Earthlight
Arthur C. Clarke
 The plot describes how political tension between the government of a politically united Earth (which maintains sovereignty over the Moon) and independent settlers and traders elsewhere in the solar system who have formed a federation, erupts into warfare over the terms for the availability to the Federation of scarce heavy metals. The trigger for hostilities is the publication of a research paper suggesting that the Moon may have previously unsuspected heavy metal resources which Earth proposes to monopolise. The Earth government's intelligence agency suspects that confidential information concerning the exploitation of these mineral riches may be being leaked to the Federation and presses an accountant, Bertram Sadler, into service. Sadler is sent to the Moon's main astronomical observatory located near the crater of Plato as a tip off has suggested that information is being routed through that location. Sadler's cover story is that he is carrying out an investigation of waste in government spending. The rising political tension is accompanied by the observatory staff enjoying the good fortune of observing a nearby supernova explosion in the constellation of Draco. Despite a relatively long preceding era of peace, Earth and the Federation each prepare technologically for war. The Federation develops a new method of spacedrive propulsion while Earth develops new shielding technology and a weapon which uses an electromagnet-propelled bayonet of liquid metal. (The weapon mistaken for a beam of light). Such a weapon is currently being developed by DARPA. A climactic battle between three Federation cruisers and the fortified mining installation ("Project Thor") is played out near Mount Pico close to the lunar observatory. Two astronomers who have delivered a top Earth scientist to Pico with only a couple of hours to spare, witness the battle. Sadler, whose investigations have had no pay off except for the unmasking of an embezzling store manager, relinquishes his cover by going to debrief the two astronomers. Of the three Federal cruisers, two are destroyed along with the mine in the battle. The third cruiser, named The Acheron, is terminally damaged and retreats towards Mars, but has little chance of reaching it before her nuclear reactor explodes. However, her new drive gives her the capability of a rendezvous with a passenger liner, The Pegasus, which is able to rescue all but one of the crew who have to make the 40 second crossing without space suits. This inconclusive duel between mother planet and formerly dependent colonists, with each side suffering stiffer resistance than anticipated, discredits the governments on both sides. Sadler is able to return to civilian life but suffers nagging frustration that he never found out whether the spy that he was searching for existed or not. Many years later the commander of the Acheron writes his memoirs and reveals that information had reached the Federation from One of Earth's most distinguished astronomers, now living in honoured retirement on the Moon. With this hint, Sadler is able to confirm the spy's identity as Robert Molton, the first one of the observatory staff to greet him on his way to the observatory. The novel concludes with Moulton enlightening Sadler and the reader as to the brilliant technical subterfuge with which he transmitted information, namely that he used the observatory's main telescope as a transmitter by placing a modulated ultra-violet source at its prime focus. The signal was received by a Federation spaceship a few million kilometers away.