Project Icarus is an ambitious five-year study into launching an unmanned spacecraft to an interstellar destination. Initiated by the Tau Zero Foundation and British Interplanetary Society, and managed by Icarus Interstellar Inc., a non-profit group of scientists dedicated to interstellar spaceflight, Icarus is working to develop a spacecraft that can travel to a nearby star.
Adam Crowl, Module Lead for Fuel and Fuel Acquisition for Project Icarus, investigates the advancement in materials technology over the last 40 years and discusses how the construction of an interstellar probe may stimulate spin-off manufacturing technologies and techniques.
When the Chinese built the first kites, nearly three thousand years ago, they used the materials available to them: silk and bamboo. Over time, the designs developed and transformed into the gigantic and graceful kites we know and love today; the more expensive designs made of modern plastics and carbon composites.
Similarly, when "Project Daedalus" was designing an interstellar vehicle nearly 40 years ago, known materials and technology were applied, naturally. Dense, refractory metal alloys handled high temperatures, low-temperature superconductors created magnetic fields, and turbo-electric power systems kept systems supplied with electrical power.
Since then, a whole new range of materials -- such as carbon allotropes, high temperature superconductors, and thermoelectric materials -- have been studied and are rapidly approaching practical application in construction, electrical and power generation equipment. Their application to the problem of interstellar travel will push our skill to the limits, with benefits to everyone.
Kites able to lift people have been around a long time, but only the invention of sufficiently powerful and light-weight engines late in the 19th Century enabled us to fly kites untethered around the sky as the first heavier-than-air aircraft. Interstellar travel faces a similar dilemma -- the need for a sufficiently low-mass engine with enough power to propel our first "star kite."
Starships based on rocket propulsion are power-limited, like the first powered aircraft. Consequentially, for a rocket, some fraction of the energy released to make a fast jet of material to push the vehicle is absorbed by its structure, and that excess energy must be released as waste heat.
Chemical rockets, like the ones used by the recently retired Space Shuttle, vent their excess heat as warmed-up coolant mixed into the main jet. Some interstellar rocket designs might allow most of the waste heat to be carried away by the exhaust, but a small fraction will still be absorbed.
This is a problem; even a small fraction of the multi-terawatt power levels need to fly between the stars in mere decades will require immense radiators to let the heat escape. A flow of liquid or gas, probably helium, must carry heat from the engine structure to the radiators and will probably need to withstand an operating temperature of several thousand degrees for several years.
That's just one of the many extremes the materials must endure. On the other end of the scale, the engine's magnetic fields will need to be generated by superconducting wires, which prior to 1986 had to be cooled to absolute zero (-273 C). The maximum temperature was thought to be -243 C for these superconducting materials, but that year the highest operating temperature of superconductors leapt to -238 C, then to -181 C.
Presently the record is about -138 C to maintain superconductivity. While that's really cold, the technology to cool to such temperatures and shield them from a nearby inferno masses is less than required for the chillier -269 C assumed in the 1970s. Also, we have newer materials for insulating the wires and protecting them from ionizing radiation produced by fusion reactions, as well as lighter, stronger materials for reinforcing the wires against simultaneously imploding and exploding from the powerful magnetic forces they generate.
Once the main engine shuts down, the vehicle will need a long-term power-supply, probably some form of compact, yet advanced, nuclear reactor.
In the 1970s, only one relatively efficient method of making useful electrical power from nuclear heat was available, in the form of heavy turbines spinning a generator. Since then, thermoelectric materials, able to turn a heat-flow into a flow of electricity, have improved in efficiency. Materials researchers are hopeful of eventually competing with the efficiency of power generators with moving parts, replacing them with a solid-state system with few or no moving parts. On a multi-decadal mission, the advantage of not having parts wearing out is obvious.
As well as better materials, the last 40 years has seen a slow revolution in manufacturing, with the rise of additive manufacturing and ever more capable automated machining equipment. Parts can now be made layer by layer, interlinked in ways impossible to join together from separate pieces, and made stronger and lighter, by requiring less material be left in place due to the limitations of traditional manufacturing processes.
Already such techniques are being applied in the construction of the next generation of aircraft, making them lighter, stronger and more rugged than ever before.
An interesting precedent can be found in the Apollo Moon Program of the 1960s, where a sophisticated automated welding system had to be developed to assemble the immense, light-weight structure of the mighty Saturn V rockets. Fundamentally, this transformed the way we manufacture more down-to-Earth products that enrich our lives on a day-to-day basis.
So, pushing ourselves to make "Interstellar Kites" will inevitably change the way we manufacture products of the future in unimaginable ways.
WIDE ANGLE: Read more about Project Icarus, its predecessor "Project Daedalus" and the motivation behind interstellar spaceflight in the exclusive Discovery News Wide Angle: "Reaching for Interstellar Space."