Editing AS-203

{{Short description|Uncrewed flight of the Saturn IB rocket, July 5, 1966}}
{{use mdy dates|date=September 2021}}
{{Infobox spaceflight
| name                  = AS-203
| image                 = Image:AS-203 launch.jpg
| image_caption         = Launch of AS-203
<!-- NO insignia for this mission; Apollo program insignia does not apply -->

| mission_type          = Launch vehicle development
| operator              = [[NASA]]
| COSPAR_ID             = 1966-059A 
| SATCAT                = 2289
| mission_duration      = ~6 hours 
| orbits_completed      = 4
| distance_travelled    = {{convert|87400|nmi|km|disp=flip|sp=us}}

| spacecraft            = None
| launch_mass           = <!--{{convert|58700|lb|kg|disp=flip}} This is incorrect and needs verification; also the term "launch mass" is misleading and irrelevant since the payload was the upper stage plus unspent fuel-->

| launch_date           = {{start date text|July 5, 1966, 14:53:13|timezone=yes}}&nbsp;UTC 
| launch_rocket         = [[Saturn IB]] SA-203
| launch_site           = [[Cape Canaveral Air Force Station|Cape Kennedy]] [[Cape Canaveral Air Force Station Space Launch Complex 37|LC-37B]]
| destroyed             = {{end date text|July 5, 1966}}

| orbit_epoch           = July 5, 1966<ref name=satcat>{{cite web|last=McDowell|first=Jonathan|title=SATCAT|url=http://planet4589.org/space/log/satcat.txt|publisher=Jonathan's Space Pages|access-date=March 23, 2014}}</ref>

| orbit_reference       = [[geocentric orbit|Geocentric]]
| orbit_regime          = [[Low Earth orbit]]
| orbit_periapsis       = {{convert|184|km|nmi|sp=us}}  
| orbit_apoapsis        = {{convert|214|km|nmi|sp=us}}  
| orbit_inclination     = 31.94&nbsp;degrees<ref name="Apollo AS-203">{{Cite web |title=Apollo AS-203 |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-059A |url-status=live |archive-url=https://web.archive.org/web/20240530221748/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-059A |archive-date=2024-05-30 |access-date=2024-10-07 |website=NASA Space Science Data Coordinated Archive}}</ref> 
| orbit_period          = 88.47&nbsp;minutes 
| apsis                 = gee

| previous_mission      = [[AS-201]]
| next_mission          = [[AS-202]]
| programme             = [[Apollo program]]
}}

'''AS-203''' (also known as '''SA-203''' or '''Apollo 3''') was an uncrewed flight of the [[Saturn IB]] rocket on July 5, 1966. It carried no [[command and service module]], as its purpose was to verify the design of the [[S-IVB]] rocket stage restart capability<ref name=":0">{{Cite web |date=2021-07-01 |title=55 Years Ago: Apollo AS-203 Mission Tests Liquid Hydrogen Behavior - NASA |url=https://www.nasa.gov/history/55-years-ago-apollo-as-203-mission-tests-liquid-hydrogen-behavior/ |url-status=live |archive-url=https://web.archive.org/web/20241007160747/https://www.nasa.gov/history/55-years-ago-apollo-as-203-mission-tests-liquid-hydrogen-behavior/ |archive-date=2024-10-07 |access-date=2024-10-07 |language=en-US}}</ref> that would later be used in the [[Apollo program]] to boost astronauts from Earth orbit to a trajectory towards the Moon. It achieved its objectives, but the S-IVB was inadvertently destroyed after four orbits during a differential pressure test that exceeded the design limits.<ref name="Apollo AS-203">{{Cite web |title=Apollo AS-203 |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-059A |url-status=live |archive-url=https://web.archive.org/web/20240530221748/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-059A |archive-date=2024-05-30 |access-date=2024-10-07 |website=NASA Space Science Data Coordinated Archive}}</ref>

==Objectives==
The purpose of the AS-203 flight was to investigate the effects of weightlessness on the [[liquid hydrogen]] fuel in the [[S-IVB-200]] second-stage tank.{{citation needed|date=October 2024}} The lunar missions would use a modified version of the S-IVB-200, the [[S-IVB#Configuration|S-IVB-500]], as the third stage of the [[Saturn V]] launch vehicle. This called for the stage to fire briefly to insert the spacecraft into an Earth parking orbit, before restarting the engine for flight to the Moon. In order to design this capability, engineers needed to verify that the anti-slosh measures designed to control the hydrogen's location in the tank were adequate, and that the fuel lines and engines could be kept at the proper temperatures to allow engine restart.

