Category:Command and Service Module (CSM)

Apollo 15 Command and Service Module (CSM), NASA. This picture would presumably have been taken from the Lunar Lander, while separated and also in orbit [image info]

The Apollo Command and Service Module (CSM) was a spaceship launched from the top of a Saturn V rocket, consisting of two parts: A conical silver self-sufficient three-man space-capsule capable of independent steering, navigation and reetry (the Command Module, CM), and a cylindrical body containing a much larger rocket engine, external manoeuvring thrusters, and large fuel tanks and auxiliary equipment designed to supply the astronauts with all their (external) needs, right up until the point of separation and capsule rentry.

Design

The CSM body was designed to be modular, built in sections surrounding the central core. An equipment bay could hold various senors and items of recording equipment that didn't need to be part of the capsule, or returned to Earth, and on one of the Apollo missions, the bay contained a separatable microsatellite.

The CSM was launched as one piece and stayed a single entity right up until final separation for reentry. On one side was a protruding umbilical clamp the took electrics, control cabling and gas tank pipes out of the side of the CSM body and into the upper side of the capsule. There could be no more direct "straight-through" connection between the two ships, as this would have violated the integrity of the thick heatshield covering the capsule's lower surface.

A small (slightly delicate-looking) antenna-array popped out at the base of the CSM cylinder after launch

Apollo 13

The Apollo 13 mission famously had to be aborted when an oxygen tank exploded.

• The CSM electrics had been redesigned from using a split-voltage power bus to just a single, higher supply voltage. This was intended to reduce complexity and the chances of anything going wrong.
• However, although almost all lower-voltage parts components could be modified or swapped out with higher-voltage replacements, this couldn't be done with the heater coil and stirrer already built into the completed oxygen tanks, which had to be fed a lower voltage.
• At some point the tank was dropped (although only by a few inches). However, it may have been dropped onto the point where the power cables for the stirrer and heater entered the tank.
• Worried that this might have caused damage, the assembly crew decided to "overnight soak test" the heater and stirrer, leaving them on for some hours to make sure that everything was still good, and that nothing was failing.
• Unfortunately, it seems that during the soak test, the lower-voltage hardware inside the tank may have been accidentally hooked up to a later-standard higher-voltage external power supply, and running them "hot", off a higher voltage than they were designed for, for some hours, may have burned off the protective insulation on the tank's internal wiring.
• As a result, when the Apollo 13 crew flipped a switch to activate the internal fuel tank stirrer, a short-circuiting electrical spark caused the take to explode, wrecking multiple support systems in the CSM body (but thankfully exploding sideways through the side of the CSM, and not damaging the capsule).

To get home, the crew had to abandon the CSM, use the already-docked lander as a lifeboat, shut down all the capsule's electronics to conserve battery life, survive in the LEM as it performed a single orbit around the Moon and returned to Earth, use the LEM's engine for larger course corrections, then reboot the capsule, evacuate the lander, and reenter the Earth's atmosphere in the capsule (almost) as originally planned ... but rather earlier.

The fact that everyone survived and got home intact meant that Apollo 13 was considered "a successful failure".

Modelling

While the capsule and body of the CSM were both silver, the capsule was covered in a layer of mirror-reflective film, and the main body of the CSM was more of a dull aluminium colour. The CSM body might look different on different missions, because of the different equipment stowed in the bay.

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