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Gemini Guidance Computer
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<h2 id="functionality">Functionality</h2> <p><a href="/facts/Project_Gemini/7PYE3AV4">Project Gemini</a> was the first with an on-board computer, as <a href="/facts/Project_Mercury/H8zqFzbC">Project Mercury</a> was controlled by computers on Earth.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The Gemini Guidance Computer was responsible for the following functions:<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <ul><li><i>Ascent </i>– serves as a backup <a href="/facts/Guidance_system/Qhjm4enq">guidance system</a>. The switchover is manually controlled by the astronauts</li> <li><i>Orbital flight</i> – gives the astronauts the capacity to navigate, allowing them to choose a safe landing spot in an emergency and calculate the timing of retrofire (on extended missions ground data may become unavailable when ground data network rotates out of the <a href="/facts/Orbital_plane/xPdMmVKP">orbital plane</a>).</li> <li><i>Rendezvous </i>– serves as primary reference by providing guidance information to the astronauts. The orbit parameters are determined by the ground tracking which are then sent to the spacecraft; the guidance computer was responsible for processing the information along with sensed spacecraft attitude. The information was presented to the astronauts in terms of spacecraft coordinates.</li> <li><i>Reentry </i>– feeds commands directly to the reentry control system for automatic reentry or provides the guidance information to the astronauts for manual reentry.</li></ul> <h2 id="specs">Specs</h2> <ul><li>The computer was architecturally similar to the <a href="/facts/Saturn_Launch_Vehicle_Digital_Computer/cPcKqDsI">Saturn Launch Vehicle Digital Computer</a>, in particular in the instruction set;<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> however its circuit integration was less advanced.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The GGC weighed 58.98 pounds (26.75 kg) and was powered by 28V <a href="/facts/Direct_current/r9MNUx84">DC</a>. During a short power outage it could be powered by the Auxiliary Computer Power Unit (ACPU).</li> <li>39-bit words memory, each composed of three <a href="/facts/13-bit_syllable/9sQACN4o">13-bit syllables</a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li> <li><a href="/facts/Ferrite_core/f60u8q2g">Ferrite core</a> memory of 4,096 words<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></li> <li>Two's complement integer arithmetic</li> <li>7.143 kilohertz clock (140 μs per instruction); all instructions took a single cycle except for multiplication and division</li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Apollo_Guidance_Computer/xGxHlrXY">Apollo Guidance Computer</a></li></ul> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Gemini Guidance Computer. <ul><li><a href="http://www.ibiblio.org/apollo/Gemini.html">Gemini Spacecraft On-Board Computer (OBC)</a></li> <li><a href="https://web.archive.org/web/20150405212055/http://www-pao.ksc.nasa.gov/kscpao/history/gemini/gemini.htm">Gemini Program Overview</a></li> <li><a href="https://web.archive.org/web/20050119055248/http://www-03.ibm.com/ibm/history/exhibits/space/space_gemini.html">IBM and the Gemini Program</a></li></ul> <p><i>As of <a href="https://en.wikipedia.org/w/index.php?title=Gemini_Guidance_Computer&oldid=653091201">this edit</a>, this article uses content from </i><a href="http://en.wikichip.org/wiki/Gemini_Guidance_Computer">"Gemini Guidance Computer"</a><i>, which is licensed in a way that permits reuse under the Creative Commons Attribution-ShareAlike 3.0 Unported License, but not under the GFDL. All relevant terms must be followed.</i> </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>McDonnell Corporation, NASA Project Gemini Familiarization Manual, 1965, vol. 2, pp. 8.7,8.45. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>8. J. C. Hundley and R. A. Watson, "A Digital Computer in Orbital Flight," TR 63-825-892, IBM Federal Systems Division, Owego, New York, October 1964. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Tomayko, James E. (1988). "The Gemini Digital Computer: First Machine in Orbit". Computers in Spaceflight: The NASA Experience. Washington, D.C.: National Aeronautics and Space Administration. Retrieved 2015-01-04. <a href="https://history.nasa.gov/computers/ch1-1.html" target="_blank">https://history.nasa.gov/computers/ch1-1.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>8. J. C. Hundley and R. A. Watson, "A Digital Computer in Orbital Flight," TR 63-825-892, IBM Federal Systems Division, Owego, New York, October 1964. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>McDonnell Corporation, NASA Project Gemini Familiarization Manual, 1965, vol. 2, pp. 8.7,8.45. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Gemini Spacecraft Computer (OBC): Layout of Memory Words". 2016 [2011]. Archived from the original on 2016-05-28. Retrieved 2016-05-28. <a href="http://www.ibiblio.org/apollo/Gemini.htp" target="_blank">http://www.ibiblio.org/apollo/Gemini.htp</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>LVDC board reverse engineering project <a href="http://www.frantone.com/designwritings/design_writings_LVDC.html" target="_blank">http://www.frantone.com/designwritings/design_writings_LVDC.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"Gemini Spacecraft Computer (OBC): Layout of Memory Words". 2016 [2011]. Archived from the original on 2016-05-28. Retrieved 2016-05-28. <a href="http://www.ibiblio.org/apollo/Gemini.htp" target="_blank">http://www.ibiblio.org/apollo/Gemini.htp</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Computers in Spaceflight: The NASA Experience, chapter one <a href="https://history.nasa.gov/computers/Ch1-2.html" target="_blank">https://history.nasa.gov/computers/Ch1-2.html</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> </ol>