under low-gravity conditions is needed. Research in in-space cryogenic fluid management includes active and passive storage, fluid transfer, gauging, pressurization, pressure control, leak detection, and mixing destratification. (T3)

2020 and Beyond: Required

Ascent and Descent Technologies. NASA will require lunar and planetary descent and ascent propulsion technologies, including engine start after long quiescent periods, combustion stability at all gravity conditions, and deep throttle. Areas of research include cryogenic fluid management, propellant ignition, combustion stability, and active thermal control of the injectors and combustors. (T14)

Inflatable Aerodynamic Decelerators for Bodies with Atmospheres. The availability of inflatable aerodynamic decelerators would reduce propulsive mass requirements. To develop these systems, physical science research is required in high-strength, low-density, high-temperature flexible materials; dynamics, stability and control; and aeroelasticity in the flight environment. (T15)

Supersonic Retro Propulsion System. A combination of a supersonic retro propulsion system with an aerodynamic decelerator completes the deceleration and landing and would reduce mass requirements. To enable development of such a system, physical sciences research is needed on flow-field interactions of the rocket plume with the atmosphere, aerothermodynamics of the flow, and the dynamic interactions and control of the vehicle. (T16)

Space Nuclear Reactors. The development and demonstration of space nuclear reactors capable of supporting nuclear thermal rockets (NTRs) are required for missions beyond Mars and/or to enhance Mars exploration transportation capabilities. Required technologies include thermal control systems, efficient energy conversion and thermal transfer technologies, and lightweight/very high temperature thermal structures, along with safe and acceptable testing facilities. Enabling physical science research has been identified in the section “Space Power and Thermal Management.” Additional physical science research is required on liquid-metal cooling under reduced gravity, thawing under reduced gravity, and system dynamics. (T17)

Solar Electric Propulsion (SEP) Technologies. SEP is an important option for the efficient transfer of propellant and cargo to distant locations. To support the development of such systems, advances are needed in understanding the complex behavioral modes of very lightweight large space structures so as to enable development of innovative control methods for such structures during flight. In addition, research is needed in condensable propellants and in propellant transfer and management in very low gravity. (T18)

2020 and Beyond: Highly Desirable

Nuclear Electric Propulsion (NEP) Technologies. NEP will enable the very efficient transfer of propellant and other cargo to extended outposts on Mars and beyond. Areas of research, in addition to those summarized above under Space Nuclear Reactors (T17), include propellant management under reduced gravity and flow processes in electric thrusters.

Extravehicular Activity Systems

A new vision for EVA systems is emerging for exploration missions—one that encompasses spacesuits, rovers, and robotic assistants working collaboratively during mobile exploration sorties. In the past, EVA has enabled complex work outside a crewed space vehicle or lunar module, contributing a supporting operational role (repair, maintenance, observation, etc.). However, since the end of the Apollo missions, EVA has not typically served a primary mission role (excluding the EVAs on the Hubble Repair Missions). For space exploration missions to



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