NASA selects 3 aneutronic fusion related projects

[Skipjack]

He claims good chance of good scaling. As does EMC2. Although his fusion is T-D the near wall is completely isolated from the expensive bits of the apparatus, and speed can be scaled so that neutron flux is what you want, spread out over different areas - it is really an ideal topology for fusion, if it works.

I can't see why so little funding except that everyone is convinced it will not work. Probably not, but I can't see chances much different from Polywell? And although aneutronic fusion is more glamorous, that does not mean as engineering solution it is necessarily better, as much-needed replacement for fission reactors.

Yeah, I wished he got some real funding for his fusion reactor work. Even the always sceptical Art Carlson gave it a good chance of actually working (he even decided to get back into researching FRCs because of Sloughs work).
Of course that does not make this an absolutely save bet, but IMHO, it would be a much better investment than ITER.

Regolith Derived Heat Shield" Isn't the heat shield needed for the entry and isn't the regolith coming from the planet's surface which is accesible only after entry?

My guess is that they are thinking about lunar return missions, where large quantities of bulk materials are returned to earth with a comparably simple spacecraft that is basically constructed from a buch of engines powered by in situ created fuels and the rest of the structure being made from in situ built materials (such as the heatshield described here).

- What is the point with metallic hydrogen as rocket fuel? Is this a (proposed) chemical propulsion or something more exotic?

IIRC, metallic hydrogen has a higher density than normal liquid hydrogen. This helps dealing with one of the biggest disadvantages of LH2- LOX powered LVs: They are structurally much larger than stages using liquid hydrocarbons. It also could require simpler pumps on the engines, because you have to pump less volume. I am not sure about that one though.

[Betruger]

Above linked paper's abstract

Wigner and Huntington first predicted that pressures of order 25 GPa were required for the transition of solid molecular hydrogen to the atomic metallic phase. Later it was predicted that metallic hydrogen might be a metastable material so that it remains metallic when pressure is released. Experimental pressures achieved on hydrogen have been more than an order of magnitude higher than the predicted transition pressure and yet it remains an insulator. We discuss the applications of metastable metallic hydrogen to rocketry. Metastable metallic hydrogen would be a very light-weight, low volume, powerful rocket propellant. One of the characteristics of a propellant is its specific impulse, Isp. Liquid (molecular) hydrogen-oxygen used in modern rockets has an Isp of ~460s; metallic hydrogen has a theoretical Isp of 1700s! Detailed analysis shows that such a fuel would allow single-stage rockets to enter into orbit or carry economical payloads to the moon. If pure metallic hydrogen is used as a propellant, the reaction chamber temperature is calculated to be greater than 6000 K, too high for currently known rocket engine materials. By diluting metallic hydrogen with liquid hydrogen or water, the reaction temperature can be reduced, yet there is still a significant performance improvement for the diluted mixture.