South Pole Diaries 1997/98



Wednesday 19th November 1997 - NISM & MISM alive!

From John Storey......

Things are moving right along. Rodney Marks arrived last night, ready to begin 12 months at the Pole. He'll be looking after Abu, and already we've pressed him into service lugging things around. Ev has been busy in the AASTO, and has been sending messages back and forth to the AGO service crew.

Last night we got *both* the nism and mism working. The mism was easily able to detect Ant's hand when he leaned out the door and waved at it. This not only proves that Ant is alive, but also that he's warm-blooded. It also gives us great encouragement that we will be able to leave two working instruments here when we depart in a couple of weeks.

Firing up the nism first, we were delighted to find that the Stirling- cycle cooler switched on immediately, and everything just worked the way it should. Scanning across the sky gives a large variation in the amplitude of the signal we see (as it should). The only problem is that the stepper motor doesn't have enough grunt to consistently move the instrument - boy do we have a surprise in store for it.

When we last talked to the mism (in May), the chopper was refusing to run above 500Hz. Naturally this was one of the first items for discussion with it when we re-established contact last night. Sure enough, 500 Hz. Tops. Maximum. This wouldn't matter a whole lot except that the entire signal chain is tuned to 1kHz. Figuring that if the mism refused to be phase-locked then we would refuse to be fazed, we plugged in the spare chopper-driver board and the chopper immediately locked up at a kHz, no argument.

This delighted both Ant and me, as neither of us has any wish to rip the optics box apart and mess with the chopper motor. However I do take any electronics failure as a personal affront, and the chopper driver board must have realised it was well and truly for it.

The "super" refuses to talk to the mism on the mism port, so we're using the nism port instead. This might be a software problem, or could be related to the fact that the mism rs232 port is on a different board to the nism. Given that the AFOS will not be running this year, a very simple fix is to reassign port 1 to the mism.

The next step was find out what when wrong with the original chopper- driver board. (I am dismayed to find that not only is the oscilloscope smarter than I am, but that the multimeter is also ahead on points. It's a bright yellow you-beaut Fluke meter, that Ant insisted I buy because it cost a lot of money. When I tried to measure a voltage with the probes plugged into the current socket, it beeped plaintively at me. I'm not sure if this intelligence, or just instinct for self preservation. Tomorrow I plan to hold it up in front of the mism and see if it is alive, too.)

Anyway, what was wrong with the chopper-driver board was that there was a tiny little bit of grunge on the board, bridging between two of the copper tracks. It was sufficiently conductive to reduce the reference signal below the CMOS threshold, with the result that the PLL simply ran at a random frequency close to the middle of its range. We will need to talk to our normally excellent electronics workshop about the hazards of leaving grunge on the circuit board.

Actually, we *had* intended to have all the boards made commercially once the workshop had done the prototypes. I think I'm going to vote for doing exactly that during 1998, especially in view of the brown slime.

Speaking of which, we ripped the nism off the roof of the AASTO and sledded it across to the MAPO building. The inside of the support bracket is covered in the last remnants of brown slime (actually white slime, being aluminium). Because the nism was exposed it acted as a big cryo-pump and is now covered in more than its share of grunge. We'll clean it up tonight and then fit the *new monster stepper motors* which Andre tested in the lab and found to be all torque (*and* all action).

By now we're fairly convinced that what hit the AASTO was a combination of HF and HCl from the decomposing freon, plus H2SO4 from the batteries. (Michelle thinks it was aliens, but she's wrong. The aliens live at Old South Pole Station, and don't cause any trouble as long as we invite them to Thanksgiving each year, which we do. I've already been enlisted as a wine waiter for the occasion). But I digress. The only really nasty in the above list is HF, which gobbles up human flesh like an offended alien. Paradoxically, it's *so* reactive that it's very unlikely for any of it to be left in the AASTO - whatever it landed on it will already have eaten and been thereby rendered harmless (or so I believe).

Weather is still very cold; still windy. They're scheduling 6 flights a day to try to get the program back on schedule, but only about half actually get here.

While I'm typing this, Amnt is cleaning up the nism. That's why this message is so long. When I finish I'm going to translate it into French, then type it backwards in morse code, and then go out and give Ant a hand.

Cheers, John




Further Information