SXT STATUS REPORT FROM ISAS Wednesday, 8 September 1992 Last week Yohkoh celebrated its first anniversary since its successful launch on 31 August 1991. To mark the happy occasion, many of the spacecraft engineers were invited to ISAS for a party. It was a good opportunity to show an SXT video which nicely demonstrated how well Yohkoh had been performing. SXT continues to function very well and there were no operational problems during the past month. It is worth noting that in the past year the serial number counters have reached about 100,500 for the full frame images and nearly 500,000 for partial frame images. Since the partial frame images are often made up of multiple exposures (2x2 OG's), the true number of shutter operations in the past year was probably in excess of a million. Sam Freeland also notes that the last filter wheel error occurred in March before the SEU correcting code was implemented and it is likely that it was not a true error but only a symptom of the SEU itself. The aspect telescope transmission continues to degrade at a familiar rate. At the beginning of August, the transmission was about 15% of the original value at launch. The CCD continues to perform well. The number of dark spikes have increased but these are not readily noticeable in short X-ray exposures. The increased dark current near the solar limbs will soon become more of a problem for the visible images and thus, may make flat fielding necessary for certain scientific objectives. The autumn meeting of the Astrophysical Society of Japan (ASJ) is soon approaching. We were informed that this year over 60 solar papers (nearly three times the previous maximum number) have been submitted and that many of these are based on Yohkoh observations. This is a partial indication of scientific activity that is based on Yohkoh data. FLARES and SOLAR ACTIVITY Solar activity remains relatively low, but many interesting solar phenomena can be seen in the on-going X-ray movie on the laser disk in Building D. Most recently, NOAA region 7270 began to produce numerous C flares and an occasional M flare. Today two X flares were recorded by GOES, but unfortunately, were not observed by Yohkoh in flare mode (one occurred at night and the other during the SAA). A beautiful example of the formation of soft X-ray loops following the disappearance of an H-alpha filament can be seen in the north west on 18 August 1992. OFF-POINT TEST #2 On 27 August 1992 the Yohkoh spacecraft was off-pointed 16 arc-min to the west during one orbit and then in the subsequent orbit was off-pointed 16 arc-min to the east so that the far corona could be observed with SXT. Since the solar X-ray luminosity was fairly low, we were able to make 1 min exposures. The far corona was similarly observed on 8 May 1992. The data show that the SXT can detect X-ray emission to very large heights above the solar limb (> 2000 arc-sec). The nature of the operations may make it too difficult to perform this kind of observation very often, but it we hope that future far corona observations can be made. One objective would be to try to monitor the heliospheric current sheet, as viewed at high temperatures, in cooperation with ground-based measurements. HRTS ROCKET SUPPORT On 24 August the NRL HRTS rocket was successfully launched from White Sands Missile Range. In the days leading up to their launch, Dr Nariaki Nitta supplied daily SXT images via ftp to an NRL computer in order to assist the planning of the rocket observations. We have recently heard from Dr John Cook (NRL) that some of the film has been developed and that the data looks very good. We look forward to comparing SXT images with HRTS data. RASM - (Remote Access Schedule Mailbox) RASM is a dial-in/dial-back system that JPL has installed for users of the DSN to obtain and request schedule information. In the past month we have begun to acquire the preliminary and final schedules with RASM using a modem connected to a one of the DECstations. We are currently exploring how we might improve the procedure of making long- term requests and for canceling unwanted passes from the preliminary schedule. For both of these tasks we currently rely on fax. Simplifying these tasks is desirable since the Yohkoh duty scientists currently spend about five to six hours per week on DSN issues alone. CCD WARM-UP During the past weekend we turned off the TEC to warm up the CCD to about 0 C. The purpose of this was to evaporate whatever is condensing on the CCD front surface. The decision to do this was based on recent diffuser images. Although the data has not been fully analyzed, the narrow band filter image signal levels will probably increase by about five percent. The last time this was done was in early June, and it appears that it may be necessary to do this in the future every two to three months. -- End of Report: J. R. Lemen --