Stephen Baxter, 11/11/13
This paper explores the future society assumed by the Project Daedalus team as background to the building of their starship.
The plausibility of Project Icarus – like Daedalus before it – will depend to some extent on the plausibility of an imagined future society that might have the capability and will, socially, economically and technically, to mount such a project. In their introductory essay in the Daedalus final report ( ppS5-S7), Bond and Martin noted that ‘Without such a background the results of the study would probably be naive, and would certainly be incorrect’ (pS6).
The Daedalus project was inspired by the propulsion system choice, so the team had to envisage a society that would naturally support a pulse-fusion starship using He3 as fuel. The team drew on precursor work such as Parkinson’s papers    on the nature of a society on the brink of interstellar flight, and as Daedalus progressed it became possible for the team to envisage such a society more clearly, a society defined not just by what the team imagined it would be capable of but also by what it would not be capable of.
But what kind of society was this?
The sketch by Bill Dillon included in the final report (pS4), of the construction of Daedalus at Callisto, gives some indication. Along with an array of specialised craft surrounding the immense bulk of Daedalus itself, we glimpse a wheel-in-space habitat and an astronaut performing an EVA. This is evidently a society capable of mounting a manned construction operation on a massive scale above a moon of Jupiter – and has the will to devote such resources to the peaceful end of scientific exploration.
The purpose of this brief review is to summarise the ‘Daedalus future’ as specifically as possible, as depicted by clues and assumptions spread throughout the report. The hope is that this review will help us more clearly to imagine the assumed ‘Icarus future’ that will underpin the plausibility of our own starship.
(Image Credit: “The Solar System”, by licoti)
Earth and the Solar System
Bond and Martin, in their introduction to the Daedalus report (ppS5-7), described a future Earth that was populous and energy-hungry. Against a background projected from the then-current ‘world energy crisis’, they predicted a demand for future energy sources of ‘minimal impact on the environment of Earth, which will by then be required to house about 1010 people’ (pS6).
What could such sources be? Bond and Martin noted the ‘apparent disadvantages’ then associated with nuclear fission (pS6). But the team did not envisage capabilities much beyond fusion. In their essays on the propulsion system, Martin and Bond said: ‘It is generally hoped that magnetic fusion reactors . . . will be operational . . . before the end of the century’. But producing antimatter for example was seen as requiring ‘large extrapolations of modern-day capabilities’ (pS45).
As for the fusion fuel choice, Martin and Bond go on to suggest a reliance on He3 because of its “cleanness”: ‘The deuterium-helium 3 reaction . . . [is] at present the only “clean” fusion reaction which can seriously be considered for application in reactors, from the point of view of achievable containment conditions and temperatures’ (pS7).
In his essay on propellant acquisition for Daedalus (ppS83-S89), notably the 30,000 tonnes of He3 required, Parkinson backed up this conclusion. With He3 impossibly scarce on Earth – the 1970s estimate of availability from various natural sources was one part in 104 to one part in 107 (pS83) – one option would be to breed the fuel load in ground-based fusion reactors, using either a D-D or D-T reaction. To produce the fuel at a rate of 1500 tons a year for 20 years (the team’s target timescale), either route would require power levels at multiples of Earth’s total present-day output, as well as consuming heroic quantities of other fuels and creating vast amounts of waste. Parkinson opined that a society capable of devoting such resources to a starship might find some other propulsion method easier, such as a laser-powered photon sail. Besides, a fusion-based society would be motivated to use any He3 available in a ‘clean reactor network’ on Earth (pS84).
Therefore, said Parkinson, the tapping of extraterrestrial sources of He3 ‘becomes a logical supply of propellant not simply for Daedalus but for mankind’ (pS84). Bond and Martin estimated that an import of 1000 tons of He3 per year from extraterrestrial sources could supply the world’s energy at 1970s levels; presumably more would be required for the more populous world of the future. And ‘the provision of the fuel for a starship may be merely an upgrading of this level of activity’ (pS7), a sensible projection if the 1500 tons per year for Daedalus is accepted.
The society of the future then would be populous, energy-rich, environmentally conscious, and connected to an interplanetary web of resource extraction and transportation, just as Earth is globally interconnected today: ‘That community will already be employing nuclear pulse rockets for space flight, and will probably be transporting helium 3 from the outer planets to the inner planets on a routine basis’ (pS7).
To build a starship would however require political will, and peace: ‘It seems probable that a Solar System wide culture making use of all its resources would easily be wealthy enough to afford such an undertaking [as Daedalus], and presumably in order to have reached the stage of extensive interplanetary flight would also have achieved reasonable political stability, and an acceptance of this new environment’ (pS7).
