Project Daedalus - Origins

I am indebted to L J Carter of the British Interplanetary Society's Special Project Laboratory for supplying the following information on the genesis of Project Daedalus. The project team included Dr. Bob Parkinson, one of Jupiter Moon's scientific advisors, who co-ordinated the "Advanced Concepts" working committee.

Daedalus (Daidalos, literally "cunningly wrought") was an ingenious Greek craftsman and was said to have built the Labyrinth for Minos of Crete. Falling under the displeasure of Minos, he made wings for himself and his son, Icarus, in order to escape to Sicily. Icarus disobeyed his father's instructions and flew too close to the Sun, the heat melted the wax holding the wings together, he fell into the sea, and was drowned. Daedalus, on the other hand, flew neither too high nor too low, and arrived safely at his destination.

Project Daedalus is the name chosen for the British Interplanetary Society's Starship study.

The idea of forming a working party composed of interested BIS members was first advanced by Alan Bond in 1972. At that time interest in the field of Communications with Extraterrestrial Intelligence (CETI) was mainly focused on the problems of communication via radio signals. The point had been made (most ably by Carl Sagan) that Man possessed, for the first time, the capability of detecting the existence of alien life, albeit from long range.

In parallel with this Alan Bond argued that Man also now possessed a sufficient knowledge of science and a level of technology that a realistic attempt could be made to design an unmanned probe to fly past a nearby star, without the necessity of invoking radically new concepts, or of extrapolating present-day capabilities too far into the future.

The idea of forming a study group was discussed with several other BIS members also interested in the general area of what is known as Interstellar Studies, and an open meeting of the society was organised and held on 10 January 1973, in London. Here the proposal and its objectives, propulsion systems, guidance methods, and navigation and electronics aspects were discussed before an audience of some 120 people.

What follows is the Starship Study Progress Report, which describes in detail, the events of that meeting back in 1973.

120 members attended the Space Study Meeting held in London on 10 Jan. 1973 to establish the degree of interest in participating in an exploratory design study of an interstellar mission.

Alan Bond introduced the proposal and its objectives and mentioned that, although many papers on specialised aspects of interstellar flight had already been published, an integrated study of a realistic mission was needed to establish just how practical a proposition such a flight would be. The simplest mission would be chosen, i.e. a stellar flyby, with all aspects carefully studied. For example, a payload of suitable experiments should be determined, a payload weight obtained, guidance and navigation problems studied. Propulsion schemes should be examined and the most practically selected for integration into an overall design study. In his opinion, a propulsion proposal was now beginning to appear which might be capable of achieving a flyby flight to Barnard's star, 6 light years away, in a period of 30-40 years from launch. A flight-time of this nature would be the maximum acceptable, for then some of the younger people involved in the mission would still be alive when the destination was reached, and so some sense of continuity would be maintained. A launch date was projected at the end of the century. The flight would involve boosting the payload up to about 15% of the speed of light and then allowing it to coast to the destination. The encounter would consist of about 70 hr. of undecelerated flyby, during which time all measurements carried out in the system would have to be made. Even this simplest of missions would not be an easy study, and some years would have to be spent on it.

The next speaker, Dr. Tony Martin, went on to describe some of the more plausible of the available propulsion proposals and systematically reduced them to a single surviving candidate.

