In fiction, a number of imaginary emissaries have sailed before Icarus into the dark interstellar ocean. There have been fewer tales featuring unmanned probes than manned starships like the Enterprise of Star Trek, purely because of the wider dramatic possibilities of the latter. But the depiction of interstellar probes in science fiction may serve to highlight cultural aspects associated with such craft, our hopes and dreams and fears, of interest to the Icarus designers.
This essay is a submission of the Project Icarus Study Group.
Plaques and Records
In reality we have of course already sent out four interstellar probes, in the Pioneers and Voyagers launched in the 1970s, and there have been a number of stories dwelling on possible consequences of these missions – especially concerning the messages from Earth the craft carried, in the forms of the Pioneers’ engraved plaques and the Voyagers’ ‘golden records’. We hope for positive responses to our invitation to contact, but fear the worst.
‘The Message’ was a season 1 episode of the TV show The Outer Limits (1995) in which a profoundly deaf woman begins to ‘hear’, through a faulty cochlear implant, voices asking for help and a string of symbols. The symbols are recognised as binary code, and when properly assembled give a reproduction of the Pioneer plaque image, to which has been added the representation of a humanoid alien with upraised arm. (It is a measure of the plaque image’s iconic status that there is no prior on-screen introduction of it.) Under this image is a ‘palimpsest’, instructions for building a powerful laser. The originators of the message turn out to be aboard a solar-sail spacecraft which intercepted a Pioneer on the edge of the solar system. They need the laser to be fired to avert the craft from a collision course with the sun, before safely passing on to their next destination.
John Carpenter’s Starman (1984) opens with the launch of Voyager 2, with the golden record playing. The probe is intercepted by an alien culture who respond to the record by sending a visitor to Earth, who crashes near the home of a young widow in Madison, Wisconsin. The visitor’s crashed ship is shown to contain the golden record, and a clone of the woman’s dead husband is grown – a ‘symbiotic transformation’ – who spouts fragments of the record’s contents. The visitor requires transport across America to Meteor Crater, Arizona, for pickup. He is pursued by sinister governmental forces in a scenario reminiscent of Spielberg’s E.T. At one point a scientist from SETI (the search for extraterrestrial life) protests at the treatment of the visitor: ‘We invited him!’
In contrast to these uplifting scenarios, in the movie Star Trek V: The Final Frontier (1989, dir. William Shatner), we see a Pioneer probe floating in space complete with plaque used for target practice by a Klingon bird of prey: ‘Shooting space garbage is no test of a warrior’s mettle!’ Again, there is no on-screen explanation of the probe’s identity.
Things can get a lot worse than that. In ‘Little Green Men’, an episode in the second season of the TV show The X-Files (1994), the contents of the Voyager golden record are apparently played back from an alien source and picked up by the Arecibo radio telescope. FBI agent Fox Mulder is drawn to the facility, apparently abandoned after the cancellation of NASA’s SETI programme in 1992, and faces a close encounter with a hostile ‘grey’ – but he fears the whole episode was faked, and is left with no evidence either way.
Worse still, in L Ron Hubbard’s novel Battlefield Earth  the predatory Psychlos are led to our world by the Pioneer plaque: ‘Man apparently sent out some kind of probe that gave full directions to the place, had pictures of man on it and everything. It got picked up by a Psychlo recon … The probe and the pictures were on a metal that was rare everywhere and worth a clanking fortune … One gas barrage and we were in business’ (Chapter 1).
Probes of the Future
Much more advanced probe designs than the Pioneers and Voyagers, indeed more advanced than Icarus, have been proposed in the literature. From the beginning of the SETI enterprise in 1960 there has been discussion of contact with ‘smart probes’: that is, devices designed not just to gather data but with artificial intelligence sufficient to establish local communication with cultures like ours . The ‘Life Probe’ of McCollum’s 1983 novel  is a just such an alien smart probe, which comes seeking civilisations with faster-than-light technology.
An interesting advanced probe of human design features in Greg Bear’s novel 1990 Queen of Angels , which drew on a study by Adelman & Adelman . Set in the relatively near future, this is based on technologies that are conceivable but just beyond our current capabilities. AXIS (for Automated eXplorer of Interstellar Space) is a probe to Alpha Centauri, fifteen years in development by a consortium of nations at a cost of $100bn. Transponders are dropped off during the interstellar cruise to aid transmissions back to Earth. During its boost phase AXIS is powered by an antimatter drive and has a design robust enough to withstand the consequent acceleration and radiation fallout, including a non-organic onboard computer. But on approach to the target AXIS rebuilds itself using nanotechnology, the blunt antimatter rocket becoming a huge, fragile sail which uses the Galaxy’s magnetic fields to decelerate. Thus a highly efficient mass ratio is enabled.
Once at Centauri, using a more delicate organic computer, an onboard AI and observational facility is allowed to develop: ‘Bioptics should be fully grown and ready for electronic interface within 21 hours’ (Chapter 4). The ‘biologic thinker system’ (Chapter 4) can design its own science programmes at the target, and can communicate with any ETI (extraterrestrial intelligence) encountered, a vastly increased capability compared to remote operations or fixed programming. As with another famous shipbound AI, HAL of Clarke’s 2001 , conflicts in the AI’s programming lead to a breakdown. In this case AXIS has been given a powerful motivation to communicate above all else; its lightspeed-delay isolation from Earth and a failure to find anybody to speak to at Alpha Centauri drive it ‘crazy’.
