I found this historical NASA document detailing the use of HP-41 calculators for various tasks aboard the Space Shuttle:

In the meantime, the astronauts themselves pioneered efforts to use small computers to add functions and back up the primary systems. Early flights used a Hewlett-Packard HP-41C programmable calculator to determine ground-station availability, as well as carry a limited version of the calculations for time-to-retrofire. Beginning with STS-9 in December, 1983, a Grid Systems Compass portable microcomputer with graphics capabilities was carried to display ground stations and to provide functions impractical on the primary computers. Mission Specialist Terry Hart, responsible for programming the HP-41Cs, said that placing the mission documentation on the computer was also being considered.

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