The Hammer of God makes an interesting contrast with Rendezvous with Rama by the same author, reviewed on this blog on 27 June this year. Both stories are set about a century in the future and concern Spaceguard, an organisation set up to monitor the paths of any large asteroids or comets which look as if they might pose a danger to Earth. In both cases, a large object is observed heading inwards from the outer reaches of the Solar System, and action is taken to send a manned spacecraft to intercept. However, there the stories diverge: the object in Rama is going to miss the Earth by a wide margin, but it turns out to be a vast alien space habitat. In Hammer, the object is more prosaic – a large asteroid – but it is heading directly for our planet. So with this story we are in familiar territory, as various books and films have covered the drama of what might happen if the Earth were threatened by a meteorite big enough to destroy our civilisation.
Hammer was first published in 1993, twenty years after Rama, and the structure is very different. Rama is a straightforward tale which progresses in chronological order throughout and focuses almost entirely on the expedition to the artefact (mainly seen through the eyes of the expedition's commander), with only an occasional diversion to the deliberations of a political committee on Earth. Most of Hammer is also seen from the point of view of the ship's captain, but that's where the similarity ends, since the chronological order is jumbled and the chapters are interspersed with various factual and fictional asides. There are brief chapters on historical incidents like Tunguska and the "dinosaur killer", plus other lesser-known meteorites. There are also chapters on the social and religious background to the world of Hammer, and many flashbacks to the earlier life of the captain. In fact, after an early mention of the threat from Kali (as the asteroid is dubbed) the first 158 pages of the 246 page story are taken up with this background material: one section consists of 23 pages of infodump with no dialogue at all. Only on page 159 does the focus turn to the expedition to Kali and the story really get going. From then on the tension starts to build along with the struggle to cope with the danger.
The book finishes with 22 pages of acknowledgements and explanation.
It has to be said that Clarke's story, while technically competent as one would expect from this author, adds little that is new to this theme. No doubt the proponents of the 'Mundane' school of SF would prefer it (see my review of Interzone 216 on 18 July) but the truth is that this story isn't a patch on Rama. Partly this is because Rama is much more tightly focused – it builds up the tension from the start and carries the reader along with the story – partly because of the novelty of its plot and the "sense of wonder" inspired by the mystery of the vast alien artefact.
That isn't to say that Hammer is a bad story. In fact, this is the one I would recommend to anyone who wanted to read something interesting about the threat from asteroid or comet strikes, because (as far as I can judge) it is so well researched and realistic. Clarke can be relied upon to get the science right. However, the focus of the story is really split three ways: between Clarke's vision of a future society in which humanity has spread through the Solar System; a non-fictional account of the threat from asteroids and what to do about them; and finally, a story about an attempt to deflect such a threat. These three elements are not well integrated but almost seem to be three separate texts which have been stitched together. It's worth reading, but not one of his classic works.