303 votes
Accepted

How did the Apollo computers evaluate transcendental functions like sine, arctangent, log?

Since the Apollo 11 code is on GitHub, I was able to find the code that looks like an implementation of sine and cosine functions: see here for the command module and here for the lunar lander (it ...
supinf's user avatar
  • 2,223
83 votes
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What makes Ada the language of choice for the ISS's safety-critical systems?

This Wikibooks link lists its strong points, some of which are: An extremely strong, static and safe type system, which allows the programmer to construct powerful abstractions that reflect the ...
Morgloz's user avatar
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73 votes
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Why don't we shield existing CPUs from radiation instead of designing new ones?

Because shielding against radiation is heavy, and weight is the enemy of getting things into space. CPUs are quite sensitive to radiation, and some types of radiation (cosmic rays) are not only quite ...
ANone's user avatar
  • 3,412
60 votes

What makes Ada the language of choice for the ISS's safety-critical systems?

Timing. Ada was developed in the 1970s and 80s with the intent of replacing the plethora of languages used in the US Department of Defense's realtime systems. NASA (and also organizations from Europe) ...
David Hammen's user avatar
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50 votes

How did the Apollo guidance computers deal with radiation?

TL;DR: It was so busy getting stuff done, it didn't care. Being old, slow, massive and inefficient (by any modern standards, not by those in 1965) is a huge benefit when it comes to radiation hardness....
asdfex's user avatar
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47 votes

Why would such a powerful computer (or a computer at all) be needed to go to the Moon?

Assuming this isn't a troll question and you are serious about wanting to know what computers are used for in spaceflight (prior to 1988), NASA has a great resource for you: Computers in Spaceflight (...
Organic Marble's user avatar
46 votes

What was the first programming language in space?

(I'm interpreting the question as "what programming language was the first spacecraft software written in?", per discussion in comments above.) This will depend on your definitions of "...
Russell Borogove's user avatar
41 votes

How did the Apollo computers evaluate transcendental functions like sine, arctangent, log?

You also asked for the logarithm, so let's do this as well. As opposed to the sine and cosine functions, this one is not implemented with a Taylor series-like approach only. The algorithm is based on ...
dlatikay's user avatar
  • 713
41 votes

Unix Epoch in International Space Station

POSIX time doesn't include leap seconds, and is not implemented the same way in every UNIX, so it routinely gets inconsistent for several seconds every couple of years. It is not a high-precision ...
Ryan C's user avatar
  • 7,778
41 votes

Why do spacecraft have small RAM? Which spacecraft had the largest memory?

Cosmic radiation represents a big threat to humans and to computing devices in space. Astronauts regularly report seeing flashes of light when they have their eyes shut. There are all kinds of things ...
David Hammen's user avatar
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39 votes
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Are the computers on Pioneer 10 & 11 still running?

There's a decent chart of RTG output on figure 2-14 of this paper. From 1985 to 2000, RTG output of Pioneer 10 fell from ~100W to ~62W as the RTGs degraded. (Radioactive material decays, thermocouples ...
TLW's user avatar
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38 votes
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What exactly turned on the light indicating Apollo 8 was starting to fall towards the Moon?

The Apollo Guidance Computer used a state vector either centered at the Earth or the Moon. The switchover point is the the lunar sphere of influence, defined in the AGC as 64,373,760 meters (https://...
indy91's user avatar
  • 1,991
35 votes
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Can you really use Arduino for a small spacecraft?

Can you have a spacecraft based on an Arduino? Sure you can! ArduSat was two kickstarter funded cubesats that were eventually launched from the International Space Station in November 2013. When you ...
SE - stop firing the good guys's user avatar
32 votes

Unix Epoch in International Space Station

No. Computer clocks are inaccurate. They rely on constant corrections to maintain the correct time. Since their inaccuracy is much bigger than the time speed difference between earth and the ISS, it ...
Antzi's user avatar
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29 votes
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How complex was the math and physics necessary to place Apollo 11 on the moon?

