How good are accelerometers these days? With a known starting point, map data, a good clock, and accelerometers you should be able to compute your position using dead reckoning.
Only good for a limited time, is the main thing. Your error increases quadratically with time, so even a really good IMU will drift dramatically at some point without some kind of periodic position fix.
I really don't understand the founding motivation for this company. For one, autonomous vehicles (e.g. Waymo) don't use GNSS as the primary means of localization. You can also achieve centimeter (and higher) precision with RTK. The main source of errors is usually reflections, which are still a problem here. A higher SNR helps, but I'm not sure it helps enough to justify the endeavor.
The problem I see with investing in such technologies:
1. Satellites are too far to fight anything on ground (Power per unit area (i.e., intensity) decreases as the square of the distance)
2. If the Satellites are relaying to things on the ground, they are also relaying their location (easy adversarial targets)
3. In a war (they mention Ukraine in the article), first thing that is toast is these satellites.
I don't think this is the right replacement for GPS. Perhaps someone here can correct me if I am wrong?
It's probably worth considering the military and non-military uses separately.
The USG military uses is attractive not as a replacement of GPS, but as a supplement/complement. If they could truly manage to use the same receivers, then this provides an extra layer of redundancy. There are 32 GPS satellites in the current constellation. Being in MEO means you need pretty beefy ASAT to take it take them down, but we could assume that China could pull it off. Xona's constellation would add redundancy (splashing 258 is just a lot more targets).
For non USG uses, I imagine Xona is making two different pitches.
a) You can achieve GPS+RTK level accuracy without needing RTK base stations.
b) Increased jamming/spoofing resiliency, intended for short of war (aka hybrid war/grey zone) situations. For example, I imagine Xona will attempt to setup a private encrypted signal which they'll sell to friendly/allied nation airliners and similar industries.
Question please, it says that jamming these is more difficult. But doesn't that mean it's not impossible, so at some point in the future it could happen?
That is true for almost all security. It is not impossible to break cryptography, but it is costly enough as to not be viable in most cases. Most of security is about to make it costly enough to break as to not be worth it.
One time pad cryptography generated with truly random pads with no reuse of keys and no leaks in key transmission being the big exception.
But yea, calling it inconvenient for most uses is quite an understatement. It did serve many spies well though during the Cold War using numbers stations, even if the Soviets were known to take short cuts by just having a room full of people randomly hitting keyboards rather than using true randomness.
