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Spacecraft navigation (in the solar system) requires that one has a mathematical model for how gravity affects the motion of a spacecraft (and in the real world one must consider other forces right down to the pressure of sunlight). Part of this model must be the positions at a given moment of every body in the solar system that can have an effect large enough to significantly affect the spacecraft (i.e. how accurate do you want the navigation to be). In practice this is done by simply computing at a given instant, the force on the spacecraft from all such bodies and effects. This is basically application of the force equation for each body then add them up. Compute the position numerically from that a very short time later. This gives a new position, new forces (because everthing has moved), add them up and move the computed spacecraft position, then repeat the process for whatever span of trajectory you need to consider. This produces a predicted future trajectory, and it is all done numerically, step by step. This is a process of numerical approximations. It is analgous to estimating the area under a curve on a piece of paper by putting a series of adjacent boxes under it like a bar-graph, multiplying height by width for each and adding them all up. Use more boxes and you get a more accurate estimate. Then one waits for a time to see how accurate the predition was by observing the actual trajectory (using sophisticated instrumentation). If the agreement is good, one can rely on it. And the computation can be updated from that point. If it isn't, one looks at the navigation observations and checks such things as forces from gas jets on the spacecraft, solar flares, or anything else that might be causing trouble that one left out or got wrong. In this sense, celestial navigation is exacly analogous to any other navigation problem: observe positions over time, in the sea for example estimate/model currents, winds, engine power, predict the future positions, and refine them as needed.[/FONT]
After reading the above response to "How do we navigate a craft in space?" I thought fine but what about factoring velocity? If we are tp reach the stars the speed will have to be "substantial" and to factor in all the above seems to be somewhat of a challenge. Thoughts?
After reading the above response to "How do we navigate a craft in space?" I thought fine but what about factoring velocity? If we are tp reach the stars the speed will have to be "substantial" and to factor in all the above seems to be somewhat of a challenge. Thoughts?
