The "jumps" are intended to be gentle enough that they won't leave Ryugu's gravity well. For that, you just need to know Ryugu's mass; they had a good guess of

The "jumps" are intended to be gentle enough that they won't leave Ryugu's gravity well. For that, you just need to know Ryugu's mass; they had a good guess of that before the mission started, and a much better idea of it now.