Controlled nuclear processes might yield two types of engine, i.e. those restricted by exhaust velocity and those restricted by weight. For example, the controlled fusion engine and the nuclear electric systems all have a very high mass associated with the hardware required to implement the system and hence the achievable acceleration is very low. This results in having to spend centuries just accelerating to the desired velocity - which is clearly not satisfactory for the present study. High thrust devices such as the thermodynamic nuclear engines of the NERVA type could achieve the acceleration, but the low exhaust velocity of about 104 m/s meant that the amount of propellant required would be enormous and was impractical. In regard to photon rockets, Dr. Martin pointed out that to attain 1g0 acceleration, the rocket would have to generate power at the rate of 3 x 109 w/Kg of vehicle mass. Not only this, but having generated the energy it was necessary to reflect it away from the starship with mirrors having absorbivity of less than 1 part in 106! Only an electron gas mirror might do that and even this raised many doubts. There were two final possibilities. First was the interstellar ramjet. Despite enormous prospects for the future of this system, the idea was not well enough advanced today to allow any realistic appraisal of what such a vehicle might look like, or its capabilities. The problems of how to scoop up the tenuous interstellar medium with a density of about 1 atom/cm3 were very difficult to resolve. If a magnetic field was employed, it would tend to reflect back into space the very particles it was attempting to collect. Even if the field problems could be overcome, bursting loads imposed on the vehicle structure were beyond our current technology. So, reluctantly, Dr. Martin moved to the only propulsion system which currently looks as though it might be practical, and capable of an interstellar mission. That was the nuclear pulse rocket. This device worked by exploding relatively small thermonuclear bombs behind the vehicle and propelling it forward by the impacts received from the expanding products of the explosion. Because bombs were small, it would be necessary to ignite them by means of a high-power laser or electron beam, produced by equipment carried on the vehicle. To make the system more effective, detonations would take place in a cusp shaped magnetic field. This would not only make the exhaust more directional, but also reduce the ablation of the vehicle protection system to a negligible level. Two nuclear reactions may be possible for the bomb, a deuterium/tritium or helium 3/deuterium reaction. The latter one had a low neutron production.

A velocity of more than 104 Km/s could be achieved with this rocket, and so might be able to meet the mission requirements.

The next speaker, Mr. James Strong, discussed some of the problems of interstellar guidance and navigation. He thought that these were alleviated by the relatively 'low' speed of the proposed vehicle and pointed out that none of the relativity effects would be very important. Normal stellar navigation should be applicable and the required guidance accuracy should be obtainable. Some degree of propulsion would be required for mid-course manouveres and for adjusting the trajectory to obtain the most profitable flyby, depending on the position of the planets on arrival. In theory, at least, all control could be left in the capable hands of an advanced autopilot. it was envisaged that, on nearing its destination - after a thirty year or so sleep - the probe would activate itself, deploy sensors and communications antennae and generally ready itself for the encounter. The general guidance system should not offer any major problems. A trial period of ship-systems could be carried out beforehand by placing the vehicle in solar orbit with human attendants until the time came for it to depart on its mission

Finally Mr. Tony Lawton returned everyone to Earth by pointing out the limitations of semiconductor devices in a cosmic radiation environment. Even the radiation received by the electronic devices from the motion of the vehicle at 15% of the speed of light relative to the interstellar medium would prevent operation of today's components after considerably less than thirty years exposure. Although future developments looked promising, this was one aspect of the study which would require a detailed investigation. The problem of communicating with the vehicle at interstellar distances was also raised. At the expected data transmission rate and distance, it would require several hundred megawatts of power to be transmitted, or a very large unfurlable antenna would have to be carried. In either case the problems to be overcome in order that a remote probe might send back its data were considerable. The interstellar ramjet was interesting from the point of view of the electronics, in that the intake could provide protection from the radiation caused by motion of the vehicle. If the ramjet should prove practical and flight times could be reduced to not much more than 6 years, the electronics would survive much better and it might be possible to overcome the relativistic navigation problems by the use of inertial guidance.

BIS Daedalus probe

An interesting discussion then developed in which speakers explored possible routes to study. It was gratifying that the theme of the discussion was on the level of 'which way is best' and not 'what on earth do we want to do that for?'.

Mr. Leonard Carter the society's secretary began with questions on how attitude control would be achieved on the pulse rocket, and also why Barnard's star had been used as the objective.

Mr. Bond explained that attitude control could be achieved by altering the alignment of shock absorbers which were necessary to absorb the momentum from the bomb detonations.

