The S-IV was the second stage of the Saturn I rocket used by NASA for early flights in the Apollo program.
The S-IV was manufactured by the Douglas Aircraft Company and later modified by them to the S-IVB, a similar but distinct stage used on the Saturn IB and Saturn V rockets.
The S-IV stage was a large LOX/LH<sub>2</sub>-fueled rocket stage used for the early test flights of the Saturn I rocket. It formed the second stage of the Saturn I and was powered by a cluster of six RL-10A-3 engines. Each one of the engines supplied of thrust for a total of about . The cryogenic LH<sub>2</sub> (liquid hydrogen) and LOX (liquid oxygen) tanks were separated by a common bulkhead. The forward bulkhead of the LOX tank formed the aft bulkhead of the LH<sub>2</sub> tank. This saved up to 20% of structural weight.
Flight history
{| class="wikitable sticky-header"
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!Mission serial number
!Launch date (UTC)
!Image
!Launch notes
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|SA-1
|October 27, 1961<br />15:06:04
|frameless|150x150px
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|SA-2
|April 25, 1962<br />14:00:34
|frameless|150x150px
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|SA-3
|November 16, 1962<br />17:45:02
|frameless|150x150px
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|SA-4
|March 28, 1963<br />20:11:55
|frameless|150x150px
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|-
|SA-5
|January 29, 1964<br />16:25:01
|frameless
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|-
|SA-6
|May 28, 1964<br />17:07:00
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|SA-7
|September 18, 1964<br />16:22:43
|frameless
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|-
|SA-9
|February 16, 1965<br />14:37:03
|frameless
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|-
|SA-8
|May 25, 1965<br />07:35:01
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|-
|SA-10
|July 30, 1965<br />13:00:00
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|}