ASTRO MECHANICA HAS INVENTED A NEW KIND OF JET ENGINE

Summary from the TLDR newsletter

Astro Mechanica's new jet engine is efficient at every speed. It uses electric motors to drive a compressor, allowing it to spin at any speed. The jet engine could be used in the first stage of an orbital vehicle to get payloads to orbit dramatically cheaper than other all-rocket systems. A video of a demonstration from last year is available in the thread - Astro Mechanica is already working on a new engine with 10x the thrust.