NASA HP-41CV donated to Ladd Observatory at Brown University

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Beautiful pictures of a space shuttle HP-41CV (pictures courtesy of Ladd Observatory and Brown University).

The date code is 2303S, meaning it was manufactured back in 1983 (probably in Singapore). It was donated to Brown University with no batteries or software installed. As you can see though, it’s fully functional. SMS means “Shuttle Mission Simulator”.


NASA tag

Module section

Open battery compartment

Custom overlay

Another shot of the overlay

Custom pouch

Recent find on eBay


It’s been awhile since I last posted in this blog. I decided to sell a few calculators today on eBay (a non-functional HP-67, a HP-41CV, a HP-38G, a HP-41 Surveryor I pac and a Sharp EL-5100) and I found by chance an auction about a vintage 1981 HP digest catalog with information about the HP-41C, HP-67 and HP-97 related to the space program. I do not have the money to buy the catalog (my other guitar hobby takes precedence these days) but the seller posted really big pics of the interesting information. I downloaded the pics and here they are…

For those interested in bidding on the catalog, here’s the link while it lasts:


The Spacelab D1 mission

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Thanks to Dan at’s forum, here’s a significant addition to this blog. The HP-41 was used by german astronaut Ernst Messerschmid for importing voltmeter readings in Spacelab D1.

Spacelab D1

Spacelab D1

Here’s the text from Deutsches Museum:

D1-SPACELAB Mission, 1985
Walcher Elektronik GmbH, Kirchheim, 1985
Hewlett-Packard, USA, 1984

The voltmeter is an instrument for measuring voltage and temperature. It contains an analog-to-digital converter that feeds the measured values to the calculator for processing. The calculator is a slightly modified standard HP 41 calculator.

Astronaut Ernst Messerschmid devised this voltmeter to be used for experiments in materials science aboard the 1985 German D1 mission.

Actual Spacelab D1 HP-41CX

Actual Spacelab D1 HP-41CX

Handwritten HP-41CX program listing and diagram

Handwritten HP-41CX program listing and diagram

Ernst Messerschmid

Ernst Messerschmid

Additional pictures taken by Dan at the Deutsches Museum:

Deutsches Museum HP-41CX exhibit

Deutsches Museum HP-41CX exhibit

Deutsches Museum HP-41CX exhibit

Deutsches Museum HP-41CX exhibit

Deutsches Museum HP-41CX exhibit

Deutsches Museum HP-41CX exhibit

Another 41 in space

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Scene description from the Johnson Space Center digital image collection (mission STS-51F; 1985):

Loren Acton, Payload specialist, is working at the Challenger’s aft flight deck station. Acton is using a TV camera for one of the modes of the Shuttle Amateur Radio Experiment (SAREX) to record scenes out of the overhead window. Other material, such as a calculator, floats nearby. Note that the overhead window is covered over except where the lens of the camera has been placed.



Once I found the picture and its associated mission number, it’s just a matter of a simple search in Youtube to find actual footage of the HP-41. It can be seen at 17:32 on the left side of the video:

HP-41’s Time Module

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Time Module

Time Module

Unbeknownst to me, the Time Module was developped at the request of NASA, according to this snippet:

HP only made two “custom” modifications to the machines NASA finally bought. First, NASA wanted a quartz clock/timer/alarm in the machine, so HP developed and debugged the Timer Module (in record time) for them. Second, NASA had HP weld shut the AC adapter hatch and the the expansion ports, to keep any static electricity from leaking in or out of the machine.

The HP-41 in space, viewed from inside Hewlett Packard II

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Excerpt from HP Key notes, March-May 1982 Vol. 6 No. 2:

HP-41’s Again Aboard Columbia

Unless you have been hiding in an igloo near the North Pole for the last year or so, you know all about the space shuttle Columbia, which we featured on the cover of V5N1. And, because you read every KEY NOTES, you know that astronauts use our HP-41 handheld computers onboard Columbia for various flight-related, radio-contact, and backup operations. And, no, their programs are not in the Users’ Library nor are they for sale. They contain NASA proprietary information and are for use only on the space shuttle.

For the last Columbia flight, near the end of last March, the two HP-41 computers were purchased over-the-counter by NASA from a Houston, Texas, office-equipment store, and were tested rigorously before being approved for flight. They are identical to the hundreds of thousands of HP-41’s sold since 1979.

One HP-41 computer, dedicated to what NASA calls the acquisition-of-signal program, was the only convenient means the shuttle crew had to estimate the time, location, and radio frequency of their next contact with Earth. Also, if the astronauts are awakened at night by an alarm, they can tell at a glance how long it will be before they can discuss the problem with Mission Control.

