posted 04-02-2015 01:36 AM              

1. Why did the Mercury suits have a zipper going diagonally in a zig zag way? It may or may not have been for the strategic placement of sensors on the body. However, the space suit was a modified Navy Mark IV high altitude pressure suit which also had diagonal zippers but which were not diagonal for sensor placement purposes.

2. Does anyone know what the 'Y' shaped harness was for that was worn over all American space suits since Mercury? (The harness has two metal wires that are along either side of the neck of the space suit and they come together in the middle of the chest, and a strap descends below the wires and between the legs of the astronaut). I have thought that this was a way of managing any 'ballooning effect' around the shoulders but it may have been for another purpose.

posted 04-07-2015 03:05 AM               

1. The pressure sealing entry zipper was placed diagonally for ease of entry into the suit. It ran from just behind the left shoulder, up over the shoulder and diagonally across the front of the suit to the right hip area. This zipper provided entry through the outer restraint layer and the pressure bladder layer into the interior of the suit.

   Another smaller donning aid zipper was positioned in the waist area. This zipper only opened up the outer aluminized nylon restraint layer of the suit. It ran from the right hip horizontally across the front of the waist, around the torso then diagonally downward ending at the right front groin area. The purpose of this zipper was to provide a donning aid by opening up the outer restraint layer of the suit, allowing the suit to elongate for ease of donning.

   Location of both zippers had nothing to do with sensor location as the sensors were attached to the astronauts skin under the suit liner (long john type underwear). As you indicated, the zipper placement was a carryover from the USN MK-IV suit design.

   Prior to that other shapes and locations of entry zippers were tried on the USN pressure suits and the diagonal zipper proved to be the easiest entry for the type of suit construction used in the Mercury suit.

2. The Y shaped "harness" is actually a combination of a wire rope cable with a pulley and webbing strap.

   The neck mobility joint on the Mercury suit, which allowed the astronaut to tilt his head, worked by pulling down on the neck ring. This created excess fabric in the neck area for neck mobility to allow tilting the head while the suit was pressurized. Also as the suit is pressurized the suit torso fabric stretches and the front strap is used to compensate for the stretch by pulling the neck ring back into proper position.

   Reliability of the neckring restraint cable was very important. Use of the close fitting helmet meant that a cable break could result in a broken neck as the unrestrained helmet would suddenly rise under pressure pulling the head upward.

   All suits that use a tight fitting conformal helmet need some type of neck mobility joint to permit head movement (tilting forward and sideways). The use of a cable restrained neckring is the most common approach. Dome helmets like the Apollo bubble helmet do not require a cable restrained neck ring mobility joint since the head is free to move within the helmet dome. However the suit torso stills requires a front pull down strap to offset the suit torso elongation under pressure.

   One exception where a cable restrained neck ring was used with a bubble helmet was the Apollo A7LB where a cable restrained neck ring was used to provide additional forward tilt to the bubble helmet when seated in the lunar rover. This helped compensate for the lean back of the LRV seat, allowing the astronauts to look directly forward and downward when seated. Another exception was the the Shuttle ACES suit which also used a cable restrained neckring with a non-conformal done helmet.

posted 07-24-2016 04:08 PM               

The placement of the zippers was even with the original Navy Mark IV pressure suit.

I have always wondered why the zippers were arranged that way. I assumed it was to allow doctors to secure sensors to the upper torso. Is there any other explanation for why the zippers were arranged that way?

posted 07-25-2016 06:22 AM               

The zig zag zippers you mentioned have nothing to do with access to body sensors but are for entry into the suit (both USN MK-IV and Mercury).

The large diagonal zipper across the front of the suit is the pressure sealing entry zipper. However since the outer nylon restraint layer is smaller that the inner pressure bladder, an additional spiral wrapped zipper is positioned in the lower abdomen/waist area. This spiral wrapped zipper is only thru the outer nylon restraint layer. Unzipping it opens up the restraint layer of the suit, effectively lengthening the suit, to make it possible to get your shoulders in thru the diagonal entry zipper.

After suit entry, the spiral zipper is closed tightening the restrain layer and the pressure sealing zipper is closed.