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NASA Project Gemini - Space Suit
The suit worn by Project Gemini astronauts was America's first true "space suit". The Project Mercury suit had been designed only to provide protection in the event of accidental cabin depressurization (which fortunately never occurred). The Gemini space suit would have to do much more.
Contrary to depictions in science fiction films, a person in a vacuum would not explode. Some unfortunate accidents in vacuum conditions have shown that internal and external damage to the body begins almost immediately, however. Loss of consciousness occurs in just a few seconds, and death occurs in less than two minutes.
When a space suit is pressurized (sealed and pumped full of gas) the gas held under pressure inside the suit exerts enough force on the astronaut's body to compensate for the lack of external atmospheric pressure.
Basic Requirements for the Gemini Space Suit
Gemini missions would be of much longer duration than the earlier Mercury flights had been. Launch weight restrictions, however, plus the limited size of the Gemini capsule itself, meant that there could be no changes of wardrobe for Gemini astronauts. A single suit would have to fulfill all the requirements of a Gemini flight, including:
- Protection during emergency ejection - in the event of an emergency during launch, astronauts would escape from the spacecraft using ejection seats. A problem with the Titan rocket might mean the astronauts would have to fly through a fireball of ignited rocket fuel.
- IVA functions - during normal activities inside the spacecraft (intravehicular activity, or IVA), the suit would be worn unpressurized, providing only ventilation (circulation of air through the suit to cool the astronaut and remove moisture from perspiration). If the cabin of the spacecraft lost pressure, however, the space suit would have to become the primary life support system, supplying oxygen for respiration and pressurization (see sidebar).
- EVA functions - for the first time, American astronauts would perform "spacewalks" (otherwise known as extravehicular activity, or EVA) during Project Gemini. In addition to providing oxygen for life support during EVA, the Gemini suit needed to protect against such hazards as extreme temperature, impact from micrometeoroids (tiny particles of rock, usually debris from comets and other objects), and the blinding glare of undiffused sunlight. Despite the added protection, the suit had to be flexible enough when pressurized for the astronaut to be able to perform tasks during EVA.
- Comfort - NASA needed to learn if astronauts could function in weightlessness long enough to get to the moon and back, so Gemini astronauts would spend up to two weeks in orbit on a single flight. The Gemini space suit had to be comfortable enough to be worn without reprieve on these long-duration missions.
The David Clark Company: An Unexpected Source
The Gemini space suits were produced by the David Clark Company, of Worcester, MA. This was unexpected, as they had not been contracted to produce a prototype for evaluation.
NASA had contracted the B.F. Goodrich Company (manufacturer of the Project Mercury suits) and the Arrowhead Products Company to produce prototypes. While those suits were being examined, the David Clark Company manufactured a prototype using their own funds, and submitted the suit to NASA for consideration. The Clark prototype was superior to the Goodrich and Arrowhead suits, and the David Clark Company was awarded the Gemini space suit contract.
X-15 Pressure Suit Technology
To create the Gemini prototype, the David Clark Company used technology it had used previously in the pressure suit for the X-15 rocket plane. This consisted of a man-shaped pressure bladder surrounded by a tight net which forced the pressurized bladder to maintain its shape when the suit's wearer moved.
Gemini Space Suit
The Gemini suit was a rear-entry suit, with a pressure-sealing zipper which ran down the back of the suit, through the crotch, and up to about the navel in front. When pressurized, it was designed to allow operation of the Gemini spacecraft controls from the seated position of astronauts inside the spacecraft. Reaching above the shoulders or below the waist was extremely difficult when the suit was pressurized.
Layers of the Gemini Space Suit
A long-underwear-type garment with biomedical sensors was worn under the suit. The suit itself consisted of a number of layers, as follows:
- Comfort layer (nylon oxford material) - the innermost layer made the suit easier to get on and off, and increased comfort for the astronaut by reducing contact with the harder sections of the suit.
- Pressure container (neoprene-coated nylon) - an inflatable, man-shaped bladder that could be pressurized when necessary.
- Restraining layer (Link-net) - a net which tightly covered the pressure bladder, preventing it from ballooning or changing shape when the astronaut moved, thereby making the suit more flexible. This net, consisting of woven cords of Dacron and Teflon, was patented under the name Link-net by the David Clark Company.
- EVA suit: Protective layers - suits designed for EVA included multiple layers of thermal and micrometeoroid protection. Mylar was used for thermal protection. Layers of HT-1 fabric (now known as Nomex fabric) and ballistic felt were initially used for protection against micrometeoroid impact. This was replaced on later missions by a single layer of neoprene-coated nylon.
- Outer layer of HT-1 fabric - the fire-resistant outer layer protected the inner layers from damage, and would help protect an astronaut ejecting through a ball of ignited rocket fuel.This layer was white, to reflect sunlight and heat. Some early training versions of the suit had an aluminized outer layer similar to the Project Mercury space suit, but the final versions used on all flights had the white outer layer.
