On clear sky, you can often see Venus and Sirius with naked eye, so surely easier still with a precise instrument.
I don't think that's what they claim. They write "tracking capacity to within a few arc-seconds, equivalent to 1 meter at a distance of 70 km.", so I interpret that as a way of visualizing how small of an angle a few arc-seconds is.
This provides an absolute navigation reference, so a relative error after a certain distance traveled doesn't make sense either. The final navigation system would use inertial navigation combined with this.
For marine celestial navigation, there are fifty-eight stars that are regularly used / have been standardized on:
* https://en.wikipedia.org/wiki/List_of_stars_for_navigation
With electronics it may be possible to see more than with the naked eye ("Mark One Eyeball"), and have a larger 'almanac' with digital storage than is practical with paper.
As a side note: using only one star and the Sun would give you two lines of position, and they would potentially intersect at two locations, so if you don't have any estimate of your position you don't necessarily know where you are between the two:
* https://en.jeandusud.com/two-equations-for-celestial-navigat...
If you do have some idea, then you'd pick the intersection which is closest.
It does say that higher in the atmosphere will always be better from an interference perspective (makes sense, as then there will be less atmosphere between the sensor and the stars), so that is why they market this specifically for use on aircraft. At 250k per unit it's not something you'll be able to mount on your car anytime soon.
<link rel="canonical" href="https://sodern.com/fr/astradia-le-viseur-detoiles-diurne-pour-un-systeme-de-navigation-sur-et-robuste/" />
If you switched to parts of the EM spectrum where you don’t need high power output, you’re back at radio waves and you’ve simply reinvented GPS.
+5 is the brightest ~1,600 stars, likely similar to whatever any star tracker would be using.
For reference, the current GPS satellites are 1000kg and transmit with 50W (1.2kWh daily).
Here on the ground, for rough calculations, 50kWh is around 450kg in batteries alone. There might be lighter chemistries but this is just to get you in the ballpark.
I think a 1kW light on 24/7 in orbit would need to be a very large vehicle (2-4x the size of the current Navstar satellites) with huge batteries and gigantic solar arrays. Falcon 9 can probably do it, FH definitely can.
An RTG might work but those are out of fashion near Earth these days for obvious reasons.
In any case it would be quite costly (you’d need lots) and its resistance to jamming would benefit your adversaries just as much as it would benefit you. Not to mention, the astronomers would hate you.
The current model (v2 mini) Starlink satellite has 105 meter^2 solar arrays, and there's thousands of those orbiting already. That should be in the 10's of kilowatts on each Starlink. (Those solar arrays are so large they're already artificial stars of their own, though they're not designed to be).
https://en.wikipedia.org/wiki/Starlink#v2_(initial_deploymen...
And to repeat what I might have underemphasized: this is an estimate of isotropic power, if you were radiating uniformly in all 4pi directions.
If you have an accurate true north compass reading, an accurate clock and assume that you’re at sea level, star positions give you all the information you need to find your location on earth.
The SR71 used a similar system.
https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na...
The stars look exactly the same from everywhere on Earth. The only thing looking at them can tell you is an absolute rotational orientation—nothing more.
Old-style navigation was based on the differential orientation of stars relative to the local orientation of the Earth's apparent horizon, but that measurement's not accurate enough for modern GNSS. (I don't think).
I don't know how the SR-71 guidance works, but your link describes it as having an inertial component.
Google claims that human-based celestial navigation done correctly can be accurate to 1 nautical mile, which seems good enough for navigation but not for any weapons targeting. Definitely way worse than GNSS. I would assume there are automated systems out there that can reduce the sources of error together get it down to less than that but probably not several orders of magnitude.
It's in the same place everywhere; it's the position of the Earth, which you're implicitly measuring by pointing out that it's obstructing your view, that's different. The things above the horizon are visible; the things below the horizon are not. That's not facetious; the core idea of this type of navigation is to measure the position of the horizon with high precision, which is hard. Very hard if you're surrounded by mountains. ("Which hemisphere am I on?" is... low precision, if easy to measure). Those classic methods aren't pure astrometry: they're differential astrometry that measure the horizon against stars, the relative orientation of the two.
You don’t need a wide field of view either, you just need an enough pairs of stars that the plate solver can provide an accurate reading of what in the celestial sphere the camera is actually looking at.
After stopping for a little while, the US Naval College brought back sextant training:
* https://www.npr.org/2016/02/22/467210492/u-s-navy-brings-bac...
