Gluing building blocks with geometry.

Using simple blocks with shapes like cubes or hourglasses, researchers have found ways to construct strong panels with no fasteners securing most of the blocks. Such constructions remain intact even after losing up to half of their units, says Yuri Estrin, a materials scientist at the Technical University of Clausthal, Germany.

In the June Philosophical Magazine Letters, he and his colleagues report making a new version of such blocks that may prove practical in heat shields for space shuttles.

During the past few years, the researchers had been experimenting with interlocking blocks with only straight edges. These arrangements, however, have jagged surfaces that are too rough for some applications. The new blocks have curved edges, which can be put together to form a smoother panel.

In all these schemes, only blocks on a panel's border require a securing mechanism, Estrin notes.

NASA officials say the new structures might be an option for a few difficult-to-tile areas on a space shuttle's surface. However, the monolithic character of the new panels might make maintenance prohibitively difficult, they point out.--P.W.