Geocentric to heliocentric vector transformation via distance guess
In the Holman et al. paper describing HelioLinC they mention a transformation from geocentric coordinates to heliocentric coordinates for an asserted heliocentric distance guess. Because of poor reading on my part, I thought that transformation was either too trivial to define or common enough that one could find it in some basic astronomy text. Not being able to find anything in my search, I tried to figure it out myself. It was a useful exercise and I'm glad I did it. I thought it'd be helpful to write it up and illustrate the problem for the benefit of someone else who might be searching for this useful bit of knowledge. I did that too. And then I saw that it was described in full in the Appendix of the HelioLinC paper. Ah well, here it is anyway. I've also published a Python function on Github that does the geocentric to heliocentric transformation for an asserted heliocentric distance.