VLM is a propellant and propulsion system entirely developed by Rocket Lab New Zealand. It has been sponsored by DARPA and ONRG over 2 programs to rapidly develop the technology for use in a wide range of rocket propulsion applications.
VLM is a single part high density monopropellant. It currently has performance and density equal or better than current solid fuel propulsion systems but has all the controllability of a liquid system with an ability to throttle arbitrarily, shut down and restart.
One of the key aspects of the propellant is that it is a thixotrope. It is a pseudo solid while static in the storage vessel however once some force or shear is applied to the propellant fluid it will thin rapidly. This shear thinning enables the propellant to be injected within the combustion chamber creating optimum combustion and full liquid controllability.