posted 09-26-2020 08:43 PM               

CSM Modifications

For Skylab, the command and service module will be called upon to transport a three-man crew and up to 1,150 pounds of stowed equipment to and from the workshop. In addition, it will:

• Serve as primary communications and command station for the orbital assembly

• Provide +X translation for orbital maintenance of cluster to assure repeatable ground track for EREP experiments.

• Provide attitude control of the cluster if required

• Support experiment activities

• Provide minimal electrical and thermal control systems during the entire stay in orbit

• Be capable of being reactivated after being in a semidormant state in space for 56 days

Since these requirements differ substantially from the requirements of the Apollo program for which the command and service modules were built, a number of modifications were required. The major changes include:

Additions

• A power transfer umbilical was added to the command module to link it with the power system of the orbital workshop.

• An atmosphere interchanging duct was added to the CM so it can be supplied with oxygen from the workshop.

• An intravehicular activity station and a 45-foot intravehicular umbilical were added to the CM to enable an astronaut to go into the orbital work-shop if it becomes depressurized.

• In the service module, a water storage tank was added to store excess water produced by the fuel cells after the CSM docks with Skylab 1. At this point, the water is an unwanted byproduct of the fuel cells, and is stored rather than dumped overboard to avoid the possibility of ice crystals forming on the windows and telescope lenses, and possible thrust forces on the workshop caused by water dumps.

• In the command module, the pyrotechnic batteries were replaced by two larger descent-type batteries for additional energy storage capability.

• A 40-channel inhibit function and a 10-channel memory unit were added to the CM caution and warning system; a CSM/workshop interface unit was added to present a master alarm lamp in the workshop.

• A descent battery pack (three 500 A-H batteries) was added to the service module because the fuel cells will not be in operation during the descent from orbit.

• A propellant storage module holding about 1,500 pounds of RCS propellants was added to the service module. This allows the RCS system to be used as a backup for attitude control of the orbital cluster, and as a backup to the service propulsion system for deorbit of the CSM.

• Heaters were added to the service propulsion system and its propellant supply, and to the service module reaction control system and its propellant supply, to prevent freezing of propellants, lines, and valves.

• A shelf and coolant line for Experiments S071 and S072 were added to the service module.

• A rescue capability kit has been developed for the Skylab program, but will not be installed in the CM unless the need for a rescue mission arises.

• In the spacecraft-lunar module adapter, a light weight truss has been added as a stabilizing device to take the place of the lunar module, which was mounted so as to have a stabilizing action on the adapter.

Deletions

• One fuel cell was removed from the service module because the requirement for fuel cell power is short-lived. The fuel cells will be used to provide power for the CSM after it docks at the MDA and cryogens are depleted. After that, CSM power requirements will be supplied by the workshop electrical system, and the CSM batteries will provide power for the return to earth.

• One helium pressurization tank and two SPS fuel and oxidizer storage tanks were removed from the service module because the mission requires far less use of the SPS engine than a lunar mission.

• The high-gain antenna was deleted from the service module because there are no requirements for communications from deep space in the Skylab program.

• Provisions for waste stowage and some food stowage were deleted from the CSM to make room for Skylab experiments.