Encyclopedia Astronautica
1973.08.14 - Skylab 4 space vehicle moved to Launch Complex 39B in readiness for rescue mission.


The space vehicle consisted of a Saturn IB launch vehicle-S-IB-208 first stage, S-IVB-208 second stage, and S-IU-207 instrument unit; a CSM-118; and a spacecraft lunar module adapter.

The SL 4 crew was made up of commander Gerald P. Carr, science pilot Edward G. Gibson, and pilot William R. Pogue. The S-IVB stage had arrived at KSC on 4 November 1971 and had been placed in storage until 15 December 1972. The CSM arrived on 10 February 1973 and was moved into the Operations and Checkout Building for systems testing. The S-IB stage arrived on 20 June 1973 and was erected on Mobile Launcher 1 on 31 July 1973. The IU arrived at KSC on 12 June 1973.

The S-IVB and IU were mated to the S IB on 1 August 1973. The processing schedule was accelerated on 3 August to a seven-day, 24-hours-per-day workweek to make SL-4 ready for a possible early flight to rescue the orbiting SL-3 crew, which was having serious leakage problems in their service module reaction control system. This accelerated schedule would support a launch on 9 September.

As a better understanding of the SL-3 problem was obtained, the SL 4 checkout flow was adjusted on 13 August to support an earliest launch date of 25 September, which allowed a complete spacecraft integrated systems test to be conducted. With this schedule, hypergolic loading, anticipated for 9 September, would he a decision point for a rescue need with earliest launch readiness of a rescue mission nine days from commitment to hypergolic load.

Upon completion of the hypergolic loading preparations on 10 September, the space vehicle remained on a launch minus nine days status until the splashdown of SL-3 on 25 September, when the schedule was readjusted for a 10 November launch.

On 15 August, the mobile launcher sustained several lightning strikes. Damaged components of the CSM, mostly guidance system units, were replaced and retested. The launch vehicle lightning retest revealed no related failures or effects on the launch vehicle or ground support equipment.

Cracks in an S-IB upper 'E' beam forging were found on 27 August; repairs were completed on 3 September. The flight readiness test was completed on 5 September. Processing of the space vehicle continued until 9 September, at which point it was ready for start of hypergolic loading. The space vehicle remained in this mode until 25 September, when the SL-3 astronauts splashed down successfully.

Scheduled processing began immediately for a standard mission November launch. A rerun of the flight readiness test was completed on 11 October Space vehicle hypergolic loading was completed on 19 October. On 23 October, two S-IB fuel tank domes were inverted due to a partial vacuum pulled on the tanks; two days later a tank pressurization returned the tanks to their original configuration.

As on SL-3, the countdown demonstration test was combined with the countdown into one function, with a launch countdown-wet (LCD-wet) followed by securing and 42 1/2 hours of final countdown tasks. The LCD-wet began at 10:00 p.m. EST on 28 October and finished at 11 :40 a.m. EST on 2 November.

Discovery and repair of cracks in the S-IB fins caused a five-day postponement of the launch date, and one additional day was needed to inspect the S-IVB structure. These delays moved the scheduled launch date to 16 November. The final countdown began at 2:30 a.m. EST on 14 November with launch at 9:01 a.m. EST, 16 November.

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