This puzzle is part of the Monthly Topic Challenge #8: Cellular Automata.
Conway's Game of Life has been creating patterns to beguile amateurs and professionals alike for more than 50 years now, and there are tons of variations. But the ones I tend to like are the ones that are easily explicable in terms of the original model of how "human" populations evolve. I looked at the lack of aging in Middle-Aged Life, and I propose another modification, namely to account for the fact that in the standard 8-cell neighborhood, the corner cells are further away from the center, and so they should have a diminished effect on the population of the center cell.
So my idea was to rescale so that when counting neighbors, corners only count as half. So for example, if a cell has one live orthogonal neighbor and one live diagonal neighbor, it is considered to have 1.5 neighbors, as a cell is not its own neighbor. Similar to Life, in each generation, a live cell with 1.5 or 2 neighbors continues living, while all other live cells die. A dead cell which has 2 neighbors is spawned as a live cell.
An eater is a stable pattern that destroys spaceships that run into it (from a fixed direction and offset). The 4-long spaceship has a very simple eater:
Your task? Find an eater for the 5-long spaceship. I hope you enjoy!
Regarding the design of the rules, because the total possible numbers of neighbors has changed from Life, it seemed wise to scale the neighbor requirements for transition as well. Being discrete, I could not get the percentages perfect, but I tried to keep these ratios as close to the original game as possible.
For those who use Golly, a rule file for HalfLife is available at https://pastebin.com/tkPLTb2f. For those who wish to use other tools, Hensel notation for this automaton is B2ei3inqy4c/S2-cn3cinqy4c.