Boeing's take on Project Orion

[Dalex]

The article on Phys.org provides little to no details so here is the Patent application.

[radtech497]

The article on Phys.org provides little to no details so here is the Patent application.

Seems more like a take on Project Daedalus, which used internal ICF (inertial confinement fusion) than Project Orion, which used external thermonuclear detonations. Alternatively, it might be a take on Project Longshot.

Radtech497

[stevebowers]

This concept seems to have the option for using either fusion or fission. I suppose that it would also be possible to use it for straight thermal propulsion, with no nuclear reaction at all.

[Ithuriel]

Seems more like a take on Project Daedalus, which used internal ICF (inertial confinement fusion) than Project Orion, which used external thermonuclear detonations. Alternatively, it might be a take on Project Longshot.

I don't think that 'internal fusion' is quite the correct description here. It gets used in the EG too, and might want updating.

To my mind, this remains 'external', because you've got empty space on one side, and a curved pusher plate on the other (albeit one made from magnetic fields). ICF and other pulse propulsion systems (ICAN, AIM, MIF) might all be reasonably considered external, because the energetic reaction happens in the nozzle itself. There's no flow of hot reaction products through the nozzle, only out of it.

Contrast with magnetically confined fusion, gasdynamic mirror or mirror cell fusion rocket designs where all the business of heating the reaction mass is done inside a reaction chamber and channeled out of a magnetic nozzle, which has a constriction (the throat). All hot reaction mass passes through the throat; no further reaction happens in the nozzle.

This concept seems to have the option for using either fusion or fission. I suppose that it would also be possible to use it for straight thermal propulsion, with no nuclear reaction at all.

Not quite so good for thermal work, though you could push out pellets of inert reaction mass and convert them to a hot plasmoid using an energetic laser pulse. Most thermal engines use an enclosed reaction chamber to get maximum heating of the reaction mass.

[radtech497]

I used the terms "internal" and "external" to describe where the energetic phase of the propulsive cycle takes place. For example, in the Orion-type drive, the "propellant" is ejected through the pusher plate and detonated some distance behind the ship; this is what I would classify as an "external" reaction (whether using fission, fusion, antimatter, or even chemical explosives). With the Daedalus, Longshot, and other ICF-based drives, the "propellant" is heated and compressed by lasers/masers/etc. located within the ship's structure. The fusion reaction takes place within a "combustion chamber" that is generally also located within the ship's structure.; these types are classified as "internal." In a magnetic or electrostatic confinement fusion (MCF/ECF) drive, the energetic portion of the cycle also takes place within the ship's structure, and can also be classified as "internal."

Radtech497

[Ithuriel]

With the Daedalus, Longshot, and other ICF-based drives, the "propellant" is heated and compressed by lasers/masers/etc. located within the ship's structure. The fusion reaction takes place within a "combustion chamber" that is generally also located within the ship's structure.

The drive beams may be inside the structure, but their intersection point is not always so. In many of these cases, the fuel pellet is shot through the forward end of the pusher field, and ignited on the aft side of it. The principle benefit of this sort of propulsive system is that the vast majority of the unwanted radiation from the reaction does not hit the ship. Any internally detonating system would have none of this benefit; moreover the power levels required to confine the blast would be most unwelcome.

Longshot is unusual in that it does have an internal reaction chamber... Daedalus, VISTA, MiniMag Orion and ICAN-II all very clearly have all reaction take place in the nozzle, not in a confined chamber. Magneto-inertial fusion is less clear (as there's a chamber behind the nozzle into which the fuel pellet is injected) but fusion only takes place as the pellet leaves the chamber and enters the nozzle. The HOPE Z-pinch fusion system is even less clear, but I do believe that the most energetic part of the reaction happens in the nozzle as trying to confine the fusion fireball is inconvenient. It is notable that with the exception of Daedalus, all of these other designs postdate Longshot, and I'd be inclined to discount it as obsolete (but that's just me).

Magnetic confinement fusion does indeed have an enclosed and internal chamber, as I described above. I agree that it is "internal"; electrostatic confinement systems would fall into the same category.