That's a remarkable result. Looks like (if I haven't misunderstood) SEXTANT a software experiment that piggybacks on the raw datastream from the NICER x-ray tel

That's a remarkable result. Looks like (if I haven't misunderstood) SEXTANT a software experiment that piggybacks on the raw datastream from the NICER x-ray telescope, and estimates the phases of the time-of-arrival of bright millisecond pulsars (in x-ray photons). From differential phases (at microsecond accuracy), they infer differential position (kilometers). I understand it's eight (8) pulsars in the catalog. https://arxiv.org/abs/1711.08507 https://arxiv.org/abs/1711.08507 I wonder if it's really that easy to extend this to interstellar scales. If you move 300 km, a 1-ms source is reset to its original phase. Go out to New Horizons distances, and all your phases are millions of cycles offset from Earth, by highly jumbled fractional parts. Is it mathematically feasible to reconstruct everything then? Or: do you maintain a continuously-updated model across the entire mission—and hope that you don't lose count of your cycles?