# How were Apollo spacesuits cooled during simulations/rehearsals on Earth?

The answer and comments to How have space suits dissipated the heat removed from astronauts? explain that the Apollo space suits used the sublimation of ice into the vacuum of space to constantly dissipate 300 to 500 Watts of heat from a space suit while in space, depending on which source you take.

The heat was produced both by the astronaut and some of the support equipment and electronics.

Water was continually exuded onto a carefully designed surface exposed to space, where it quickly froze, and then sublimated from solid to gas molecules, carrying away heat.

The Gizmodo article Real Apollo 11 Training Photos Look Like Prep For a Fake Moon Landing shows many photos of Apollo astronauts rehearsing specific movements and operations on Earth that would later be done on the Moon. They appear to be wearing complete space suits, though it's questionable if they were wearing fully equipped support systems since on Earth their weight would be quite different than when they'd be in the Moon's 1/6 Earth gravity.

1. Did they use fully operational suits and support equipment despite the large weight?
2. If so were they tuned on in order to provide the astronauts cooling inside the suits?
3. If so, how was the circulating water then cooled? I don't think the sublimators would work at room temperature and 1 atmosphere.

below: Two example images from Real Apollo 11 Training Photos Look Like Prep For a Fake Moon Landing

above: "Neil Armstrong practices using a video camera during a lunar surface simulation at the Manned Spacecraft Center in Houston."

below: "Neil Armstrong opens a sample return container next to the Modular Equipment Stowage Assembly and the Lunar Module mock-up on April 18, 1969."

• Lunar surface daytime temp is 100C in daylight and -175C at night. Temperature in Florida is in the mid 20s centigrade. I don't think the astronauts are at serious risk of overheating here. – user21233 Jul 12 '19 at 13:46
• @Snow at rest the human body generates roughly 100 W. Once you start doing work, it rises substantially. Sweating no longer removes heat when you are sealed inside an air-tight bag. It's the heat generated inside the suit that is the problem; it has no place to go. – uhoh Jul 12 '19 at 13:54
• @Snow check the portable air-conditioner: apolloexplorer.co.uk/photo/html/ma9/10073767.htm and these thoughtco.com/the-evolution-of-the-space-suit-3073502 There's almost always a cooler attached to a suit when a live astronaut is inside it, except for short photoshoots. Also see en.wikipedia.org/wiki/Liquid_cooling_and_ventilation_garment also see quora.com/… – uhoh Jul 12 '19 at 14:00
• It's clear from many references that there were training versions of the suits and training versions of the backpacks. Not so clear, however, is how the cooling worked. Also, there's the odd case of a suit that went to the Moon being used later in training! hq.nasa.gov/office/pao/History/alsj/a17/ap17-KSC-72PC-347.jpg Definitely needs looking into. – Organic Marble Jul 12 '19 at 14:09
• I'm planning on researching an answer, but my first impression is that the visor assembly is all wrong in these pictures. No need to carry oxygen or CO2 scrubber. Would still wear and use the liquid-cooling ventilation garment. – DrSheldon Jul 12 '19 at 14:40

1. Nearly all Earth training was performed in the A6L model spacesuit (seen in the pictures above). Actual missions flew with the A7L model suit. Differences include:

• The outer (EVA) layer of the A6L had separate torso and pants, with entry at the waist. The EVA layer of the A7L was one piece, with entry at the back.

• Some astronauts were never expected to leave the vehicle (Apollo 7 and 8, and the CMP through 14). To save weight, they were given an A7L without the extravehicular parts. But all A6Ls were the same.

• The A7L had a visor assembly with a protective transparent visor, a gold sun visor, and side shades. These did not exist on the A6L, and you can see them missing in the pictures above.

• The arm joints were modified between the A6L and the A7L.

• The layers of the outer garment were modified to protect against tearing.

• EVA versions of the A7L had a second set of hose ports for the Buddy Life Support System, so astronauts could share their air supply if one failed. The A6L and the pictures in the article have only one set of hose ports.

• The A7L was modified for Apollo 15-17 to bend at the waist, so they could sit in the lunar rover. The CMP for these missions was given a proper EVA suit to retrieve experiments from the service module.

2. During training, the astronauts wore a cryogenic pack on their back, instead of the Portable Life Support System:

The cryogenic pack (fig. 51) is a liquid-air ventilator housed in the same envelope as the PLSS and worn on the back for mission simulations. The cryogenic pack pressurizes the suit to 17 to 25.5 kN/m$$^2$$ (2.5 to 3.7 psi) and operates for 90 minutes on a full charge. The suit interfaces are the same as for an actual PLSS except that the cryogenic pack does not have the water and communication connections. The charged weight, with mockups of the OPS and controls, is approximately 31.75 kilograms (70 pounds).

So they were cooled by the evaporated liquid air. I'm not sure they even wore the liquid cooling garment, as they carried no cooling water. Also, the pictures above show only one hose; a second hose would be needed to return exhaust air back to the PLSS.

3. There were also suitcase-like units for ventilation. The Portable Oxygen Ventilator was used with the helmet, and the Open Loop Ventilator was used without the helmet. Either could be used to cool the astronaut between training sessions.

Source: Apollo Experience Report: Development of the Extravehicular Mobility Unit. NASA Tech Note D-8093. PDF, 9 MB

(I'm one point short of 10k reputation. Hope this puts me over the top!)

Update: @OrganicMarble posted a discussion board link that quotes Dave Scott and Jim Irwin:

IRWIN: The work on the lunar surface was not much different from what we experienced on the rock pile. We didn't sweat as much, but it seemed like the work was about the same.

SCOTT: If we could get LCGs in the training suits, and the training backpacks, we'd have an excellent simulation of the lunar surface, in spite of the fact that you'd have the heavy backpacks. That was excellent training. I agree with Jim. The surface operations were not too much different from what we'd experienced on the rock pile. You gain an awful lot by going out there and working on the rock pile back of the simulator building.

The addition of the geology stops there at the Cape is good. We didn't have the opportunity to exercise all those rocks they'd put out there for us, but I think the following crews will find it very useful to drive the Rover and go through the procedures of getting off the Rover and doing the geology, the sequence of events with the high gain antenna, the LCRU, and everything. It was very good training.

Some the pictures there show training in the later A7Ls that could be worn on the rover.

Apparently due to budget reasons, some of the later training had to use suits that were already used on the moon. Sad.

• ding ding ding ding ding Congratulations! – Russell Borogove Jul 12 '19 at 16:12
• You're over the top on this one! I've always seen LOX and LN2 handled completely separately, and thought that air liquide was the name of a company or a band. So they both breathed and were cooled by boil-off from the mixture? There must have been some kind of heat exchanger, gas that cold would be strongly condensing, I wonder how they warmed it up before it came in contact with humidity? – uhoh Jul 12 '19 at 16:15
• @uhoh: I added the picture of the cryo pack. Not sure how condensation was handled. Considering that metabolism uses oxygen and produces heat in the same proportion, I think it was as simple as the astronaut breathing as needed, and that air would also provide the right amount of cooling. Good enough for training. – DrSheldon Jul 12 '19 at 16:37
• @RussellBorogove: Thank you. Also got my Yearling badge this week, and am only three days away from the Socratic gold badge. – DrSheldon Jul 12 '19 at 16:40
• BTW, a quote I saw from Cernan stated that they didn't wear the liquid-cooled undergarment in training, but I've lost the reference. – Organic Marble Jul 12 '19 at 19:15