31st January 1995

From Michael Ashley.....

John started bright and early working on a mounting bracket for the ion pump (which arrived in the cargo flight yesterday, together with some crucial fluorosilicone o-rings). John chose to use some 1.4mm sheet material that looked like aluminium. Tin-snips wouldn't cut it, so John got out a power jig-saw. Within a few seconds the jig-saw blade was red hot and the teeth had been ground off - it turned out that the material was Conetic, a magnetic shielding material that is only slightly softer than diamond. John comments that one of the advantages of working at this altitude is that it provides you with a ready-made excuse for doing perfectly idiotic things that you probably would have done at sea-level anyway.

The remainder of the day was spent working hard on IRPS. We tracked down the source of the stepper motor controller problem: it's simply noise on the mains - we measure bursts of 5 volt 500 ns pulses on the 5 volt computer power supply. Hopefully this can be fixed with a few strategically placed ceramic capacitors and a line-filter. We leak-tested the dewar and found a problem with the sapphire entrance-window, so we pulled it apart, cleaned it thoroughly, and reinstalled it. The dewar now appears to be OK, and we will leave it on the pump for at least 2 days. I worked some more on the IRPS software, and John made up some cables to connect the ion pump controller and the LN2 solenoid controller to the computer. We should now be able to measure the vacuum pressure in IRPS from the computer.

We are now sweltering under a heatwave (-29C), due to the presence of thin cloud. It is noticeably more comfortable walking around outside.

Michael Ashley (with contributions and bubble-wrap accompaniment, from John `Banjo' Storey)