Filing is concentrated: the leading assignee alone accounts for 22 of the 78 records in scope, and the top five combined hold 55.1% of all records. The remainder is a long tail of 27 ranked companies, many with only a handful of filings, spanning legacy aerospace primes, newer launch companies and materials suppliers. This concentration pattern means a freedom-to-operate check should prioritise the top few filers’ portfolios before scanning the long tail.

Common bulkhead designs share a single dome structure between two propellant tanks to save mass and length, while isogrid designs use a machined or formed triangular rib pattern to stiffen a tank wall against axial buckling with less material than a solid skin. In this dataset, isogrid and stiffened-skin approaches show up densely under the sheet-metal-working class B21D (15.4% of records), while common bulkhead claims appear more often as a feature within broader spacecraft structure filings (B64G) rather than as a separately coded technology. Anyone comparing the two should look at the underlying structural claim language rather than the class code alone.

Yes. Welding and joining claims (B23K) appear in 15.4% of the 78 records in scope, and two of the five most-cited records in the dataset are friction stir welding patents, including one specifically on welding dissimilar aluminum alloy grades. High citation counts on older welding patents indicate the technique remains a reference point for newer filings rather than a closed area. New filings in this space still need to check against the foundational weld-repair and dissimilar-alloy claims before drafting.