Mechanical model of hollow-external-screw drill rod for lunar soil particle vertical conveying
This paper presents a mechanical model of drilling rod in lunar soil deep drilling process by expanding the theory of vertical screw conveyor. Space systems on lunar surface need to adapt to extremely bad environment and a drilling system would represent the fittest tool to collect soil sample to be analyzed in lunar exploration. Hollow-external-screw drill rod is a kind of most commonly used and reliable drill rod configuration which is one of the core executive components of lunar drilling- sampling mechanism. Drilling cuttings at the bottom of the hole are continuously sent to the lunar surface and the interaction between the drilling rod and the soil is difficult to model by numerical tools. Solid vertical transport theory in vertical screw conveyor and a soil-transporting mechanical model of long earth boring auger are applied to model the aforementioned interaction. In this force analysis of the mechanical model, not only the spiral angle variation is considered, but also the radial distribution and soil pressure in the particle vertical conveying. All these make the theoretical analysis more comprehensive than traditional methods. This paper also provides mathematical simulation of the soil-transporting process and the validation of the theoretical model mentioned above will be confirmed by the numerical and physical experiments.
Influence of soil properties on lunar rover's wheel-soil interaction mechanics
In order to understand the influence of lunar soil's properties on wheel-soil interaction mechanics,physical and mechanical properties of lunar soil were analyzed;lunar soil simulant was made and experiments were performed to measure soil parameters and wheel-soil interaction mechanics.The parameters of lunar soil simulant are estimated or identified according to the experimental data.Theoretical and numerical analysis have been done by substituting typical lunar soil parameters into the model,and the results are compared with the experimental data which shows that the soil parameters of bearing property primarily influence the wheel sinkage,the resistance moment of wheel is mainly influenced by shearing property of soil,and the contact angle coefficients that can reflect the physical property of soil has relatively small influence on wheel-soil interaction.
A technique for large-field, superficial electron therapy.
The application of electron beams to radiation therapy has received increased attention in recent years. This interest stems largely from the special characteristics of the electron depth-dose distribution; the fall-off in depth dose near the end of the range of the electrons is particularly rapid for electron beams having energies less than about 10 Mev. Such an electron beam is suitable for the treatment of widespread, superficial lesions, where it is desirable to minimize the dose to deep tissues. All the common sources of super-voltage x-rays, apart from radioactive substances, are inherently capable of producing an external beam of electrons, though with varying degrees of complexity. Electrons of about the energy suitable for superficial therapy (several Mev) may be used to produce an x-ray beam which is sufficiently penetrating for the treatment of even the deepest lesions. The Stanford medical linear accelerator was designed to provide both x-rays and electron beams. The accelerator and its applic...