[time-nuts] uses of time-nuttery Re: Fast than light neutrino
Jim Lux
jimlux at earthlink.net
Fri Sep 23 13:11:53 UTC 2011
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.
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