For the last two years, tests have been conducted at Sandia National Laboratories' National Solar Thermal Test Facility to apply heat equivalent to 1,500 suns to spacecraft shields called Advanced Charring Ablators. The ablators protect spacecraft entering atmospheres at hypersonic speeds. The test facility includes a "solar tower" surrounded by by a field of hundreds of sun-tracking mirror arrays called heliostats. The heliostats direct sunlight to the top of the tower where the test objects are located.