Which individual's work primarily focused on improving the accuracy of rockets?

The correct answer is William Hale. His work significantly contributed to the development of more accurate rocket designs during the 19th century. Hale is particularly known for his innovations in fin stabilization, which helped to guide rockets more precisely and significantly enhance their performance. This addressed some of the inherent challenges of rocket accuracy in terms of trajectory and stability, laying important groundwork for future advancements in rocketry.

In contrast, the other individuals listed did not primarily focus on improving rocket accuracy. Hero, an ancient Greek engineer, is known for his early work on steam and pneumatics, but his contributions do not relate to rocket technology. Roger Bacon, a medieval scholar, is more associated with the early exploration of the scientific method and alchemy rather than rocketry. Jean Froissart, a chronicler of the 14th century, is not linked to any technological advancements in rocketry at all. Thus, William Hale stands out as the individual whose efforts were directly aimed at enhancing the accuracy of rockets.