chapter 2

ECLSS (Environmental Control & Life Support System)

The Environmental Control and Life Support System (ECLSS) Group of the Flight Projects Directorate at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, is responsible for designing and building the life support systems that will provide the crew of the International Space Station (ISS) a comfortable environment in which to live and work. This is a close-up view of ECLSS Oxygen Generation System (OGS) rack. The ECLSS Group at the MSFC oversees the development of the OGS, which produces oxygen for breathing air for the crew and laboratory animals, as well as for replacing oxygen lost due to experiment use, airlock depressurization, module leakage, and carbon dioxide venting. The OGS consists primarily of the Oxygen Generator Assembly (OGA), provided by the prime contractor, the Hamilton Sundstrand Space Systems, International (HSSSI) in Windsor Locks, Cornecticut and a Power Supply Module (PSM), supplied by the MSFC. The OGA is comprised of a cell stack that electrolyzes (breaks apart the hydrogen and oxygen molecules) some of the clean water provided by the Water Recovery System and the separators that remove the gases from water after electrolysis. The PSM provides the high power to the OGA needed to electrolyze the water. less

Date Created:2000-09-01

🧩 What ECLSS Does

The ECLSS ensures astronauts can breathe, drink, and live comfortably in the closed environment of the ISS by managing:

Air (O₂, CO₂, pressure, humidity, and temperature)
Water (recycling and purification)
Temperature and humidity control

🧪 LEFT SIDE — System Description

📊 RIGHT SIDE — Telemetry Readouts

🔵 TOP RIGHT: WRM and IATCS Buttons

WRM = Water Recovery and Management — controls water recycling and storage functions.
IATCS = Internal Active Thermal Control System — circulates fluid to remove heat from ISS electronics and equipment, maintaining proper module temperatures.

💡 Summary

This ECLSS screen shows a healthy, nominal environment:

Temperature and pressure within safe range.
Both water and oxygen systems functioning.
Life-support valves open and circulating.
Active water recovery and oxygen production.

Internal Active Thermal Control System

This diagram shows the flow of water recovery and management in the International Space Station (ISS). The Environmental Control and Life Support System (ECLSS) Group of the Flight Projects Directorate at the Marshall Space Flight Center is responsible for the regenerative ECLSS hardware, as well as providing technical support for the rest of the system. The regenerative ECLSS, whose main components are the Water Recovery System (WRS), and the Oxygen Generation System (OGS), reclaims and recycles water oxygen. The ECLSS maintains a pressurized habitation environment, provides water recovery and storage, maintains and provides fire detection/ suppression, and provides breathable air and a comfortable atmosphere in which to live and work within the ISS. The ECLSS hardware will be located in the Node 3 module of the ISS.

🌡️ Overview: What IATCS Does

In microgravity, heat doesn’t rise — it just builds up.

So, instead of air cooling, the ISS uses liquid cooling loops (with water and ammonia mixtures) to collect heat from electronics and crew areas and transfer it to radiators, where it’s released into space.

There are two main water loops:

LTL – Low Temperature Loop (blue lines) → Cools delicate hardware like science racks and payloads.
MTL – Moderate Temperature Loop (red lines) → Cools higher temperature systems such as avionics and power equipment.

Both loops circulate through each module (Node 2, Node 3, US Lab) and are linked through heat exchangers (IFHX) that transfer heat between internal and external cooling loops.

🧩 LEFT PANEL — Module Data

Each section (US LAB, NODE 2, NODE 3) shows real-time readings:

⚙️ CENTER DIAGRAM — Thermal Flow Path

🔵 Low Temperature Loop (LTL)

Purpose: Absorbs heat from payload racks and sensitive equipment.
Key components:
- PPA (Pump Package Assembly): Circulates coolant through the system.
- System Flow Control Assembly: Directs flow to specific modules.
- Heat Loads (Racks): Represent sources of heat.
- Three-Way Mixing Valve: Controls fluid temperature by mixing warm and cool flows.
- IFHX (Interface Heat Exchanger): Transfers heat to or from the Moderate Temperature Loop or external ammonia loops.

🔴 Moderate Temperature Loop (MTL)

Purpose: Handles avionics and more robust hardware that can tolerate higher temps.
Key components:
- PPA: Circulates coolant for this loop.
- System Flow Control Assembly: Distributes flow to avionics or regenerative mixing valves.
- Regenerative Three-Way Mixing Valve: Maintains loop temperature stability.
- IFHX: Exchanges heat between MTL and external ammonia system.

⚫ LCA (Loop Crossover Assembly)

Connects the MTL and LTL for redundancy — if one loop fails, heat can still be managed by routing through the other.

🔄 Heat Flow Summary

Electronics and racks generate heat → absorbed by water loops.
Heat moves through Pump Package Assemblies (PPAs).
Mixing valves regulate fluid temperature.
Heat is sent to Interface Heat Exchangers (IFHX) → transfers to External Thermal Control System (ETCS).
Ammonia coolant outside the ISS radiates that heat into space through radiator panels.

🧠 In Simple Terms

Think of this as the ISS’s air conditioner and radiator system combined:

Water is the “coolant.”
Pumps are the “heart.”
Valves are the “thermostats.”
IFHXs are the “heat bridges” to the outside radiators.

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