Additional elements of the Project Gemini space suit are illustrated on the diagram above, and are described here:
Helmet, Gloves and Boots
The Clark suit was adapted to use the helmet designed by BF Goodrich, a removable fiberglass helmet which connected via a locking ring on the suit. The ring had rotating bearings, allowing the astronaut to turn his head from side to side. The helmet was lined and padded for comfort and protection, and contained communications equipment (earphone and microphone) and an oral thermometer for monitoring the astronaut's temperature.
The retractable visor, which became pressure-sealed when closed, was initially made of plexiglass. This was replaced with polycarbonate on later missions. A port on the helmet below the visor allowed the attachment of a water nozzle, so the astronaut could drink while the suit was pressurized and the visor was closed.
Pressurized gloves attached to the suit via locking rings at the cuffs of the suit. On some flights, small, battery-operated lights were added to the backs of two fingers. Boots, also pressurized, were integrated into suits designed for EVA, but were removable on IVA-only suits.
Helmet Tie-down Assembly
As with any inflatable object when it is pumped full of air, a space suit increases in size when it is pressurized. This can change the position of the helmet relative to the astronaut's head. The helmet tie down, a feature seen on many pressure suits, is an adjustable strap that enables the wearer to set the position of the helmet when the suit is pressurized.
All connections to external equipment were made via connectors on the torso of the suit. Keeping the Gemini helmet free of connections meant it could be put on or taken off more quickly.
A single connector was shared by communications and biomedical equipment. Biomedical measurements, such as blood pressure, respiration, temperature, and electrocardiogram were either transmitted to earth for real-time monitoring or stored on recorders for post-flight analysis.
Oxygen from the spacecraft's Environmental Control System (ECS) flowed through the suit via inlet and outlet connections. Normally the astronauts breathed oxygen that was pumped into the spacecraft cabin, and the flow of oxygen through the suit was only for ventilation. When the cabin was depressurized, however, the flow of oxygen into the suit was also used for respiration and pressurization of the suit.
Prior to launch, a portable cooling unit was attached to the suit to keep the astronauts comfortable until they could be connected to the spacecraft's ECS. Astronauts can be seen carrying these units as they walk to the spacecraft.
A harness of nylon webbing was worn over the Gemini space suit. Inside the spacecraft, the harness became part of the spacecraft's restraint system, holding the astronaut in place. The harness was also connected to a personal parachute, which would be engaged in the event of an emergency firing of the ejection seats. The harness could have flotation devices clipped onto it (as seen in photographs below), and was also useful for attachment of chest-mounted EVA gear.
Generations of the Gemini Space Suit
Several different versions of the space suit evolved over the course of the Gemini program. The earliest versions, knows as G1C and G2C, were used in spacecraft development and astronaut training. The first version of the suit to be used on an actual mission was the G3C suit.
G3C - IVA-only Suit
The G3C suit was an IVA-only suit. It was worn by Gus Grissom and John Young on the first manned Gemini flight, Gemini 3. Based on the serial numbers in NASA documentation, the G3C suit also appears to have been worn by Wally Schirra on Gemini 6.
G4C - IVA/EVA Space Suit
To make the Gemini suit EVA-ready, additional layers of protection were added to the G3C suit. The resulting suit, known as the G4C space suit, was the first NASA space suit to serve as both an IVA and EVA suit. Combined IVA/EVA suits would continue to be used on the Apollo and Skylab projects.
A gold-coated visor was snapped over the helmet's main visor during EVA. The visor offered protection against visible sunlight, which is blinding when unfiltered by Earth's atmosphere, and against UV rays. A thermal overglove was worn over the standard glove during EVA on Gemini 4. A separate EVA glove was developed for the remaining Gemini spacewalks.
Only one astronaut would exit the spacecraft during EVA, so a less bulky version of the G4C suit was developed for the crew member who remained inside.
The G4C suit was first worn on Gemini 4, and some variation of the suit was used on every Gemini flight thereafter, with the exception of Gemini 7. That flight was a long-duration mission for which a special suit was developed.
G5C - Long-duration (14 day) IVA-only Suit
For the 14-day Gemini 7 mission, a special lightweight space suit, the G5C, was developed. All unnecessary elements were stripped from the body of the G3C design, resulting in a lighter, softer suit. The fiberglass helmet was also replaced with a soft hood, which could be unzipped and rolled back (a standard test pilot crash helmet could be worn underneath the hood).
The G5C suit was designed so that an astronaut could remove the suit and wear only the undergarment during portions of the flight. The Gemini 7 crew became the first astronauts to remove their spacesuits while in space, although doing so took over an hour inside the cramped Gemini spacecraft.
EVA - Life Support
During EVA, an umbilical provided the astronaut with a steady flow of oxygen from the spacecraft's Environmental Control System. The umbilical also provided electrical power, communications and biomedical monitoring. Insulating material was used to was wrap the umbilical together with a safety tether, forming a single cord.
