A Review of Aerospike Nozzles: Current Trends in Aerospace Applications

The abstract brings up SSTOs, but has there been anything in recent invention that will make them anything other than the white whale people have been chasing since forever?

The 1990s were a lost decade for reusable space flight because instead of chasing incremental improvements to the Space Shuttle (an orbiter with reusable tiles that could be turned around in days, not months) or something like the Falcoln 9 or the fly-back version of Saturn V that O'Neill's students drew in 1979, it was all about SSTO.

SSTO is just marginally possible, if it is possible you need exotic materials and engines and you're never going to get a good payload fraction and adding wings, horizontal takeoff, horizontal landing and such just makes it worse. The one good thing about it is that you get closer to "aircraft-like operations" because in principle you can inspect it, refill it, and relaunch it -- whereas something like the STS or Falcoln 9 or Starship will require stacking up multiple parts for each launch.

My guess is aerospikes are making a comeback though because of interest in hypersonic weapons system. I could also see them being useful for the second stage of something like Starship which mostly operates at high altitudes but has to land at low altitudes. There are a lot of other technical problems, like the thermal management system, which really have to be solved before worrying about that optimization.