24 June Evening Update
Another great day for GLAST. The turn-on of LAT components went much faster than the nominal plan. At this time, all the electronics in the LAT have been powered on (LAT has about one million channels of electronics, plus three onboard computers that are part of a sophisticated data gathering system — all of it running on <650 Watts or about half the power used by an ordinary hand-held hair dryer), and everything looks good so far. We could not be happier! The next step tonight will be to turn on the high voltage to the sensors in the anticoincidence detector (see below for links to information about the detectors), and tomorrow morning the LAT will start detecting individual particle events, at least 1-2 days ahead of schedule. The fluxes of high-energy charged particles in space are surprisingly uncertain, and we expect it will take the next few weeks to tune the LAT to operate in its new environment. The `rain’ of high-energy charged particles through the LAT (many thousands of particles per second) is much larger than the rate of celestial gamma rays (just a few per second), so the name of the game in gamma-ray astrophysics is background rejection — the detective work to identify the gamma rays. The LAT design is very well suited to this task, of course.
Some of you have asked for pointers to more information about the detectors. Thanks for the suggestion! The Stanford University LAT page has a link to a brief description of the LAT subsystems, and there is also this description on the Mission site. Please also have a look at the introductory posting for this blog. Even more detailed information can be found on the SLAC LAT Project Website.
Tomorrow we will start detecting individual particles passing through the LAT. After several more days, we should be able to isolate a few individual gamma-ray candidate events. Building up a first glimpse of the sky in gamma rays will take a few more weeks, while the instrument tuning takes place. I’ll keep posting updates describing this process and the progress. An overview of the science timeline is here (also linked to other entries in this blog and to the mission site.)
Tomorrow, the GBM will also turn on the high voltage to its sensors. In other words, by the end of the day tomorrow both GLAST instruments should be operational.
As I was leaving the Mission Operations Center this evening, the lead engineer for the spacecraft commincations system asked me how I was feeling. `Grateful and very lucky’, I said. He replied we have a great team of very hardworking people, and that is why things have been going well. He’s absolutely right — but I still feel very lucky, too.