RESIK & Diogeness on the Payload & Coronas-F pointing This week, we show the location of both Polish spectrometers within the CORONAS-F satellite payload. This picture will help in understanding the relationship between the S/C attitude and positions of strong emission lines observed on the spectra. In the picture below, we show the photograph of the payload in the final stage of pre-flight proeparations in Plesetsk. (picture from official experiment web page: RESIK Diogeness (hidden)

A more detailed scheme of the placement of the instrument on the payload is shown below. The II is the main reference (X) axis of the satellite. For description of the other instruments, visit Scheme of Coronas-F Payload A B II RESIK dispersion planes Diogeness dispersion planes

The dispersion planes of both RESIK and Diogeness are coaligned, normal to the satellite main axis. The uncertainty of coalignment is given by the accuracy of mechanics and mounting and is expected to be better than 5 arcmin. Within each instruments, the dispersion planes of each individual crystal are coaligned to much better accuracy of ~30 arcsec. For RESIK, the internal coalignment took place at MSSL in 2000, and has been made by Dr. Charlie Brown from NRL with the use of special co-alignment tools and the autocollimator. Below is the photograph of crystals of one RESIK section being co-aligned.

The CORONAS-F S/C is not fully three-axis stabilised. Its pointing is however very stable in time, much better than the technical specifications for the system required. Below is a scheme, how the S/C pointing is achieved: x 10, SUN The Z-axis (small circle) pointing towards the optical Sun centre is drifting (see blue line in a diagram) within 10 arcmin box. The roll may assume any position in respect to the solar coordinates, however the rate of change is very slow (~1deg/day). We have now way to determine the actual roll angle from RESIK or Diogeness data. However, the stellar sensors constitute a part of the SPIRIT instrument designed by FIAN group.

Thanks to their generosity (dr. I.A. Zhitnik, dr. S. Kuzin, we can access a very accurate attitude CORONAS-F data base. In the plots below,we show the history of CORONAS_F roll angle, as well as the (slightly smoothed) offset of the Z axis from the centre of the solar disk. It is seen that the roll angle variations are small, less than 1 degree/day, and the normal to the payload axis is usually within less than 5 arcmin from the solar disk centre. Knowledge of the S/C attitude is vital for determinations of the accurate wavelength scale for the spectra recorded during flares, provided the flare location on the solar disk is known. This subject will be elaborated in one of the forthcoming Notes.

II

Scheme of Coronas-F Payload A B II S N

S N A B  Dispersion plane N12 E63 φ ψ tgψ = (N12)/ (E63) II