Epoch State: What’s it all about?


Epoch state is spacecraft-navigation-speak for the beginning, the thing that kicks everything off, specifically a trajectory. It’s the position and velocity that initializes the problem Where are we and where are we going? The spacecraft trajectory propagates downstream from there, subject to all the gravitational and non-gravitational accelerations acting on the spacecraft—such as the pull of gravity from the sun and all the planets as well as the firing of thrusters that maintain its attitude. There’s always a fair amount of uncertainty in the trajectory because you never know the epoch state perfectly and there are always errors in your model of the accelerations. Think of a trajectory as an animal path through the jungle: It’s a bit wide and fuzzy because you don’t know it exactly, but if you wait long enough you’ll see an animal come along, by-and-by.

Well, that’s a little bit like what this initial post is supposed to do: kick off a trajectory of blogs subject to the forces of reality and non-reality (i.e., imagination) as they impinge on my consciousness, as well as dollops of whimsy bubbling up from the subconscious and elsewhere (e.g., from you). And like errors in a spacecraft trajectory that grow and grow after you depart the epoch state, I expect these blogs to also wander considerably. They’ll start off oriented towards my last novel, The Darkest Side of Saturn, but after a while you can expect to see them drift farther and farther from that fuzzy animal path.


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