NECP MEASUREMENTS AND COMPARISON WITH GROUND MEASUREMENTS

Measurements obtained during the NECP are discussed in this section. The NECP was the post-launch phase that involved the first operations of all spacecraft instruments, including check-out and calibration activities. During this phase, the OH was at a temperature of 133.5 K. One of the major goals of the NECP is to ensure the integrity of the instruments and the data pipeline via the spacecraft. For MAJIS, the measurements provide some constraints about calibration variation resulting from the various ground tests (thermal, shock, and vibration) performed after the mechanical integration of MAJIS on the spacecraft as well as from the vibrations of the launch and spacecraft separation. These flight measurements are acquired with the ICU subsystem, as no specific pointing was allowed during the NECP. We first compare the pre- and post-launch absolute calibration using the spectral signatures of the didymium (VISNIR) and the polystyrene (IR) filters of the ICU. We observe an absolute calibration shift for both channels (see Fig. 26). This spectral shift is -3.8 nm in the VISNIR and -5.4 nm in the IR; it is constant over the wavelength range available for comparison (between 0.7 µm and 0.9 µm in the VISNIR and 3.2 µm and 3.55 µm in the IR), suggesting it may be constant over each channel. The IR shift is mitigated by the difference in OH T° (see Section IV.E.1), leading to an actual shift of -4.0 nm.

A B

[Figure: Fig. 26. (A) Comparison of the VISNIR ICU data before (on-ground calibration) and after (NECP) launch. A shift of -2.0 physical spectels (corresponding to a spectral shift of -3.8 nm) is observed. (B) Same as (A) but for the IR channel. A shift of -1.7 physical spectels (equivalent to a spectral shift of -5.4 nm) is observed.]

Section III.A.2.b mentions that the spectral response could not be characterized accurately with the NECP data set.
However, the spectra measured before and after the launch can be compared using the approach described in Section III.A.2.b.

[Figure: Fig. 27 shows that the spectral response has not changed significantly after the launch (< 10% relative variations), the slight variations being within the uncertainties of the methodology.]

[Figure: Fig. 27. Examples of the FWHM estimation using an SSD algorithm between on-ground calibration and NECP derived from the convolution of the ICU signatures. (A) Best fits (crosses) for the didymium signature around 790 nm. (B) Same as (A) but for a signature around 880 nm.]

(C) Same as (A) but for a polystyrene signature around 3380 nm (IR channel).
The algorithm to characterize the smile using ICU data was also applied to the NECP ICU acquisitions. The comparison of the NECP and on-ground ICU data is shown in Fig. 28. Both channels show similar smile trends between the in-flight and on-ground data sets for most of the available data. A small change is observed for the lower parts of the FOV (< Row N°200) of the IR channel with the 3.3 µm signature. At this very edge of the FOV, the smile is reduced by about 22% (0.5 nm).

[Figure: Fig. 28. Comparison of the smile characterization using ICU signatures for both channels before and after launch.]