June 15, 2002 H. S. Hudson RHESSI tohban report for June 8-15, 2002 0. Comment This tohban report is early and only covers until today, June 15. David Smith is now taking over as tohban. This week has been devoted to preparation for the Crab transit, and there was also an eclipse sequence June 10. Many things went wrong operationally and at the time of writing it is not clear if an offpoint to observe the Crab directly will be possible. The observation of the Crab during normal solar pointing is proceeding well enough. 1. Solar activity. Activity was low, fortunately. 2. Memory management To reduce the SSR level to zero for the Crab data, the write pointer was reset several times. As of today, even with shutter open and with reduced decimation rules, we seem to be holding steady. Autonomous shutter operation is enabled. 3. Autonomous shutter thresholds 4. Coordinated observations Too busy for them. Max Millennium did some support for the VAULT rocket, but I do not know about its schedule or target. 5. Problems There were many, of which the most important was the loss of the Berkeley ground station owing to a mechanical failure in the dish's altitude drive. It apparently will be down until at least mid-week. This did not help with memory management, but permission to use Santiago came quickly and now we're getting full dumps from there as well as Wallops, plus some Weilheim coverage, and using Wallops for uplinks. Another general area of problems has to do with planning the offpoint. It is all very interesting, but we tohbans have great faith in the offpoint committee's ability to get there eventually (the Friday meeting, led by Gordon, involved Lewis, McTiernan, Zehnder, Smith, and Hudson, plus remarkable plots made by Fivian. As of that meeting, there was a fundamental lack of knowledge about the on-board command sequencing or even the meaning of the commands. Finally, during offpoint practice a misunderstanding of the ACS modes resulted in Idle mode replacing Precession mode, with HESSI about a degree off its normal solar pointing. This unfortunately lasted for an entire sequence of invisible orbits. The problem is understood and fixed, but the data have not been looked at yet. 6. Eclipse On the brighter side, the eclipse observations went well (see http://sprg.ssl.berkeley.edu/~hhudson/eclipse/eclipse.html ) and it may be possible to extract a roll calibration from them. We don't know yet how good this calibration will be, however. Analysis will continue after the ephemeris is understood better. 7. Links http://sprg.ssl.berkeley.edu/~hhudson/tohban_links.html