Excerpt from HP Key notes, January-April 1981 Vol. 5 No. 1:
Two HP-41’s Shuttled Into Space
While the entire world’s attention was riveted to tracking the progress of Columbia on its initial space shuttle flight and its spectacular, letter-perfect return to Earth, did you know that two HP-41C calculators were being used onboard Columbia? Well, we are proud to say they were used, and we thought that KEY NOTES readers would enjoy reading about this historic event.
In 1980, when the National Aeronautics and Space Administration (NASA) of the U.S. began studying available calculators for use on space shuttle flights, they soon realized that the most important initial factor was large memory, an absolute necessity in order to accomodate the lengthy programs that had been proposed. The search for a calculator soon narrowed down to two machines, and a “fly-off” was held between the two. The HP-41C was chosen, NASA said, for a variety of reasons, chief of which was the HP-41C’s alphanumeric LCD display.
Then the HP-41C was subjected to rigorous tests, as well as shuttle hardware, before being judged flightworthy. Some of those tests were conducted at NASA’s station at the White Sands Missile Range in New Mexico, and included shock and vibration tests, and tests for outgassing. As a result of the tests, some minor changes in the HP-41C were made, and it was certified for flights in the space shuttles.
Two calculators were set up for the flight. Each HP-41C was outfitted with four Memory Modules, giving each the memory to handle more than 2000 program lines. The flight suit pouches for the calculators also held extra Memory Modules, extra batteries, and a card reader and magnetic cards containing the programs, just in case they had to be reloaded in flight.
For the first shuttle flight, one HP-41C was dedicated to the Center of Gravity program, and one to the Acquisition of Signal program. These programs were loaded into the calculators shortly before launch. The Center of Gravity program was used before reentry into the Earth’s atmosphere to compute the shuttle’s present center of gravity and the amount of fuel to be burned in each tank to reach the required center of gravity for reentry. This center of gravity program was termed “flight critical” by NASA and necessitated extensive pre-launch testing of the calculators.
The other program, the Acquisition of Signal program, ran continually in the second calculator, starting at launch, so it could display at any time the next ground station that Columbia could contact, when it would be in contact, the duration of that contact, and which frequency (UHF or S-band) could be used. And, thanks to Continuous Memory, the calculator did not have to be on during the whole flight.
You will be interested to know that NASA is committed to using HP-41C’s in future shuttle missions, and that it plans more exotic applications. One likely program will let the HP-41C compute the “navigational” commands to be given to a mechanical arm so it can reach out and grab a nearby satellite. Another program would take, as input data, coordinates of the shuttle’s big hatch and determine if it is closed.
Hewlett-Packard is very pleased that the HP-41C was chosen for this application, and we are working to support NASA’s future needs. HP may produce custom ROM modules containing the special shuttle programs, and thus eliminate the need for Memory Modules.
NASA also foresees the day when astronauts will carry into orbit HP printer /plotters that work as peripherals with the HP-41C, making hard copy immediately available.