A team of Boeing employees (Budica/Herzberg/Chandler 1) have patented an inertial confinement fusion engine (the basic principle going back to C.D.Orth's VISTA from 1999 and Rod Hyde's 1983 ICF proposal, but with a few quirks of their own):
It's not your ordinary Orion, since it:
- uses much smaller "pulse units" (hence avoids the whole recoil problem);
- works on D-T fusion, not (as a primary mechanism) fission;
- doesn't achieve thermonuclear breakeven (pumps more energy through lasers than obtains from fusion), and potentially cannot be considered to violate the "no nukes in space yadda yadda" treaties;
- uses fast neutron flux from fusion to fission depleted uranium in a reactor that powers the lasers;
- and, in the traditional NERVA/NTR fashion, uses liquid hydrogen to a) cool the reactor, b) cool the chamber, c) provide extra thrust.
My question is about the nuclear reactor part. How does one guarantee the reactor's stability if there are, say, power excursions - a pellet is too large, and corresponding neutron flux higher than expected? What are the negative feedback mechanisms that keep the reactor under control?
1 Director of Advanced Vehicle Subsystems and Technologies at Boeing's Phantom Works.