Was standard Newtonian mechanics sufficient or were relativistic effects included? Relativistic effects didn't have to be modeled; other sources of error would have swamped the effects of relativity,...
Russell Borogove's user avatar
29 votes

Why would such a powerful computer (or a computer at all) be needed to go to the Moon?

Your spacecraft would need to be several orders of magnitude larger than the Saturn-Apollo. No human pilot has successfully performed a rendezvous without a computer. Note that rendezvous is ...
DrSheldon's user avatar
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28 votes
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How is Voyager 1 still operating?

The Voyagers have been so reliable due to careful design, plus lots of redundancy. Voyager employs three dual-redundant computer systems per spacecraft. The first, the CCS, is nearly identical to ...
Hobbes's user avatar
  • 125k
28 votes

Unix Epoch in International Space Station

It doesn’t yet matter for most practical purposes. The slowdown from faster motion and speedup from a weaker gravitational field partly cancel out, and the net effect is that time on the ISS is only 0....
Mike Scott's user avatar
27 votes

Why would such a powerful computer (or a computer at all) be needed to go to the Moon?

First of all, the ground team could have, and in fact did, do most of the orbital navigation remotely. This report mentions the fact that the on board computer was secondary for Apollo 8, with primary ...
PearsonArtPhoto's user avatar
  • 121k
26 votes

Can you really use Arduino for a small spacecraft?

You can, but it will suffer from a number of problems. These problems can probably be overcome with a short term mission. Problems include: Radiation- Degrading the long term effect of the ...
PearsonArtPhoto's user avatar
  • 121k
25 votes

How were these NASA engineers able to take men to the moon and bring them back with this limited computing capability?

The equations required for flight to the moon are not all that complicated, particularly given that much of the work was done by larger computers based on the Earth. Some of the computer programs (e.g....
Russell Borogove's user avatar
25 votes

Are the computers on Pioneer 10 & 11 still running?

In the case of Pioneer 10, it has been twenty years since the last signal was received from the spacecraft. While attempts were made to contact the craft afterwards, no answer was received. Without ...
Oscar Lanzi's user avatar
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24 votes
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What space applications, projects and agencies are using the Ada programming language?

What other space applications, projects and agencies are using the Ada programming language? In the US, old stuff such as the Delta rockets, the Atlas rockets, and the TDRSS ground terminal (but this ...
David Hammen's user avatar
  • 73.2k
23 votes

Why would such a powerful computer (or a computer at all) be needed to go to the Moon?

“Do I have a very naive concept of space travel?“ - honestly, yes you do. Here is an excerpt from Don Eyles’s wonderful book Sunburst and Luminary: An Apollo Memoir: Guidance would be processed every ...
gandalf61's user avatar
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23 votes
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How did the Apollo Lunar Rover navigation system computer work?

The rover computer was an analog/digital hybrid system called the Signal Processor Unit (SPU). As explained in answers to this question How did astronauts navigate the Lunar Roving Vehicle (LRV) over ...
Organic Marble's user avatar
22 votes

What makes Ada the language of choice for the ISS's safety-critical systems?

I remember taking Computer Science courses in the late 90s. The professor of CS explained to our meager group of CS majors that he was going to teach us C, rather than COBOL or Ada, because it would ...
Machavity's user avatar
  • 7,780
21 votes

How did the Apollo guidance computer handle parity bit errors?

1. How did the Apollo guidance computer handle parity bit errors? According to Apollo 15 Hardware by Delco Electronics, Parity Alarm Occurs if any accessed word in fixed or erasable memory ...
DrSheldon's user avatar
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21 votes
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Did the Curiosity and Perseverance rover brains do the driving from Earth to Mars?

Yes and no. The no part first: Mars 2020 had sensors and effectors attached to the non-important parts of your diagram, many of which had various degrees of smarts. Star trackers are very ...
David Hammen's user avatar
  • 73.2k
20 votes
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Which operating systems is the International Space Station running?

I would think that e.g. life support isn't running on a laptop and isn't using an off-the-shelf operating system. That is correct. The heart and soul of the computational system in the Russian ...
David Hammen's user avatar
  • 73.2k

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