBF may contact Danny Ball, head of operations, or Dwight Bawcom, site manager, both in Palestine at 903-729-0271.