3 ms·

The actual policy has pretty clear explanation why LTC is needed: > Additionally, the navigation accuracy a system can achieve with signals from multiple space

by zokier 3y ago

The actual policy has pretty clear explanation why LTC is needed: > 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

aftbit 3y ago
>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. 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?
- CuriousCosmic 3y ago
  It's true for exactly the same reason. 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.
masswerk 3y ago
However, wouldn't the inclusion of a coefficient solve this easier in a much more general and flexible way than defining a frame of reference for each individual case?

by zokier 3y ago

aftbit 3y ago

>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. 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?

CuriousCosmic 3y ago
It's true for exactly the same reason. 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.

masswerk 3y ago

However, wouldn't the inclusion of a coefficient solve this easier in a much more general and flexible way than defining a frame of reference for each individual case?