Yeap. 3 images per second adds up quick.
I assume you're compositing them since astrophotos usually use long exposure times...
Compositing them, yeah, but for a slightly different reason. Deep-sky objects (galaxies, nebulae, etc) have very low surface brightness and thus require very long exposure times (minutes to hours!) to collect enough data. Many of these objects also have too much contrast between the brightest and faintest areas (high dynamic range), so a single shot won't properly expose the whole thing. The Andromeda Galaxy is a classic example of this, where a single shot will either only record the intensely bright core while leaving the fainter surrounding disk mostly unexposed, or it will record the disk while the core is over-exposed. Combining several images with different exposure times can help bring out all the details without over/under exposing anything.
In my case I'm photographing planets and the moon, which requires a different strategy. These objects have much higher surface brightness, and the dynamic range is usually low enough, such that a very quick shot (a few 1/100ths to 1/10ths of a second generally) will provide a proper exposure. The problem then is the magnification required. The planets have much smaller angular sizes than most galaxies and nebulae, so to get any surface detail you have to use very high magnification, at which point the blurring effects of the atmospheric turbulence wreak havoc on the image quality. It's like looking through water or heat haze sometimes. Taking hundreds or even thousands of images very rapidly, then selecting and combining the best ones, can help counteract this turbulence and bring out the finer details -- at least to a certain extent. Nothing beats adaptive optics or space-based telescopes!
