The RF-15I instrument is designed to study solar flare X-ray radiation with emphasis on flare energetics. It consists of two parts: soft and hard X-ray photometer observing the whole disk solar emission with high time resolution; and solar soft X-ray imager KRF (Rotating Modulation Collimator) called the tomograph.
The detectors nominally point toward the Sun. The spacecraft spin axis is to be repointed towards the centre of the solar disk each time it move more than 10 degrees from the Sun due to motion of the Earth around the Sun. One satellite revolution takes about 118 seconds.
The soft and hard X-ray photometer has two detector systems:<br> <sp>(1) A proportional argon gas-filled (350 Torr) detector of aperture 4.5 mm2 with a Be filter of 150 mm thickness. The largest cross-sectional area of the detector for gamma radiation is 10.5 cm2. This detector nominally registers the soft X-ray solar flux in the three energy channels 2-3-5-8 keV every 2 seconds.<br> <sp>(2) A Na(I) scintillation detector of 15.2 cm**2 aperture and crystal thickness 8 mm. This detector registers every 0.125 seconds the hard X-ray flux in five energy bands 10-15-30-60-120-240 keV provided that appropriate rate thresholds are exceeded in each of the upper four energy ranges. In the lowest energy range 10-15 keV, the data are collected every 2 seconds simultaneously with the softer proportional detector channels.
The tomograph images solar flare emission in two energy bands 2-4 keV and 4-8 keV by means of the numerical reconstruction of the soft X-ray signal modulated by the collimator due to the rotation of the satellite.
The signals coming from both low and high energy channels are processed in real time by the onboard PRAM computer and the decision is made whether to store the modulated signal (about 10 kbytes) to memory for image reconstruction on the ground. If so, before being stored, the information is compressed and periods when the source is outside narrow fields of view are discarded. About 80 images can be stored between telemetry dumps. Generally the intention is that for each flare of the GOES class above C5, at least one sequence of modulated signal will be recorded, usually at the flare maximum when the time variation of the signal influences the image restoration process least. Average unmodulated signals from both energy channels are recorded once per revolution. The data gather time unit is 1/128 s for the X-ray detector while outside the radiation belts. During belt crossing the detector high voltage is turned off.
The web pages at http://www.cbk.pan.wroc.pl/RF15-I_www/default.htm provide more information on the instrument and also access to the data