S-IVB

S-IVB

S-IVB-206 which was used for the Skylab 2 flight
Manufacturer	Douglas
Country of origin	USA
Used on	Saturn IB (stage 2) Saturn V (stage 3)
General characteristics
Height	17.81 m (58 ft, 5 in)
Diameter	6.60 m (21 ft, 8 in)
Gross mass	271,000 pounds (123,000 kg)
Propellant mass	241,300 lb (109,000 kg)
Empty mass	29,700 lb (13,500 kg)
Launch history
Status	Retired
Total launches	21
Successes (stage only)	20
Other	Restart failure (Apollo 6)
First flight	February 26, 1966
Last flight	July 15, 1975
S-IVB 200 series
Powered by	1 J-2
Maximum thrust	200,000 pounds-force (890,000 N)
Specific impulse	420 s (4.1 km/s)
Burn time	480 s
Propellant	LH2 / LOX
S-IVB 500 series
Powered by	1 J-2
Maximum thrust	232,250 pounds-force (1,033,100 N)
Specific impulse	421 s (4.13 km/s)
Burn time	500 s
Propellant	LH2 / LOX

The S-IVB (pronounced "S-four-B") was the third stage on the Saturn V and second stage on the Saturn IB launch vehicles. Built by the Douglas Aircraft Company, it had one J-2 rocket engine. For lunar missions it was fired twice: first for Earth orbit insertion after second stage cutoff, and then for translunar injection (TLI).

The S-IVB evolved from the upper stage of the Saturn I rocket (the S-IV) and was the first stage of the Saturn V to be designed. The S-IV used a cluster of six RL-10 engines but used the same fuels as the S-IVB – liquid hydrogen and liquid oxygen. It was also originally meant to be the fourth stage of a planned rocket called the C-4, hence the name S-IV.

Eleven companies submitted proposals for being the lead contractor on the stage by the deadline of 29 February 1960. NASA administrator T. Keith Glennan decided on 19 April that Douglas Aircraft Company would be awarded the contract. Convair had come in a close second but Glennan did not want to monopolize the liquid hydrogen-fueled rocket market as Convair was already building the Centaur stage of the Atlas-Centaur rocket.

In the end, the Marshall Space Flight Center decided to use the C-5 rocket (later called the Saturn V), which had three stages and would be topped with an uprated S-IV called the S-IVB featuring a single J-2 engine, as opposed to the cluster of 6 RL-10 engines on the S-IV. Douglas was awarded the contract for the S-IVB because of the similarities between it and the S-IV. At the same time, it was decided to create the C-IB rocket (Saturn IB) that would also use the S-IVB as its second stage and could be used for testing the Apollo spacecraft in low Earth orbit.

12 200-series and 16 500-series S-IVB stages were built, alongside 3 test stages. NASA was working on acquiring 4 additional 200-series stages (as part of 4 new Saturn IB rockets, SA-213 to 216), but funding never materialized and the order was canceled in August 1968 before S-IVB hardware was assembled.^[1] Similarly, an order for two additional 500-series stages (for Saturn V rockets 516 and 517) was canceled around the same time.^[2]

Douglas built two distinct versions of the S-IVB, the 200 series and the 500 series. The 200 series was used by the Saturn IB and differed from the 500 in that it did not have a flared interstage and it had less helium pressurization on board since it did not have to be restarted. In the 500 series, the interstage flared out to match the larger diameter of the S-II stage of the Saturn V. The 200 series also had three solid rockets for separating the S-IVB from the S-IB during staging. On the 500 series this was reduced to two, and two small Auxiliary Propulsion System (APS) thruster modules were added as ullage motors for restarting the J-2 engine and to provide attitude control during coast phases of flight.

The S-IVB carried 73,280 litres (19,360 US gal) of liquid oxygen (LOX), massing 87,200 kilograms (192,200 lb). It carried 252,750 litres (66,770 US gal) of liquid hydrogen (LH2), massing 18,000 kilograms (40,000 lb). Empty mass was 10,000 kilograms (22,000 lb)^[3][4]

Attitude control was provided by J-2 engine gimbaling during powered flight and by the two APS modules during coast. APS modules were used for three-axis control during coast phases, roll control during J-2 firings, and ullage for the second ignition of the J-2 engine.^[3][4] Each APS module contained two 150-pound-force (670 N) thrusters providing thrust for roll and pitch, another 150-pound-force thruster for yaw, and one 70-pound-force (310 N) thruster for ullage. Each module contained its own propellant tanks of 150 pounds (68 kg) dinitrogen tetroxide and 115 pounds (52 kg) monomethyl hydrazine as well as compressed helium to pressurize its propellants.^[5]

A surplus S-IVB tank, serial number 212, was converted into the hull for Skylab, the first American space station. Skylab was launched on a Saturn V on May 14, 1973, and it eventually reentered the atmosphere on July 11, 1979. A second S-IVB, serial number 515, was also converted into a backup Skylab, but this one never flew.

From Apollo 13 onward, the S-IVB stages were crashed into the Moon to perform seismic measurements used for characterizing the lunar interior.

• 
  Apollo 7 S-IVB in orbit over Cape Canaveral.
• 
  Distant view of Apollo 7 S-IVB stage
• 
  Apollo 8 S-IVB, shortly after separation

(* See List of artificial objects on the Moon for location.)

The second stage of the Ares I rocket and the proposed Earth Departure Stage (EDS) would have had some of the characteristics of the S-IVB stage, as both would have had an uprated J-2 engine, called the J-2X, with the latter performing the same functions as that of the Series 500 version of the stage (placing the payload into orbit, and later firing the spacecraft into trans-lunar space).

The MS-IVB was a proposed modification of the S-IVB that would have been used on a Mars flyby, but it was never produced.^[12]

• S-IC
• S-II
• S-IV
• Saturn IB
• Saturn V
• Apollo (spacecraft)
• List of artificial objects on the Moon

• Marshall Space Flight Center, Apollo Systems Description Volume II - Saturn Launch Vehicles, 1 February 1964. (Archived copy, pdf)

• NASA New Reference: Saturn third stage

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