Mr A.V. Cleaver suggested that, on a vehicle of this type, it would probably be easier simply to reorientate the whole vehicle using small auxiliary engines, and then continue to thrust in the new direction.

Dr. Martin explained that the choice of Barnard's star had been made on the belief that it had an interesting attendant planetary system.

Mr. Bond added that the ability to achieve a mission to that particular star also implied that easier missions, e.g. to the Alpha Centauri system, could also be carried out. Longer missions were more difficult, due to the flight time: with present knowledge it seemed that this was about as far as the pulse rocket would be practical for.

The point was made by another speaker that, by the time such a mission was attempted, much more would be known about other planetary systems from space based telescopes and the choice would be less arbitrary.

Dr. R.C. Parkinson added a further candidate propulsion scheme for examination namely the laser-powered sail. Here, a very high powered laser in a fixed orbit provides the photons to be reflected by a light weight sail. The sail accelerates along the beam until no further useful velocity gain can be achieved. Dr. Parkinson recognised there would be heat transfer and mechanical difficulties, but thought that the advantages of not having to carry the power generation equipment along should be incentive enough to make examination worthwhile.

Several speakers thought that the society should look rather further ahead than immediate technology and advocated study of the interstellar ramjet. Both Dr. Martin and Mr. Bond said that the pulse rocket was the only system which was well enough defined to do any useful study on, but agreed that some effort should go into reviewing ramjet prospects.

Mr. Lawton suggested that the vehicle should carry simple experiments to announce its presence to any intelligent life in the target system. A large luminous cloud was suggested as an example, and some easily detachable artifacts should be carried which would identify the probe with Earth.

Mr. Cleaver said that with regard to the nature of the study, one should not try to relate it too closely to the BIS space ship study of the late 1930's. With that study, there was far less untrod technical ground. Rockets of the solid propellant type had existed for many years and it was largely a question of tying together a lot of reasonably known entities. With the current starship proposal much was new territory. The non-nuclear ignition of thermonuclear reactions, for example, had not yet been achieved. He went on to add that, although the study could be valuable and should be done, it should be expected that the technology of a century or so hence would be as foreign to ourselves as transistors would be to Newton, and he suspected that when interstellar flight finally came it probably would not be done with any means we are aware of today.

Mr. Carter replied that although Mr. Cleaver was correct with regard to the technical aspects of the study, the present study had a far more receptive technical community to approach for contributions to the work. he took the view that the concept of a lunar flight in the 30's represented a much greater hurdle to even the scientific mind than does the concept of extrapolating interplanetary flight to interstellar flight today.

A member of the group put forward the suggestion that the main pulse rocket could be used for signalling purposes at the great distance involved, but Mr. Lawton thought this would prove impracticable, owing to the required rate of data transmission.

Replying to a question on the economics of an interstellar mission, Dr. Parkinson said that, by the turn of the century, the world's population will have doubled and projects of the sort that we are considering might actually be essential for employment and economic reasons.

The proposed Starship study will involve examining all aspects of an interstellar flyby mission to see if it is realistic and to establish some of important interactions that occur on such a mission, e.g. how does the engine type compromise the payload and vice versa. Obviously one of the fundamental questions to be answered is the one of payload size required.

As the study will need to cover many disciplines, support is required from interested members. Three basic levels of effort are required. Firstly, those who can afford to spend a fair amount of time involved in the co-ordination of the study and integration to separate areas of work into a complete study. Next, and this will be one of the most sought-after contributions, are those that can contribute short technical papers in which suggestions on particular aspects are made and taken through to analytical completion. The origins of the topic may either be the individual himself or a suggestion from the co-ordinating committee. Finally but still important will be those members who are able to make suggestions of new routes to follow, but have not the time or possibly the necessary knowledge to follow them through.

It is hoped that many members will join in this venture, and even, where possible solicit material from expert sources not directly connected with the society.

Reproduced with permission of the BIS.

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