id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc
760	Can't write NaN or Inf to a FITS header	Paul Price	Paul Price	"Due to a deficiency in cfitsio, writing NaN or Inf to a FITS header (at least as
a floating-point type) is not possible.

Here's the cfitsio error stack from attempting to write an F32 NaN to a header
keyword:

FITSIO status = 402: bad float to string conversion
Error in ffr2e: float value is a NaN or INDEF

Note that cfitsio seems to be explicitly blocking NaN.  This is affirmed by
inspection of putkey.c:

    /* test if output string is 'NaN', 'INDEF', or 'INF' */
    if (strchr(cval, 'N'))
    {
        ffpmsg(""Error in ffr2f: float value is a NaN or INDEF"");
        *status = BAD_F2C;
    }"	defect	closed	high		fits	unspecified	normal	fixed		rhl@…