The sketched future scenario was in the end quite specific: ‘In summary, then, we envisage Daedalus-type vehicles being built by a wealthy (compared to the present day) Solar System wide community, probably sometime in the latter part of the 21st century’ (my italics) (pS7).
But people would still be people. In their essay on the mission profile ( ppS37-S42), Bond and Martin assume in passing that the mankind of the future era of the launch date will be much the same as today, with a ‘useful working life of about 40 years’ (pS38).
(Image Credit: “Over Mars”, by William-Black)
An interplanetary society this might be, but Parfitt and White in their paper on structural material selection (ppS97-S103) assumed that most materials for spacecraft and spaceborne structures, including Daedalus, would come from the Earth-moon system. For reasons of economy their choice of materials for Daedalus therefore concentrated on those most abundant on Earth, such as aluminium, ‘even if this imposes a small mass penalty’ (pS99).
In-space construction techniques were assumed by Strong and Bond in their paper on the vehicle configuration (ppS90-96); because Daedalus would not have to withstand the rigours of a planetary launch (and because the ship’s acceleration would be low), the main systems could be hung from a ‘slender structural spine’ (pS90). Bond and Martin sketched the construction programme: ‘The vehicle would be assembled in the inner Solar System, the exact location depending on where the manufacturing complexes may be located at that time. It would be fuelled either in Lunar or Jovian orbit depending on the source of helium 3. During preceding years several engineering mock-up and flight test vehicles would have been flown in an extensive test programme to develop system reliability to the required level’ (pS40). In his paper on navigation (ppS143-8) Richards suggested a full-scale rehearsal flight through the solar system (pS143).
As for other structures in space, in their paper on communications (ppS163-171) Lawton and Wright envisaged ‘the use of a very large array (VLA) “Cyclops” type system as the receiving antenna for the radio link. This can be either sited on Earth itself or (preferably) in space but in the vicinity of Earth’ (pS165). Indeed, it was anticipated that such arrays might be in operation for other purposes by the time Daedalus was launched. Cyclops  had been a 1972 study by NASA advocating an array of 1000 radio telescopes 10 miles across for the purposes of SETI.
Parkinson however ruled out very much larger structures. In his essay on propellant acquisition for Daedalus (ppS83-S89) Parkinson considered mining the solar wind for He3, but the number density of He3 nuclei in the solar wind is such that ‘to capture the propellant requirement in 20 years would require a cross-section of some 1011 km2 – or a circle 30 times the diameter of the Earth. Even allowing for large numbers of collecting units operating close to the Sun, it is difficult to imagine the individual collecting units having diameters less than thousands of kilometres’ (pS84). Parkinson remarks that a society capable of handling magnetic fields on this scale could well prefer alternative propulsion schemes.
Similarly an interstellar ramjet, which would require the control of electric and magnetic fields over very large length scales, was considered ‘not within a reasonable extrapolation of modern technology’ (pS45) by Bond and Martin in their notes on the choice of propulsion system.
The main space operation described was of course propellant acquisition. In his paper on the topic (ppS83-89) Parkinson speculated on specific sources of extraterrestrial He3. Mining Titan’s atmosphere might be relatively straightforward: ‘The extraction plant would not be mass-limited, and manned operation would ensure fairly continuous operation. In addition the escape velocity is low and transport costs would be minimal’ (pS89). However the available resource on Titan was probably limited; ‘one starship-load would take away 0.1% of the total available’.
Parkinson settled on mining Jupiter’s atmosphere, envisaging 128 ‘aerostat’ extraction factories, each weighing 130t, operating for 20 years in the Jovian atmosphere, with a power expenditure of ~500MW. Parkinson briefly speculated on the operational requirements of this spectacular venture (pS89): ‘Jupiter’s radiation belts make manned operations difficult within the satellite system, and so it is expected that most of the operation will be unmanned. Callisto, which appears to be outside the hazardous radiation zone, could be used as a base camp, and if manned operations have to be conducted in an orbit at the fringes of the Jovian atmosphere a well-shielded “transfer station” might be placed in an elliptical orbit between Callisto and the minimum altitude orbit.’
(Image Credit: “The Art of Intelligence”, by BonusExperiment)
Artificial intelligence was seen as key to the success of Daedalus. Grant, in his paper on Daedalus’s computer systems (ppS130-142), gave a clear description of the requirements of those systems, including systems control, data management, navigation, and fault detection and rectification. All this would be beyond the influence of ground control, and so ‘the computers must play the role of captain and crew of the starship; without them the mission is impossible’ (pS130).