3kg! That's a very high price to pay for reliability under GNSS denied environments in the day time. Surely you can get ~altitude from a barometer, ~position from inertial + IMU + prior position, and if you want more accuracy maybe DEM models + topography is better.
Therefore I'd suggest this is not going to be very useful on anything with a view toward efficiency (drones). This is more likely a 'quick fix' plugin for existing fat-plane avionics for 'identified risk' reasons. OK move commercially, but technically meh. The go to market plan would presumably be FUD around GNSS denied situations. Reality: unlikely to be problematic in most cases (known flight path, high altitude, low GNSS-denied environment dwell time).
That's the annual salary of of 2-3 airline pilots, which you pay year after year in OpEx. This is a one-time CapEx that will work for years and may allow you to fly (i.e., generate revenue) when otherwise you would be grounded:
* https://www.cbc.ca/news/world/gps-interference-airlines-1.72...
If you tend to operate near / around the yellow and red zones shown here:
Like an airport in Estonia:
* https://www.cbc.ca/news/world/gps-interference-airlines-1.72...
* Part 1: https://www.youtube.com/watch?v=nkvN74wuT8w
* https://www.youtube.com/playlist?list=PL-_93BVApb5_Gufx3xFN9...
(The translation used by Sodern, "Star Tracker", gets me only camera gimbals to take astrophotography pictures)
Edit: found some leads around the cubesat community. Still to see if it works from the ground or in daytime.
* https://en.wikipedia.org/wiki/Loran-C
China built out a GNSS backup with it:
* https://www.gpsworld.com/china-completes-national-eloran-net...
* https://rntfnd.org/2024/10/03/china-completes-national-elora...
* https://www.mdpi.com/2076-3417/13/23/12703
And there's been some rumblings from Korea and UK:
* https://www.gpsworld.com/south-korea-partners-with-broadcast...
* https://www.gpsworld.com/uk-leading-the-west-in-pnt-with-clo...
but no major moves in most countries, even though there's a recognition of GPS/GNSS vulnerabilities by even the (US) military:
* https://fedtechmagazine.com/article/2022/05/dod-transportati...
* https://www.militaryaerospace.com/rf-analog/article/14181490...
And even if your ground transmitters can be taken out, it's a lot easier to build some new Loran transmission gear and radio towers than it is to launch new GNSS satellites (which are also vulnerable to attack).
I think in reality, it’s easier to put little star trackers on your boats and planes.
And it’s way easier to launch another cruise missile at the rebuilt LORAN site.
Which can become a target themselves.
> I think in reality, it’s easier to put little star trackers on your boats and planes.
The star tracker in this article is €250K: that may be 'affordable' for a plane manufacturer or a >5000 TEU cargo ship, but perhaps less so for smaller commercial and recreational boats. Meanwhile a survey of Loran-C receivers published in 1984 had some units available down to the USD 2000 range:
* https://rosap.ntl.bts.gov/view/dot/11795/dot_11795_DS1.pdf
I would think that the development of electronics over the intervening decades would allow for units to be much cheaper now. A (touch-screen) chart plotter with built-in GPS is available for as little as USD 800:
* https://www.westmarine.com/multifunction-displays-combos/?sr...
Compare its capabilities to a (LCD screen) Loran-C receiver from 1990:
* https://sarmarine.com/product/raymarine-raynav-780-loran-c-r...
* https://www.manualslib.com/manual/313978/Raymarine-Raynav-78...
At the end of the day, it's probably more about both-and and not either-or. The more you want to reduce risk, the more independent systems you want to use to tie together to create a better model of reality with regards to where your location "is".
And if you don't want to rely on electronics at all, then you can also get a mechanical watch and a sextant, which was done even on aircraft:
It’s not directly tied to geolocation, but it could integrate nicely with something like Astradia. Since Astradia provides high-fidelity attitude data without relying on GNSS, SpinStep could use that orientation stream to drive autonomous behavior trees, scanning patterns, or state transitions — all without depending on coordinates or maps. Basically: orientation in, logic out.
Would love to hear from others thinking about orientation-first autonomy or mapless navigation.
blacklion•8mo ago
ck45•8mo ago
blacklion•8mo ago
And, oh, yes, all ships before last century, too, of course. So it is more spiral than circle :)
defrost•8mo ago
https://www.beadelltours.com.au/lb_survey.html
* "the largest land-based test range in the western world"
https://en.wikipedia.org/wiki/RAAF_Woomera_Range_Complex
nickspacek•8mo ago
https://timeandnavigation.si.edu/multimedia-asset/nortronics...