Zeno was activated at MET 00:03:04, and telemetry started arriving smoothly. However, we had a bit of excitement because we needed to command the instrument to pause in the execution of its automatic sequence within 5 minutes of power on, and there were problems with the command uplink. But, we finally got the command in just seconds before things would have gotten troublesome, and started with the instrument in a good configuration. Phew.

It's important that we keep the xenon sample from cooling to a temperature below its critical temperature (17 degrees Centigrade). During launch, it is kept warm by a separate circuit with ascent power. The ascent power was turned on hours before launch, and one of the first things we did on orbit was verify that it had kept the sample warm. It worked as planned.

Our first day of operations are mainly concerned with getting the fluid sample to a good place to start the experiment. The first step was to determine the sample temperature as it was maintained by ascent power, and then turn over control of the sample temperature to the thermostat that contains it; this thermostat is our special, temperature-control device that can control the sample temperature with a precision of 3-thousandths of a (Centigrade) degree. We were also watching that the optics module, which contains the light-scattering spectrometer and thermostated sample, was reaching a comfortable operating condition.

Within a couple of hours we were able to determine the sample temperature as maintained by ascent power and switch control to the thermostat. That all went smoothly, and the entire system started coming under high-precision thermal control.

With the thermostat under control, we finally began a controlled cooling of the sample from its initial state to our official starting point at a temperature about 4K above Tc (the critical temperature). That was still underway as MET Day 0 ended.

And now for a look at some early data.

South Atlantic Anomoly

A central part of the light-scattering spectrometer is the photomultiplier tubes (PMTs), which are very sensitive light detectors, able to see single photons. It also turns out that they are sensitive to certain kinds of high-energy radiation.

There is a region above the South Atlantic where there is an anomolously high amount of high-energy radiation; the region is known appropriately as the South-Atlantic Anomoly (SAA). Our PMTs are sensitive enough to detect the SAA when the Shuttle passes through it. Here is some data from one PMT:

The time between the peaks represent the 90 minutes it takes for the Orbiter to make one revolution around the Earth. The peaks are the increase in signal level caused by the high-energy SAA radiation. From left to right the level of the peaks increases then decreases as the Shuttle orbit precesses into then out of the SAA on successive orbits.