Re Bob Ford of SLI's assertion that "there is not a great benefit in hydrogen over kerosene" (Flight International, 8-14 October).

There is in fact an enormous benefit. The specific impulse of hydrogen/oxygen is double that of kerosene/oxygen, overwhelming its extra bulk and handling difficulties; and this advantage is multiplied because what matters is the residual mass that can be lifted into orbit by a given amount of fuel. Hydrogen-powered shuttles thereby become many times lighter.

Noel Falconer

Couiza, France

Source: Flight International