The unclaimed savings are in the upper stage. On September 23, 2025, Blue Origin Manufacturing was granted US12421921B2, “Reusable upper stage rocket with aerospike engine,” classified in F02K 9/64 with reuse ties in B64G 1/62 and B64G 1/641. Blue Origin is privately held — the thesis reads through the patent record.
Reusable launch has so far meant reusable first stages — the big, expensive booster that flies back and lands. The upper stage, which carries the payload the rest of the way to orbit, is typically thrown away on every flight. That expended upper stage is a recurring cost on every launch, and it is the savings current reusability does not capture. Reusing it is widely seen as both the next prize and the harder problem.
An aerospike engine adds a second wrinkle. Aerospikes maintain efficiency across a wide range of altitudes, which is attractive for a stage that operates from the upper atmosphere to vacuum — but they are notoriously difficult to build, and few have flown. Pairing aerospike propulsion with upper-stage reusability is a bet on two hard technologies at once, aimed at the costliest remaining piece of the launch ledger.
The honest caveat: this is frontier IP. Reusable upper stages and operational aerospikes are both unproven at scale, and a patent describes an architecture, not a flight-demonstrated cost saving. The risk is correspondingly high.
But the patent points where the next launch savings have to come from. Once first stages are reusable, the expended upper stage is the obvious target — and a reusable-aerospike-upper-stage patent is a bet on capturing the part of launch cost everyone else still throws away.