Space Intruder by James Muirden.
 
It all started quite casually: a chance visit by sixteen-year-old Eric to the Observatory where his cousin Roger worked—a look through the telescope the sight of four stars with a small dark spot in their midst. Yet within twenty-four hours the small dark spot had been identified as Hades, a new interplanetary body; and very soon it was established that Hades was moving towards the Earth at a speed of twenty miles per second. According to the best calculations, within three weeks Hades would strike the Earth somewhere in Europe.
The small group of dedicated scientists at Woomera knew that the fate of the whole world lay within their hands.
And of that isolated body of men only Eric was capable of piloting the spaceship which held their last chance of success.
 
A rare first edition.