Editing Space capsule (section)

=== Gemini===
{{Main|Project Gemini#Spacecraft}}
[[File:Gemini1.png|thumb|right|Gemini capsule internal diagram, with equipment adapter]]
Many components in the capsule itself were reachable through their own small access doors. Unlike Mercury, Gemini used completely solid-state electronics, and its modular design made it easy to repair.<ref>{{cite journal| last= Dryden| first= Hugh  | title = Footprints on the Moon  | journal = National Geographic Magazine  | volume = 125| issue = 3 | publisher= [[National Geographic Society]]  | location = Washington, D.C.  | url = http://ngm-beta.nationalgeographic.com/archive/footprints-on-the-moon/  | access-date= 2015-01-04 | date = March 1964|page=362 }}</ref> The Gemini spacecraft was the precursor to the Apollo program which aimed to land humans on the Moon. It was designed to test new techniques for orbital rendezvous and docking, but it also featured improvements in life support systems, spacecraft reentry, and other critical areas.<ref name="Baker1981"/>
[[File:Gemini 12 spacecraft at the Adler Planetarium.jpg|thumb|The [[Gemini 12]] capsule from the 1966 10th and final mission of [[Project Gemini]], flown by [[Jim Lovell]] and [[Buzz Aldrin]] (exhibited at Chicago's [[Adler Planetarium]])]]
Gemini's emergency [[launch escape system]] did not use an escape tower powered by a [[solid-fuel rocket]], but instead used aircraft-style [[ejection seat]]s. The tower was heavy and complicated, and NASA engineers reasoned that they could do away with it as the Titan II's [[hypergolic propellant]]s would burn immediately on contact. A Titan II booster explosion had a smaller blast effect and flame than on the cryogenically fueled Atlas and Saturn. [[Ejection seat]]s were sufficient to separate the astronauts from a malfunctioning launch vehicle. At higher altitudes, where the ejection seats could not be used, the astronauts would return to Earth inside the spacecraft, which would separate from the launch vehicle.{{sfnp|Dryden|1964|page=364}}

The main proponent of using ejection seats was Chamberlin, who had never liked the Mercury escape tower and wished to use a simpler alternative that would also reduce weight. He reviewed several films of Atlas and Titan II ICBM failures, which he used to estimate the approximate size of a fireball produced by an exploding launch vehicle and from this he gauged that the Titan II would produce a much smaller explosion, thus the spacecraft could get away with ejection seats.

[[Maxime Faget]], the designer of the Mercury LES, was on the other hand less-than-enthusiastic about this setup. Aside from the possibility of the ejection seats seriously injuring the astronauts, they would also only be usable for about 40 seconds after liftoff, by which point the booster would be attaining Mach 1 speed and ejection would no longer be possible. He was also concerned about the astronauts being launched through the Titan's exhaust plume if they ejected in-flight and later added, "The best thing about Gemini was that they never had to make an escape."<ref>{{cite book|editor-first =Glen E.|editor-last = Swanson |title =Before This Decade Is Out: Personal Reflections on the Apollo Program|isbn = 9780160501395|url = https://books.google.com/books?id=PUgfGiP9fMQC&pg=PA354 |publisher = NASA|date = 1999|page= 354}}</ref>

The Gemini ejection system was never tested with the Gemini cabin pressurized with pure oxygen, as it was prior to launch. In January 1967, the fatal [[Apollo 1]] fire demonstrated that pressurizing a spacecraft with pure oxygen created an extremely dangerous fire hazard.<ref>{{cite magazine |last=Betancourt |first=Mark |date=October–November 2018 |title=Abort! |url=https://www.airspacemag.com/space/abort-180970364/ |magazine=[[Air & Space/Smithsonian]] |page=39 |volume=33 |issue=5 |access-date=March 16, 2019}}</ref> In a 1997 oral history, astronaut [[Thomas P. Stafford]] commented on the [[Gemini 6]] launch abort in December 1965, when he and command pilot [[Wally Schirra]] nearly ejected from the spacecraft:

{{Blockquote|text=So it turns out what we would have seen, had we had to do that, would have been two Roman candles going out, because we were 15 or 16 psi, pure oxygen, soaking in that for an hour and a half. You remember the tragic fire we had at the Cape. (...) Jesus, with that fire going off and that, it would have burned the suits. Everything was soaked in oxygen. So thank God. That was another thing: NASA never tested it under the conditions that they would have had if they would have had to eject. They did have some tests at China Lake where they had a simulated mock-up of Gemini capsule, but what they did is fill it full of nitrogen. They didn't have it filled full of oxygen in the sled test they had.<ref>{{cite web |url=https://historycollection.jsc.nasa.gov/JSCHistoryPortal/history/oral_histories/StaffordTP/StaffordTP_10-15-97.htm |title=Thomas P. Stafford Oral History |last=Vantine |first=William |work=Johnson Space Center Oral History Project |date=October 15, 1997 |access-date=March 16, 2019 |publisher=[[NASA]]}}</ref>}}

Gemini was the first astronaut-carrying spacecraft to include an onboard computer, the [[Gemini Guidance Computer]], to facilitate management and control of mission maneuvers. This computer, sometimes called the Gemini Spacecraft On-Board Computer (OBC), was very similar to the [[Saturn Launch Vehicle Digital Computer]]. The Gemini Guidance Computer weighed {{convert|58.98|lb}}. Its [[core memory]] had 4096 [[memory address|addresses]], each containing a 39-bit [[Word (computer architecture)|word]] composed of three 13-bit "syllables". All numeric data was [[26-bit computing|26-bit]] [[two's-complement]] integers (sometimes used as [[fixed-point number]]s), either stored in the first two syllables of a word or in the [[accumulator (computing)|accumulator]]. [[Instruction set|Instructions]] (always with a 4-bit [[opcode]] and 9 bits of operand) could go in any syllable.<ref>{{cite book| last1= Tomayko| first1 = James E.| year = 1988| title= Computers in Spaceflight: The NASA Experience| chapter= The Gemini Digital Computer: First Machine in Orbit| publisher= National Aeronautics and Space Administration| location= Washington, D.C.| url= https://history.nasa.gov/computers/ch1-1.html | access-date= 2015-01-04|pages=10–19}}</ref><ref>{{cite web|last1= Burkey |first1= Ronald |title= Gemini Spacecraft On-Board Computer (OBC) |url= http://www.ibiblio.org/apollo/Gemini.html |access-date = 2015-01-04 |archive-url= https://web.archive.org/web/20141215051553/http://www.ibiblio.org/apollo/Gemini.html |archive-date = 2014-12-15 |date = 2012-01-08}}</ref><ref>{{cite web|url=http://www-03.ibm.com/ibm/history/exhibits/space/space_gemini.html|archive-url=https://web.archive.org/web/20050119055248/http://www-03.ibm.com/ibm/history/exhibits/space/space_gemini.html|url-status=dead|archive-date=January 19, 2005|title=IBM Archives: IBM and the Gemini Program|date=23 January 2003}}</ref><ref>C. A. Leist and J. C. Condell, [http://ed-thelen.org/comp-hist/gemini_manual_rev_a_9-30-11.pdf "Gemini Programming Manual"], 1966</ref>