(written from a Production point of view)
According to an okudagram created for TNG: "The Royale", which was not visible on screen, the Jacob was a NASA spaceship launched in the late 2030s or early 2040s. Its mission was to conduct a follow-up investigation on the missing spaceship Charybdis, which NASA lost contact with in early 2038. According to official NASA reports, the Jacob's mission resulted in negative track.
The okudagram mentioning the Jacob, reproduced in Star Trek: The Next Generation - The Continuing Mission, contains the information Picard read on screen with regards to the Charybdis. Reference to the Jacob itself was not made in Picard's dialog, but too was contained in the okudagram, however, in an unread portion of the text.