Airlock (US)

General Description

Development & Program History 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000

Launch

General Description

The US segment Airlock was developed to have a large airlock and EVA stowage space for the ISS. The US Airlock can accomodate US EMU's and Russian Orlan-M spacesuits.

The Airlock consisted of three major components, the airlock itself which was very similar to the Space Shuttle airlock, the equipment bay which was a short section of module of equal diameter to other US modules, and external air tanks which could be replaced periodically to provide air for the airlock to operate.

			The Airlock and Equipment lock concept
						The US Airlock as launched

The Airlock is to provide the ISS with a robust EVA facility to significantly replace the Russian Service Module docking node airlock facility (which only interfaces with Russian Orlan suits). The US airlock serves both shuttle EMU space suits, and Russian Orlan suits. Using the Russian airlock is risky if for some reason it can't be repressurized, it would divide the station in two. Just using it causes disruptions in air flow between modules and communications and control lines that have to be disconnected to close hatches. It also has more limited air replentishment tanks (those carried onboard some Progress resupply flights), and limited space for tools and equipment.

These factors make EVA's from the Russian segment of the station very undesirable and disruptive to routine station operations, hense all ISS EVA's (except for a minor Service Module hatch movement) have been done from docked space shuttles. With the addition of the US Airlock, ISS crews can now perform maintenance EVA's, station construction, and shuttle assembly missions can use the station airlock instead of the shuttles, reducing interruptions in shuttle docked operations (the shutle airlock use blocks the shuttle-station docking port). The airlock is depressurized to 10.2 psi by pumping air into the rest of the station. After that, the airlock is vented to space loosing the rest of the air.

The airlock consists of a large pressurized module for space suit storage, serviceing tools and EVA tools, and a smaller airlock module similar to the space shuttle airlock, capable of holding 2 astronauts and some equipment. The outside of the airlock is used to attach air tanks to replentish whats lost when the airlock is depressurized to space (air is not reclaimed when depressurizing). These tanks can be replaced periodically by shuttle serviceing missions. Each ank is installed separately and capable of recharge on-orbit (limited for O2). The Airlock contains 2 system racks and 2 stowage racks and has the total pressurized volume of approximately 950 cubic feet.

The large section of the airlock or equipment lock contains an:

• Avionics rack incuding 3 communications panels for wired microphones, or EVA spacesuit radio repeaters to pass signals from the suits radios to the station radio system.
• Another rack in the equipment space provides the ability to regenerate space suit carbon dioxide filters, using high temeratures to bake carbon dioxide out of spacesuit filters enabling them to absorbe carbon dioxide again on another EVA. Previously all filters were returned to Earth once they were used up and fresh ones replaced in suits.
• Along with the airlock, 2 sets of 2 tanks (oxygen and nitrogen) will be attached to the Airlock once its installed to be used to pressurize the airlock, the station when needed, and supply experiments in the US segment modules.

			Airlock racks above for Air handling (left), and space suit servicing and regeneration (right)						The Airlock's 3 communications panels and other systems (left)
				Airlock jumper panel of high pressure gas lines for Oxygen and Nitrogen					The Airlock trainer at JSC Houston

The Joint Airlock is a pressurized flight element consisting of two cylindrical chambers attached end-to-end by a connecting bulkhead and hatch. Once installed and activated, the Airlock becomes the primary path for International Space Station space walk entry and departure for U.S. spacesuits, which are known as Extravehicular Mobility Units, or EMUs. In addition, the Joint Airlock is designed to support the Russian Orlan spacesuit for EVA activity.

The Joint Airlock acts as a stowage area for EMU hardware as well as a staging area for crewmembers preparing to conduct a space walk. A combination of the Russian depress pump and pressure equalization valves located within the hatches accommodate the depressurization /pressurization capability of the Airlock. The addition of the Airlock permits space station-based space walks to be performed without major loss of environmental consumables such as air.

			The Airlock section which is similar in design and function to the Shuttle airlock			The Equipment lock end of the Airlock. The hatch shown was to be moved to be the actual airlock hatch after being attached to Node-1 in orbit.

High Pressure Gas Tanks (HPGT)

Two oxygen and two nitrogen High Pressure Gas Tanks are attached externally to the Airlock and will be transported to the space station attached to a Space Lab Double Pallet in the orbiter's cargo bay. These tanks provide a replenishable source of gas to the Atmosphere Control and Supply System and 900 psi oxygen for recharging the EMUs. Recharging the high pressure tanks is accomplished by the orbiter when it is docked to the station's Pressurized Mating Adapter 2 or Pressurized Mating Adapter 3, using lines that are routed through the pressurized elements. The Oxygen Recharge Compressor Assembly is used to pump oxygen from the shuttle tanks into the high-pressure oxygen tanks on the space station.

				Utility connectors surround the hatch of the airlock where it mates to Node-1. high pressure gas and electrical connections are made though these connectors.
									High pressure gas tanks are mounted on a space lab pallet for delivery to the ISS. Tanks like there were accidently lost during Airlock construction in Huntsville Alabama.
			The Airlock and equipment lock (in background) during manufacture at Boeing Huntsville Alabama USA
								The Airlock as envisioned in 1997

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