I've posted two documents. Please take a look and suggest improvements/corrections:
File Formats - This document is intended to discuss the nitty gritty of file formats. It starts with a recap of the format published in Challenge #26 and used GDW's TRADER application for the Apple II, attempts to document the format used by Joe Fugate for the GEnie data upload, loosely specify the "sec" files found on the Internet, and define two canonical T5 data file formats, as used by the site. We'll see if they catch on.
Second Survey Data - This recaps the definition of the fields describing a world. For many of the fields this is covered in the Traveller 5 Core Rules but this document goes into more detail on some specifics hidden in the data (like sophont populations) and legacy fields.
I aim for these to be "live specifications" - that is, updated over time as new formats emerge. Right now they try to balance being rather formal specifications with being readable by non-programmers. We'll see how things go.