Other fictional dramatisations of what happens when a smart(ish) probe goes wrong come from Star Trek. In the TV show’s second series episode ‘The Changeling’ (1967), the crew of the Enterprise, investigating the destruction of the four billion inhabitants of the Malurian system, encounters a malevolent entity that turns out to be a much-modified life-seeking probe from Earth called Nomad. It tries to communicate with the Enterprise in ‘old style interplanetary code’. Having been launched in the early 2000s, Nomad suffered a meteor strike and then merged with an alien probe that it calls ‘the Other’. Nomad’s programming, to seek out all life, merged with the Other’s, which was to sterilise soil samples, the result being a distorted imperative to sterilise all imperfect life. Kirk eventually uses logic to trap Nomad; the probe mistakes Kirk for its creator, and having been proved imperfect destroys itself.
This story was one seed of the movie Star Trek: The Motion Picture (dir. Robert Wise, 1979). NASA’s Voyager 6, launched in the late twentieth century, falls through ‘what used to be called a black hole’ and is projected across the Galaxy to a planet of ‘living machines’. The machines respond to Voyager’s programming and purpose – ‘to collect data and transmit it back to Earth’ – and build a tremendous artefact, surrounded by a destructive energy cloud 82AU across, to ferry Voyager back across the Galaxy to fulfil its mission. Three hundred years later this arrives in human space to be met by the crew of the Enterprise. As ‘V’ger’, the merged machine is characterised by ‘insatiable curiosity’, says Mr Spock. Unfortunately, when Voyager tries to report its findings, there’s nobody left on Earth who can ‘recognise the old signals and send a response’, and the merged probe becomes destructive when it suspects that humans are an infestation standing between it and the ‘creator’ to whom it wishes to report. Ultimately V’ger merges with a human to become a new transcendent life form. Of course the movie’s storyline is fantastical, but it is built on the idea that our science probes are an embodiment of our curiosity, our wish to know and understand, and to communicate; in fact Voyager’s exploratory mission gives the machine-world forms an existential purpose they otherwise lacked.
Perhaps Icarus should take good care with planetary protection. A lurid fictional example of what happens if you don’t was given in ‘Voyager’s Return’, an episode from the first season of the TV drama Space: 1999 (1975). After fifteen years in space an exploratory interstellar probe called Voyager One (with no relation to the Voyagers of reality) is returning to Earth when it is intercepted by the castaway members of Moonbase Alpha. The heroes are eager for the craft’s data, but are wary of its deadly ‘Queller Drive’: ‘fast neutrons spewed out into space annihilating everything in their path’. It turns out that the craft is being followed back to its source by three craft of the Federated Worlds of Sidon; on Voyager’s arrival in their system the craft accidentally sterilised two inhabited worlds with its drive. Now the Sidons come to destroy the originating world: ‘You came proclaiming peace and you brought destruction.’ In the end the drive itself is used to eliminate the craft, and the vengeful Sidon.
Senescence and Obsolescence
Icarus’s terms of reference indicate that the mission should be completed in a century or less. But back on Earth, even in a century an awful lot can change. We might abandon the probe, or forget it exists, or even lose the capability of talking to it. Perhaps Icarus should be equipped with some emergency communications protocols.
Frederik Pohl’s ‘The Gold at the Starbow’s End’  is a complex tale in which an America disintegrating under internal tensions launches a slower-than-light (manned) starship to a non-existent planet of Alpha Centauri, the purpose being hopefully to stimulate the isolated astronauts into lateral-thinking fundamental breakthroughs. The project succeeds too well; the astronauts, genius, godlike and cheated, turn on Earth and trash its technological infrastructure. And with the radio telescopes gone, their final message has to be sent to Earth using optical laser light and Morse code, to be picked up by a Schmidt telescope.
The most wistful peril, perhaps, faced by Icarus over a long enough journey timescale is that technological advances may render it obsolete even before it reaches its target. Van Vogt’s ‘Far Centaurus’  was the earliest of several tales to dramatise interstellar obsolescence. A (manned) starship travels at less than one per cent lightspeed to Alpha Centauri, with the four-man crew in suspended animation for the five-hundred-year flight. But the crew arrive at their destination to find the system already inhabited, as they have been overtaken thanks to technological developments after their departure: ‘We’re the prize fools in creation … They can make the trip from Earth to Centauri in three hours.’ The crew do, however, find the four worlds of the system named in their honour, and ultimately hop through time back to their own era.
Even if obsolescence overtakes Icarus, then perhaps at least it will be sampled or retrieved, just as Surveyor 3 was visited on the Moon by the Apollo 12 astronauts. The probe’s condition may yield useful data on interstellar conditions, and it may make a wistful museum piece in a future annex to the Science Museum.
 L Ron Hubbard, Battlefield Earth, L Ron Hubbard Library, 1982.
 Bracewell, R. (1960) ‘Communications from Superior Galactic Communities’, Nature, 186, pp670-71.
 M. McCollum, Life Probe, New York, 1983.
 G. Bear, Queen of Angels, Warner Books, 1990.
 S.J. and B. Adelman, Bound for the Stars, Prentice Hall, 1981.
 A.C. Clarke, 2001: A Space Odyssey, Hutchinson, 1968.
 Frederik Pohl, ‘The Gold at the Starbow’s End’, Analog Magazine, Conde Nast Publications, March 1972.
 A.E. van Vogt, ‘Far Centaurus’, Astounding Science Fiction, Street & Smith Publications, January 1944.