5 ms·

And then you try to actually build a GPS network, and ask yourself: what kind of antennas should we use? what should be the freq? how much power? how will the r

And then you try to actually build a GPS network, and ask yourself: what kind of antennas should we use? what should be the freq? how much power? how will the receiver detect the precise nanosecond when it receives an incredible weak signal? (in current GPS the signal is bellow thermal noise)

empiricus 6mo ago
(also you receive the signal from all satellites at the same time, on the same freq, and some random reflections. and then you need to extract independent streams of bits for each satellite, each with its own nanosecond timestamp for receive time)
zikduruqe 6mo ago
The last time I built my own GPS network, I used a sextant, a watch set to UTC and nautical tables to determine where the orbiting bodies were.
- srean 6mo ago
  Harrison time pieces were indeed the cutting edge GPS technology of its day. That and moon watching. Nowadays we have GPS and Pulsar / Quasar watching. https://en.wikipedia.org/wiki/Very-long-baseline_interferometry https://en.wikipedia.org/wiki/Very-long-baseline_interferome...
minetest2048 6mo ago
You can go into a really deep rabbit hole thinking about those questions.. this page explains the design decisions behind LunaNet AFS navigation signal: https://insidegnss.com/the-augmented-forward-signal-afs-defining-the-navigation-signal-standard-for-future-lunar-missions/ https://insidegnss.com/the-augmented-forward-signal-afs-defi... Some considerations: - They don't use GPS frequencies because there is receiver on the moon that receives GPS L1 signals (LuGRE and potentially more in the future) - Make it easy to acquire for low complexity hardware - Use 5G forward error correction code to reuse existing hardware implementation - Design the signal in a way so that the user can easily find start of a data frame And those are RF level considerations... there will be more considerations needed for the data transmitted over those navigation signal that the receivers need to use to determine navigation satellite position as lunar orbit is much more complicated than Earth orbit

empiricus 6mo ago

(also you receive the signal from all satellites at the same time, on the same freq, and some random reflections. and then you need to extract independent streams of bits for each satellite, each with its own nanosecond timestamp for receive time)

zikduruqe 6mo ago

The last time I built my own GPS network, I used a sextant, a watch set to UTC and nautical tables to determine where the orbiting bodies were.

srean 6mo ago
Harrison time pieces were indeed the cutting edge GPS technology of its day. That and moon watching. Nowadays we have GPS and Pulsar / Quasar watching. https://en.wikipedia.org/wiki/Very-long-baseline_interferometry https://en.wikipedia.org/wiki/Very-long-baseline_interferome...

minetest2048 6mo ago

You can go into a really deep rabbit hole thinking about those questions.. this page explains the design decisions behind LunaNet AFS navigation signal: https://insidegnss.com/the-augmented-forward-signal-afs-defining-the-navigation-signal-standard-for-future-lunar-missions/ https://insidegnss.com/the-augmented-forward-signal-afs-defi... Some considerations: - They don't use GPS frequencies because there is receiver on the moon that receives GPS L1 signals (LuGRE and potentially more in the future) - Make it easy to acquire for low complexity hardware - Use 5G forward error correction code to reuse existing hardware implementation - Design the signal in a way so that the user can easily find start of a data frame And those are RF level considerations... there will be more considerations needed for the data transmitted over those navigation signal that the receivers need to use to determine navigation satellite position as lunar orbit is much more complicated than Earth orbit