and a man's heart normally simply doesn't ever feel tired. It became
more and more difficult to see clearly.

But he had work to do. Important work. The take-off rockets were
solid-fuel jobs, like those which launched the Platform. They were
wire-wound steel tubes lined with a very special refractory, with
unstable beryllium and fluorine compounds in them. The solid fuel burned
at so many inches per second. The refractory crumbled away and was
hurled astern at a corresponding rate--save for one small point. The
refractory was not all exactly alike. Some parts of it crumbled away
faster, leaving a pattern of baffles which acted like a maxim silencer
on a rifle, or like an automobile muffler. The baffles set up eddies in
the gas stream and produced exactly the effect of a rocket motor's
throat. But the baffles themselves crumbled and were flung astern, so
that the solid-fuel rockets had always the efficiency of gas-throated
rocket motors; and yet every bit of refractory was reaction-mass to be
hurled astern, and even the steel tubes melted and were hurled away with
a gain in acceleration to the ship. Every fraction of every ounce of
rocket mass was used for drive. No tanks or pumps or burners rode
deadhead after they ceased to be useful.

But solid-fuel rockets simply can't be made to burn with absolute
evenness as a team. Minute differences in burning-rates do tend to
cancel out. But now and again they reinforce each other and if
uncorrected will throw a ship off course. Gyros can't handle such
effects. So Joe had to watch his instruments and listen to the tinny
voice behind him and steer the ship against accidental wobblings as the
Earth fell away behind him.

He battled against the fatigue of continuing to live, and struggled with