hp calculators on space shuttle 
 

From: rrd@fc.hp.com (Ray Depew) 
Newsgroups: alt.folklore.urban 
Subject: Re: Apollo 13 
Date: 18 Nov 1994 16:13:57 GMT 
 
John M. Vogel (jvogel@crl.com) wrote: 
: Here's some encouraging news: 
: The Space Shuttles' 5 computers are based on 1970's technology. 
: Each has 248 K of memory. 
 
... and that, children, is why they take up a pile of HP handheld 
calculators with them.  Used to be the HP41C/CV/CX series, today 
it's the HP48SX/GX series.  Without going into extended/expanded 
memory, the older 48SX can hold 288 K of memory.  With 
extended/expanded memory, the new 48GX can hold over 1 M of memory. 
 
T. The handheld calculators aboard the Space Shuttle are more 
   powerful than the Shuttle's on-board computers. 
T. They play better games, too. 
 
Before the first shuttle flight, the astronauts expressed an 
interest in taking handheld computation devices on the Shuttle. 
(I assume that the slide rules were out of the running.) A pair 
of the non-flying astronauts was given the assignment of going out 
and buying them. 
 
NASA didn't want this to be a big deal, so the guys took petty cash 
and went incognito (that's Latin for "in their street clothes") to the 
university bookstore.  They asked the salesnerd behind the counter 
for the best scientific calculator he had.  Without knowing who they 
were, he demonstrated the TI-59 and the then-new HP 41, pushing the 
41 because it was so cool.  (It still is cool.  Just like a classic 
Corvette.) 
 
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. 
 
NASA added a removable custom keypad overlay, took off the little 
rubber footies, and glued Velcro (tm) to every square inch of 
unused surface on the 41s.  Each crew member had a personal 41 
slapped somewhere on their space suit, and two more rode on the 
dashboard of the Shuttle. 
 
Fb. Handheld calculators do not work if you remove the little rubber 
    footies. 
 
Excerpts from a way-cool article (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). 
 
On the first page of the article is a picture of Sally Ride 
and three HP 41s floating in midair. 
 
For more information, see the Followup-To: line. 
 
Regards 
Ray Depew 
Integrated Circuits Business Division 
Hewlett Packard Co, Fort Collins, Colorado 
rrd@fc.hp.com 
Disclaimer:  I don't speak for HP, and I don't make calculators. 
 
                                  [Image] 
                             January 25, 1995