During the final metres of the powered descent of Apollo 11, astronauts Neil Armstrong and Buzz Aldrin lost sight of the lunar surface. As the retro-rockets fired towards the lunar dust - or regolith - to decelerate the spacecraft, soil erosion occurred and the blowing dust led to severe visual obstruction. After a successful landing, the presence of dust continued to impact the mission with adverse effects including respiratory problems and difficulty in performing tasks due to clogging of mechanisms, amongst others. As these effects were observed in subsequent missions, the dust problemwas identified as one of the main challenges of extra-terrestrial surface exploration. In this work, the focus is placed on dust dispersal, which arises from the interaction between a rocket exhaust flow - or plume - and the planetary surface. Termed plume-surface interactions (PSI), this field of study encompasses the complex phenomena caused by the erosion and lofting of regolith particles. These particles, which are ejected at high-speeds, can lead to damage to the spacecraft hardware or a reduction in functionality. Moreover, plumes redirected back towards the landers can induce destabilising loads prior to touch-down, risking the safety of the landing. To achieve a sustained presence on the Moon, as planned by NASA's Artemis programme, it is essential that PSI are well understood and mitigating measures are put in place, particularly if spacecraft are to land in the vicinity of lunar habitats. Although experimental work began in the 1960s and mission PSI were first recorded in 1969, a fundamental understanding of this phenomena has not yet been achieved. In this paper, a compendium of experimental PSI is presented, identifying the main challenges associated with the design of tests, stating important lessons learnt and the shortcomings of available experimental data and findings. Lastly, recommendations for future experimental work are presented.

Rocket launch failure rate is slightly higher than five percent. Concerned citizens are likely to protest against private-sector launches involving fission reactors. Yet, fission reactors can power long-duration lunar operations for science, observation, and in situ resource utilization. Furthermore, fission reactors are needed for rapid trans-port around the solar system, especially considering natural radiation doses for crews visiting Mars or an asteroid. A novel approach is to create nuclear fuel on the Moon. In this way, a rocket launched from the earth with no radioactive material can be fueled in outer space, avoiding the risks of spreading uranium across Earth's bio-sphere. A solution is to harvest fertile thorium on the lunar surface, then transmute it into fissile uranium using the gamma ray fog which pervades the deep sky. It is only at lunar orbit, at the very edge of cislunar space, that the Earth-launched machine becomes a nuclear thermal rocket (NTR). Thorium is not abundant, but can be con-centrated by mechanical methods because of its very high specific density relative to the bulk of lunar regolith. Thorium dioxide (ThO2) has an extremely high melting point, such that skull crucible heating can be used to separate it from supernatant magma. When filled into a graphite-lined beryllium container (brought from Earth) and set out on the lunar surface, high-energy gamma rays will liberate neutrons from the Be. After moderation by the graphite, these thermal neutrons are captured by the thorium nucleus, which is transmuted into protac-tinium (Pa91). This element can be extracted using the THOREX process, and will then decay naturally into U-233 within two or three lunar days. The uranium is oxidized and packed into fuel pellets, ready to be inserted into a non-radioactive machine, which now becomes an NTR. Additionally, hydrogen can be extracted from deposits in permanently-shadowed regions on the Moon, providing reaction mass for the NTR. A novel method of solid-state hydrogen storage, which can be entirely fabricated using in situ resources, can deliver said hydrogen to the fis-sion reactor to provide high and efficient propulsive thrust. These combined operations lead to an ultra-safe (for the Earth) means for private sector, commercial transport and power generation throughout the Solar System. With the hydrogen storage material used as radiation shielding for crewed spacecraft, and greatly-reduced transit times relative to chemical rocketry, this innovative approach could fundamentally transform how humans work, play, and explore in outer space.

Water ice and other volatile compounds may be present on the Moon's surface within permanently shadowed regions (PSRs) near the lunar poles. Understanding the composition, quantity, distribution, and form of water and other volatiles associated with lunar PSRs is identified as a Strategic Knowledge Gap (SKG) for NASA's human exploration program, projected to visit the lunar south pole in the next decade. These polar volatile deposits are also scientifically interesting, having potential to reveal important information about the delivery of water to the Earth-Moon system.