When using the native FITS encoding, multiple Objects may be stored and all I/O operations are sequential. This means that you can simply write a sequence of Objects to a FitsChan. After each write operation, the Card attribute will be updated so that the next write appends the next Object description to the previous one.
If you then rewind the FitsChan, you can read the Objects back in the original order. Reading them back will, of course, remove their descriptions from the FitsChan () but the behaviour of the Card attribute is such that successive reads will simply return each Object in sequence.
The only thing that may require care, given that a FitsChan can always
be addressed randomly by setting its Card attribute, is to avoid
writing one Object on top of another. For obvious reasons, the Object
descriptions in a FitsChan must remain separate if they are to make
sense when read back.
AST A Library for Handling World Coordinate Systems in Astronomy