Go to HETG at XRCF
The results to date suggest adopting the following calibration values:
|Grating||Average Period||error||XRCF Rowland Spacing||error|
|LEG||9912.16||+/- 0.99||8788.04||+/- 0.5|
|MEG||4001.41||+/- 0.10||8782.8||+/- 0.5|
|HEG||2000.81||+/- 0.05||8782.8||+/- 0.5|
|Grating||XRCF mean Angle||error||Opening Angle||error|
|HETG||-0.225||+/- 0.05||9.934||+/- 0.008|
The periods (in A) are the sub-assembly values because XRCF measurements (and spacing) are not accurate (double checked) enough to require a change. The mean dispersion angles are for XRCF and are a good starting point for flight; the HETG opening angle should be the same for XRCF and flight.
The HEG/MEG period difference seen between sub-assembly (HeCd,HeNe) and XRCF-AL-K (assuming a spacing of 8788.04)(of about a part in 500) is assumed to be due to a mis-placing of the HETG at XRCF. Thus, for now the HETG position at XRCF is set to be 8782.8 mm to have reasonable agreement between XRCF and sub-assembly periods. The cause for the (alleged) displacement has not been determined.
The period errors are all taken as the sub-assembly values, again because (with an HETG displacement assumption) XRCF measurements are in agreement and do not provide any smaller error bounds.
The XRCF Rowland Spacing, 8788.04 +/- 0.5 mm is based on data supplied by Scott Texter (TRW) in a diagram dated 8/15/97. The HETG and LETG were each measured to be within 0.05 mm of this mean spacing value. (HETG = 345.984 inches, LETG = 345.986 inches). This value differs by 5.24 mm from the value implied by design documentation (see Location of HETG at XRCF).
Scott Texter reports that EK measures the as-installed HETG to be 0.009 inches closer to the HRMA than designed, so expected flight spacing is 8633.69+0.009*25.4 = 8633.92 mm. The error on this is probably 0.2 mm or less (HRMA-grating spacing). However the HRMA-focus spacing may still have error of order 0.5 mm. Likewise, the as-installed LETG distance is 8633.69 - 0.0043*25.4 = 8633.58 mm.
Assumptions: Rowland distance = 8788.04 mm, hc = 12.3985, Al-K is at 1.4867 keV. TOGA rowland distance = 5366.55 mm.