Hydroxylammonium nitrate—the next generation green propellant

The space race in the 1960s had led to the continuous development of rocket fuel as traditional liquid propellant options are known to be carcinogenic. In the search of new propellant that fits into the new propulsion application, the concept of new decomposition or combustion mechanism, green and high energy density are being prioritized as more different scales of space missions were proposed along the past 6 decades. In this chapter, the focus will be given to a new class of energetic ionic liquid (EIL)-based liquid propellant, hydroxylammonium nitrate. This EIL has demonstrated promising results, be it the synthesis process, safety feature, and energy released from combustion that caught much attention over the last 3 decades. This chapter, therefore, aims to provide comprehensive coverage to this particular EIL, from its synthesis to catalytic combustion mechanism. The chapter aims to target readers ranging from new readers to researchers in the field.