Map? Check. Countersheet? Check. Log sheets and rulebook? Check. Two six-sided dice? Check. One twenty-sided d10? Um, check?
I’ve worked with all manner of odd polyhedron in my time, from oblong d3s (which have more than three faces) to those hundred-sided “Zocchihedrons” that never quite stop rolling. But a twenty-sider that serves as a d10? New one by me. Silly me—I’ve always used a ten-sided die for a one to ten random distribution.
The typical twenty-sided die, in the shape of an icosahedron, caries the numbers one through twenty, one number per face. The twenty-sider in Star Explorer carries the numbers zero through nine, each number appearing on two faces.
The oddity of this die required special rules for its use in Star Explorer:
1.2 Game Equipment and Scale
6) Dice. Two six-sided dice and one twenty-sided die are included. The twenty-sided die is labelled 0-9 twice. When a roll of 1D10 is required by the rules, players should roll the twenty-sided die, treating a roll of 0 as a roll of 10. When a roll of 1D20 is required by the rules, players should roll the twenty-sided die and a six-sided die. If the six-sided die roll is 1, 2, or 3, the twenty-sided die is read from 1 to (1)0. If the six-sided roll is 4, 5, 6, the twenty-sided roll is read from 11 to (2)0, creating a range from one to twenty. (Players also have the option of coloring in one set of numbers on the twenty-sided die with a fine point felt-tipped marker and reading the colored numbers as 11-20, while the uncolored numbers are read 1-10.)
Ostensibly, providing a single twenty-sider (albeit with oddly numbered faces) to serve as both d10 and d20 proved less expensive than providing a separate d10 and d20. Indeed, SPI stopped providing any dice at all with their games at one point in the 1970’s, blaming the “world-wide petro-chemical shortage,” but likely owing to cost . Whatever FGU’s reason, this little die provides for a great bit of rules verbiage, even if I will break out my own d20 and d10 when I play Star Explorer.
 Balkoski, Joseph. "The Perils of Youth: The Lighter Side of SPI." Strategy & Tactics: 128 (Origins 1989), 48-49.