Originally posted by leisurelysloth
Sonhouse, I'm curious now, what work did you do with the atomic clocks at NASA?
Sorry, I missed your post. I was on the Apollo project, at Goddard Space Flight Center in the years 70 and 71 working on Apollo timing and tracking, the timing part was the successful attempt to co-ordinate the timing of the reception of apollo (and subsequent space program projects) data to within 100 nanoseconds. That is to say, when a deep space probe of any kind is way out there and being tracked, say first by Goldstone, the time Goldstone gets to aquire the signal is limited to the time the probe is actually in line of sight. Once it goes over the horizon, another dish had better be ready to take up the slack and that slack window established by NASA was one hundred nanoseconds or one tenth of a microsecond. By now, it might be down to ten nanoseconds, not sure, but in order to do that NASA and all the downrange tracking stations needed to have all the timing co-ordinated to well under that one hundred nanosecond window. Thats where the timing part comes in. We had three kind of clocks, well four counting the mighty hydrogen clock, but at our humble tracking station we had three: a master whoopdidoo cesium beam atomic clock accurate to within (ATT) one second in 6,000 years and a Rhrubidium
atomic clock accurate to within one second in a few hundred years as the primary BACKUP and a back up back up, a quartz clock accurate to within one second in a couple three years. I never saw anything but the cesium beam clock run myself, it never crapped out. Anyway thats what the timing part was. My job was called timing and TRACKING.
the tracking part was, on the apollo (of course Skeeter denies all this), how do you figure out exactly how far away the lunar craft is on a line going away from earth? So they had this transponder, a signal, a very special signal, was transmitted to the craft and the transponers job was simply to sling the same signal back to earth like a mirror reflection. So a complicated code was embedded in the signal, I mean, REAL complicated!, and when the signal got back to Goddard, the exact timing of the signals, the transmitted one and the reflected one, was compared. Due to the complicated nature of the signal, there was only one distance that a particular signal/reflection would match so that was the distance to the apollo, kind of like extending a long arse ruler into space and bringing the end back to earth, you then knew by comparing the ends, what distance the ship had to be.
Sorry to be so long winded about it, its not easy to condense into a few hundred words.