[image-36]By Anna Heiney
NASA's Kennedy Space Center, Fla.
[image-51][image-80][image-96]When countdown clocks are ticking, the launch team closely monitors information about the wind speeds and direction along the rocket's planned flight path. Soon forecasters at NASA's Kennedy Space Center and nearby Cape Canaveral Air Force Station (CCAFS) will have a new tool to help characterize those winds to maximize launch success.
Kennedy's Ground Systems Development and Operations Program is replacing NASA's aging 50 Megahertz Doppler radar wind profiler with a state-of-the-art version. Decommissioning of the original system began March 3 and will clear the way for the new system to be installed in the same location, a 3.7-acre field northeast of the center's Shuttle Landing Facility (SLF).
Winds below 60,000 feet are a major concern during a countdown. Every liftoff requires a rocket to pass through the atmosphere, and launch team members need accurate data in order to program the vehicle's guidance and steering commands to ensure the vehicle reaches its proper orbit without exceeding its aerodynamic wind load limits.
"The existing 50 MHz profiler has been used as a backup, because it couldn't be certified as a primary instrument," explained Lisa Huddleston, chief of NASA-Kennedy's Applied Meteorology Unit. That means the profiler could rule out a launch, if conditions were "no-go," but launch managers could not base a "go" decision based on its data. The new system is expected to be certified for primary use in 2015.
The new profiler joins a suite of instruments across the spaceport that forecasters use to analyze and predict wind and weather conditions along the Eastern Range.
The U.S. Air Force has a network of 915 MHz profilers that sense the boundary layer, which extends from the ground up to about 6,000 feet. That's where the 50 MHz profiler goes on watch, observing wind conditions from that point up to about 60,000 feet. Weather balloons released from CCAFS also are used.
A profiler transmits beams into the atmosphere and from the returned energy calculates wind velocity aloft, Huddleston said. In the case of Kennedy's 50 MHz profiler, that information is received at the Doppler antenna field located near the SLF, then sent electronically to a weather station on CCAFS. From there, the data also goes to the Air Force's weather display system.
Winds aloft can change rapidly, and meteorologists need a system that updates quickly and provides data as close to the flight path as possible. Wind balloons known as jimspheres traditionally have been the primary sources of upper altitude wind data, but the profiler will replace these.
"Especially in the winter, the jet stream dips down over Florida. That's a very fast-moving stream of air, and it can move a balloon a hundred miles out to sea," Huddleston explained.
"Another advantage is that the profiler can compute a wind profile every five minutes, versus the hour it takes for a balloon to get to altitude," she added.
The profiler comprises a phased array of dipoles, mounted on poles several feet above the ground and arranged across the octagonal antenna field. A trailer at the facility houses the system's electronics.
Once installed, the new system will feature new electronics and a new pattern of dipoles, which together will provide greater flexibility and reliability while reducing interference. A modern system also will be easier to maintain, because parts will be readily available.
Kegman, Inc. of Melbourne, Fla. is in charge of the decommissioning. The team's first task will be to remove the radar equipment inside the shelter. It will be transferred to the Air Force to serve as spares on the Western Range's 50 MHz wind profiler. Next, all other equipment in the shelter will be taken out, followed by removal of the components from the antenna field. The new system will be installed by Detect, Inc.'s Meteorological Radar Systems Operations division, based in Longmont, Colo. The company is headquartered in Panama City, Fla.
The process was carefully timed to ensure forecasters would have a profiler available during the winter months. Removal of the existing profiler is expected to continue until late April. The new system will be installed between May and September, followed by acceptance testing through the middle of October. Once testing is complete, the new profiler will be ready for use, and will run continuously so meteorologists can compare its measurements to balloon data in order to verify its performance. During this timeframe, it will be used as a secondary instrument, like the previous system.
The new profiler is expected to be certified for primary use in the fall of 2015, giving weather forecasters and launch managers one more way to decide whether a rocket is "go" for liftoff.