Robot Nemesis by E.E. Smith

Ferdinand Stone was hollow-eyed and gaunt from his practically sleepless days and nights of toil, but he was as grimly resolute as ever. Struggling against the terrific weight of three gravities he made his way to the desk of the Chief Computer and waited while that worthy, whose leaden hands could scarcely manipulate the instruments of his profession, finished his seemingly endless calculations.

"We will escape the sun's mighty attraction, Doctor Stone, with approximately half a gravity to spare," the mathematician reported finally. "Whether we will be alive or not is another question. There will be heat, which our refrigerators may or may not be able to handle; there will be radiations which our armor may or may not be able to stop. You, of course, know a lot more about those things than I do."