Wouldn't be easier to just calibrate the clocks and use UTC?
It even makes a voltmeter read incorrectly.
Moon-meters would be different from Earth-meters.
Careful.
That’s exactly what I want! takeMyMoney.jpg
If an independence movement on Luna gets hold, it might want to differentiate Luna from Earth, and introduce a "lunar foot" based on lunar people.
Kinda feels like agreement on the definition of the Newton would be the difference between "guidance and propulsion systems worked perfectly" and "debris was scattered across the landing zone".[1]
[1] Not an astrodynamicist, but have done enough problems with inclined planes, pulleys, springs etc to know it's quite important to get the magnitude of the forces right.
This would have required to apply a relativistic correction to the measured frequency of any atomic clock, but it would have provided unit definitions independent of the position in the Universe.
However, before contemplating the idea of time keeping on other celestial bodies it was decided to define the second based on an atomic clock that works on the surface of the geoid.
I believe that this was a big mistake, because it ties all the SI units to the Earth and especially because it does not really avoid the use of relativistic corrections. Now the precision of the atomic clocks is so great that for most of them it is necessary to apply relativistic corrections depending on the altitude of the laboratory.
Thus, it is impossible to perform the suggested procedure. We don't (and probably can't) know what zero potential looks like.
Furthermore, we would probably measure those potential differences using clocks that rely upon the SI as presently defined.
> Additionally, the navigation accuracy a system can achieve with signals from multiple space-based assets, such as a person navigating on Earth with signals from Global Positioning System satellites, depends on the synchronization of those assets with each other. At the Moon, synchronizing each lunar asset with an Earth-based time standard is difficult — due to relativistic effects, events that appear simultaneous at the Earth (e.g., the start of a broadcast signal) are not simultaneous to an observer at the Moon.
...
> Precision applications such as spacecraft docking or landing will require greater accuracy than current methods allow
...
> Beyond these operational challenges, the direct use of UTC at the Moon (i.e., without correction) as the local time scale would have cascading effects for applications that require precise metrology. International System of Units (SI) core unit definitions, including the meter and kilogram, rely on the SI definition of time. Due to relativistic effects, a non-SI unit would introduce uncertainty in core unit definitions. These types of errors will have undesired impacts, such as reducing the accuracy of mapping and inertial navigation products
Isn't this true on Earth as well, just to a slightly lesser degree? Why are the synchronization mechanisms used to correct for drift in LEO suddenly unable to cope when used on Luna?
You have
- TAI: i.e. Atomic time which is basically the aggregate of a bunch of major atomic clocks to get as close as possible to "true time" on earh.
- UT: i.e. Universal Time on earth with the different UT0, UT1, etc providing different levels of correction based on where you are on earth.
- UTC: i.e. coordinated time that is the same anywhere on earth. This is derived from TAI but receives leap seconds when it is sufficiently out of sync from UT1.
- GPS time: i.e. the specific time standard kept on GPS satellites based on their orbit. This time is derived from UTC(UNSO) which is a specific UTC clock at the US Naval Observatory and the offsets are recorded by the satellites.
So you have your GPS time and your UTC time. What this proposal is doing is effectively the same thing. i.e. creating a new coordinated time standard for the moon (LTC) that tracks an offset of how far it's drifted from UTC so you can effectively coordinate. And eventually when the moon gets it's own GPS (which it will eventually), you'll have GPS(LTC), i.e. GPS time relative to LTC.
> the only corrections made on atomic clocks located on satellites are very small adjustments to ensure that they remain perfectly synchronized with atomic clocks installed on the Earth (usually to correct drifts due to relativistic effects).
this takes care of the effect mentioned in the article. However the more relevant (and debatable) question is if "Moon time" should also observe the leap seconds (which are introduced to account for variations in Earth's rotation, so have nothing to do with the Moon).
For all internal operations requiring high precision, they'd actually have to keep their own time reference (or calculate a dynamic offset from "GPS time") or they'd get unexpected results since the atomic clocks they carry run fast with regards to the SI definition of a second.
(It could be the other way around, i.e. the clocks running correctly with regards to the satellite's frame of reference and an offset being applied to the signal, but I suspect skewing clocks to fit the Earth-based frame is easier.)