Unlike its predecessors both in the national space program and at Garrett, the Apollo system is the first designed for operation with the crew primarily in shirtsleeves. Operation of the system is essentially the same whether or not the spacesuit connections are attached.

Because of the lengthy aboard requirement, designed must be such that the system can be controlled, regulated and repaired, if necessary, with the crew in pressurized spacesuits for as long as four days.

Emergency features include an oxygen surge tank to provide an immediate supply of oxygen in the case of meteorite puncture or other loss of pressurization, as well as redundancy in key subsystems in case of malfunctions.

The earth orbital or block I version, with a slightly less stringent requirement, differs from the block II unit in that it has only a single glycol cooling loop instead of two. Provisions also are made for other block II equipment. Differences in the two systems amount to about 10% of the total design.

Both have another unique emergency provision stemming from the fact that the Apollo spacecraft could come down in a recovery area on the opposite side of the world then originally planned with recovery forces deployed many hours away.

The capsule has a post-landing ventilation system, and two inlet valves and an exhaust port which may be opened when the astronauts have touched down, A battery-powered fan, capable of operation for two days, is provided to circulate air.

Design for the block II system was frozen in December 1965, although block I design was firm some two years ago. The block I unit has been flown on the unmanned Apollo flights. While there was no way to test its capability in terms of a crew, telemetered data proved that it successfully cooled electronic gear.

All rotating equipment has undergone thousands of hours of life testing, Garrett Apollo project director Charles Clarke told MISSILES and ROCKETS. The entire systems have been run with Garrett’s three-man simulator or “man-can.”

In addition, a three-man simulated 14-day mission was carried out success-fully at North American Aviation’s Apollo checkout facility.

Normal leakage in the Apollo capsule is 0.5 lbs./hr., maximum. However, the system is designed to take a leakage rate of 0.67 lbs./min., the rate calculated for a puncture in the cabin wall ½ sq. in.

In the event of a meteorite puncture, an increase in oxygen flow rate will automatically trigger the opening of a value on a gaseous oxygen surge tank, which will maintain cabin pressure for five minutes at the maximum flow rate. This would allow crew members to don suits or patch the wall.

Oxygen is stored in the surge tank at 1,000 psi, rather then in cryogenic form since the latter would require some time to be ready for use. Oxygen in the oxygen supply system is used at 20 psi to move water and glycol from tanks to various parts of the system.

The potable water tank, for instance, is equipped with a bladder of oxygen which forces out water as needed. The oxygen supply system is also used as a source of pressure in case of a leak in the glycol cooling system. A rubber diaphragm, which separates the glycol and a source of oxygen in the glycol reservoir, forces glycol into the system when required.

There are two blowers in the suit circuit, as well as two in the cabin, The air stream is moved at a rate of 35 cu. Ft./min. by the suit compressors and 90 cu. ft./min by the cabin fan. Power required by the blowers is a maximum of 85 watts, with 28 watts for operation of each cabin fan.

Oxygen is supplied to the suit circuit after passage through three flow limiters. After use, it is returned to the suit blowers, which send it through a debris trap and then over the carbon dioxide absorbers.

As with Gemini and Mercury, lithium hydroxide canisters are used for removal of carbon dioxide. However, while with Gemini all the granules used for the mission were carried in one canister, the Apollo system is divided into small canisters capable of operation for 24 hours each.

About 20 canisters will be carried on the lunar mission. Two are in operation at all times. One is changed the crew every 12 hours.

Philosophy for the design change is that the small canisters can easily be replaced on the pad in case of a long hold before launch. Thus, the entire supply would not be wasted if a long hold caused usage of one portion.

While in operation, the air stream passes over the two canisters simultaneously. However, the system is designed so that access cannot be made to one canister unless the air stream is sealed off the affected side and is being passed over the other canister.

The lithium hydroxide canisters, described by the company as resembling grocery strawberry baskets, are 8 in. square, and 5 in. deep. A filter membrane covers the absorbent, which in addition to LiOH includes a 1/8-in.-thick layer of activated charcoal at the base to handle trace contaminants.

Rate of use of the canisters is both telemetered to the ground and shown on a display in the Command Module.

The droplets are trapped by wicks which move away from the heat exchanger and pumped by cyclic accumulators which work like vacuum-operated windshield wipers.

The glycol cooling system, Clarke points out, has a faster response then just the water evaporator used on previous systems. Suit temperature control was a problem never really solved in the Mercury program.

The Apollo system also differs from the Gemini system, which also used glycol for cooling, in that it has more capability for supplemental cooling in case of the loss of the radiators. The boilers or evaporators that cool the glycol can be cooled with water if necessary.

The block II system is supplied with two completely redundant glycol loops completely isolated from each other and are on different circuits. Switchover is manual.

Glycol is used in the spacesuit heat exchanger, is sent to the drinking water supply for chilling, to the cabin cycle and to electrical heat loads. It is cooled at the space radiator, but if this is not sufficient, the evaporator provides additional cooling.

A unique feature of the system is the magnetic drive on the glycol pump, destined to keep glycol from fouling the motor. The magnetic drive, enclosed in a plastic seal, drives an impeller which rotates at 12,000 rpm. It operates at 29.5 psi and produces a 200 lbs./hr. flow.

There are three pumps in the block II system and two in the block I system. Power requirement is 35 watts per pump.