Image Caption: A sprite glows red (inset) in this image captured by astronauts on the International Space Station on April 30, 2012. Credit: Image Science & Analysis Laboratory, NASA Johnson Space Center

April Flowers for redOrbit.com Your Universe Online

Just as you might keep a spare tire in your car, or a spare filter for your air conditions, NASA keeps spares as well. These spare flight hardware units allow NASA to continue work without interruption in the event that something goes down for repair. These spare parts are kept even after the project ends, sometimes finding second lives in new areas.

A sophisticated piece of flight hardware, called a Lightning Imaging Sensor (LIS), was developed by researchers at NASAs Marshall Space Flight Center and launched into space in 1997 as part of NASAs Tropical Rainfall Measuring Mission (TRMM). The sensor, used to detect and locate lightning over the tropical region of the globe, undertook a three year primary mission to return data that could be used to improve weather forecasts. LIS continues to operate aboard the TRMM satellite today.

Of course, the researchers responsible for building LIS in the 1990s built a spare unit as a precaution. That other unit is now being brought into play as well. The second LIS sensor is scheduled to launch aboard a Space Exploration Technologies (SpaceX) rocket to the International Space Station (ISS) in February 2016. LIS will be mounted to the station for a two year baseline mission as part of a U.S. Department of Defense (DoD) Space Test Program (STP)-H5 science and technology development payload.

The LIS hardware was selected by NASA to take advantage of the ISSs high inclination, which will give the sensor the ability to look farther towards Earths poles than the original LIS aboard the TRMM satellite. The sensor will have many duties once installed, including monitoring global lightning for Earth science studies, providing cross-sensor calibration and validation with other space-borne instruments, and ground-based lightning networks. LIS will also supply real-time lightning data over data-sparse regions, such as oceans, to support operational weather forecasting and warning.

Only LIS globally detects all in-cloud and cloud-to-ground lightning what we call total lightning during both day and night, said Richard Blakeslee, LIS project scientist at Marshall. As previously demonstrated by the TRMM mission, better understanding lightning and its connections to weather and related phenomena can provide unique and affordable gap-filling information to a variety of science disciplines including weather, climate, atmospheric chemistry and lightning physics.

Without land-ocean bias, LIS measures the amount, rate and radiant energy of global lightning, providing storm-scale resolution, millisecond timing, and high, uniform-detection efficiency.

The LIS hardware consists of an optical imager enhanced to locate and detect lighting from thunderstorms within its 400-by-400-mile field-of-view. As it orbits Earth, the ISS travels more than 17,000 mph. This will allow LIS to observe a point on Earth, or a cloud, for almost 90 seconds each time it passes overhead. This viewing duration, despite its short length, is long enough to estimate the lightning-flashing rate of most storms.

More than 70 percent of all lightning occurs during daylight hours, making daytime detection the driving force for the technical design of LIS. Lightning, when seen from space, looks like a pool of light on top of a thundercloud. During the day, however, sunlight reflected off the cloud tops can completely mask the lightning signal. This makes it challenging to detect the lightning. LIS applies special techniques that take advantage of the differences in the behavior and physical characteristics between lightning and sunlight, however, allowing LIS to extract the lightning strikes from background illumination.

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