Colour and Stereo Surface Imaging System - CaSSIS

Push-Frame Camera

Those of you who have read all about CaSSIS will know that it is a push-frame camera. We take 2D pictures every 350-400 ms as the spacecraft flies over the planet's surface. Now that means timing is important. At 400 km above the surface in a circular orbit, that framing rate must be ...

... one image every 367 milliseconds. But when we command that, do we get what we asked for?

We devised a little test with an LED and an arbitrary waveform generator operating in pulse mode. We slightly offset the pulsing with respect to 367 ms so that we could see the images changing from bright to dark over a period of 40 images. And sure enough, it showed that the instrument is roughly correct. I say roughly because the error bar on the number is a couple of milliseconds. But we have allowed about 10 milliseconds in the requirements - it is the overlap that we need to stitch the individual framelets together. OK. It's complicated but ...... The test shows that CaSSIS has no timing issues.