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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Visual satellite position fix
From: Peter Monta
Date: 2013 Aug 12, 18:53 -0700
From: Peter Monta
Date: 2013 Aug 12, 18:53 -0700
Yes, I think there were several satellite optical triangulation projects in the mid-1960s. They used the large passive Mylar-balloon satellites (Echo and friends). There's a really entertaining film describing the teams and equipment that went to northern Canada to test the technology---this would have been around 1963 or 1964---with their large, ~20 cm cameras (using silver-halide film of course), paper-tape sequencers, quartz clocks. It apparently developed into a near-worldwide system of a few dozen baselines, just before Doppler satellites took over. It's interesting to think of ways these projects could be replicated with modern, low-cost equipment. I'd like to get back to playing with photographic techniques. What can be done with handheld point-and-shoot cameras, especially the recent high-zoom image-stabilized types? A lot, I suspect. Crazy idea: it would be a good joke to use GPS in optical mode. Frank mentions ISS, and of course that's great for detection and photography, since it's so incredibly bright. But he rightly points out that since it's an LEO object, the orbital prediction degrades beyond a few weeks. Maybe there's some fun to be had in considering dimmer objects that are in higher orbits and are thus more predictable, far away from atmospheric drag and Earth's lumpy gravity field. The extreme example would be GPS. The orbits are very well characterized (~few cm), and if they don't maneuver very often, the orbital predictions should last a long time. Same goes for the geodetic satellites (no risk of maneuvering there) or geosynchronous communications satellites. The downside is that all of these are dim, visual magnitude at best around 12. But with a modest telescope they could certainly be imaged against the background star field, and then it's just triangulation. GPS satellite shots are really just lunars, but 20 times better. If brighter objects are wanted for use aboard ship, where motion might limit exposures to 1/100 second or so, how about the Cosmos rocket bodies? Those are magnitude 3.5 or so, and they don't maneuver. There are a lot of them, so availability should be pretty good. They're in LEO, though. Cheers, Peter ps: speaking of geodetic satellites: a satellite-laser-ranging station on ship? Fire the laser at the top of the swell? I know, totally, *totally* impractical. Probably. :-)