NASA NIAC phase 1 studies development of a nuclear fission fragment rocket engine (FFRE) that is exponentially more propellent efficient than rocket engines currently used to power today’s space vehicles and could achieve very high specific impulse (>100,000 sec) at high power density (>kW/kg).
Fission Fragment rockets are several proposed nuclear rocket designs made since the 1980s with the highest potential theoretical top speed. The fission-fragment rocket is a rocket engine design that directly harnesses hot nuclear fission products for thrust, as opposed to using a separate fluid as working mass. The designs can, in theory, produce very high specific impulse while still being well within the abilities of current technologies. The new aerogel design proposal seems to be the most buildable version yet. It should be smaller, cheaper and simpler to make.
A previous proposal by Rodney L. Clark and Robert B. Sheldon theoretically increases efficiency and decreases complexity of a fission fragment rocket at the same time over the rotating fibre wheel proposal. In their design, nanoparticles of fissionable fuel (or even fuel that will naturally radioactively decay) are kept in a vacuum chamber subject to an axial magnetic field (acting as a magnetic mirror) and an external electric field. As the nanoparticles ionize as fission occurs, the dust becomes suspended within the chamber. The incredibly high surface area of the particles makes radiative cooling simple. The axial magnetic field is too weak to affect the motions of the dust particles but strong enough to channel the fragments into a beam which can be decelerated for power, allowed to be emitted for thrust, or a combination of the two. With exhaust velocities of 3% – 5% the speed of light and efficiencies up to 90%, the rocket should be able to achieve over 1,000,000 sec Isp.
Current proposed designs for Fission Fragment Rocket Engines are prohibitively massive, have significant thermal constraints, or require implementing complex designs, such as dusty plasma levitation, which limits the near-term viability. Ryan Weed and his team propose to develop a small prototype low-density nuclear reactor core and convert the nuclear energy stored in a fissile material into a high velocity rocket exhaust and electrical power for spacecraft payloads.
The key improvements over previous concepts are:
1. Embed the fissile fuel particles in an ultra-low density aerogel matrix to achieve a critical mass assembly
2. Utilize recent breakthroughs in high field, high temperature superconducting magnets to constrain fission fragment trajectories between moderator elements to minimize reactor mass.
The aerogel matrix and high magnetic field (B>20T) allows for fission fragments to escape the core while increasing conductive and radiative heat loss from the individual fuel particles. NIAC work will provide detailed mission analysis of fast transit to SGL for direct imaging and high-resolution spectroscopy of a habitable exoplanet at a distance of up to 100 light years. The FFRE propulsion system could provide delta-V to reach the SGL in less than 15yrs and provide the slowdown and maneuvering capability at SGL. The telescopes would act as a single pixel detector while traversing the Einstein Ring region, building an image of the exoplanet with enough resolution to see its surface features and signs of habitability.
Fission Fragment Concepts Review
Theoretically, there was the idea that a mature fission fragment rocket capability could have a 200 gigawatt system enabling a 10% of lightspeed travel to Alpha Centauri. The 200 gigawatt system is 200 times larger than most commercial nuclear fission energy reactors and it is about double the power of all nuclear fission reactors in the USA currently and about 40% of the nuclear fission reactors on earth.
The ultimate potential is there but the NASA NIAC study is lets make something much smaller and simpler.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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