4 ms·
More details: + 44dBm GPS transmit power -210dB path loss + 15dB rx antenna gain -151dBm received signal strength That's slightly worse (5dB) than sign
by querbu 2y ago
More details:
+ 44dBm GPS transmit power
-210dB path loss
+ 15dB rx antenna gain
-151dBm received signal strength
That's slightly worse (5dB) than signal strength of a handheld device/ phone (~15dB typical handheld loss, urban environment). There is still ~15dB margin. They are cheating a little with the 15dB narrow antenna gain, which requires accurate pointing. Nice result and there is room for improvement. Note: -210dB = 10^-21
- slow_typist 2y agoThat number doesn’t tell much without knowing the background noise on the L-bands out there. It would also be interesting to know whether they achieved this with commercial Gnss receivers.
- querbu 2y agoSince the high gain antenna is pointed at the entire earth, the noise temperature is similar earth temperature. Semi-custom gnss receiver, they collect mostly correlator outputs, and 2.5 seconds of raw IQ
- slow_typist 2y agoAngular size of the earth should be about 2 degrees. That is about nothing compared to the beam width of a 15 dB antenna. So space noise is definitely a factor here. However they made it work, and could have used an antenna with much more gain (think voyager dish) if necessary. Probably the idea behind the experiment is to track rovers on the surface where the antenna is only roughly pointed at earth - without the complexity and energy budget coming with a rotator.
- zokier 2y ago> It would also be interesting to know whether they achieved this with commercial Gnss receivers They used Qascom QN400 receiver.
- slow_typist 2y agoThanks. Using your info I found a masters thesis from 2022 on the subject: https://www.researchgate.net/publication/368292806_Study_of_high_sensitivity_GNSS_receivers_for_space_applications_and_lunar_missions https://www.researchgate.net/publication/368292806_Study_of_... And there is a Qascom company profile: https://italianspaceindustry.it/listing/qascom/ https://italianspaceindustry.it/listing/qascom/
- H8crilA 2y agoAre those reference numbers for L1 signals, or for L5 signals? I remember that L5 uses much longer chip sequences, and thus can deliver much higher processing gains.
- querbu 2y agoL5 can achieve 10-15 dB in ideal circumstances, with tuned loops. Not more. And those aren't ideal circumstances - the GPS signals are received mostly when satellites are grazing the earth (from the moon POV).
- JumpCrisscross 2y ago> They are cheating a little with the 15dB narrow antenna gain, which requires accurate pointing Stars. Finding Earth is a necessarily solved problem for E-L communication.
- kridsdale1 2y agoOnly for 2 weeks per month!
- JumpCrisscross 2y ago> Only for 2 weeks per month Why?
- datadrivenangel 2y agoLunar night is 2 weeks, so you get earth visible 50% of the time from any point on the lunar surface... and earth will be the biggest thing in the sky
- querbu 2y agoEr.... No. Earth is either visible 100% or 0% of the time, the Moon is tidally locked
- shagie 2y agoThe Moon is locked in rotation with its revolution. A location on the Moon that has the Earth above the horizon will always have the Earth above the horizon. Lunar night means that the Sun has set - but the Earth remains in the sky in the same position.
- wildzzz 2y agoThe moon doesn't spin relative to earth so if you can see the earth in the sky, it will always be in the sky. If you watch the phases of the moon, you can easily see that the darkness is just covering the same face that we always see. A moon base would always have line of sight to earth but would be in darkness half the time. Great for comms, not as great for solar power.