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Concentrated solar power helps Nasa test heat shields for a Titan probe. |
To test the shields, NASA has been using Sandia National Lab's Solar Thermal Test Facility, which can focus the heat of 1,500 suns onto 5-in. material samples. The shields are currently made of low-density silicones and phenolics that weigh less than 20 lb/ft3.
The test facility is a 200-ft tower surrounded by 220 computer-aimed heliostats. Each heliostat contains 25 mirrors, each 16 ft2. So the total collection area is 88,000 ft2. All that solar power is directed to the top of the tower where test samples are mounted in water-cooled copper plates. During exposure, which is controlled by a fast-moving shutter, air blows over the sample at Mach 0.3 while a sublayer of high-speed nitrogen flows close to the sample surface. The nitrogen replicates the Titan atmosphere. Samples are exposed to square pulses of the solar beam at flux levels up to 150 W/cm2. Testing can only be done in the 4 hr bracketing solar noon, and haze clouds and high winds can affect test conditions.