While fascinating, the original visualization is a bit difficult to read. The biggest issue with it is the diagonal lines, which make interpreting the axes confusing.
My remix fixes that issue and adds a couple of features that go further in making the visualization easier to read. I opted to nix the guiding lines altogether and instead leverage interactivity: users can hover over the heatmap and see live updated values below: one for each of the axes, as well as the delta-v value.
I also added a secondary view - a line graph that shows, for each possible launch day, the best possible delta-v value. There's also a simple guideline that updates as the user hovers over the heatmap.
Finally, to augment the interactivity of the visualization, I implemented a feature that allows the user to modify the color scheme of the heatmap. This allows them to explore the thresholds that might not be readily apparent with the default color scheme.