CDF
Common Data Format. DYN files
DYN files contain auxiliary data for precise orbit determination and non-gravitational accelerations. The x stands for the satellite number (A,B or C) and 1B means this is a level 1B product. Note this is a compressed CDF file. In fact the structure of the files is a bit more complicated. Inside the ZIP file there are two files: a .HDR file containing the headers for the product in xml and a Common Data Format File (CDF) containing the product proper. Note there is another cdf file called computable document format created by Wolfram inc. This last file is completely unrelated. Please do no confuse the two!
The DYN files are produced daily and the data rate is 1Hz. The total file size is approx 3.7 Mbytes/files