On May 3, 1958, the configuration of the S794-6 suit to be delivered to Crossfield was frozen during a meeting in Worcester between representatives of David Clark Company, North American, and the USAF. The decision was somewhat premature since the suit configuration was still in question during a meeting 3 months later at Wright Field. This indecision had already resulted in a 2-month delay in delivery, and the need for further tests was apparent. Fortunately, in a perverse way, the entire X-15 program was running behind schedule, so the delay in the suit was not critical—yet.
Nevertheless, the X-15 Project Office advised the newly assigned chief of the Aero Medical Laboratory, Col. John P. Stapp, that the suit delays might postpone the entire X-15 effort. To maintain the schedule, the X-15 program needed to receive Crossfield’s suit by January 1, 1959, a second suit by February 15, and the remaining four suits by May 15. Simultaneously, the X-15 Project Office confronted Stapp with a growing controversy concerning the use of a face seal instead of the neck seal preferred by the Aero Medical Laboratory.
In a full-pressure suit, a mechanical separation is needed between the air space in the suit and the space surrounding the mouth and nose. To control the temperature within the suit, it is necessary to continually ventilate the free space between the suit and the wearer’s skin to carry off heat and water vapor, both of which rapidly accumulate to uncomfortable levels in an unventilated suit in the usual cockpit environment. Oxygen for breathing is carried aloft at considerable expense in terms of weight and space requirements. Before the advent of liquid oxygen systems, it was impractical to ventilate the suit with oxygen; therefore, the suit was usually ventilated with ambient air or nitrogen, and a seal separated the suit space from the breathing space.
As with many things in life, the use of a face seal has some advantages and some disadvantages. Its chief advantage is the smallness of the breathing space and the resultant limited rebreathing. To obtain a truly satisfactory seal, the wearer’s face is pushed into a rubber seal by an adjustable harness behind the head. Such a method makes each helmet a truly personal piece of equipment, as some time is required to fit the seal properly to the face so that it is reasonably comfortable. With his face firmly held in the face seal, the wearer must move the entire helmet in order to turn his head to either side. This is accomplished by rotating the helmet on its neck ring. Not only must the head be rotated in a fixed and somewhat unnatural plane, but movements are slow and difficult. An advantage, however, is that since most of the head is removed from the breathing space, it can be ventilated with the rest of the suit, generally increasing comfort. This arrangement became known as a conformal helmet.