The second HP-41 computer acts as an electronic secretary for the astronauts – reminding them of daily chores with alarms and flashing messages. Each morning, the astronauts programmed their computer with five to ten alarms. That way they didn’t have to write down on paper all their scheduled activities. In other words, the HP-41 helped them to keep on top of all of their daily “housekeeping” activities.

In addition to helping the crew organize its time, the second HP-41 computer was kept ready for flight-critical, deorbit-burn calculations. Once during each orbit around the Earth, the shuttle has an opportunity to land at one of six contingency locations. During a routine flight, Mission Control supplies the shuttle crew with deorbit-burn information. Should the shuttle encounter an emergency, however, the astronauts would rely on the HP-41 for these calculations.

Two other programs – one to help balance the Columbia prior to re-rentry, and another to pin-point Earth observation sites – also are available to the crew and would be run on the HP-41’s.

The HP-41’s do not take the place of the shuttle’s larger, general-purpose computers. However, they do complement the shuttle’s larger systems and provide the crew with personal-computer convenience. Also, new and different HP-41 programs can be written between flights – quickly enough to keep up with with many of the astronauts’ changing computational needs.

We are very proud of the HP-41, and we are happy that NASA chose this handheld marvel for use on the space shuttle. Already the new Time Module is an asset to this mission and, in the future, the new HP-IL Module and the various HP-IL peripherals¬† will surely prove their usefulness. We’ll keep you informed as NASA makes more use of the HP-41 system.

Astronaut Gordon Fullerton aboard Columbia on the last flight, using his HP-41. Notice that he is sitting in midair, in the zero gravity of outer space. (Photo courtesy of NASA.)

Astronaut Gordon Fullerton aboard Columbia on the last flight, using his HP-41. Notice that he is "sitting" in midair, in the "zero" gravity of outer space. (Photo courtesy of NASA.)

The HP-41 in space, viewed from inside Hewlett Packard I

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Excerpt from HP Key notes, January-April 1981 Vol. 5 No. 1:

Astronaut Robert Crippen in weightless suspension in mid-deck area of Columbia, somewhere in orbit. The two HP-41 Cs, in protective cases marked CG and AOS, (for the Center of Gravity and Acquisition of Signal programs) appear in the center of the photograph. (Photo by astronaut John Young, courtesy of NASA.)

Astronaut Robert Crippen in "weightless suspension" in mid-deck area of Columbia, somewhere in orbit. The two HP-41 C's, in protective cases marked "CG" and "AOS", (for the Center of Gravity and Acquisition of Signal programs) appear in the center of the photograph. (Photo by astronaut John Young, courtesy of NASA.)

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.

A NASA technician in the Space Shuttle Simulator stores the HP-41C Calculator in a special pouch in the astronauts flight suit.

A NASA technician in the Space Shuttle Simulator stores the HP-41C Calculator in a special pouch in the astronauts' flight suit.

How the HP-41 came to be used aboard the space shuttle

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Excerpt from Professional Computing, Oct/Nov 1984:

Six months before the first shuttle flight, Terry Hart was asked to find the best calculator for the astronauts. He looked at the TI-59 and the HP 41, the most powerful units available, and decided that the 41’s alphanumeric display capability made it the clear winner.

Once he decided on the 41, Hart realized he had more than just the handheld scientific calculator NASA had wanted. He started to look for more complex jobs to use it for. The deorbit program is one example. Computation of a deorbit opportunity would have been easy for the on-board computers, but the software for it was never developed.

Since the 41s would already be on board as general-purpose calculators, Hart began to develop additional programs for them. …

CG, the first 41 shuttle program, computes the center of gravity of the orbiter as fuel from the tanks is consumed.

Another program, Landtrack, computes the ground track of the shuttle, identifying points of interest on the earth’s surface for observation (such as the Great Wall of China? — rrd). These two programs were on board the first two shuttle flights.

The most widely used 41 shuttle program is Deorbit/Alarm/AOS…

Acquisition of Signal (AOS), which runs continuously throughout the mission, is important because there is direct communication with ground controllers only during passes over one of 13 earth stations. These passes last about 10 minutes, less if the shuttle does not pass directly over the earth station.

AOS beeps at the start of a pass over an earth station and displays the time remaining to loss of signal (LOS).

Computers in space flight – The NASA experience

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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.

Confessions of a rocket scientist

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I just found this very interesting video on Youtube from Mr. Gerry Ouellet (sorry about the spelling, I couldn’t quite catch his last name) reminiscing about his use of various HP calculators while he was a “rocket scientist” as he puts it.

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