&gt; The Doom install image was 35x the size of the Apollo guidance computer.<p>Keep in mind that the AGC was a necessary but not sufficient piece of hardware for navigating to the moon, and was <i>extremely</i> special-purpose.  NASA had several big (for the time) mainframes that<p>1) calculated the approximation tables that were stored in AGC ROM (each mission required a new table because the relative positions of the earth, sun and moon was different)<p>2) reduced soundings from earth-based radars to periodically update the AGC&#x27;s concept of its position.<p>3) other things that I&#x27;ve forgotten<p>In other words, the AGC <i>required</i> the assistance of a ground-based computer with dozens of megabytes of RAM and hundreds of megabytes of storage.  That will fit on your phone quite easily, but let&#x27;s not minimize the requirements for celestial navigation.