Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Ion drive for spacecraft

The ion drive of the Deep Space 1 spacecraft, pictured on page 76 and discussed in example 2, produces a thrust of 90 mN (millinewtons). It carries about 80 kg of reaction mass, which it ejects at a speed of 30,000 m/s. For how long can the engine continue supplying this amount of thrust before running out of reaction mass to shove out the back?

Solving the equation F = Δp/Δt for the unknown Δt, and treating force and momentum as scalars since the problem is one-dimensional, we find

Last Update: 2010-11-11