Todd Barber
Cassini Lead Propulsion Engineer (bio)
Hello again from Pasadena, California! As I type these words, our spacecraft is dutifully executing a dynamic encounter with Saturn’s perplexing satellite, Enceladus. Some of you have expressed an interest in the engineering particulars of our daringly close flyby, with respect to its effects on the spacecraft. I’m happy to say that even though scientists should gather plenty of material for chemical and physical analysis, the icy plumes of Enceladus are rather tenuous, even with our very close flyby distance of only 25 kilometers (16 miles). One reason this is true is our dive into the plumes occurs at a much higher altitude than the closest approach, as you can see in the image below. As such, we don’t expect Cassini to slow down or change course due to impacts. However, gaseous plume material may place small torques on the spacecraft which will cause our thruster deadbands to be exceeded, a common occurrence while in thruster control. In that case, our small hydrazine thrusters (0.2 pounds or 0.9 Newtons) will fire to correct the pointing of the spacecraft. In fact, our attitude control engineers may be able to estimate the density of the Enceladus plume by studying these rocket firings!
As far as the potential for ice damage to Cassini, fortunately the ejecta from Enceladus consist of very tiny particles only. This, coupled with our micrometeoroid shielding and relatively high altitude while within the plume, will help keep Cassini safe and sound. It’s truly the best of both worlds–we’ll be close enough to really ingest the smorgasbord offered up by Enceladus, but we’ll still be comfortably far from the surface and well away from affecting the spacecraft adversely.
A new Cassini video update was recently released, further explaining our busy October plans for twin Enceladus flybys. You may view the video here
Unfortunately, I won’t be here to report our first signal tomorrow after the flyby, as I am leaving for a leaf-peeping vacation to New England this evening. Rest assured I’ll be thinking of our intrepid robotic friend and the flood of science data to come. Go, Cassini, go!