In order to keep residual propellants in the tanks on orbit, there would be no [[command and service module]] payload as there was on [[AS-201]] and [[AS-202]], with an aerodynamic [[nose cone]] in the place of the payload. Also, the full load of [[liquid oxygen]] [[oxidizer]] was shorted slightly so that the amount of hydrogen remaining would approximate that of the Saturn V parking orbit.<ref name=":1">{{Cite web |last=Ward |last2=Toole |last3=Ponder |last4=Meadows |last5=Simmons |last6=Lytle |last7=McDonald |last8=Kavanaugh |date=1968-01-13 |title=EVALUATION OF AS-203 LOW GRAVITY ORBITAL EXPERIMENT |url=https://ntrs.nasa.gov/api/citations/19680012073/downloads/19680012073.pdf |url-status=live |archive-url=https://web.archive.org/web/20221018213944/https://ntrs.nasa.gov/api/citations/19680012073/downloads/19680012073.pdf |archive-date=2022-10-18 |access-date=2024-10-07 |website=NASA Technical Reports Server}}</ref> The tank was equipped with 88 sensors and two TV cameras to record the fuel's behavior.<ref name=":2">{{Cite web |title=Apollo 203 (Saturn SA-203) |url=https://space.skyrocket.de/doc_sdat/apollo-203.htm |url-status=live |archive-url=https://web.archive.org/web/20240303183855/https://space.skyrocket.de/doc_sdat/apollo-203.htm |archive-date=2024-03-03 |access-date=2024-10-07 |website=Gunter's Space Page |language=en}}</ref>

This was also the first launch of a Saturn IB from [[Cape Canaveral Air Force Station Space Launch Complex 37|Pad 37B]].<ref name=":2" />

==Preparation==
In the spring of 1966, the decision was made to launch AS-203 before [[AS-202]], as the CSM that was to be flown on AS-202 was delayed.  The S-IVB stage arrived at [[Cape Canaveral Air Force Station|Cape Kennedy]] on 6 April 1966; the S-IB first stage arrived six days later, and the Instrument Unit came two days after that.

On April 19, technicians began to erect the booster at Pad 37B. Once again, the testing regimen ran into problems that had plagued AS-201, including cracked solder joints in the printed-circuit boards, requiring over 8,000{{clarify|reason=Probably not 8000 circuit boards, maybe 8000 solder joints? If so, then "replaced" isn't the correct word. "Reworked"?|date=May 2024}} to be replaced.{{citation needed|date=October 2024}}

==Flight==
The rocket launched on the first attempt on July 5. The [[S-IVB]] and [[Saturn V instrument unit|Instrument Unit]] (IU) were inserted into a {{convert|100|nmi|km mi|adj=on}} circular orbit.<ref name=":0" />

The S-IVB design test objectives were carried out on the first two orbits, and the hydrogen was found to behave mostly as predicted, with sufficient control over its location and of engine temperatures required for restart. The next two orbits were used for extra experiments to obtain information for use in future cryogenic stage designs. These included a free-coast experiment to observe and control the negative acceleration of the fuel caused by the small amount of aerodynamic drag on the vehicle; a rapid fuel tank depressurization test; and a closed fuel tank pressurization test.<ref name=":1" />
[[File:AS 203 separation of S-IVB stage.webm|thumb|Video of the S-IVB separation]]
The closed fuel tank experiment involved pressurizing the hydrogen tank by closing its vents, while depressurizing the oxygen tank by allowing it to continue venting. It was expected that the pressure difference between the two tanks (measured as high as {{convert|39.4|psi|kPa}} would collapse the common bulkhead separating them, as happened in a ground test. The rupture occurred during the two-minute loss of signal between the [[Lyndon B. Johnson Space Center|Manned Spacecraft Center]] and the [[Trinidad]] [[Missile Test Project#Tracking stations|tracking station]]. The Trinidad radar image indicated the vehicle was in multiple pieces, and telemetry was never re-acquired. NASA concluded that a spark or impact must have ignited the propellants, causing an explosion.{{citation needed|date=October 2024}}

Despite the destruction of the stage, the mission was classified as a success, having achieved all of its primary objectives and validating the design concept of the restartable S-IVB-500 version. In September [[Douglas Aircraft Company]], which built the S-IVB, declared that the design was ready for use on the Saturn V to send men to the Moon.

==References==
{{Include-NASA}}
{{Reflist}}

==External links==
{{Commons category}}
{{Portal|Spaceflight}}
*[https://www.youtube.com/watch?v=fIwhRSoeZSE AS-203 Launch Video] {{Webarchive|url=https://web.archive.org/web/20160729130413/https://www.youtube.com/watch?v=fIwhRSoeZSE |date=2016-07-29 }}
*[https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-059A NASA Space Science Data Coordinated Archive]
*[http://www.hq.nasa.gov/office/pao/History/SP-4204/cover.html Moonport: A History of Apollo Launch Facilities and Operations ] {{Webarchive|url=https://web.archive.org/web/20110318012712/http://www.hq.nasa.gov/office/pao/History/SP-4204/cover.html |date=March 18, 2011 }}
*[http://www.hq.nasa.gov/office/pao/History/SP-4205/cover.html Chariots for Apollo: A History of Manned Lunar Spacecraft ] {{Webarchive|url=https://web.archive.org/web/20151020095653/http://www.hq.nasa.gov/office/pao/History/SP-4205/cover.html |date=October 20, 2015 }}

{{Apollo program| before=[[AS-201]]| after=[[AS-202]]}}
{{Orbital launches in 1966}}

{{Use American English|date=January 2014}}

[[Category:Apollo program]]
[[Category:Spacecraft launched in 1966]]
[[Category:Test spaceflights]]
[[Category:Spacecraft launched by Saturn rockets]]
[[Category:Saturn IB]]
[[Category:Successful space missions]]