Solid rocket motors are today the most cost effective, competitive and reliable propulsion technology for space launch systems. State of the art solid rocket propellants are based on the oxidizer ammonium perchlorate, AP, and aluminium powder, embedded in a polymer binder matrix. Unfortunately, AP has a negative impact on the environment and on personal health due to ozone depletion, thyroid gland interference and acid rain formation. The objective of the GRAIL project is to determine if it is possible to replace AP by using a mixture of the new green high energy density oxidizer ammonium dinitramide, ADN, and the low cost oxidizer ammonium nitrate, AN. A high energy density green solid propellant will be developed and compared with state of the art solid propellants with respect to safety, performance and cost, to determine if replacing AP with ADN/AN is a feasible option. The results will serve as important input for decision makers when considering development of future European launch systems.