Complex sentence: The lander is expected to achieve the first controlled touchdown on a comet nucleus where the lander's instruments should obtain the first images from a comet's surface and make the first "in situ" analysis to find out what it is made of.
Split into simpler sentences: The lander is expected to achieve the first controlled touchdown on a comet nucleus. Its instruments should obtain the first images from a comet's surface and make the first "in situ" analysis to find out what it is made of.