From https://sxi.ngdc.noaa.gov/sxi_data_notes.html as of May 2018 :


GOES SXI File Naming Convention
Image data: 
SXI_yyyymmdd_hhmmssfff_pv_nn.FTS (29 characters) 
'yyyymmdd_hhmmssfff' UTC date (DATE_OBS). The fff section represents fraction of a second.
'p' data product code, i.e., 
p = 'A' => Level-0 
p = 'B' => Level-1 The remainder of the alphabet is available for Level-2 product codes. 
'v' processing version code, i.e., Reprocessed data will be differentiated by incrementing the version code. 
'nn' satellite ID (i.e., GOES-nn)

...and I'm seeing names like :

-rw-rw-r-- 1 noien noien    1497600 May 18 09:26 SXI_20180308_000400152_BA_15.FTS
-rw-rw-r-- 1 noien noien     650880 May 18 09:35 SXI_20180308_025900157_AB_15.FTS
-rw-rw-r-- 1 noien noien    1497600 May 18 09:35 SXI_20180308_025900157_BA_15.FTS
-rw-rw-r-- 1 noien noien     547200 May 18 09:53 SXI_20060815_000018110_AA_12.FTS
-rw-rw-r-- 1 noien noien    1074240 May 18 09:53 SXI_20060815_000018110_BB_12.FTS





GOES-12 SXI Instrument Summary :
The SXI telescope images the sun in wavelengths ranging from soft X-rays to extreme ultraviolet. These filters are available [#, wavelength in angstroms, filter name, (Metadata entry)]
01, 6-65, Poly thin (P_THN_A)
02, UV, UV diffuser
03, 6-65, Poly thin (P_THN_B)
04, 6-60, Poly medium (P_MED_B)
05, 6-20, Be thin (B_THN_B)
06, 6-16, Be medium (B_MED)
07, 6-12, Be thick (B_THK)
08, 0-0, Radiation shield (RDSH)
09, 6-80, Open (OPEN)
10, 6-20, Be thin (B_THN_A)
11, 6-50, Poly thick (P_THK)
12, 6-60, Poly medium (P_MED_A)
Each image is a 512 x 512 array with 5 arcsec pixels.





GOES-12 SXI Metadata :
The browse display includes a drop list containing a short set of metadata:
DATE_OBS - Earth-adjusted time of observation, UT
IMG_CODE - Intent of the images:
FL = Flares
CS = Coronal Structures
AR = Active Regions
BG = Background
TST = Test
MSFC = Startup sequence
WAVELENGTH - filter name.
MCPGAIN - Microchannel Plate detector gain setting in volts.
EXP_TIME - measured exposure duration..
IMG_WDI - Whole disk intensity (units TBD)
IMG_MIN - Image minimum intensity (units TBD)
IMG_MAX - Image maximum intensity (units TBD)
SAT_PIX - Saturated pixel count.
Filename.