Project TOKNEP

Tokamak Nuclear Electric Propulsion

[ For further information, visit the project website ]

In order for mankind to effectively traverse and colonise the solar system, time-of-flight must be reduced. To achieve this, high-energy density is required and currently the greatest hope for both terrestrial electricity generation and such space travel is nuclear fusion.

Project TOKNEP

Project TOKNEP

This study’s aims are to produce a realistic and viable fusion space platform design using modifications to terrestrial fusion power plant concepts that can produce a power plant that can deliver specific powers over 1kW/kg with times between maintenance greater than 3 years.

The project would aim over several years, to describe the important subsystems. These would include (but not limited to):

  • Fusion plasma characteristics and tokamak specification,
  • Space platform systems engineering
  • Combined biological shield and primary working fluid
  • High temperature and efficiency thermal to electric conversion from neutron flux to power bus
  • Nitrogen cooled high field (~30T) high temperature superconducting magnet sets
  • Mechanical analysis on low density, high strength advanced materials
  • Energy storage and tokamak operation
  • Tritium breeding, launch and handling
  • Qualification
  • Orbital build and maintenance
  • Space segment (i.e. main thrusters, RCS, propellant, space structures etc.)
  • Mission specification and potential payloads

This research will be delivered via papers and reports potentially leading to a book using the design to explain the technological advances needed for fusion to become a reality in a space platform and how those advances are relevant to machines on Earth.

The group contains several leading academics in both fusion and the space sector and are currently engaging with universities to gain further research capacity through MSc Titles and Group Projects.

The Technology

Propulsion based on magnetically confined nuclear fusion can be performed in two separate ways either Nuclear Electric Power (NEP), or a ‘direct-drive’ method, where the propellant (either an external propellant source or the spent fusion fuel itself) is directly heated via the fusion plasma thermal power and is ejected through a magnetic nozzle at high exhaust velocity.

The production of electricity from a terrestrial fusion power plant will be derived from the transformation of kinetic energy from the flux of neutrons being deposited in the surrounding material via inelastic and elastic collisions, producing heat. This heat can then be transformed into electricity via traditional methods. In NEP this leads to a mass penalty for high energy neutron shielding and the thermal to electrical conversion turbomachinery. This mass penalty has meant that most previous nuclear fusion space studies derived from magnetic confinement have presented a direct-drive approach using exotic forms of aneutronic fusion fuel and novel containment techniques.

The majority of the world’s current fusion research activities are based on magnetically confined fusion using deuterium and tritium (D-T) fuels. This research will enable a future terrestrial baseline production of electricity, where the fuel comes from nothing more elaborate than seawater. Due to this large knowledge base obtained from theory and facilities, it makes these fuels by far the most likely and expedient source of high-energy density for space applications.

It is proposed in this study that magnetically confined fusion, within a magnetic bottle called a spherical tokamak, be used to create electricity for nuclear electric propulsion using deuterium and tritium as fuels. The significant advantage is that the tokamak conditions of a D-T plasma are far less onerous than in the so called aneutronic fusion fuels and remove confinement problems caused by magnetically detaching the plasma and propellant needed in the ‘direct-drive’ method. With aneutronic fusion fuels still creating neutrons (and therefore requiring shielding) and both the fusion reactor and other spacecraft systems still demanding external electricity the issues of fusion based NEP are still present in the direct-drive approach. Added to these concerns are the logistical problems of obtaining some of these rare fuels including the requirement of industrial scale lunar mining. Methods of reducing mass through novel materials and modifying systems with mass reductions as a priority, is viewed as far more likely route to space fusion power than the formidable challenges of confinement, temperature and power balance of aneutronic fusion plasmas.

Leader/contact:  David Homfray
For further information e-mail: [email protected]
Paper: D. A. Homfray, et al.,

“Technology Roadmap for a Magnetically Confined Fusion Powered Spacecraft”- Proceedings of the 14th Reinventing Space Conference RISpace14, London, UK, 24th -27th October, 2016

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