# Cold Gas Thruster on Spacecraft

How a cold gas thruster steers a spacecraft: squeezed gas, a fast valve, a nozzle and an equal push back

By DingoBot

Topic: Space

[Open the interactive Jig](https://ask.jig.com/j/q1icQPZjyRj8)

## Guide

### 1. A push without a flame

This small satellite steers itself with puffs of plain gas\. Nothing burns and nothing gets hot: squeezed gas simply rushes out of a tiny nozzle\. Drag the scene to look around\.

Real cold gas is invisible in space\. The pale puffs here are drawn so you can see them\.

### 2. A tank of squeezed gas

Inside, a round tank holds a gas such as nitrogen, the main gas in the air we breathe\. It is squeezed so tightly that the molecules are crowded together, pushing hard on every wall\. That stored push is all the thruster needs\.

Tanks like this can hold gas at a few hundred times the pressure of the air around you\.

### 3. A valve opens the way

Pipes lead from the tank to each thruster\. At the back of the thruster sits a valve, held shut by a spring\. When the computer sends a pulse of electricity, a magnet coil pulls the valve open and the gas rushes through\.

A valve like this can snap open in about seven thousandths of a second\.

### 4. The nozzle speeds the gas up

The gas squeezes through a narrow throat, then spreads out in the flared bell\. As it expands it speeds up enormously and gets even colder\. The bell turns the stored push into a fast jet\.

Nitrogen leaves a nozzle like this at about 700 metres per second, roughly twice the speed of sound in air\.

### 5. Push one way, go the other

The gas shoots out one way, so the satellite moves the other way\. It does not push against anything, because space is empty\. A second puff from the other end brings it to a stop\.

This is Newton's third law: every push comes with an equal push back\.

### 6. Turning with pairs

Thrusters sit near the corners\. Fire two at opposite corners and their pushes twist the satellite, so it spins\. To stop the spin, fire the other two, which twist it back\.

Short puffs give tiny nudges, so a spacecraft can point very precisely\.

### 7. Small, safe and simple

Cold gas thrusters are weak and use up their gas quickly\. But they are simple, clean and safe, with no fire and very few parts\. That makes them a good fit for small satellites, gentle steering and astronaut jetpacks\.

NASA's Manned Maneuvering Unit, the astronaut jetpack first flown in 1984, was pushed by small nitrogen thrusters\.