We just had the CSBF weather briefing and discussed upcoming launch opportunities. The next few days (Friday-Sunday) all present possible launch windows in terms of the low-level winds. However, possible thunderstorms make it quite uncertain when we can actually launch. The wind at 125,000 feet has a velocity about 11 knots and is still going westward. By the middle of next week, the stratosphere will be in the midst of the bi-annual turnaround with an expected velocity of 6 knots eastward.
We are running the system each day for a few hours to make sure that everything is ready when we launch. In the meantime, we have practiced our checkout procedure (which we do every launch day at 1:30am to test the functionality of the system) to perfection. We power on all systems, check if they behave as expected, and power them down again. During our routine checks yesterday, we noticed that the stepping motor which spins the polarimeter to minimize systematics associated with detector non-uniformities draws somewhat unexpectedly less current and power when operated at higher speeds. We thus decided to spin the experiment faster (at 4-5 RPM rather than 2 RPM) during the flight to save some power and to reduce systematic errors even more effectively. We evaluated the truss deformation data obtained on Tuesday morning when X-Calibur was carried to the runway and back. The drive and the associated vibrations did not change the mirror-detector alignment at all within the accuracy of the measurements (0.1 mm per measurement).