The flow of oxygen during EVA was regulated by a unit worn on the astronaut's chest. This unit also contained an emergency oxygen supply. Two different life support units were used during Project Gemini.
Ventilation Control Module (VCM)
The VCM, which contained a nine minute emergency supply of oxygen, was used by Ed White on Gemini 4. The EVA itself went perfectly, but White had difficulty closing the hatch after returning to the spacecraft. The body heat generated by his efforts exceeded the cooling capacity of the VCM. White became overheated, and it took several hours for his body temperature to return to normal following his EVA.
Extravehicular Life Support System (ELSS)
The ELSS was used on all other Gemini spacewalks. In addition to a 30 minute emergency supply of oxygen, the ELSS had a greater cooling capacity than the VCM. Even this was inadequate, however. EVA on both Gemini 9 and Gemini 11 had to be terminated early because the cooling capacity of the ELSS had been exceeded.
The failure of Project Gemini's gas-cooling system led to the development of a liquid-cooling system for Project Apollo. In this system, liquid flows through a network of hoses inside the suit, drawing out body heat, and then flows into the astronaut's backpack, where it is chilled and recirculated. Liquid-cooling continues to be used on modern space suits.
EVA - Maneuvering
Two methods were developed to enable an astronaut to maneuver during EVA. A hand-held unit was successfully tested on two Gemini flights. A larger backpack unit was developed, but never tested.
Hand-held Maneuvering Unit (HHMU)
The HHMU used pressurized gas, which was released in small bursts to provide thrust. The unit had nozzles facing in two directions, and a rocking trigger which enabled the astronaut to select which nozzles the gas would fire through.
A camera could be mounted on the HHMU, allowing an astronaut to take photographs during EVA. The HHMU was used on Gemini 4 and Gemini 10. There were plans to use it during Gemini 8 and Gemini 9, but an emergency situation made EVA impossible on Gemini 8, and the Gemini 9 EVA was terminated early when the ventilation capacity of the ELSS was exceeded.
Another unit, a backpack called the Astronaut Maneuvering Unit, is discussed in the next section.
Untested EVA Equipment
Two pieces of EVA equipment were designed and actually carried into space on Gemini flights, but never used.
Extravehicular Support Package (ESP)
The ESP was a backpack containing an independent 1 hour supply of oxygen which could be plugged into the astronaut's ELSS, replacing the flow of oxygen supplied by the spacecraft. The unit also contained a supply of Freon propellant for the HHMU. The unit was to have been tested during the Gemini 8 mission, but that flight was cut short before EVA could take place.
The US Air Force intended to use the Astronaut Maneuvering Unit as part of "Blue Gemini", a military space program based on Gemini hardware. The program was eventually cancelled.
Astronaut Maneuvering Unit (AMU)
The AMU was a jetpack-like unit with built-in thrusters, which could replace the HHMU. The unit also contained a 1 hour independent supply of oxygen. The AMU was developed by the US Air Force, and NASA agreed to test the unit.
NASA planned to test the AMU while still tethered to the spacecraft during Gemini 9. To protect against the heat of the thruster plumes, additional layers of protective material were added to the legs of the Gemini 9 EVA suit (as seen in the photo to the right). Unfortunately, the Gemini 9 EVA was cut short before the AMU could be tested.
Plans to test the unit again on Gemini 12 were dropped entirely. EVA was turning out to be much harder than NASA had expected, and they felt that testing the AMU was simply not feasible at that time.
Both the Extravehicular Support Package and the Astronaut Maneuvering Unit were stored outside of the spacecraft, in the adapter section. An astronaut would have to perform a spacewalk to the rear of the spacecraft to access either unit.
Lessons for Project Apollo
One of the most important goals of the Gemini program was to bridge the technological gap between the short, one man flights of Project Mercury and the far more ambitious lunar excursions planned for Project Apollo. In terms of space suit design, Gemini did exactly that. The lessons learned during Project Gemini were crucial to the successful design of the suit worn by Apollo astronauts on the moon.
Information for this hub was taken from the following sources:
NASA documents available online:
- Grimwood, James M. et al., Project Gemini Technology and Operations A Chronology, NASA, 1969.
- Hacker, Barton C and Grimwood, James M., On the Shoulders of Titans: A History of Project Gemini, NASA, 1977
- Office of Human Resources and Education, Education Division, Suited for Spacewalking—A Teacher’s Guide with Activities for Technology Education, Mathematics,and Science, NASA, 1994
Additional NASA documents:
- Manned Spacecraft Center, Gemini Summary Conference, NASA, 1967
- NASA, Gemini 4 Press Kit, NASA, 1965
- NASA, Project Gemini, NASA, 1966
- Shayler, David J., Gemini Steps to the Moon, Springer Praxis Books, 2001.
- Thomas, Kenneth S. and McMann, Harold J., US Spacesuits. Springer Praxis Books, 2006.