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How feasible would you estimate passive positioning systems? For example consider solar radio noise at frequencies that are partially reflected, partially tran

How feasible would you estimate passive positioning systems? For example consider solar radio noise at frequencies that are partially reflected, partially transmitted by the ionosphere. Do you consider it possible for an SDR to geolocate by comparing multiple antenna signals say: 1: "direct signal" : sun -DOWN-> partial transmitted through ionosphere -DOWN-> antenna 1 aimed at sun 2: "geography / terrain fingerprinted signal" : sun -DOWN-> partially transmitted through ionosphere -DOWN-> reflection on Earth -UP-> partial reflection from ionosphere -DOWN-> antenna 2 Or any suggested variations? (reflection from moon for example). https://commons.wikimedia.org/wiki/File:Ionospheric_layers_from_night_to_day.png https://commons.wikimedia.org/wiki/File:Ionospheric_layers_f... i.e. can Western citizens prepare to still have geopositioning in case of an adversarial (successful) first strike against GPS and Galileo where the citizen refuses to rely on adversary positioning systems.

londons_explore 3y ago
With a clock and a telescope, you can get super precise positioning the same as the 16th century way... Atomic clocks are now good enough to make those positions really good. You can do the same with radio frequencies and a phased array antenna if you like. I'm not sure if other approaches would perform better.
- DoctorOetker 3y ago
  I mean without a clock, the reference being the direct path of noise from the sun. Telescopes are impeded by clouds. During night there is no line of sight to the sun, so I concede my rudimentary idea or question has similar drawbacks.
  - DoctorOetker 3y ago
    It would be interesting if precise time could be derived from imaging the night sky, so that the synchronized clock becomes unnecessary.
- amalcon 3y ago
  I've actually heard of research into putting celestial navigation in guided missiles (from people who've worked on it -- so the idea that this is possible seems to not be a secret). Cameras and optics have become good enough to make this plausible with those kind of constraints. I don't know if it's been deployed, but I would not be surprised.
  - nradov 3y ago
    Some ballistic missiles have already been using celestial navigation operationally for decades. That is used primarily during the mid-course phase, and then they switch over to inertial (or maybe radar in a few cases) for the terminal phase.
  - kcb 3y ago
    https://en.wikipedia.org/wiki/UGM-133_Trident_II https://en.wikipedia.org/wiki/UGM-133_Trident_II
kube-system 3y ago
check this out: https://en.wikipedia.org/wiki/Pulsar-based_navigation https://en.wikipedia.org/wiki/Pulsar-based_navigation
- DoctorOetker 3y ago
  this is interesting, thanks for the reference, but it doesn't seem affordable for average citizens: "The main error sources that impact the instrument design are the number of collected photons (related to the detector size and the integration time) and the timing accuracy." Detecting and filtering for appropriate X-rays would seem to require a large and thus expensive detector. Being able to self-locate during aerobraking (as described in following URL) is a very neat application though... https://web.archive.org/web/20170316044511/http://gsp.esa.int/documents/10192/43064675/C4000106174ExS.pdf/8a26a304-9d5f-447d-aa75-bc0c955a4b78 https://web.archive.org/web/20170316044511/http://gsp.esa.in... I wonder what materials withstand the heat and plasma during aerobraking, yet are transparent enough for X-rays?
KaiserPro 3y ago
> How feasible would you estimate passive positioning systems? Totally feasible. DECCA and LORAN-C basically work on the same principle. have a number of transmitters at known locations and measure the phase/interference to get location. However, there are other ways. Visual navigation is totally possible (think SLAM, but with a pre-computed map)
- DoctorOetker 3y ago
  DECCA and LORAN-C are not passive but rely on second parties maintaining transmitters. I may be wrong, but I would hazard SLAM would require an enormous amount of data
  - KaiserPro 3y ago
    > rely on second parties maintaining transmitters. yeah, this is true. Passive radar does the same thing. its passive because the system isn't transmitting, something else is. SLAM data can be pretty sparse. The keypoints for a city the size of london is under 100gigs. (although that depends on your algorithm) but if you think about the amount of effort required to make GPS work, keeping an active visual map of a country isn't actually that much in comparison.

londons_explore 3y ago

With a clock and a telescope, you can get super precise positioning the same as the 16th century way... Atomic clocks are now good enough to make those positions really good. You can do the same with radio frequencies and a phased array antenna if you like. I'm not sure if other approaches would perform better.

DoctorOetker 3y ago
I mean without a clock, the reference being the direct path of noise from the sun. Telescopes are impeded by clouds. During night there is no line of sight to the sun, so I concede my rudimentary idea or question has similar drawbacks.
- DoctorOetker 3y ago
  It would be interesting if precise time could be derived from imaging the night sky, so that the synchronized clock becomes unnecessary.
amalcon 3y ago
I've actually heard of research into putting celestial navigation in guided missiles (from people who've worked on it -- so the idea that this is possible seems to not be a secret). Cameras and optics have become good enough to make this plausible with those kind of constraints. I don't know if it's been deployed, but I would not be surprised.
- nradov 3y ago
  Some ballistic missiles have already been using celestial navigation operationally for decades. That is used primarily during the mid-course phase, and then they switch over to inertial (or maybe radar in a few cases) for the terminal phase.
- kcb 3y ago
  https://en.wikipedia.org/wiki/UGM-133_Trident_II https://en.wikipedia.org/wiki/UGM-133_Trident_II

kube-system 3y ago

check this out: https://en.wikipedia.org/wiki/Pulsar-based_navigation https://en.wikipedia.org/wiki/Pulsar-based_navigation

DoctorOetker 3y ago
this is interesting, thanks for the reference, but it doesn't seem affordable for average citizens: "The main error sources that impact the instrument design are the number of collected photons (related to the detector size and the integration time) and the timing accuracy." Detecting and filtering for appropriate X-rays would seem to require a large and thus expensive detector. Being able to self-locate during aerobraking (as described in following URL) is a very neat application though... https://web.archive.org/web/20170316044511/http://gsp.esa.int/documents/10192/43064675/C4000106174ExS.pdf/8a26a304-9d5f-447d-aa75-bc0c955a4b78 https://web.archive.org/web/20170316044511/http://gsp.esa.in... I wonder what materials withstand the heat and plasma during aerobraking, yet are transparent enough for X-rays?

KaiserPro 3y ago

> How feasible would you estimate passive positioning systems? Totally feasible. DECCA and LORAN-C basically work on the same principle. have a number of transmitters at known locations and measure the phase/interference to get location. However, there are other ways. Visual navigation is totally possible (think SLAM, but with a pre-computed map)

DoctorOetker 3y ago
DECCA and LORAN-C are not passive but rely on second parties maintaining transmitters. I may be wrong, but I would hazard SLAM would require an enormous amount of data
- KaiserPro 3y ago
  > rely on second parties maintaining transmitters. yeah, this is true. Passive radar does the same thing. its passive because the system isn't transmitting, something else is. SLAM data can be pretty sparse. The keypoints for a city the size of london is under 100gigs. (although that depends on your algorithm) but if you think about the amount of effort required to make GPS work, keeping an active visual map of a country isn't actually that much in comparison.