# When did NASA stop sending slide rules into space? **URL:** \ **Category:** Factual Questions\ **Created:** [March 30, 2017, 6:21pm UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364 "2017-03-30T18:21:37Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [March 30, 2017, 6:21pm UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364/1 "2017-03-30T18:21:37Z")
According to [the Wikipedia page for the slide rule,](https://en.wikipedia.org/wiki/Slide_rule#Modern_form) slide rules flew on at least a couple of Apollo missions. Portable electronic calculators became available in the 1970s, rapidly pushing slide rules out of common use down here on Earth. When did NASA stop including slide rules on manned space flights? Or did they never stop? ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [March 30, 2017, 6:35pm UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364/2 "2017-03-30T18:35:43Z")
I can’t comment on the space flight part but slide rules (aka “whiz wheels”) are still used in general aviation especially for training and backup. They are common, not some anachronistic thing and I have one myself. I wouldn’t be surprised if space agencies sent one as an emergency backup “computer” in the recent past or even now. > **[E6B](https://en.wikipedia.org/wiki/E6B)** > > The E6B flight computer is a form of circular slide rule used in aviation and one of the very few analog calculating devices in widespread\[citation needed\] use in the 21st century. > They are mostly used in flight training, because these flight computers have been replaced with electronic planning tools or software and websites that make these calculations for the pilots. These flight computers are used during flight planning (on the ground before takeoff) to aid in calculating fuel burn, wind cor... ---
**Author:** ![Kent\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kent_clark/32/105_2.png) [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)\ **Post date:** [March 30, 2017, 9:59pm UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364/3 "2017-03-30T21:59:25Z")
The last Apollo mission was in December 1972. The first (American) handheld calculator, the Bomar Brain, hit the market in September 1971. The Brain, however, wasn’t exactly portable - it required an external power source, so it wasn’t really any more versatile than the Apollo’s primitive on-board computer. The first reference I can find for an actual calculator in space with the [HP-65, on the Apollo-Soyuz mission](http://www.dvq.com/ads/hp65_sa_9_75.jpg) in July 1975. I found some slide rule message boards (sure, why not?) that claim NASA put slide rules on every manned mission up to the Shuttles. Many of the early Shuttle pilots had grown up with slide rules, and it may be that some of them took a flight calculator or slipstick with them, but as a personal item, not standard issue. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [March 30, 2017, 11:16pm UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364/4 "2017-03-30T23:16:42Z")
> [@Machine\_Elf](#): > > According to [the Wikipedia page for the slide rule,](https://en.wikipedia.org/wiki/Slide_rule#Modern_form) slide rules flew on at least a couple of Apollo missions. Portable electronic calculators became available in the 1970s, rapidly pushing slide rules out of common use down here on Earth. When did NASA stop including slide rules on manned space flights?.. Buzz Aldrin carried a Picket N600-ES slide rule on his Apollo 11 mission to the moon’s surface in 1969: [Apollo | HP calculators and space exploration](https://hpinspace.wordpress.com/category/apollo/) The HP-35 replaced slide rules on the three manned Skylab missions in 1973: > **[HP-35](https://en.wikipedia.org/wiki/HP-35)** > > The HP-35 was Hewlett-Packard's first pocket calculator and the world's first scientific pocket calculator: a calculator with trigonometric and exponential functions. It was introduced in 1972. > In about 1970 HP co-founder Bill Hewlett challenged his co-workers to create a "shirt-pocket sized HP-9100". At the time, slide rules were the only practical portable devices for performing trigonometric and exponential functions, as existing pocket calculators could only perform addition, subtraction, ... > **[HP-35 and Skylab](https://hpinspace.wordpress.com/2009/07/16/hp-35-and-skylab/)** > > The book “Homesteading Space” recounts how the HP-35 was used in one of the Apollo flights to Skylab. However, if you read carefully, you will notice that the writer describes a calcula… The probability of needing one of these was very low. The Apollo Lunar Module had double redundant computers, and no computer ever failed in the entire Apollo program. They were custom built and components carefully selected for the highest reliability. E.g, if a single transistor failed in a entire manufacturing batch they’d discard the entire batch, even if all the others passed. The Command Module had a single computer and on both Skylab and Apollo-Soyuz missions there was no Lunar Module, so there was no backup. However those were earth orbital missions so in the event of a computer failure which precluded rendezvous, they could rapidly return to earth. Both Command/Service Module and Lunar Module were fly-by-wire but could be flown without any computer. There was completely redundant wiring from the joystick to each thruster and redundant propellant solenoid valves. If they simply pressed the joystick to the stop (called a “hard over”) it would bypass the computer and use the backup control path. Unlike early science fiction depictions of space missions where communication to earth was unreliable and intermittent, Apollo had extremely reliable and multiply redundant communications for both telemetry and voice. There was largely no need for on-board manual calculation since (a) The on-board computer could do it, or (b) If that failed Mission Control could do it and tell them verbally. When the Apollo program was first planned, the navigational concept emphasized on-board navigation via sextant and computer with ground-based radar and voice communication as backup. By the time flights began, such great improvements had been made in ground-based tracking and communications reliability that this became the primary navigation mode and on-board was backup. Ground-based radar tracking was so sensitive they could determine the spacecraft position and velocity to high accuracy even when orbiting the moon. On-board navigation was given priority when behind the moon and during lunar descent when the on-board system gave even higher accuracy. Because of the high reliability and redundant navigation methods, the chance of actually needing a slide rule or pocket calculator was low. In a fast-paced flight regime like lunar liftoff, lunar landing and reentry, you don’t want an astronaut distracted by doing slow-paced manual calculations. However rendezvous and docking is slower paced. They apparently performed manual backup calculations during the rendezvous and docking phases of Skylab and Apollo-Soyuz. In certain rare failure combinations of computer, rendezvous radar and communications, they might in narrow circumstances be able to continue the mission. However I think in most cases a computer failure required a mission abort. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 31, 2017, 1:41am UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364/5 "2017-03-31T01:41:51Z")
Even if you don’t need a calculating device for mission purposes, it might still come in handy for payload purposes. If you’re monitoring some experiment, it’d be inconvenient to call home every time you need to make a calculation. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [March 31, 2017, 1:07pm UTC](https://boards.straightdope.com/t/when-did-nasa-stop-sending-slide-rules-into-space/783364/6 "2017-03-31T13:07:05Z")
“Slipstick” Libby, despite his name, didn’t need to take a slide rule into space > **[Andrew Jackson Libby](https://en.wikipedia.org/wiki/Andrew_Jackson_Libby)** > > Andrew Jackson "Slipstick" Libby is a fictional character featured in the "Future History" series of science fiction novels by Robert A. Heinlein. He is an enormously talented and intuitive mathematician, but received little formal education. His talent was first appreciated in the short story "Misfit", where he helps guide an asteroid into the correct orbit after the guidance computer has failed. > In later stories, his consciousness is transferred into a clone body, called Elizabeth Andrew Jac... In the 1960 Arthur C. Clarke Story _Inside the Comet_ (retitled _Into the Comet_ when republished in the collection _Tales of Ten Worlds_) astronauts have to use a set of jerry-rigged abacuses (abaci?) for ballistic calculations when their computer breaks down. [http://amazingstoriesmag.com/2014/09/comet-arthur-c-clarke/](http://amazingstoriesmag.com/2014/09/comet-arthur-c-clarke/) [http://www.isfdb.org/cgi-bin/title.cgi?62808](http://www.isfdb.org/cgi-bin/title.cgi?62808)