In his paper on reliability and repair (ppS172-179) Grant pointed out that Daedalus would have to survive ‘for up to 60 years with gross events such as boost, mid-course corrections and planetary probe insertions occurring during its lifetime’ (pS172). A projection of modern reliability figures indicated that a strategy of component redundancy and replacement would not be sufficient; Daedalus would not be feasible without on-board repair facilities (pS176). AI would be used in the provision of these facilities, partly through the use of mobile ‘wardens’ capable of manipulation.
A high degree of artificial intelligence was also a key assumption for Webb in his discussions of payload design for Daedalus (ppS149-161). Because the confirmation of the position and nature of any planets at the target system might come only weeks before the encounter (ppS153-S154), it would be the task of the onboard computer systems to optimise the deployment of the subprobes and backup probes.
In addition, during the cruise the wardens could construct such additional instruments as ‘temporary (because of erosion) radio telescopes many kilometres across from only a few kilograms of conducting thread’ (pS154), and even rebuild or manufacture equipment afresh after receipt of updated instructions from Earth (pS156). One intriguing possibility was a response to the detection of intelligent life in the target system, in which case ‘the possibility of adjusting the configuration of the vehicle for the purposes of CETI (Communication with Extraterrestrial Intelligence) in the post-encounter phase should always be borne in mind’ (pS151).
Grant foresaw the continuing miniaturisation of hardware, as was already evident in the 1970s, and envisaged Daedalus being equipped with hierarchies of ‘picocomputers’ (pS132). The design of the controlling artificial intelligence could only be sketched; it would have to be capable of ‘adaptive learning and flexible goal seeking’, which would necessitate ‘heuristic qualities’ beyond the merely logical (pS131). Grant imagined the system being capable of in-flight software development – indeed, Grant speculated that pre-launch Daedalus, given a general design by a human team, would be able to write most of its own software! (pS141).
This theme of humans working in partnership with smart machines is evident elsewhere. Parkinson (pS89), describing the Jupiter atmospheric mining operation, noted that ‘The degree of autonomy demanded of unmanned components in the system is illustrated by the fact that the delay time of communications between Callisto and a station within the Jovian atmosphere will be about 12 seconds.’
(Image Credit: “The Daedalus”, by Adrian Mann)
Summarising the Daedalus future, Parkinson argued that ‘[An] undertaking on the scale of Daedalus fits naturally into the context of a Solar System wide society making intelligent use of its resources, rather than a heroic effort on the part of a planet-based society’ (pS89). That society would evidently be capable of massive manned operations conducted at Jupiter, but would be limited to fusion as a power source, would not yet be capable for instance of building gigantic structures to harvest He3 from the solar wind, and would be suffused with artificial intelligences working mostly in partnership with humans. The fuel required for Daedalus would represent a sizeable increase in the extraction effort already extant at Jupiter to satisfy the terrestrial energy demand, but not the establishment of an entirely new capability, and not an increase in capacity of orders of magnitude.
The Daedalus assumptions have of course been extensively revisited, in internal Icarus discussions and elsewhere. Forty years on it does seem unlikely that the Daedalus future will come to pass ‘sometime in the latter part of the 21st century’. Recently Zubrin  has sketched a developed solar system with fuel transportation networks on an interplanetary scale, and Hein et al  tested the assumptions behind the use of interplanetary sources of He3. Parkinson meanwhile  revisited the idea of using He3-powered pulse-fusion rockets for interplanetary transport.
These retrospective considerations are however irrelevant to the success of Project Daedalus in its time. The ‘Daedalus future’, the social and economic basis the team assumed would be in place to support their interstellar mission, was logical, reasonable as a projection from the time the report was written, internally consistent, an essential underpinning to the feasibility of the report, and a model for our work on Icarus.
 A. Bond et al, Project Daedalus Final Report, British Interplanetary Society, 1978.
 R.C. Parkinson, ‘The Starship as Third Generation Technology’, JBIS 27, pp295ff, 1974.
 R.C. Parkinson, ‘The Starship as an Exercise in Economics’, JBIS 27, pp692ff, 1974.
 R.C. Parkinson, ‘The Starship as a Philosophical Vehicle’, JBIS 28, pp745ff, 1975.
 J. Billingham et al, ‘Project Cyclops: A Design Study of a System for Detecting Extraterrestrial Intelligent Life’, NASA Ames, report CR114445, 1972.
 R. Zubrin, ‘On the Way to Starflight: Economics of Interstellar Breakout’, in Starship Century, eds. J. and G. Benford, Microwave Sciences, 2013.
 A. Hein, A. Tziolas and A. Crowl, ‘Architecture Development for Atmospheric Helium 3 Mining of the Outer Solar System Gas Planets for Space Exploration and Power Generation,’ IAC-10-D4.2.6, 2010.
 R. Parkinson, ‘Using Daedalus for Local Transport’, JBIS 62 pp422-426, 2009.