PG: I'm glad this now has references to the extensions (and is no longer called Astrid). I like the idea of turtlifying it, though only the hint directs students away from a turtle solution. Using the method of locating the points by algorithm, storing them, then using that list of coordinates will be simpler than pure turtle, possibly even for the cardioid and other such envelopes inside a circle). I'd be inclined to have it start with just the animated image, and another one, a bit slower, animating the cardioid development in a circle (one end moves a step at a time, the other end two steps for cardioid), letting kids figure out what generating rule is involved. It's just personal taste, but I find "With your partner discuss" to be such a lame schoolish Micky Mouse instruction—no real setting tells us to discuss with our partner. And what business, in an optional project do we have saying "develop an algorithm and then use abstraction"? What sense does it make for us to say how to do what students don't have to do at all? With the slowly developing image (the current animation is just fine) students should have enough information to invent, if they like.

BH: See the red boxes.

MF: Needs rewrites

Why do this? To give the students a chance to apply their skills of developing algorithms and using abstractions in the context of a visual arts project. To motivate students with interest in arts and to give them an opportunity to synthesize their artistic skills with their knowledge of algorithms and coding.
Why here? At this point in the curriculum the students know enough to be able to complete a computational visual art project with minimal hand-holding.