Metastable helium

ToughSf points to a patent (pdf) for metastable helium. At first I thought that was the nucleus but, no, not this time. This is the sort where one electron (or maybe muon or antiproton) is in the low state; the other electron higher. Chemically this helium is now ionic, acting like an alkali metal or like hydrogen.

News to me is that we don't need an antiproton or a muon to form a metastable helium ion. Such actually gets formed in helium-heavy planets, like WASP-107b; here on Earth the patent suggests discharge-methods corona or radio-frequency.

These ions last for 8000 seconds = 2.2 hours thus the metastability: "He_m". Meanwhile the ion is, well, ionic so reactive. The patent suggests mixing the excited helium with ammonia and freakin' magnets.

Let's contrast what we got now, in the world of chemistry. Liquid hydrox - considered the highest Isp - is 32 kcal/g so exhaust-velocity 5180 m/s, 528 (N/N)s although space-shuttle only got 453 s. In practice hydrox has proven godawful to work with. Most rockets use kerosene (353 s); the Raptor is methane promising 382 s.

Atomic (ionic) hydrogen is the usual science-fiction upgrade at 2100 "seconds" but it's... science-fiction. Metastable helium would be 3100 "s", ejecta 30 km/s. The patent is claiming that this isn't science-fiction.

Ammonia-helium_m would still be a pain-in-the-posterior to work with. Also it's unfit for propulsion much longer after the initial thrust given that, after two hours, it's just good for making clown balloons anymore.

I take it the patent hopes the posterior-pain would match that of the old hydrox. In return we get almost an order-of-magnitude better than what we've seen from kerosene or methane, and five times better than unlamented hydrox. Also - like hydrox - we're not coating everything and the air and LEO with soot. And still no nukes; so it's permissible for equatorial launches from Earth.

How expensive is it to make, I wonder. More expensive than the antiproton variant? (We've agreed to ignore millisecond muons.) The antiproton variant looks to stick around longer. Which means it doesn't have to be made in Boca Chica and used immediately. Also I expect the antiproton variant to be heavier, cutting down on the tank-size.