Historical research guide · 1061 · 2010
Inertial Confinement Fusion Propulsion for Deep Space Missions Revisited
George H. Miley · Xiaoling Yang · Kirk Flippo
In one minute
Laser fusion has been proposed as a deep-space engine for decades, and George Miley, Xiaoling Yang and Kirk Flippo argue that the old proposals were built on the wrong version of it. Those studies assumed deuterium and tritium as fuel, which needs tritium bred on board and puts four fifths of its energy into neutrons — energy that cannot be aimed out of a nozzle — and they assumed compression schemes that returned only modest gain. Two things have changed. Chirped lasers now deliver ultra-short pulses at up to a few petawatts, which makes fast ignition possible: compress the capsule first, then light it with a separate short pulse so a burn wave spreads outward through the surrounding fuel. And in the variant these authors use, the igniting kick is not a laser at all but a block of plasma driven into the target, which keeps the electron temperature low. Low temperature is what lets you burn proton and boron-11, whose alpha particles a magnetic nozzle can steer into thrust.
Connection
Chapter 8 wants propulsion that is not a rocket burning propellant, and this is a fully specified route to it: no tritium, no neutron shielding to carry, and charged reaction products that a magnetic nozzle turns directly into thrust. Chapter 12 supplies the reason it matters on the ground as well — the same aneutronic reaction, ignited the same way, is the reaction the site’s energy case is built on.
From the source
The earlier inertial confinement fusion propulsion design studies rest on older target irradiation — either direct drive or indirect, x-ray driven drive — and that choice is what limits them, because it leads to rather low energy gains.Abstract, sentences 2 and 3
Deuterium and tritium is the wrong fuel for a spacecraft. It requires tritium to be bred, and it delivers eighty per cent of the fusion energy as neutrons, which cannot be directed through an exhaust nozzle.Abstract, sentence 4
Chirped lasers changed the arithmetic. Ultra-short pulses at powers from terawatts up to a few petawatts made fast ignition possible: the petawatt beam strikes an already compressed target and creates a hot spot in its interior, and the burn propagates outward into the surrounding fuel. The gain rises because part of the input energy that would otherwise be required is replaced by that propagating burn.Abstract, sentences 5 to 7
The igniter in this study is not a laser pulse at all. A non-laser interaction accelerates a block of plasma into the target to ignite the hot spot. The authors report that this is very efficient, gives very high gains, and — the decisive property — maintains a low electron temperature.Abstract, sentences 8 and 9
A low electron temperature is what allows ignition of more demanding fuels, and the fuel chosen here is proton and boron-11. It releases its energy as energetic alpha particles, which can be guided very effectively through a magnetic nozzle to produce thrust, while avoiding any tritium involvement and any neutron-induced radioactivity.Abstract, sentences 9 and 10
The paper’s own verdict on the comparison: these advances are shown to meet and exceed the requirements anticipated for an optimum inertial confinement fusion propulsion ship design — requirements the earlier design studies had identified but could not then satisfy.Abstract, final sentence
The way in
https://doi.org/10.2514/6.2010-6576How to cite it
George H. Miley, Xiaoling Yang, Kirk Flippo (2010) Inertial Confinement Fusion Propulsion for Deep Space Missions Revisited doi:10.2514/6.2010-6576