Historical Photo of the Month - December 2008

Cellular Glass
Photograph Number 354-1754Bc

In October 1978 engineer Michael Giovan was part of the JPL Materials Research and Technology Group. The image at left appeared in Universe and shows him with samples of cellular glass, one of many materials tested for possible use as the support structure for solar concentrator mirrors.

Cellular glass is made from finely ground glass mixed with a foaming agent, then heated. It was tested to determine tensile strength, compression strength, and ability to resist cracks (left to right in the color photo). Materials needed to be strong for their weight, rigid, able to withstand temperature and humidity extremes, and be inexpensively mass-produced. Easy maintenance and long term performance were also important.

A solar concentrator was built the following year at Edwards Test Station, using solar mirrors bonded to structural cellular glass. The study revealed some limitations of cellular glass, including the need for a coating to prevent slow crack growth and freeze/thaw degradation, and very high initial cost of specialized manufacturing. The Solar Thermal Power Systems Project was sponsored by the U.S. Department of Energy.

For more information about the history of JPL, contact the JPL Archives for assistance. [Archival and other sources: photo index; Universe, 12/8/1978; Evaluation of Cellular Glasses for Solar Mirror Panel Applications, JPL Publication 79-61; and JPL Highlights 1979.]