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TechCrunch's Tesseract makes spacecraft propulsion smaller, greener, stronger tells us to "ditch the hazmat suits" and https://www.tesseract.space/products-and-services lists the Lyra 22 (i.e. 22 Newton) thruster with an exhaust velocity of 3040 m/s under it's Green Bipropellant Thrusters.
Question: What are the ingredients in Tesseract's "secret sauce", i.e. it's green bi-propellant combination? Just how green could rocket fuel be?
Based on the SEC document and the paper by Rusek et al. (1996) found by Polygnome, I managed to locate what I believe to be (one of) the relevant patent(s): US5932837A: "Non-toxic hypergolic miscible bipropellant" by John J. Rusek, Nicole Anderson, Bradley M. Lormand and Nicky L. Purcell, assigned to the US Secretary of Navy, filed in 1997 and granted in 1999:
"The non-toxic bipropellent of the present invention contains a non-toxic hypergolic miscible fuel (NHMF) and a rocket grade hydrogen peroxide. This non-toxic hypergolic miscible fuel (NHMF) has rapid ignition capability. The non-toxic hypergolic miscible fuel (NHMF) contains 3 species. Namely, a polar organic species miscible with hydrogen peroxide, a propagator, which may be substituted or unsubstituted amines, amides or diamines, and an inorganic metal salt, which reacts to form a catalyst in solution or as a colloid."
The patent, as patents are wont to do, covers quite a broad variety of possible fuel mixtures:
"The non-toxic hypergolic miscible fuel of the bipropellent consists of 50 to 75 weight % polar organic species miscible with hydrogen peroxide. In the preferred embodiment, C1 to C6 alcohols and C1 to C4 ketones are used as the polar organic species. As the propagator, 0.1 to 15 weight % of amides, substituted diamines, ethylene diamine tetraacetic acid (EDTA) or basic disubstituted EDTA are used.
In a preferred embodiment, the catalyst comprises either hydrated or unhydrated manganese acetate, copper acetate, iron acetate, cobalt acetate, manganese nitrates, copper nitrates, iron nitrates and cobalt nitrates. The catalyst is formed by adding a soluble inorganic metal salt into the solution consisting of the polar organic species and the propagator. When added to the solution, in situ formation of a microdispersed colloidal metal oxide and acetic acid occurs, which act as the catalyst."
However, the "most preferred" mixtures appear to consist of methanol (possibly mixed with propargyl alcohol) as the primary bulk fuel, mixed with a manganese acetate catalyst and, optionally, either urea or EDTA as the "propagator":
"In a most preferred embodiment of the invention, about 600 g methanol as the organic polar species, about 200 g manganese acetate tetrahydrate as the catalyst and about 90 g urea as the propagator are mixed in solution to form the NHMF.
In another most preferred embodiment, about 7 g methanol as the polar organic species, about 3 g manganese acetate tetrahydrate as the catalyst and about 0.05 g K2 EDTA as the propagator are mixed to form the NHMF.
In another preferred embodiment, a mixture of methanol and propargyl alcohol may also be used with the chosen propagator.
In another most preferred embodiment, about 7 g of a 50/50 volume ratio mixture of methanol and propargyl alcohol as the polar organic species, about 3 g manganese acetate as the catalyst and about 0.05 g K2 EDTA as the propagator are mixed to form the NHMF.
In yet another most preferred embodiment, about 175 g manganese acetate tetrahydrate as the propagator and about 600 g of methanol as the polar organic species are mixed to form the NHMF. As described earlier, the manganese acetate tetrahydrate reacts in solution to form a microdipersed colloidal manganese oxide and acetic acid. The acetic acid acts as the propagator."
What the patent does not tell is which (if any) of these mixtures might be the "composition 17B" described in the 1996 paper — nor, of course, which (if any) of these mixtures Tesseract might be using today.
In any case, while the fuel mixtures described in the patent aren't something you'd want to drink (well, most of them aren't; some of the possible mixtures covered by the patent, such as iron acetate in ethanol, could actually be safe to ingest might not kill you right away in small amounts!) they're still pretty safe to handle and relatively harmless to the environment, especially compared to most traditional hypergolic fuels like hydrazine. By far the nastiest substance involved is actually the concentrated hydrogen peroxide used as the oxidizer.
Ps. Here's another potentially relevant patent: US6419771B1: "Non-toxic hypergolic miscible fuel with stable storage characteristics" by Bradley M. Lormand, filed in 2000 and granted in 2002. It references the earlier patent cited above, and notes an issue with the storability of the mixtures described there:
"Unfortunately, the NHMF of U.S. Pat. No. 5,932,837 was found to form a precipitate over time. The formation of the precipitate is accelerated by heat and by the presence of water. This raises a concern regarding the long term storability and subsequent performance of the NHMF in a propulsion system."
The patent solves this problem by "buffering the pH of the NHMF in the origin of acidity with acetic acid and alkali acetate and the addition of a polar amide species to increase the polarity of the polar species of a lower alcohol."
(BTW, the "detailed description of the invention" section of this patent provides a surprising amount of background detail regarding the development process of these fuels. For the sake of brevity I won't quote it here, but it's well worth a read for anyone curious.)
Pps. Here's a random Washington Post article from 1998 about these fuels that I happened upon while Googling for this stuff.
