Think of the space shuttle orbiter as a big puzzle with each of its heat shield tiles a puzzle piece.

All space shuttle thermal protection system (TPS) tiles are assigned a serial number identifying where on the orbiters they are to be installed. Each tile is individually made to fit a specific location.

Tile serial numbers normally consist of four segments, the first three separated by dashes, such as:

VO70-395901-379 TTBOPJ
VO70-291353-033-008283
VO70-191001-011 7EBIEX

The first two elements of the serial number are letters 'VT' or 'VO'. The 'V' is for Vehicle, the 'O' is orbiter.

The second set of six digits is the location on the vehicle. The following table provides basic locations.

All tiles in NASA's Tiles for Teachers program are unflown. In general, flown tiles are only removed from the orbiters after they are damaged or need to be removed to service the vehicle. Since this is the case, most flown tiles are in very bad condition and not circulated.