On 9/23/11 4:15 AM, Peter Gottlieb wrote:
I was just wondering, what real use is the kind of accuracy most of the list members strive for, and there is the answer.
I can give you some other day to day practical uses of what gets discussed on this list: - radio science in deep space exploration. At JPL we accurately measure the round trip propagation delay from earth to spacecraft and back, and from that, calculate radial velocity (accuracy of around 1 mm/s at Jupiter or Saturn). That lets you do precision orbit determination, which in turn, lets you infer the internal mass distribution of what you're orbiting around. Typical specs for gravity science measurement on Juno, launched a couple months ago, are ADEV<1E-15 with tau of 1000 seconds. - testing of the equipment used in radio science (yep.. Sometimes I think we spend more time proving the box works than building the box)
- GRACE and now, GRAIL, use precise timing to measure the distance between two orbiting satellites that fly in formation a short distance apart. The changes in distance allow even more information about the gravitational field. For GRAIL, the link between the spacecraft is at Ka-band, but there's also an X-band beacon back to earth from both spacecraft. All of it is driven by a pair of really high performance OCXOs in vacuum bottles.
- Mars Science Laboratory (Curiosity) Landing Radar. This is a multi beam doppler Ka band radar used on the SkyCrane. We had to build a system to generate simulated returns for all 6 beams while executing a simulated landing profile (subsequently, modified to be "machine in the loop"). The pulses have to be timed to about 0.5 nanosecond, and are anywhere from 4 ns to several microseconds long. Just as for the radio science thing, testing this beast was a challenge.
- Next May (launch gods willing), a software defined radio with a loadable GPS "waveform" will go up to ISS. It will be the first reprogrammable receiver in space to handle the L5 signal. That same radio will also be used to do "time and frequency transfer" experiments (funding gods willing) to basically build a GPSDO in space. That will demonstrate that it's possible to transfer high precision time/frequency from earth, to an orbiter, to a lander, where you don't have 100% visibility.
- NASA just funded a $100M project to fly a trapped Mercury Ion atomic clock and to measure its performance in space (using an advanced state of the art GPS receiver). They may also do time transfer experiments.
So, there's a huge number of practical applications of the topics of this list.
Catching hyperluminal neutrinos is just another. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
